Android课程---计算器的实现

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hanqi.test5">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".LongClickActivityActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".UIActivity1">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".CalculatorActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".Activity1" />

    </application>

</manifest>

package com.hanqi.test5;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class CalculatorActivity extends Activity implements View.OnClickListener {
    EditText et;
    Button bt_clear;
    Button bt_goback; //全局变量
    Button bt_7;
    Button bt_8;
    Button bt_9;
    Button bt_6;
    Button bt_5;
    Button bt_4;
    Button bt_3;
    Button bt_2;
    Button bt_1;
    Button bt_0;
    Button bt_jia;
    Button bt_jian;
    Button bt_cheng;
    Button bt_chu;
    Button bt_dian;
    Button bt_deng;

    //存储显式的内容
    //StringBuilder:操作字符串的工具类
    private StringBuilder str_show = new StringBuilder();//实例化

    //当前运算符按钮的id
    private int id_yunsf = 0;
    //运算符前面的数值  Double:包装类
    private Double number_1;
    //运算符后面的数值
    private Double number_2;

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

        et = (EditText)findViewById(R.id.et);
        bt_clear = (Button)findViewById(R.id.clear);
        bt_goback = (Button)findViewById(R.id.goback);
        bt_7 = (Button)findViewById(R.id.bt_7);
        bt_8 = (Button)findViewById(R.id.bt_8);
        bt_9 = (Button)findViewById(R.id.bt_9);
        bt_6 = (Button)findViewById(R.id.bt_6);
        bt_5 = (Button)findViewById(R.id.bt_5);
        bt_4 = (Button)findViewById(R.id.bt_4);
        bt_3 = (Button)findViewById(R.id.bt_3);
        bt_2 = (Button)findViewById(R.id.bt_2);
        bt_1 = (Button)findViewById(R.id.bt_1);
        bt_0 = (Button)findViewById(R.id.bt_0);
        bt_jia = (Button)findViewById(R.id.bt_jia);
        bt_jian = (Button)findViewById(R.id.bt_jian);
        bt_cheng = (Button)findViewById(R.id.bt_cheng);
        bt_chu = (Button)findViewById(R.id.bt_chu);
        bt_dian = (Button)findViewById(R.id.bt_dian);
        bt_deng = (Button)findViewById(R.id.bt_deng);

        bt_clear.setOnClickListener(this);
        bt_goback.setOnClickListener(this);
        bt_7.setOnClickListener(this);
        bt_8.setOnClickListener(this);
        bt_9.setOnClickListener(this);
        bt_6.setOnClickListener(this);
        bt_5.setOnClickListener(this);
        bt_4.setOnClickListener(this);
        bt_3.setOnClickListener(this);
        bt_2.setOnClickListener(this);
        bt_1.setOnClickListener(this);
        bt_0.setOnClickListener(this);
        bt_jia.setOnClickListener(this);
        bt_jian.setOnClickListener(this);
        bt_cheng.setOnClickListener(this);
        bt_chu.setOnClickListener(this);
        bt_dian.setOnClickListener(this);
        bt_deng.setOnClickListener(this);

    }
    //事件源组件
    public void onClick(View v)
    {
        Button bt = (Button)v;

        int id = bt.getId();

        switch (id)
        {
            case R.id.clear:
                str_show = new StringBuilder();  //重新实例化就可以清除
                //设置显示框内容
                et.setText(str_show);  //et:显示框

                number_1 = null;
                number_2 = null;
                id_yunsf = 0;

             break;

            case R.id.goback:

            if (str_show.length()>0)
            {
                //删除最后一个字符  索引值减1
                str_show.deleteCharAt(str_show.length()-1);
                et.setText(str_show);
                break;
            }

            case R.id.bt_7:
            case R.id.bt_8:
            case R.id.bt_9:
            case R.id.bt_6:
            case R.id.bt_5:
            case R.id.bt_4:
            case R.id.bt_3:
            case R.id.bt_2:
            case R.id.bt_1:
            case R.id.bt_0:

                if (id == R.id.bt_0
                        ||(id == R.id.bt_0 && !str_show.toString().equals("0")))
                {
                    str_show.append(bt.getText());
                }
                et.setText(str_show);
                break;
            case R.id.bt_deng:
            case R.id.bt_jia:
            case R.id.bt_jian:
            case R.id.bt_cheng:
            case R.id.bt_chu:

                if (number_1 == null)
                {
                    if (str_show.length()>0)
                    {
                        //把字符串转成Double
                        number_1 = new Double(str_show.toString());
                        id_yunsf = bt.getId();
                        str_show = new StringBuilder();  //重新实例化就可以清除
                        //设置显示框内容
                        //et.setText(str_show);  //et:显示框
                    }
                }
                else//计算
                {
                    if (str_show.length()>0)
                    {
                        //把字符串转成Double  赋值
                        number_2 = new Double(str_show.toString());
                    }

                    switch (id_yunsf)
                    {
                        case R.id.bt_jia:
                            //运算
                            double res = number_1.doubleValue() + number_2.doubleValue();
                            break;

                        case R.id.bt_jian:
                            //运算
                            number_1 = number_1.doubleValue() - number_2.doubleValue();
                            break;
                        case R.id.bt_cheng:
                            //运算
                            number_1 = number_1.doubleValue() * number_2.doubleValue();
                            break;
                        case R.id.bt_chu:
                            //运算
                            if (number_2 !=0)
                            {
                                number_1 = number_1.doubleValue() / number_2.doubleValue();
                            }
                            else
                            {
                                Toast.makeText(this,"不能除0",Toast.LENGTH_LONG).show();
                            }
                            break;
                    }
                    //运算符
                    id_yunsf = bt.getId();
                    //显示当前运算结果
                    et.setText(number_1.toString());
                    //清空
                    str_show = new StringBuilder();

                }
                break;
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:rowCount="6"
    android:columnCount="4">
    <!--行:rowCount   列:columnCount-->

    <EditText
        android:layout_columnSpan="4"
        android:layout_gravity="fill_horizontal"
        android:layout_rowWeight="1"
        android:textSize="30sp"
        android:editable="false"
        android:gravity="right|center_vertical"/>
    <!--水平填充:fill_horizontal  竖直填充:fill_vertical
        行号:layout_row    列号:layout_column（行号和列号都可以指定，但注意都是从0开始的）-->
    <Button
        android:text="清除"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/clear"/>
    <Button
        android:text="后退"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:textColor="#0ff"
        android:id="@+id/goback"/>
    <Button
        android:text="/"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_chu"/>
    <Button
        android:text="x"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_cheng"/>
    <Button
        android:text="7"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_7"/>
    <Button
        android:text="8"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_8"/>
    <Button
        android:text="9"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_9"/>
    <Button
        android:text="-"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_jian"/>
    <Button
        android:text="4"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_4"/>
    <Button
        android:text="5"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_5"/>
    <Button
        android:text="6"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_6"/>
    <Button
        android:text="+"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_jia"/>
    <Button
        android:text="1"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_1"/>
    <Button
        android:text="2"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_2"/>
    <Button
        android:text="3"
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_3"/>
    <Button
        android:text="="
        android:layout_rowSpan="2"
        android:layout_gravity="fill_vertical"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="20sp"
        android:id="@+id/bt_deng"/>
    <Button
        android:text="0"
        android:layout_columnSpan="2"
        android:layout_gravity="fill_horizontal"
        android:layout_columnWeight="1"
        android:layout_rowWeight="1"
        android:textSize="20sp"
        android:background="#FF0000"
        android:id="@+id/bt_0"/>
    <Button
        android:text="."
        android:layout_rowWeight="1"
        android:layout_columnWeight="1"
        android:textSize="20sp"
        android:textColor="#FF0000"
        android:id="@+id/bt_dian"/>

</GridLayout>

这些代码可以实现计算器的基本功能

效果：