制作一个简易计算器——基于Android Studio实现

一个计算器Android程序的源码部分分为主干和细节两部分。

一、主干

1. 主干的构成

• 计算器的布局
• 事件（即计算器上的按钮、文本框）监听
• 实现计算

2. 详细解释

　　假设我们的项目名为Calculator，而布局名称（Layout Name）为默认的activity_main 。即设置如下图所示：

       

　　在这种前提下，有：

• 设置计算器布局的文件：Calculator/app/src/main/res/layout/activity_main.xml
• 事件监听和计算实现在同一个文件里：Calculator/app/src/main/java/下的一个子目录里的MainActivity.java

　　即如下图所示：

      

3. 主干代码部分

• 计算器布局代码（写在activity_main.xml文件里）：

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    >
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="vertical" >
        <EditText
            android:id="@+id/input"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:editable="false"
            android:hint="@string/shuru" />

        <EditText
            android:id="@+id/output"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:editable="true"
            android:gravity="right"
            android:hint="@string/shuchu" />

        <RelativeLayout
            android:layout_width="fill_parent"
            android:layout_height="wrap_content" >

            <Button
                android:id="@+id/seven"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentLeft="true"
                android:text="@string/seven"
                android:textSize="40sp" />

            <Button
                android:id="@+id/eight"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_toRightOf="@id/seven"
                android:text="@string/eight"
                android:textSize="40sp" />

            <Button
                android:id="@+id/nine"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_toRightOf="@id/eight"
                android:text="@string/nine"
                android:textSize="40sp" />

            <Button
                android:id="@+id/add"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentRight="true"
                android:layout_toRightOf="@id/nine"
                android:text="@string/add"
                android:textSize="40sp" />

            <Button
                android:id="@+id/four"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentLeft="true"
                android:layout_below="@id/seven"
                android:text="@string/four"
                android:textSize="40sp" />

            <Button
                android:id="@+id/five"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_below="@id/eight"
                android:layout_toRightOf="@id/four"
                android:text="@string/five"
                android:textSize="40sp" />

            <Button
                android:id="@+id/six"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_below="@id/nine"
                android:layout_toRightOf="@id/five"
                android:text="@string/six"
                android:textSize="40sp" />

            <Button
                android:id="@+id/subtract"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentRight="true"
                android:layout_below="@id/add"
                android:layout_toRightOf="@id/six"
                android:text="@string/subtract"
                android:textSize="40sp" />

            <Button
                android:id="@+id/one"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentLeft="true"
                android:layout_below="@id/four"
                android:text="@string/one"
                android:textSize="40sp" />

            <Button
                android:id="@+id/two"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_below="@id/five"
                android:layout_toRightOf="@id/one"
                android:text="@string/two"
                android:textSize="40sp" />

            <Button
                android:id="@+id/three"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_below="@id/six"
                android:layout_toRightOf="@id/two"
                android:text="@string/three"
                android:textSize="40sp" />

            <Button
                android:id="@+id/multiply"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentRight="true"
                android:layout_below="@id/subtract"
                android:layout_toRightOf="@id/three"
                android:text="@string/multiply"
                android:textSize="40sp" />

            <Button
                android:id="@+id/zero"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentLeft="true"
                android:layout_below="@id/one"
                android:text="@string/zero"
                android:textSize="40sp" />

            <Button
                android:id="@+id/clear"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_below="@id/two"
                android:layout_toRightOf="@id/zero"
                android:text="@string/clear"
                android:textSize="40sp" />

            <Button
                android:id="@+id/result"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_below="@id/three"
                android:layout_toRightOf="@id/clear"
                android:text="@string/result"
                android:textSize="40sp" />

            <Button
                android:id="@+id/divide"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentRight="true"
                android:layout_below="@id/multiply"
                android:layout_toRightOf="@id/result"
                android:text="@string/divide"
                android:textSize="40sp" />

            <Button
                android:id="@+id/dot"
                android:layout_width="80dp"
                android:layout_height="70dp"
                android:layout_alignParentLeft="true"
                android:layout_below="@id/zero"
                android:text="@string/dot"
                android:textSize="40sp" />
            <Button
                android:id="@+id/writeButton"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentLeft="true"
                android:layout_below="@id/dot"
                android:text="@string/write"
                android:textSize="40sp" />
            <Button
                android:id="@+id/readButton"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentRight="true"
                android:layout_below="@id/dot"
                android:text="@string/read"
                android:textSize="40sp" />

            <CheckBox
                android:id="@+id/appendBox"
                android:text="@string/appendBox"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_alignParentBottom="true"
                android:layout_toLeftOf="@+id/divide"
                android:layout_toStartOf="@+id/divide"
                android:layout_marginBottom="12dp"
                />

        </RelativeLayout>

        <EditText

            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/textView" />

        <EditText

            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/displayView" />

        <EditText
            android:id="@+id/errorzero"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:editable="false"
            android:gravity="center"
            />
        <EditText
            android:id="@+id/resultText"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:editable="false"
            android:gravity="left"
            android:text="@string/resultText"
            />
    </LinearLayout>
</ScrollView>

• 事件监听和实现计算代码（写在MainActivity.java文件里）

package com.example.lenovo.calculator;



        import android.app.Activity;
        import android.content.Context;
        import android.os.Bundle;
        import android.view.View;
        import android.view.View.OnClickListener;
        import android.widget.Button;
        import android.widget.CheckBox;
        import android.widget.EditText;

        import java.io.FileInputStream;
        import java.io.FileNotFoundException;
        import java.io.FileOutputStream;
        import java.io.IOException;

public class MainActivity extends Activity {
    /**
     * Called when the activity is first created.
     */
    private EditText output = null;
    private EditText input = null;
    private Button btn0 = null;
    private Button btn1 = null;
    private Button btn2 = null;
    private Button btn3 = null;
    private Button btn4 = null;
    private Button btn5 = null;
    private Button btn6 = null;
    private Button btn7 = null;
    private Button btn8 = null;
    private Button btn9 = null;
    private Button btnadd = null;
    private Button btnsubtract = null;
    private Button btnmultiply = null;
    private Button btndivide = null;
    private Button btnclear = null;
    private Button btnresult = null;
    private Button btndot = null;

    private EditText errorzero = null;

    private EditText resultText = null;
    private Button writeButton = null;
    private Button readButton = null;
    private CheckBox appendBox = null;
    private EditText textView = null;
    private EditText displayView = null;
    public String FILE_NAME = "fileDemo.txt";


    private String str = "";//保存数字
    private String strold = "";//原数字
    private char act = ' ';//记录“加减乘除等于”符号
    private int count = 0;//判断要计算的次数，如果超过一个符号，先算出来一部分
    private Float result = null;//计算的输出结果
    private Boolean errBoolean = false;//有错误的时候为true，无错为false
    private Boolean flagBoolean = false;//一个标志，如果为true，可以响应运算消息，如果为false，不响应运算消息，只有前面是数字才可以响应运算消息
    private Boolean flagDot = false; //小数点标志位



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

        output = (EditText) findViewById(R.id.output);
        input = (EditText) findViewById(R.id.input);

        errorzero = (EditText) findViewById(R.id.errorzero);
        resultText = (EditText) findViewById(R.id.resultText);
        writeButton = (Button) findViewById(R.id.writeButton);
        readButton = (Button) findViewById(R.id.readButton);
        textView = (EditText) findViewById(R.id.textView);
        displayView = (EditText) findViewById(R.id.displayView);
        appendBox = (CheckBox) findViewById(R.id.appendBox);

        btn0 = (Button) findViewById(R.id.zero);
        btn1 = (Button) findViewById(R.id.one);
        btn2 = (Button) findViewById(R.id.two);
        btn3 = (Button) findViewById(R.id.three);
        btn4 = (Button) findViewById(R.id.four);
        btn5 = (Button) findViewById(R.id.five);
        btn6 = (Button) findViewById(R.id.six);
        btn7 = (Button) findViewById(R.id.seven);
        btn8 = (Button) findViewById(R.id.eight);
        btn9 = (Button) findViewById(R.id.nine);
        btnadd = (Button) findViewById(R.id.add);
        btnsubtract = (Button) findViewById(R.id.subtract);
        btnmultiply = (Button) findViewById(R.id.multiply);
        btndivide = (Button) findViewById(R.id.divide);
        btnclear = (Button) findViewById(R.id.clear);
        btnresult = (Button) findViewById(R.id.result);
        btndot = (Button) findViewById(R.id.dot);
        //设置按钮侦听事件
        btn0.setOnClickListener(listener);
        btn1.setOnClickListener(listener);
        btn2.setOnClickListener(listener);
        btn3.setOnClickListener(listener);
        btn4.setOnClickListener(listener);
        btn5.setOnClickListener(listener);
        btn6.setOnClickListener(listener);
        btn7.setOnClickListener(listener);
        btn8.setOnClickListener(listener);
        btn9.setOnClickListener(listener);
        //执行运算
        btnadd.setOnClickListener(listener);
        btnsubtract.setOnClickListener(listener);
        btnmultiply.setOnClickListener(listener);
        btndivide.setOnClickListener(listener);
        btnclear.setOnClickListener(listener);
        btnresult.setOnClickListener(listener);

        btndot.setOnClickListener(listener);

        writeButton.setOnClickListener(writelistener);
        readButton.setOnClickListener(readlistener);


        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
    }


    private OnClickListener listener = new OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub
            switch (v.getId()) {
                //输入数字
                case R.id.zero:
                    num(0);
                    break;
                case R.id.one:
                    num(1);
                    break;
                case R.id.two:
                    num(2);
                    break;
                case R.id.three:
                    num(3);
                    break;
                case R.id.four:
                    num(4);
                    break;
                case R.id.five:
                    num(5);
                    break;
                case R.id.six:
                    num(6);
                    break;
                case R.id.seven:
                    num(7);
                    break;
                case R.id.eight:
                    num(8);
                    break;
                case R.id.nine:
                    num(9);
                    break;

                case R.id.dot:
                    dot();
                    break;
                //执行运算
                case R.id.add:
                    add();
                    break;
                case R.id.subtract:
                    sub();
                    break;
                case R.id.multiply:
                    multiply();
                    break;
                case R.id.divide:
                    divide();
                    break;
                case R.id.clear:
                    clear();
                    break;
                //计算结果
                case R.id.result:
                    result();
                    if (!errBoolean && flagBoolean) {
                        output.setText(String.valueOf(result));
                    }
                    resultText.setText(strold + act + str + "=" + result+"                          ");
                    break;

                default:
                    break;

            }
            input.setText(strold + act + str);
            output.setText(String.valueOf(result));


        }
    };

    private OnClickListener writelistener = new OnClickListener() {
        @Override
        public void onClick(View view) {
            //textView.setText("");

            FileOutputStream fos = null;
            try {
                if (appendBox.isChecked()) {
                    fos = openFileOutput(FILE_NAME, Context.MODE_APPEND);
                } else {
                    fos = openFileOutput(FILE_NAME, Context.MODE_PRIVATE);
                }
                String text = resultText.getText().toString();
                fos.write(text.getBytes());
                textView.setText("文件写入成功，写入长度：" + text.length());
                //resultText.setText("");

            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }
            finally {
                if (fos != null)
                    try {
                        fos.flush();
                        fos.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
            }
        }
    };
    private OnClickListener readlistener = new OnClickListener() {
        @Override
        public void onClick(View view) {

            displayView.setText("");
            FileInputStream fis = null;
            try {
                fis = openFileInput(FILE_NAME);
                if (fis.available() == 0) {
                    return;
                }
                byte[] readBytes = new byte[fis.available()];
                while (fis.read(readBytes) != -1) {

                }
                String text = new String(readBytes);
                displayView.setText(text);
                textView.setText("文件读取成功，写入长度：" + text.length());

            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    };

    private void dot() {
        // TODO Auto-generated method stub

        if (!flagDot) {
            str = str + ".";
            flagBoolean = false;
            flagDot = true;
        }
    }

    private void clear() {
        // TODO Auto-generated method stub
        str = strold = "";
        count = 0;
        act = ' ';
        result = null;
        flagBoolean = false;
        flagDot = false;
        input.setText(strold + act + str);
        output.setText("");
        errorzero.setText("");
        displayView.setText("");
        textView.setText("");
        resultText.setText("");
    }

    private void divide() {
        // TODO Auto-generated method stub
        if (flagBoolean) {
            check();
            act = '/';
            flagBoolean = false;
        }
    }

    private void multiply() {
        // TODO Auto-generated method stub
        if (flagBoolean) {
            check();
            act = '*';
            flagBoolean = false;
        }
    }

    private void sub() {
        // TODO Auto-generated method stub
        if (flagBoolean) {
            check();
            act = '-';
            flagBoolean = false;
        }
    }

    private void add() {
        // TODO Auto-generated method stub
        if (flagBoolean) {
            check();
            act = '+';
            flagBoolean = false;
        }
    }

    private void check() {
        // TODO Auto-generated method stub
        if (count >= 1) {
            result();
            str = String.valueOf(result);
        }
        strold = str;
        str = "";
        count++;
        flagDot = false;
        errorzero.setText("");
    }

    //计算输出结果
    private void result() {
        // TODO Auto-generated method stub
        if (flagBoolean) {
            Float a, b;

            a = Float.parseFloat(strold);
            b = Float.parseFloat(str);

            if (b == 0 && act == '/') {
                clear();
                errorzero.setText("除数不能为零!");
                //output.setText("除数不能为零!");


                //errBoolean=true;
            }


            if (!errBoolean) {
                switch (act) {
                    case '+':
                        result = a + b;
                        break;
                    case '-':
                        result = a - b;
                        break;
                    case '*':
                        result = a * b;
                        break;
                    case '/':
                        result = a / b;
                        break;

                    default:
                        break;
                }
            }


        }
    }

    private void num(int i) {
        // TODO Auto-generated method stub
        str = str + String.valueOf(i);
        flagBoolean = true;
        errorzero.setText("");
    }

}

二、细节

　　仅仅将主干部分代码copy下来并不能运行程序，因为主干代码调用了一些文件的代码，这些文件就是我们所说的细节。

1. 字符串资源

• 文件位置：Calculator/app/src/main/res/values/strings.xml
• 代码部分：

<resources>
    <string name="app_name">Calculator</string>
    <string name="action_settings">Settings</string>
        <string name="zero">0</string>
        <string name="one">1</string>
        <string name="two">2</string>
        <string name="three">3</string>
        <string name="four">4</string>
        <string name="five">5</string>
        <string name="six">6</string>
        <string name="seven">7</string>
        <string name="eight">8</string>
        <string name="nine">9</string>
        <string name="add">+</string>
        <string name="subtract">-</string>
        <string name="multiply">*</string>
        <string name="divide">/</string>
        <string name="clear">CE</string>
        <string name="result">=</string>
        <string name="shuru">请按数字键盘输入数字</string>
        <string name="shuchu">计算器输出结果</string>
        <string name="dot">.</string>
        <string name="write">写入</string>
        <string name="read">读取</string>
        <string name="resultText">计算式</string>
        <string name="appendBox">追加模式</string>

</resources>

2. 其他可能要改的文件

• Calculator/app/src/main/res/drawable：设置相关的背景颜色、按钮特效
• Calculator/app/src/main/AndroidManifest.xml：设置这个项目的整体配置

 

三、备注

1. 本文提供的简易计算器仅需要修改前三个文件（布局文件、监听实现文件、字符串资源文件）
2. 纯复制粘贴是一定会报错的，留意一点将有些地方改动一下