<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical">
 <!-- 加法器名稱-->
 <TextView
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:text="加法器"
 android:textSize="40sp"
 android:textColor="#E6BD1A"
 android:gravity="center"
 android:layout_marginTop="20sp"
 android:textStyle="bold"/>

 <!-- 第1個數字輸入框 -->
 <EditText
 android:id="@+id/input1"
  />

 <!-- 加法符號 -->
 <TextView
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:text="+"
 android:textStyle="bold"
 android:textSize="40sp"
 android:textColor="#1A94E6"
 android:gravity="center"
 android:layout_marginTop="50sp"/>

 <!-- 第2個數字輸入框-->
 <EditText
 android:id="@+id/input2"
  />

 <!-- 等于和歸零符號 -->
 <LinearLayout

 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:orientation="horizontal"
 android:layout_gravity="center"
 android:layout_marginTop="20sp"
 android:layout_marginBottom="20sp">
 <!-- 等于符號 -->
 <Button
 android:id="@+id/btn1"
 
 android:text="="
 android:layout_marginRight="20sp"/>
 <!-- 歸零符號 -->
 <Button
 android:id="@+id/btn2"
 
 android:text="C"/>

 </LinearLayout>

 <!-- 結果輸入框 -->
 <EditText
 android:id="@+id/input3"
 
 android:enabled="false"/>

</LinearLayout>

<resources>

 <!-- Base application theme. -->
 <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
 <!-- Customize your theme here. -->
 <item name="colorPrimary">@color/colorPrimary</item>
 <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
 <item name="colorAccent">@color/colorAccent</item>
 </style>

 <!-- 3個輸入框的樣式 -->
 <style name="input_style">
 <item name="android:layout_gravity">center</item>
 <item name="android:gravity">center</item>
 <item name="android:layout_width">350sp</item>
 <item name="android:layout_height">wrap_content</item>
 <item name="android:color">#000000</item>
 <item name="android:layout_marginTop">15sp</item>
 <item name="android:inputType">number</item>
 </style>

 <!-- 等于和歸零按鈕樣式 -->
 <style name="button_style">
 <item name="android:layout_width">wrap_content</item>
 <item name="android:layout_height">wrap_content</item>
 <item name="android:textSize">30sp</item>
 <item name="android:gravity">center</item>
 </style>

</resources>

package cn.itcast.totalizator;

import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;

import android.content.DialogInterface;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
 //輸入框input1 input2
 // 結果框input3
 private EditText input1 = null;
 private EditText input2 = null;
 private EditText input3 = null;
 //等于按鈕btn1
 //歸零按鈕btn2
 private Button btn1 = null;
 private Button btn2 = null;


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

 input1 = (EditText) findViewById(R.id.input1);
 input2 = (EditText) findViewById(R.id.input2);
 input3 = (EditText) findViewById(R.id.input3);

 btn1 = (Button) findViewById(R.id.btn1);
 btn2 = (Button) findViewById(R.id.btn2);

 //點擊等于按鈕觸發監聽事件
 btn1.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 String input1Str = input1.getText().toString();
 String input2Str = input2.getText().toString();

 if (! input1Str.equals("") && ! input2Str.equals("")) {
 double number1 = Double.parseDouble(input1Str);
 double number2 = Double.parseDouble(input2Str);
 double result = number1 + number2;

 input3.setText(result + "");
 }
 else{
 Toast.makeText(getApplicationContext(),"請輸入合法的數字",Toast.LENGTH_SHORT).show();
 }
 }
 });
 //點擊歸零按鈕觸發監聽事件
 btn2.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 //把三個輸入框都設置為空
 input1.setText("");
 input2.setText("");
 input3.setText("");
 }
 });


 }

 //點擊退出按鈕，彈出是否確認退出對話框
 @Override
 public void onBackPressed() {
 //聲明對象
 AlertDialog dialog;
 //綁定當前界面窗口，設置標題
 dialog = new AlertDialog.Builder(this)
 .setTitle("Dialog對話框")
 .setMessage("是否確定退出")
 .setIcon(R.mipmap.ic_launcher)
 .setPositiveButton("確定",listener)
 .setNegativeButton("取消", listener)
 .create();
 dialog.show();

 }

 //監聽對話框里面的button點擊事件
 DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener()
 {
 public void onClick(DialogInterface dialog, int which)
 {
 switch (which)
 {
 case AlertDialog.BUTTON_POSITIVE:// "確認"按鈕退出程序
 finish();
 break;
 case AlertDialog.BUTTON_NEGATIVE:// "取消"第二個按鈕取消對話框
 break;
 default:
 break;
 }
 }
 };
}