（七）android 通知对话框，并且监听了返回键，当按下返回键也会创建一个对话框

一、activity_main.java中代码

 1 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 2     xmlns:tools="http://schemas.android.com/tools"
 3     android:layout_width="match_parent"
 4     android:layout_height="match_parent"
 5     android:gravity="center"
 6     tools:context="com.example.Dialog.MainActivity" >
 7     <Button
 8         android:onClick="click"
 9         android:layout_width="wrap_content"
10         android:layout_height="wrap_content"
11         android:text="对话框" />
12 </LinearLayout>

二、MainActivity.java中的代码
 1 package com.example.Dialog;
 2 
 3 import android.app.Activity;
 4 import android.app.AlertDialog;
 5 import android.app.AlertDialog.Builder;
 6 import android.app.Dialog;
 7 import android.content.DialogInterface;
 8 import android.content.DialogInterface.OnClickListener;
 9 import android.os.Bundle;
10 import android.view.KeyEvent;
11 import android.view.View;
12 import android.widget.Toast;
13 
14 public class MainActivity extends Activity {
15 
16     @Override
17     protected void onCreate(Bundle savedInstanceState) {
18         super.onCreate(savedInstanceState);
19         setContentView(R.layout.activity_main);
20     }
21 
22     public void click(View view) {
23         AlertDialog.Builder builder = new Builder(this);
24         builder.setTitle("提示");
25         builder.setIcon(R.drawable.ic_launcher);
26         builder.setMessage("是否要进行软件升级");
27         // builder.setCancelable(false);
28         builder.setPositiveButton("确定", new OnClickListener() {
29             @Override
30             public void onClick(DialogInterface dialog, int which) {
31                 // TODO Auto-generated method stub
32                 Toast.makeText(MainActivity.this, "确定被点击了", 0).show();
33             }
34         });
35         builder.setNegativeButton("取消", new OnClickListener() {
36 
37             @Override
38             public void onClick(DialogInterface dialog, int which) {
39                 // TODO Auto-generated method stub
40                 Toast.makeText(MainActivity.this, "取消被点击了", 0).show();
41             }
42         });
43         builder.create().show();
44     }
45 
46     @Override
47     public boolean onKeyDown(int keyCode, KeyEvent event) {
48         // TODO Auto-generated method stub
49 
50         if (keyCode == KeyEvent.KEYCODE_BACK) {
51             AlertDialog.Builder builder = new Builder(this);
52             builder.setTitle("提示");
53             builder.setMessage("确定要退出吗");
54             builder.create();
55             Dialog dialog;
56 
57             builder.setPositiveButton("确定", new OnClickListener() {
58 
59                 @Override
60                 public void onClick(DialogInterface dialog, int which) {
61                     // TODO Auto-generated method stub
62                     dialog.dismiss();
63                 }
64             });
65             builder.setNegativeButton("取消", new OnClickListener() {
66 
67                 @Override
68                 public void onClick(DialogInterface dialog, int which) {
69                     // TODO Auto-generated method stub
70 
71                 }
72             });
73             dialog = builder.show();
74 
75         }
76         return false;
77     }
78 }