android开发分享Android App开发：Handler消息处理

Handler消息传递机制

子线程不允许操作主线程的U界面

Handler是android中提供的一个消息处理的机制
1.在任意线程中发送消息
2.在主线程中获取并处理消息

package com.example;  import androidx.annotation.NonNull; import androidx.appcompat.app.AppCompatActivity;  import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.view.View; import android.widget.Button; import android.widget.TextView;  public class MainActivity extends AppCompatActivity {      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         TextView textView = findViewById(R.id.tv);         Button button = findViewById(R.id.btn);         Handler handler = new Handler(){             @Override             public void handleMessage(@NonNull Message msg) {                 super.handleMessage(msg);                 if (msg.what == 0x123){                     textView.setText("你今天的努力是新云的伏；当下的付出，是明日的花开");                  }             }         };         button.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 //创建线程                 Thread thread = new Thread(new Runnable() {                     @Override                     public void run() {                         handler.sendEmptyMessage(0x123);//发送空消息 //                        textView.setText("你今天的努力是新云的伏；当下的付出，是明日的花开");                     }                 });                 thread.start();//开启线程             }         });     } } 

Message

Message对象的属性
arg1,arg2 整形
obj Object类型
replyTo 发送到何处
what 自定义的消息代码

创建Message对象
1.Message.obtain()
2.Handler.obtainMessage()

模拟手机淘宝使用Handler和Message实现轮播广告

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"     xmlns:app="https://schemas.android.com/apk/res-auto"     xmlns:tools="https://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:orientation="vertical"     android:background="@drawable/taobao"     tools:context=".MainActivity">      <ViewFlipper         android:id="@+id/vf"         android:layout_width="match_parent"         android:layout_height="wrap_content"/>   </LinearLayout> 

package com.example;  import androidx.annotation.NonNull; import androidx.appcompat.app.AppCompatActivity;  import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.view.animation.Animation; import android.view.animation.AnimationUtils; import android.widget.ImageView; import android.widget.ViewFlipper;  public class MainActivity extends AppCompatActivity {     private ViewFlipper flipper;     private int[] images = new int[]{R.drawable.icon1,R.drawable.icon2,R.drawable.left             ,R.drawable.like,R.drawable.line};     private Animation[] animation = new Animation[2];     private final int FLAG_MSG = 0x001;     private Message message;     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         flipper = findViewById(R.id.vf);         for (int i = 0; i < images.length; i++) {             ImageView imageView = new ImageView(this);             imageView.setImageResource(images[i]);             flipper.addView(imageView);         }          animation[0] = AnimationUtils.loadAnimation(this, R.anim.slide_in_right);         animation[1] = AnimationUtils.loadAnimation(this, R.anim.slide_out_left);         flipper.setInAnimation(animation[0]);         flipper.setOutAnimation(animation[1]);         message = Message.obtain();         message.what = FLAG_MSG;         handler.sendMessage(message);      }     Handler handler = new Handler(){         @Override         public void handleMessage(@NonNull Message msg) {             super.handleMessage(msg);             if (msg.what ==FLAG_MSG){                 flipper.showPrevious();                 message = handler.obtainMessage(FLAG_MSG);                 handler.sendMessageDelayed(message,3000);             }         }     }; } 

Looper

Looper对象的创建
handler在主线程中创建时，系统自动创建Looper对象
handler在子线程中创建时，手动创建Looper对象

子线程中创建Looper对象的步骤
1.初始化Looper对象prepare()
2.创建Handler对象new Handler()
3.启动Looper loop()

package com.example;  import android.os.Handler; import android.os.Looper; import android.os.Message; import android.util.Log;  import androidx.annotation.NonNull;  public class LooperThread  extends Thread{     private Handler handler;     @Override     public void run() {         super.run();         Looper.prepare();//初始化Looper对象         handler = new Handler(){             @Override             public void handleMessage(@NonNull Message msg) {                 super.handleMessage(msg);                 Log.i("Looper",String.valueOf(msg.what));             }         };         Message message = handler.obtainMessage();         message.what = 0x7;         handler.sendMessage(message);         Looper.loop();//启动Looper     } }  

package com.example;  import androidx.appcompat.app.AppCompatActivity;  import android.os.Bundle;  public class MainActivity extends AppCompatActivity {      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         LooperThread thread = new LooperThread(){};         thread.start();     } }