Android Handler的使用

最新推荐文章于 2025-03-31 17:54:40 发布

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最新推荐文章于 2025-03-31 17:54:40 发布

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分类专栏： java

本文链接：https://blog.youkuaiyun.com/qq_33938417/article/details/103156467

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Android Handler主要用于在线程间更新UI，其核心是消息处理机制。文章介绍了Handler的工作原理，阐述了如何在新线程中绑定到Message Queue进行UI回调，以及生命周期方法与Handler的关联。

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package com.example.handler_01;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.os.Handler;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    private TextView textView;
    private Handler handler = new Handler();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        textView = findViewById(R.id.tv);
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
//                  android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
                    Thread.sleep(1000);
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            textView.setText("HAHA");
                        }
                    });
                }catch (Exception e) {
                    e.printStackTrace();
                }

            }
        }).start();
    }
}

在线程中更新UI 要用handler

handler 是什么

android 更新ui的机制消息处理的机制

生命周期的回调的方法都是通过handler

新创建一个线程会绑定到message queue 中

package com.example.handler_01;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.os.Handler;
import android.widget.ImageView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {
    private TextView textView;
    private Handler handler = new Handler();

    private int[] images = {
        R.drawable.image1,R.drawable.image2,R.drawable.image3
    };
    private int index = 0;
    private MyRunnable myRunnable = new MyRunnable();
    class MyRunnable implements  Runnable{
        @Override
        public void run() {
            index++;
            index = index % 3;
            imageView.setImageResource(images[index]);
            //要做的事情，这里再次调用此Runnable对象，以实现每两秒实现一次的定时器操作
            handler.postDelayed(this,1000);
        }
    }
    private ImageView imageView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        imageView = findViewById(R.id.iv);
        handler.postDelayed(myRunnable,1000);

    }
}

package com.example.handler_01;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.TextView;

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

import com.example.handler_01.entity.Person;

public class Main2Activity extends AppCompatActivity{
    private TextView textView;

    private Handler handler = new Handler(){
        @Override
        public void handleMessage(@NonNull Message msg) {
            Person p = (Person) msg.obj;
            String name = p.getName();
            Integer age = p.getAge();

            textView.setText(msg.arg1+""+msg.arg2+msg.obj+"  name  "+name);
        }
    };

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        textView = (TextView) findViewById(R.id.tv2);

        new Thread(new Runnable() {
            @Override
            public void run() {
                //message
                Message message = handler.obtainMessage();
                message.arg1 = 12;//这玩意儿是INT类型
                message.arg2 = 14;
                Person person = new Person("zhangsan",12);
                message.obj = person;

                handler.sendMessage(message);
            }
        }).start();


    }

}