Andorid 多线程(三)：Handler 消息传递机制

haovin   https://blog.csdn.net/haovin/article/details/89600054

一、Android中的HandlerThread

1.1主要用途

a、定时器，未来某时做某事

b、线程之间传递消息

c、嵌入式：apk 调用SystemService 时，权限不够，由Handler 传递消息，可以获得 system  jurisdiction

注意：handler对线程的处理post，并不是启动了一个新的线程，而是在当前线程调用run方法。

二、Handler的使用

 2.1 定时器

package com.gatsby.handlerdelaytime;

import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    Button btn1,btn2;
    int count = 0;

    Handler handler = new Handler();//创建一个Handler对象:
    private Runnable runnable = new Runnable() {

        @Override
        public void run() {
            Log.d("gatsby", "Thread.currentThread().getId()->"+Thread.currentThread().getId());
            count++;
            Log.d("gatsby", "count=" + count);
            handler.postDelayed(runnable, 1000);//1秒后调用此Runnable对象
        }

    };

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

        btn1 = (Button) this.findViewById(R.id.btn1);
        btn2 = (Button) this.findViewById(R.id.btn2);

        btn1.setOnClickListener(new View.OnClickListener() {
            public void onClick(View arg0) {
                Thread thread = new Thread(runnable);
                thread.start();
            }
        });

        btn2.setOnClickListener(new View.OnClickListener() {
            public void onClick(View arg0) {
                handler.removeCallbacks(runnable);//关闭此定时器
            }
        });
    }


}

package com.gatsby.handlerrunnable;

import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    Button btn1, btn2;

    Handler mhandler = new Handler();//创建一个Handler对象

    private Runnable runnable = new Runnable() {
        @Override
        public void run() {
            Log.d("gatsby", "Handler  DelayRunable!");
        }
    };

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

        btn1 = (Button) findViewById(R.id.btn1);
        btn2 = (Button) findViewById(R.id.btn2);

        btn1.setOnClickListener(this);
        btn2.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {

        switch (v.getId()) {
            case R.id.btn1:
                Log.d("gatsby","onClick btn1!");
                mhandler.postDelayed(runnable, 2000);
                break;
            case R.id.btn2:
                mhandler.removeCallbacks(runnable);
                break;

        }
    }
}

 2.2 使用方式

Handler的使用方式可以根据发送消息的方式不同而分为两种:

Handler.sendMessage()和Handler.post()

2.3 Ed Sheeran 

方式一、使用Handler.sendMessage()

a、创建Handler子类

package com.gatsby.handlertest;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    TextView tv1;
    Button btn1;

    // 2、在主线程中创建自定义Handler（mHandler）的实例
    private CrushHandler crushHandler = new CrushHandler();

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

        tv1 = (TextView) findViewById(R.id.tv1);
        btn1 = (Button) findViewById(R.id.btn1);

        btn1.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn1:
                MyRunnable();
                break;
        }
    }

    public void MyRunnable() {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                // 3、创建所需消息对象
                Message msg = Message.obtain();
                msg.what = 1;
                //4、发送消息
                crushHandler.sendMessage(msg);
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();
    }

    //1、自定义Handler子类，继承Handler，重写handleMessage()方法
    class CrushHandler extends Handler {

        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            //执行的UI操作
            tv1.setText("新建Handler子类方法");
        }
    }


}

创建Handler子类
1、自定义Handler子类，并重写handleMessage()方法
    class CrushHandler extends Handler {
        //重写handleMessage()方法
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);
            //执行的UI操作
            tv1.setText("新建Handler子类方法");
        }
    }
2、主线程中创建mHandler的实例
    private CrushHandler crushHandler = new CrushHandler();
3、在子线程中创建需要发送的消息对象
    Message msg = Message.obtain();
    msg.what = 1;
4、在子线程中通过Hander发送消息到消息队列
    crushHandler.sendMessage(msg);
5、启动子线程

b、使用匿名内部类

package com.gatsby.handlertest;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    TextView tv1;
    Button btn1;

    //1、在主线程中通过匿名内部类创建Handler类对象
    private Handler mHandler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            //执行的UI操作
            tv1.setText("匿名内部类方法");
            return false;
        }
    });


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

        tv1 = (TextView) findViewById(R.id.tv1);
        btn1 = (Button) findViewById(R.id.btn1);

        btn1.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn1:
                MyRunnable();
                break;
        }
    }

    public void MyRunnable() {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                // 2、创建所需消息对象
                Message msg = Message.obtain();
                msg.what = 1;
                //3、发送消息
                mHandler.sendMessage(msg);
            }
        };
        Thread thread = new Thread(runnable);
        thread.start();//4、开启线程
    }

}

方式二、post方法

post机制将runnable对象运行在主线程中的

package com.gatsby.handlertest;

import android.os.Bundle;
import android.os.Handler;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    TextView tv1;
    Button btn1;

    //1、在主线程中创建Handler的实例
    private Handler mHandlerPost = new Handler();

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

        tv1 = (TextView) findViewById(R.id.tv1);
        btn1 = (Button) findViewById(R.id.btn1);

        btn1.setOnClickListener(this);
    }
    
    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn1:
                Thread thread = new CrushThread();
                thread.start();
                break;
        }
    }

    class CrushThread extends Thread {
        @Override
        public void run() {
            Runnable runnable = new Runnable() {
                @Override
                public void run() {
                    tv1.setText("post方法");
                }
            };
            mHandlerPost.post(runnable);
        }
    }

}