Android实现加法计算器

<?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" 
 <!-- 加法器名称-- 
 <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个数字输入框 -- 
 <EditText
 android:id="@+id/input1"
 style="@style/input_style" / 

 <!-- 加法符号 -- 
 <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个数字输入框-- 
 <EditText
 android:id="@+id/input2"
 style="@style/input_style" / 

 <!-- 等于和归零符号 -- 
 <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" 
 <!-- 等于符号 -- 
 <Button
 android:id="@+id/btn1"
 style="@style/button_style"
 android:text="="
 android:layout_marginRight="20sp"/ 
 <!-- 归零符号 -- 
 <Button
 android:id="@+id/btn2"
 style="@style/button_style"
 android:text="C"/ 

 </LinearLayout 

 <!-- 结果输入框 -- 
 <EditText
 android:id="@+id/input3"
 style="@style/input_style"
 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个输入框的样式 -- 
 <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 

 <!-- 等于和归零按钮样式 -- 
 <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 {
 //输入框input1 input2
 // 结果框input3
 private EditText input1 = null;
 private EditText input2 = null;
 private EditText input3 = null;
 //等于按钮btn1
 //归零按钮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);

 //点击等于按钮触发监听事件
 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(),"请输入合法的数字",Toast.LENGTH_SHORT).show();
 }
 }
 });
 //点击归零按钮触发监听事件
 btn2.setOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 //把三个输入框都设置为空
 input1.setText("");
 input2.setText("");
 input3.setText("");
 }
 });


 }

 //点击退出按钮，弹出是否确认退出对话框
 @Override
 public void onBackPressed() {
 //声明对象
 AlertDialog dialog;
 //绑定当前界面窗口，设置标题
 dialog = new AlertDialog.Builder(this)
 .setTitle("Dialog对话框")
 .setMessage("是否确定退出")
 .setIcon(R.mipmap.ic_launcher)
 .setPositiveButton("确定",listener)
 .setNegativeButton("取消", listener)
 .create();
 dialog.show();

 }

 //监听对话框里面的button点击事件
 DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener()
 {
 public void onClick(DialogInterface dialog, int which)
 {
 switch (which)
 {
 case AlertDialog.BUTTON_POSITIVE:// "确认"按钮退出程序
 finish();
 break;
 case AlertDialog.BUTTON_NEGATIVE:// "取消"第二个按钮取消对话框
 break;
 default:
 break;
 }
 }
 };
}