Android开发教程:Handler+thread 加载网络图片
Android开发教程:Handler+thread 加载网络图片
关于Android多线程处理UI-我在网上查了下资料发现有好几种,本次学习只是其中一种,主要是利用handler结合Thread更新UI。
下面是我写的小Demo:
Handler+thread 加载网络图片,我在网上随便找了三张图片,分别开三个线程加载他们,然后在Activity中显示。
其中一个线程出现异常不会影响到其他线程更不会阻塞主线程(UI线程) ,这是多线程带来的好处之一。
本次Demo主要是利用Handler.sendMessage(...)把消息压进消息队列,过后通过Handler.handleMessage(...)在UI线程中处理压入的消息。从队列中取出消息时会根据压入的不同消息来更新UI。图片在外部线程中加载,加载完后sendmessage在主线程中更新UI。外部线程只顾加载图片,而更新UI是主线程(UI线程)的事,这个就达到了多线程异步加载网络图片的目的
ThreadDemo.java ThreadDemo是一个Activity,UI在这里面更新
- package com.study.thread;
- import android.app.Activity;
- import android.app.ProgressDialog;
- import android.graphics.Bitmap;
- import android.os.Bundle;
- import android.os.Handler;
- import android.os.Message;
- import android.util.Log;
- import android.view.View;
- import android.view.View.OnClickListener;
- import android.widget.ImageView;
- import android.widget.Toast;
- public class ThreadDemo extends Activity {
- private static final String TAG = "ThreadDemo";
- // 我把三个线程编了号
- private static final int THREAD_1 = 1;
- private static final int THREAD_2 = 2;
- private static final int THREAD_3 = 3;
- private ImageView mImgView1;
- private ImageView mImgView2;
- private ImageView mImgView3;
- // 记录消息
- int count = 0;
- ProgressDialog mDialog ;
- // 网上找的三张图片的地址
- String[] urls = new String[]
- {
- "http://hiphotos.baidu.com/yuangengqiang/pic/item/252196ca222b88ad50664f58.jpg",
- "http://hiphotos.baidu.com/lzc196806/pic/item/d84f738da76514d2f11f3665.jpg",
- "http://hiphotos.baidu.com/735216726/pic/item/2488f146f7ea415e72f05d75.jpg"
- };
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- this.getView();
- System.out.println("ThreadDemo-----"+Thread.currentThread().getName());
- // 处理按钮按下
- findViewById(R.id.btnStart).setOnClickListener(new OnClickListener()
- {
- @Override
- public void onClick(View v)
- {
- count = 0;
- mDialog = ProgressDialog.show(ThreadDemo.this, "",
- "Loading. Please wait...", true);
- // 开启线程:第一个线程处理第一张图片以此类推
- new Thread(new LoadImageRunnable(mHandler,THREAD_1,urls[0])).start();
- new Thread(new LoadImageRunnable(mHandler,THREAD_2,urls[1])).start();
- new Thread(new LoadImageRunnable(mHandler,THREAD_3,urls[2])).start();
- ThreadDemo.this.setTitle("线程已近创建完毕");
- }
- });
- }
- private void getView()
- {
- mImgView1 = (ImageView)findViewById(R.id.img01);
- mImgView2 = (ImageView)findViewById(R.id.img02);
- mImgView3 = (ImageView)findViewById(R.id.img03);
- }
- private Handler mHandler = new Handler()
- {
- // 利用handleMessage更新UI
- public void handleMessage (Message msg)
- {
- switch(msg.what)
- {
- case ThreadDemo.THREAD_1:
- mImgView1.setImageBitmap((Bitmap)msg.obj);
- Log.i(TAG, "thread-1");
- break;
- case ThreadDemo.THREAD_2:
- mImgView2.setImageBitmap((Bitmap)msg.obj);
- Log.i(TAG, "thread-2");
- break;
- case ThreadDemo.THREAD_3:
- mImgView3.setImageBitmap((Bitmap)msg.obj);
- Log.i(TAG, "thread-3");
- break;
- // 如有异常会有提示
- default:
- String info = "第"+msg.what%10+"个线程"+"出现异常";
- Toast.makeText(ThreadDemo.this, info , Toast.LENGTH_LONG).show();
- break;
- }
- count++;
- if(3==count)
- {
- mDialog.dismiss();
- }
- }
- };
- }
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