Android-入门学习笔记-交互

resvalues目录下dimens.xml、strings,xml

Button文本自动大写

Java知识 Java官方开发文档

Java变量命名规则:不可过短或过长、首字母小写驼峰式。Language Basics-Variables

bug复现后易于debug（通过查看系统日志，搜索关键词并Google，逐行阅读不现实），难以复现的bug最难debug。即使是拥有11年经验编程经验的程序员，依然有许多不懂且需每天学习。

@Override，伪代码，复写/重载。

•   帮助自己检查是否正确的复写了父类中已有的方法
•   告诉读代码的人，这是一个复写的方法

局部变量、全局变量。局部变量作用域，使用后销毁、其他方法中重复定义。

int 整型 integer

 String message = "The total trip will be: " + totalLength + " miles.";//定义并赋值字符串类型的变量可使用字符串与数字变量的组合形式，具体方式如左边所示。

　　

确保已开启 Auto Import：

• 对于 Windows，请依次转到“文件 (File)”>“设置 (Settings)”>“编辑器 (Editor)”>“常规 (General)”>“自动导入 (Auto Import)”
• 对于 Mac，请依次转到 Android Studio >“偏好设置 (Preferences)”>“编辑器 (Editor)”>“常规 (General)”>“自动导入 (Auto Import)”

选中以下所有选项：

• Show import popup
• Optimize imports on the fly
• Add unambiguous imports on the fly
• Insert imports on paste → All

断点调试

断点的使用

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingBottom="@dimen/activity_vertical"
    android:paddingLeft="@dimen/activity_horizon"
    android:paddingRight="@dimen/activity_horizon"
    android:paddingTop="@dimen/activity_vertical"
    tools:context="com.example.administrator.justjava.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/quantity"
        android:textAllCaps="true" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:paddingBottom="@dimen/linear_vertical"
        android:paddingTop="@dimen/linear_vertical">

        <Button
            android:layout_width="@dimen/small_button"
            android:layout_height="@dimen/small_button"
            android:onClick="decrement"
            android:text="@string/minus"
            android:textSize="@dimen/text_size" />

        <TextView
            android:id="@+id/quantity_text_view"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingLeft="@dimen/quantity_horizon"
            android:paddingRight="@dimen/quantity_horizon"
            android:text="@string/value"
            android:textColor="@android:color/black"
            android:textSize="@dimen/text_size" />

        <Button
            android:layout_width="@dimen/small_button"
            android:layout_height="@dimen/small_button"
            android:onClick="increment"
            android:text="@string/plus"
            android:textSize="@dimen/text_size" />

    </LinearLayout>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/price"
        android:textAllCaps="true" />

    <TextView
        android:id="@+id/price_text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="@dimen/price_vertical"
        android:layout_marginTop="@dimen/price_vertical"
        android:text="@string/price_value"
        android:textColor="@android:color/black"
        android:textSize="@dimen/text_size" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="submitOrder"
        android:text="@string/button"/>

</LinearLayout>

 　　android中xml tools属性详解

<resources>
    <string name="app_name">Just Java</string>
    <string name="quantity">Quantity</string>
    <string name="value">2</string>
    <string name="price">price</string>
    <string name="price_value">$0</string>
    <string name="button">Order</string>
    <string name="plus">+</string>
    <string name="minus">-</string>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <dimen name="activity_vertical">8dp</dimen>
    <dimen name="activity_horizon">16dp</dimen>
    <dimen name="linear_vertical">16dp</dimen>
    <dimen name="small_button">48dp</dimen>
    <dimen name="quantity_horizon">8dp</dimen>
    <dimen name="text_size">16sp</dimen>
    <dimen name="price_vertical">16dp</dimen>
</resources>

package com.example.administrator.justjava;

/**
 * Add your package below. Package name can be found in the project's AndroidManifest.xml file.
 * This is the package name our example uses:
 *
 * package com.example.android.justjava;
 */

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;

import java.text.NumberFormat;

/**
 * This app displays an order form to order coffee.
 */
public class MainActivity extends AppCompatActivity {

    int quantity = 2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    /**
     * This method is called when the add button is clicked.
     */
    public void increment(View view) {
        quantity = quantity + 1;
        display(quantity);
    }

    /**
     * This method is called when the minus button is clicked.
     */
    public void decrement(View view) {
        quantity = quantity - 1;
        display(quantity);
    }

    /**
     * This method is called when the order button is clicked.
     */
    public void submitOrder(View view) {
        int price = quantity * 5;
        String priceMessage = "Total $" + price;
        priceMessage = priceMessage + "
Thank you!";
        displayMessage(priceMessage);
    }

    /**
     * This method displays the given quantity value on the screen.
     */
    private void display(int number) {
        TextView quantityTextView = (TextView) findViewById(R.id.quantity_text_view);
        quantityTextView.setText("" + number);
    }

    /**
     * This method displays the given price on the screen.
     */
    private void displayPrice(int number) {
        TextView priceTextView = (TextView) findViewById(R.id.price_text_view);
        priceTextView.setText(NumberFormat.getCurrencyInstance().format(number));
    }

    /**
     * This method displays the given text on the screen.
     */
    private void displayMessage(String message) {
        TextView priceTextView = (TextView) findViewById(R.id.price_text_view);
        priceTextView.setText(message);
    }

}