<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout

    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:background="#FF85C17E"

    tools:context="com.example.lesson7_2_id19_dialog.MainActivity">

</RelativeLayout>

 <?xml version="1.0" encoding="utf-8"?>

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

     android:layout_width="match_parent"

     android:layout_height="match_parent"

     android:background="@mipmap/timg">

     <TextView

         android:id="@+id/tv_time"

         android:gravity="center"

         android:background="@drawable/oval"

         android:layout_width="wrap_content"

         android:layout_height="wrap_content"

         android:text="3s"

         android:layout_alignParentRight="true"

         android:layout_margin="20dp"/>

 </RelativeLayout>

 <?xml version="1.0" encoding="utf-8"?>

 <shape xmlns:android="http://schemas.android.com/apk/res/android"

     android:shape="oval">

     <padding

         android:bottom="5dp"

         android:left="5dp"

         android:right="5dp"

         android:top="5dp" />

     <stroke

         android:width="1dp"

         android:color="#7bf0f2" />

 </shape>

 package com.example.lesson7_2_id19_dialog;

 import android.app.Dialog;

 import android.content.Context;

 import android.os.Bundle;

 import android.os.CountDownTimer;

 import android.support.annotation.NonNull;

 import android.widget.TextView;

 /**

  * Created by Administrator on 2017/3/8 0008.

  */

 public class StartDialog extends Dialog {

     // 继承dialog重写构造方法

     public StartDialog(@NonNull Context context) {

         super(context, R.style.DialogStyle);

     }

     TextView tv_time;

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.dialog_start);

         // 设置是否可以关闭当前控件

         setCancelable(false);

         // 找到tv_time控件

         tv_time = (TextView) findViewById(R.id.tv_time);

         new DownTimer().start();

     }

         // 继承CountDownTimer类

     class DownTimer extends CountDownTimer {

         public DownTimer() {

             // 设置时间4秒

             super(4000, 1000);

         }

         // 重写CountDownTimer的两个方法

         @Override

         public void onTick(long millisUntilFinished) {

             tv_time.setText(millisUntilFinished / 1000 + "s");

         }

         @Override

         public void onFinish() {

             StartDialog.this.dismiss();

         }

     }

 }

 package com.example.lesson7_2_id19_dialog;

 import android.content.DialogInterface;

 import android.os.Bundle;

 import android.support.v7.app.AppCompatActivity;

 import android.widget.Toast;

 public class MainActivity extends AppCompatActivity {

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         StartDialog dialog = new StartDialog(this);

         dialog.show();

         dialog.setOnDismissListener(new DialogInterface.OnDismissListener() {

             @Override

             public void onDismiss(DialogInterface dialog) {

                 Toast.makeText(MainActivity.this, "应用开始页面关闭", Toast.LENGTH_SHORT).show();

             }

         });

     }

 }