（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

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    tools:context="com.example.Dialog.MainActivity" >
    <Button
        android:onClick="click"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="对话框" />
</LinearLayout>

二、MainActivity.java中的代码
 1 package com.example.Dialog;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.app.Dialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Toast;

public class MainActivity extends Activity {

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

    public void click(View view) {
        AlertDialog.Builder builder = new Builder(this);
        builder.setTitle("提示");
        builder.setIcon(R.drawable.ic_launcher);
        builder.setMessage("是否要进行软件升级");
        // builder.setCancelable(false);
        builder.setPositiveButton("确定", new OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                Toast.makeText(MainActivity.this, "确定被点击了", 0).show();
            }
        });
        builder.setNegativeButton("取消", new OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub
                Toast.makeText(MainActivity.this, "取消被点击了", 0).show();
            }
        });
        builder.create().show();
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // TODO Auto-generated method stub

        if (keyCode == KeyEvent.KEYCODE_BACK) {
            AlertDialog.Builder builder = new Builder(this);
            builder.setTitle("提示");
            builder.setMessage("确定要退出吗");
            builder.create();
            Dialog dialog;

            builder.setPositiveButton("确定", new OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    // TODO Auto-generated method stub
                    dialog.dismiss();
                }
            });
            builder.setNegativeButton("取消", new OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int which) {
                    // TODO Auto-generated method stub

                }
            });
            dialog = builder.show();

        }
        return false;
    }
}