四则运算APP版

（一）四则运算APP版

这这个Demo的目的就是强化一下本周学习的Android的Jetpack里的新内容，接下来我将通过这个Demo来展示我所学到的新知识。

先列出新学到的知识：ViewModel，Navigation，MutableLiveData，ViewModelSaveState,SharedPreferences,AndroidViewModel,DataBinding

设计思路：

UI设计思路：

一共四个页面：首页，习题页，成功页，失败页

将这四个页面通过Navigation连接起来形成一条逻辑关系。

 接下来就是对每个页面进行设计。

首页：一个TextView和一个ImageView还有一个Button，顶部还有一个最高分Textview，通过button来进入出题页面

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="data"
            type="com.example.calculation.MyViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".TitleFragment">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.1" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.9" />

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/CalName"
            android:textSize="@dimen/huge_size"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toStartOf="@+id/guideline2"
            app:layout_constraintStart_toStartOf="@+id/guideline"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.106" />

        <ImageView
            android:id="@+id/imageView"
            android:layout_width="320dp"
            android:layout_height="349dp"
            android:contentDescription="@string/title_image"
            android:src="@drawable/size"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintDimensionRatio="w,1:1"
            app:layout_constraintEnd_toStartOf="@+id/guideline2"
            app:layout_constraintHorizontal_bias="0.56"
            app:layout_constraintStart_toStartOf="@+id/guideline"
            app:layout_constraintTop_toTopOf="parent" />

        <Button
            android:id="@+id/button"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:text="@string/title_button"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toStartOf="@+id/guideline2"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="@+id/guideline"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.862" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{@string/higer_score(data.highScore)}"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.883"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.036"
            tools:text="High Score:%d" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

出题页面：顶部一个textview代表目前的得分情况，中间是一个算式，下面是你的答案，接下来是4行3列，12个按钮代表你的操作。

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="data"
            type="com.example.calculation.MyViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".QuestionFragment">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.1" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.2" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.33" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.4" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline10"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.5" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline11"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.6" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline12"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.7" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.8" />

        <TextView
            android:id="@+id/textView3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{@string/Current_Score(data.currentScore)}"
            app:layout_constraintBottom_toTopOf="@+id/guideline3"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintHorizontal_bias="0.537"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/guideline3"
            app:layout_constraintVertical_bias="0.473"
            tools:text="Score:0" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline8"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.1" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="vertical"
            app:layout_constraintGuide_percent="0.9" />

        <TextView
            android:id="@+id/textView4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="@dimen/huge_size"
            android:text="@{String.valueOf(data.leftNumber)}"
            app:layout_constraintBottom_toBottomOf="@+id/textView5"
            app:layout_constraintEnd_toStartOf="@+id/textView5"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/textView5"
            tools:text="1" />

        <TextView
            android:id="@+id/textView5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="@dimen/huge_size"
            android:text="@{String.valueOf(data.operator)}"
            app:layout_constraintBottom_toBottomOf="@+id/textView6"
            app:layout_constraintEnd_toStartOf="@+id/textView6"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/textView4"
            app:layout_constraintTop_toTopOf="@+id/textView6"
            tools:text="+" />

        <TextView
            android:id="@+id/textView6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="@dimen/huge_size"
            android:text="@{String.valueOf(data.rigthNumber)}"
            app:layout_constraintBottom_toBottomOf="@+id/textView7"
            app:layout_constraintEnd_toStartOf="@+id/textView7"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/textView5"
            app:layout_constraintTop_toTopOf="@+id/textView7"
            tools:text="2" />

        <TextView
            android:id="@+id/textView7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="="
            android:textSize="@dimen/huge_size"
            app:layout_constraintBottom_toBottomOf="@+id/textView8"
            app:layout_constraintEnd_toStartOf="@+id/textView8"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/textView6"
            app:layout_constraintTop_toTopOf="@+id/textView8"
            tools:text="=" />

        <TextView
            android:id="@+id/textView8"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/Cal_Answer"
            android:textSize="@dimen/huge_size"
            app:layout_constraintBottom_toTopOf="@+id/guideline4"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/textView7"
            app:layout_constraintTop_toTopOf="@+id/guideline4" />

        <TextView
            android:id="@+id/textView9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Your Answer:"
            android:textSize="@dimen/mid_size"
            app:layout_constraintBottom_toTopOf="@+id/guideline5"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/guideline5" />

        <Button
            android:id="@+id/button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="1"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toTopOf="@+id/guideline10"
            app:layout_constraintEnd_toStartOf="@+id/button2"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/guideline6" />

        <Button
            android:id="@+id/button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="2"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/button1"
            app:layout_constraintEnd_toStartOf="@+id/button3"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button1"
            app:layout_constraintTop_toTopOf="@+id/button1" />

        <Button
            android:id="@+id/button3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="3"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/button2"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button2"
            app:layout_constraintTop_toTopOf="@+id/button2" />

        <Button
            android:id="@+id/button4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="4"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toTopOf="@+id/guideline11"
            app:layout_constraintEnd_toStartOf="@+id/button5"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/guideline10" />

        <Button
            android:id="@+id/button5"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="5"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/button4"
            app:layout_constraintEnd_toStartOf="@+id/button6"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button4"
            app:layout_constraintTop_toTopOf="@+id/button4" />

        <Button
            android:id="@+id/button6"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="6"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/button5"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button5"
            app:layout_constraintTop_toTopOf="@+id/button5" />

        <Button
            android:id="@+id/button7"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="7"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toTopOf="@+id/guideline12"
            app:layout_constraintEnd_toStartOf="@+id/button8"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/guideline11" />

        <Button
            android:id="@+id/button8"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="8"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/button7"
            app:layout_constraintEnd_toStartOf="@+id/button9"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button7"
            app:layout_constraintTop_toTopOf="@+id/button7" />

        <Button
            android:id="@+id/button9"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="9"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/button8"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button8"
            app:layout_constraintTop_toTopOf="@+id/button8" />

        <Button
            android:id="@+id/clear"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Clear"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toTopOf="@+id/guideline7"
            app:layout_constraintEnd_toStartOf="@+id/button0"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toStartOf="@+id/guideline8"
            app:layout_constraintTop_toTopOf="@+id/guideline12" />

        <Button
            android:id="@+id/button0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="0"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/clear"
            app:layout_constraintEnd_toStartOf="@+id/submit"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/clear"
            app:layout_constraintTop_toTopOf="@+id/clear" />

        <Button
            android:id="@+id/submit"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="OK"
            android:textSize="@dimen/button_size"
            app:layout_constraintBottom_toBottomOf="@+id/button0"
            app:layout_constraintEnd_toStartOf="@+id/guideline9"
            app:layout_constraintHorizontal_bias="0.5"
            app:layout_constraintStart_toEndOf="@+id/button0"
            app:layout_constraintTop_toTopOf="@+id/button0" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

成功页面：一个Imageview笑脸，两个Textview还有一个Button来返回首页

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="data"
            type="com.example.calculation.MyViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".WinFragment">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline13"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.1" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline14"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.35" />

        <ImageView
            android:id="@+id/imageView2"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:contentDescription="@string/image_win"
            android:src="@drawable/ic_sentiment_satisfied_black_24dp"
            app:layout_constraintBottom_toTopOf="@+id/guideline14"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline13" />

        <TextView
            android:id="@+id/textView10"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="恭喜你！创下新纪录"
            android:textSize="@dimen/bige_size"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline14"
            app:layout_constraintVertical_bias="0.1" />

        <TextView
            android:id="@+id/textView11"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{@string/New_Score(data.highScore)}"
            android:textSize="@dimen/bige_size"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/imageView2"
            app:layout_constraintVertical_bias="0.3"
            tools:text="你的成绩是:%d" />

        <Button
            android:id="@+id/button10"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="返回"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline14"
            app:layout_constraintVertical_bias="0.5" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

失败页面：一个Imageview哭脸，两个Textview还有一个Button来返回首页

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">

    <data>
        <variable
            name="data"
            type="com.example.calculation.MyViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".LoseFragment">

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline15"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.1" />

        <androidx.constraintlayout.widget.Guideline
            android:id="@+id/guideline16"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            app:layout_constraintGuide_percent="0.35" />

        <ImageView
            android:id="@+id/imageView3"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:src="@drawable/ic_sentiment_dissatisfied_black_24dp"
            app:layout_constraintBottom_toTopOf="@+id/guideline16"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline15" />

        <TextView
            android:id="@+id/textView13"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@{@string/New_Score(data.currentScore)}"
            android:textSize="@dimen/bige_size"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline16"
            app:layout_constraintVertical_bias="0.3"
            tools:text="你的成绩是:%d" />

        <Button
            android:id="@+id/button11"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="返回"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.498"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="@+id/guideline16"
            app:layout_constraintVertical_bias="0.5" />

        <TextView
            android:id="@+id/textView14"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="挑战失败!"
            android:textSize="@dimen/bige_size"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/imageView3"
            app:layout_constraintVertical_bias="0.1" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

程序设计：

首先是设计我们的MyViewModel里的数据，有最高分，目前得分，左操作数，右操作数，操作符，答案

通过SharedPreferences来保存数据，livedata可以随时的刷新数据，故用它来显示数据。

package com.example.calculation;

import android.app.Application;
import android.content.Context;
import android.content.SharedPreferences;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.SavedStateHandle;
import androidx.lifecycle.ViewModel;

import java.util.Random;

public class MyViewModel extends AndroidViewModel {
    private SavedStateHandle handle;
    private static String KEY_HIGH_SCORE="key_high_score";
    private static String KEY_LEFT_NUMBER="key_left_number";
    private static String KEY_RIGHT_NUMBER="key_right_number";
    private static String KEY_OPERATOR="key_operator";
    private static String KEY_ANSWER="key_answer";
    private static String SAVE_SHP_DATA_NAME="save_shp_data_name";
    private static String KEY_CURRENT_SCORE="key_current_score";
    public boolean win_flag=false;



    public MyViewModel(@NonNull Application application,SavedStateHandle handle) {
        super(application);
        if(!handle.contains(KEY_HIGH_SCORE)){
            SharedPreferences shp=getApplication().getSharedPreferences(SAVE_SHP_DATA_NAME, Context.MODE_PRIVATE);
            handle.set(KEY_HIGH_SCORE,shp.getInt(KEY_HIGH_SCORE,0));
            handle.set(KEY_LEFT_NUMBER,0);
            handle.set(KEY_RIGHT_NUMBER,0);
            handle.set(KEY_OPERATOR,"+");
            handle.set(KEY_ANSWER,0);
            handle.set(KEY_CURRENT_SCORE,0);
        }
        this.handle=handle;
    }
    public MutableLiveData<Integer> getLeftNumber(){
        return handle.getLiveData(KEY_LEFT_NUMBER);
    }
    public MutableLiveData<Integer> getRigthNumber(){
        return handle.getLiveData(KEY_RIGHT_NUMBER);
    }
    public MutableLiveData<String> getOperator(){
        return handle.getLiveData(KEY_OPERATOR);
    }
    public MutableLiveData<Integer> getHighScore(){
        return handle.getLiveData(KEY_HIGH_SCORE);
    }
    public MutableLiveData<Integer> getCurrentScore(){
        return handle.getLiveData(KEY_CURRENT_SCORE);
    }
    public MutableLiveData<Integer> getAnswer(){
        return handle.getLiveData(KEY_ANSWER);
    }

    public void setCurrentScore(){
        handle.set(KEY_CURRENT_SCORE,0);
    }

    void generator(){
        int level=100;
        Random random=new Random();
        int a=random.nextInt(level)+1;
        int b=random.nextInt(level)+1;
        if(a%4==0){
            getOperator().setValue("+");
            if(a>b){
                getAnswer().setValue(a);
                getLeftNumber().setValue(b);
                getRigthNumber().setValue(a-b);
            }else{
                getOperator().setValue("+");
                getAnswer().setValue(b);
                getLeftNumber().setValue(a);
                getRigthNumber().setValue(b-a);
            }
        }
        else if(a%4==1){
            getOperator().setValue("-");
            if(a>b){
                getAnswer().setValue(a-b);
                getLeftNumber().setValue(a);
                getRigthNumber().setValue(b);
            }else{
                getOperator().setValue("-");
                getAnswer().setValue(b-a);
                getLeftNumber().setValue(b);
                getRigthNumber().setValue(a);
            }
        }
        else if(a%4==2){
            getOperator().setValue("*");
            getLeftNumber().setValue(a);
            getRigthNumber().setValue(b);
            getAnswer().setValue(a*b);
        }
        else if(a%4==3){
            getOperator().setValue("/");
            while(a%b!=0){
                a=random.nextInt(level)+1;
                b=random.nextInt(level)+1;
            }
            getLeftNumber().setValue(a);
            getRigthNumber().setValue(b);
            getAnswer().setValue(a/b);
        }
    }
    void save(){
        SharedPreferences shp=getApplication().getSharedPreferences(SAVE_SHP_DATA_NAME,Context.MODE_PRIVATE);
        SharedPreferences.Editor editor=shp.edit();
        editor.putInt(KEY_HIGH_SCORE,getHighScore().getValue());
        editor.apply();
    }
    void answerCurrent(){
        getCurrentScore().setValue(getCurrentScore().getValue()+1);
        if(getCurrentScore().getValue()>getHighScore().getValue()){
            getHighScore().setValue(getCurrentScore().getValue());
            win_flag=true;
        }
        generator();
    }
}

TieleFragment的设计：设计一个按钮的绑定事件，进行跳转到出题页面

package com.example.calculation;

import android.app.AppComponentFactory;
import android.app.Application;
import android.content.pm.ApplicationInfo;
import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.calculation.databinding.FragmentTitleBinding;


/**
 * A simple {@link Fragment} subclass.
 */
public class TitleFragment extends Fragment{


    public TitleFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, final ViewGroup container,
                             Bundle savedInstanceState) {

        FragmentTitleBinding binding;
        binding= DataBindingUtil.inflate(inflater,R.layout.fragment_title,container,false);
        MyViewModel myViewModel = ViewModelProviders.of(requireActivity(), new SavedStateViewModelFactory(requireActivity().getApplication(),requireActivity())).get(MyViewModel.class);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(requireActivity());
        binding.button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                NavController controller=Navigation.findNavController(v);
                controller.navigate(R.id.action_titleFragment_to_questionFragment);
            }
        });
        return binding.getRoot();
        // Inflate the layout for this fragment
        //return inflater.inflate(R.layout.fragment_title, container, false);
    }


}

QuestionFragment的设计：通过按钮点击来获取用户的答案，然后从数据里获取当前的viewmodel，判断结果是否相同，之后进行相应的操作。

里面有代码注释

package com.example.calculation;

import android.os.Bundle;

import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;

import com.example.calculation.databinding.FragmentQuestionBinding;


/**
 * A simple {@link Fragment} subclass.
 */
public class QuestionFragment extends Fragment {

    public QuestionFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, final ViewGroup container,
                             Bundle savedInstanceState) {
        final MyViewModel myViewModel;
        myViewModel= ViewModelProviders.of(requireActivity(),new SavedStateViewModelFactory(requireActivity().getApplication(),requireActivity())).get(MyViewModel.class);
        //获取运算表达式
        myViewModel.generator();
        //设置初始得分为0
        myViewModel.setCurrentScore();
        //获取页面的控制binding
        final FragmentQuestionBinding binding;
        binding= DataBindingUtil.inflate(inflater,R.layout.fragment_question,container,false);
        //设置数据与生命周期
        binding.setData(myViewModel);
        binding.setLifecycleOwner(requireActivity());
        //builder用来保存用户输入的数据
        final StringBuilder builder=new StringBuilder();
        View.OnClickListener listener=new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                    switch (v.getId()){
                        case R.id.button0:
                            builder.append(0);
                            break;
                        case R.id.button1:
                            builder.append(1);
                            break;
                        case R.id.button2:
                            builder.append(2);
                            break;
                        case R.id.button3:
                            builder.append(3);
                            break;
                        case R.id.button4:
                            builder.append(4);
                            break;
                        case R.id.button5:
                            builder.append(5);
                            break;
                        case R.id.button6:
                            builder.append(6);
                            break;
                        case R.id.button7:
                            builder.append(7);
                            break;
                        case R.id.button8:
                            builder.append(8);
                            break;
                        case R.id.button9:
                            builder.append(9);
                            break;
                        case R.id.clear:
                            //清楚代表用户的输入长度未0
                            builder.setLength(0);
                            break;
                    }
                    if(builder.length()==0){
                        binding.textView9.setText("请输入你的答案：");
                    }else{
                        //显示到UI页面上
                        binding.textView9.setText(builder.toString());
                    }
            }
        };
        //设置每一个按钮的点击事件
        binding.button0.setOnClickListener(listener);
        binding.button1.setOnClickListener(listener);
        binding.button2.setOnClickListener(listener);
        binding.button3.setOnClickListener(listener);
        binding.button4.setOnClickListener(listener);
        binding.button5.setOnClickListener(listener);
        binding.button6.setOnClickListener(listener);
        binding.button7.setOnClickListener(listener);
        binding.button8.setOnClickListener(listener);
        binding.button9.setOnClickListener(listener);
        binding.clear.setOnClickListener(listener);
        //提交按钮的设计
        binding.submit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(builder.length()!=0) {
                    //当答案相同时
                    if (Integer.valueOf(builder.toString()).intValue() == myViewModel.getAnswer().getValue()) {
                        myViewModel.answerCurrent();
                        builder.setLength(0);
                        binding.textView9.setText("回答正确! 请继续!");
                    } else {
                        NavController controller = Navigation.findNavController(v);
                        if (myViewModel.win_flag) {
                            //当创造新纪录时，进入成功页面
                            controller.navigate(R.id.action_questionFragment_to_winFragment);
                            myViewModel.win_flag = false;
                            myViewModel.save();
                        } else {
                            //否则进入失败页面
                            controller.navigate(R.id.action_questionFragment_to_loseFragment);
                        }
                    }
                }else{
                    Toast.makeText(v.getContext(), "请输入答案", Toast.LENGTH_SHORT).show();
                }
            }
        });
        return binding.getRoot();
        // Inflate the layout for this fragment
        //return inflater.inflate(R.layout.fragment_question, container, false);
    }
}

WinFragment的设计：设置它的返回按钮，与LoseFragment一样

package com.example.calculation;

import android.os.Bundle;

import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.SavedStateHandle;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.calculation.databinding.FragmentWinBinding;


/**
 * A simple {@link Fragment} subclass.
 */
public class WinFragment extends Fragment {

    public WinFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        MyViewModel myViewModel;
        myViewModel= ViewModelProviders.of(requireActivity(), new SavedStateViewModelFactory(requireActivity().getApplication(),requireActivity())).get(MyViewModel.class);
        FragmentWinBinding binding;
        binding= DataBindingUtil.inflate(inflater,R.layout.fragment_win,container,false);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(requireActivity());
        binding.button10.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                NavController controller= Navigation.findNavController(v);
                controller.navigate(R.id.action_winFragment_to_titleFragment);
            }
        });
        return binding.getRoot();
        // Inflate the layout for this fragment
        //return inflater.inflate(R.layout.fragment_win, container, false);
    }
}

package com.example.calculation;

import android.os.Bundle;

import androidx.databinding.DataBindingUtil;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;
import androidx.lifecycle.ViewModelProviders;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.calculation.databinding.FragmentLoseBinding;


/**
 * A simple {@link Fragment} subclass.
 */
public class LoseFragment extends Fragment {

    public LoseFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, final ViewGroup container,
                             Bundle savedInstanceState) {
        MyViewModel myViewModel;
        myViewModel= ViewModelProviders.of(requireActivity(),new  SavedStateViewModelFactory(requireActivity().getApplication(),requireActivity())).get(MyViewModel.class);
        FragmentLoseBinding binding;
        binding= DataBindingUtil.inflate(inflater,R.layout.fragment_lose,container,false);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(requireActivity());
        binding.button11.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                NavController controller= Navigation.findNavController(v);
                controller.navigate(R.id.action_loseFragment_to_titleFragment);
            }
        });
        return binding.getRoot();
        // Inflate the layout for this fragment
        //return inflater.inflate(R.layout.fragment_lose, container, false);
    }
}

MainActivity的设计：用来设置左上角的返回与手机左下方左三角的返回

package com.example.calculation;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.NavigationUI;

import android.app.Dialog;
import android.content.DialogInterface;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
    NavController controller;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        controller= Navigation.findNavController(this,R.id.fragment);
        NavigationUI.setupActionBarWithNavController(this,controller);
    }
//设置页面的左上角的返回操作
    @Override
    public boolean onSupportNavigateUp() {
        if(controller.getCurrentDestination().getId()==R.id.questionFragment){
            AlertDialog.Builder builder=new AlertDialog.Builder(this);
            builder.setTitle("你确定要退出吗？");
            builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    controller.navigateUp();
                }
            });
            builder.setNegativeButton("取消", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {

                }
            });
            AlertDialog dialog=builder.create();
            dialog.show();
        }else{
            controller.navigate(R.id.titleFragment);
        }
        return super.onSupportNavigateUp();
    }
//设置手机的左三角的返回操作
@Override
    public void onBackPressed() {
        onSupportNavigateUp();
    }
}

整个项目到此完结。。。
花费时间：
2020/3/29：上午10：00-11：10，休息10分钟，11：30-12：30，
2020/3/29：下午15：00-15：45，吃东西喝水10分钟，16：00-19：00，吃饭30分钟。
2020/3/29：晚上19：30-20：45，完成。
共花费：420分钟，代码量：450行，UI设计代码除外。