双击退出和Notification通知

双击退出

实现的基本原理就是，当按下BACK键时，会被onKeyDown捕获，判断是BACK键，则执行exit方法。
判断用户两次按键的时间差是否在一个预期值之内，是的话直接直接退出，不是的话提示用户再按一次后退键退出。

package com.example.day03_homework;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.KeyEvent;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private long exitTime=0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode== KeyEvent.KEYCODE_BACK) {
            if (System.currentTimeMillis()-exitTime>=2000) {
                Toast.makeText(this, "再点退出", Toast.LENGTH_SHORT).show();
                exitTime=System.currentTimeMillis();
                return true;
            }else {
                finish();
            }
        }
        return super.onKeyDown(keyCode, event);
    }
}

Notification通知

定义：是在系统的通知栏中呈现多样式持久性消息的类
1、在通知栏显示
2、消息持久性
3、种类多样性
用处:
显示客户端的推送消息（如有新版本发布、广告、推荐新闻等）
显示正在进行的事物（如音乐播放器、版本更新时候的下载进度等）
显示接收到短消息，即时消息等信息（如QQ、微信、新浪、短信）

常用方法：

setSmallIcon() 与 setLargeIcon()

当 setSmallIcon() 与 setLargeIcon() 同时存在时, smallIcon 显示在通知的右下角, largeIcon 显示在左侧；当只设置 setSmallIcon() 时, smallIcon 显示在左侧。

发送一个最简单的通知(无交互)

package com.example.day03_homework;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Notification;
import android.app.NotificationManager;
import android.content.Context;
import android.os.Bundle;
import android.view.View;

public class Main2Activity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
    }
	//按钮的点击
    public void click(View view) {
        sendNntification();
    }

    private void sendNntification() {
        Notification.Builder builder = new Notification.Builder(this);
        //设置属性
        builder.setSmallIcon(R.mipmap.ic_launcher);//必须设置
        builder.setContentTitle("标题");//建议设置
        builder.setContentText("内容");//建议设置

        //builder.setTicker("我是提示信息");
        //builder.setContentInfo("我是附加消息");//7.0以后淘汰

        Notification build = builder.build();//创建对象，发送的消息就是这个对象
        //过去通知管理器，负责发通知，清除通知等
        NotificationManager notificationManager= (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        notificationManager.notify(1,build);//发送通知    参数一：通知的id  参数二：通知对象
    }
}

自定义通知

package com.example.day03_homework;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Notification;
import android.app.NotificationManager;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.RemoteViews;
import android.widget.TextView;

public class Main3Activity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main3);
    }

    public void click(View view) {
        userNotification();
    }

    private void userNotification() {
        Notification.Builder builder = new Notification.Builder(this);
        builder.setSmallIcon(R.mipmap.ic_launcher_round);
        builder.setContentTitle("标题");
        builder.setContentText("内容");
        /**
         * RemoteViews是可以在别的进程（系统进程）中显示的View，并且提供了一组跨进程更新它界面的操作
         * 两个参数,第一个布局所在包名
         * 第二个是布局Id
         * 布局文件是自己创建的,随便一个线性布局,加一个textView和ImageView即可
         */
        RemoteViews remoteViews = new RemoteViews(getPackageName(), R.layout.layout_notification_zi);
        //将自定义布局的控件赋值
        remoteViews.setImageViewResource(R.id.image_id,R.mipmap.ic_launcher_round);
        remoteViews.setTextViewText(R.id.text_id,"永远十八岁");

        builder.setCustomContentView(remoteViews);
        Notification build = builder.build();
        NotificationManager notificationManager= (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        notificationManager.notify(1,build);
    }
}

进度条通知

package com.example.day03_homework;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Notification;
import android.app.NotificationManager;
import android.content.Context;
import android.os.Bundle;
import android.view.View;

import java.util.Timer;
import java.util.TimerTask;

public class Main4Activity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main4);
    }

    public void click(View view) {
        progress_Notification();
    }

    private void progress_Notification() {
        final Notification.Builder builder = new Notification.Builder(this);
        builder.setSmallIcon(R.mipmap.ic_launcher_round);
        builder.setContentTitle("标题");
        final NotificationManager notificationManager= (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);

        final Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            int progress=0;
            @Override
            public void run() {
                //模拟下载
                builder.setContentText("正在下载，当前下载进度"+progress);
                //参数一 最大值 参数二：当前进度 参数三 是否模糊
                builder.setProgress(100,progress,false);
                progress+=10;
                notificationManager.notify(1,builder.build());
                if (progress==100) {
                    //进度达到100安装
                    builder.setContentText("正在安装……");
                    //安装模糊
                    builder.setProgress(0,0,true);
                    notificationManager.notify(1,builder.build());
                    try {
                        Thread.sleep(5000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    //安装完成
                    notificationManager.cancel(1);//取消置顶通知
                    timer.cancel();
                }
            }
        },0,1000);
    }
}

通知分组

将App中的相同类型的消息可以合并

private void groupNotification() {
        NotificationManager notificationManager= (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        Notification.Builder builder1 = new Notification.Builder(this);
        Notification.Builder builder2 = new Notification.Builder(this);
        Notification.Builder builder3 = new Notification.Builder(this);
        Notification.Builder builder4 = new Notification.Builder(this);

        builder1.setSmallIcon(R.mipmap.ic_launcher_round);
        builder1.setContentTitle("111");
        builder1.setContentText("222");
        builder1.setGroup("1");
        //builder1.setGroupSummary(true);

        builder2.setSmallIcon(R.mipmap.ic_launcher_round);
        builder2.setContentTitle("333");
        builder2.setContentText("444");
        builder2.setGroup("1");
        builder2.setGroupSummary(true);

        builder3.setSmallIcon(R.mipmap.ic_launcher_round);
        builder3.setContentTitle("555");
        builder3.setContentText("666");
        builder3.setGroup("1");
        //builder3.setGroupSummary(true);

        builder4.setSmallIcon(R.mipmap.ic_launcher_round);
        builder4.setContentTitle("777");
        builder4.setContentText("888");
        builder4.setGroup("1");
        //builder4.setGroupSummary(true);

        notificationManager.notify(1,builder1.build());
        notificationManager.notify(2,builder2.build());
        notificationManager.notify(3,builder3.build());
        notificationManager.notify(4,builder4.build());
    }

锁屏通知

Android 5.0(API level 21)开始，通知可以显示在锁屏上，通过设置选择是否允许敏感的通知内容显示在安全的锁屏上。

//builde的时候 
//通过 setVisibility() 方法设置即可
.setVisibility(VISIBILITY_PUBLIC)
.build();

setVisibility() 方法共有三个选值：
1.VISIBILITY_PRIVATE : 显示基本信息，如通知的图标，但隐藏通知的全部内容；
2.VISIBILITY_PUBLIC : 显示通知的全部内容；
3.VISIBILITY_SECRET : 不显示任何内容，包括图标。