主要用于异步处理： 存在于线程中
开启子线程：异步处理

image.png

image.png

主要接受子线程发送的数据，并用此数据配合主线程更新UI

···
//1.创建Handler对象
private Handler handler=new Handler(){
//2.重写handleMessage
public void handleMessage(android.os.Message msg) {
5.获取消息：
String data= msg.obj;
Toast.makeText(getApplicationContext(), data, 1).show();
tv.setText("这是Hander")
}
}；

在子线程：
String s='你好'；
3.创建消息对象
Messge message = new Message();
message.obj=data;
message.what=10086; //消息编号

4.发送消息
mHandler.sendMessage(message);

···
---------------------handler--------------------
···
switch (msg.what) {
case 10086:
String data2=(String) msg.obj;
tv.setText(data2);
break;
case 10087:
Integer data3=(Integer) msg.obj;
tv.setText(data3+"");
break;

    default:
        break;
    }

···
··················子线程···························
···
new Thread(new Runnable() {

    @Override
    public void run() {
        try {

//
Thread.sleep(3000);

            String data="你好";
            //4.创建Message
            Message message = new Message();
            message.obj=data;
            message.what=10086;//编号
            //3.发送消息
            handler.sendMessage(message);
            handler.sendEmptyMessage(10086);
            handler.sendMessageDelayed(message, 2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }           
    }
}).start();
int data=12542;//主线程 先显示
Message message = new Message();
message.obj=data;
message.what=10087;

// //3.发送消息
handler.sendMessage(message);

···
*****************Handler****开启子线程***************************
private Handler handler=new Handler(){
public void handleMessage(android.os.Message msg) {
// //2.重写handleMessage
// //获取消息

    switch (msg.what) {
    case 10086:
        String data2=(String) msg.obj;
        tv.setText(data2);
        break;
    case 10087:
new Thread(new Runnable() {
    
    @Override
    public void run() {
    try {
        Thread.sleep(3000);
        
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
        
        
    }
}).start();
        Integer data3=(Integer) msg.obj;
        tv.setText(data3+"");
        break;

    default:
        break;
    }
};

};