前面介紹了異步任務的處理，這里來學一下Handler和Message機制吧。下面這個代碼和之前的一樣，都是從網上下載圖片的。 ~~~ package com.example.myasynctask; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.InputStream; import org.apache.http.HttpEntity; import org.apache.http.HttpRequest; import org.apache.http.HttpResponse; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.DefaultHttpClient; import org.apache.http.util.EntityUtils; import android.os.AsyncTask; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.app.Activity; import android.app.ProgressDialog; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.view.Menu; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.ImageView; public class MainActivity extends Activity { private Button button; private ImageView iv; private String path = "http://cdn.duitang.com/uploads/item/201310/17/20131017194234_eZfFU.thumb.600_0.png"; private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { Bitmap bm = null; byte[] data = (byte[])msg.obj; bm = BitmapFactory.decodeByteArray(data, 0, data.length); iv.setImageBitmap(bm); }; }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); button = (Button) this.findViewById(R.id.bt); iv = (ImageView) this.findViewById(R.id.iv); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub new Thread(new myThread()).start(); } }); } private class myThread implements Runnable { @Override public void run() { HttpClient httpClient = new DefaultHttpClient(); HttpGet httpGet = new HttpGet(path); InputStream inputStream = null; try { HttpResponse httpResponse = httpClient.execute(httpGet); if (httpResponse.getStatusLine().getStatusCode() == 200 ) { HttpEntity httpEntity = httpResponse.getEntity(); byte[] data = EntityUtils.toByteArray(httpEntity); Message message = Message.obtain(); message.obj = data; handler.sendMessage(message); } } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } } } } ~~~ ~~~ ~~~ ~~~ ~~~ Looper維護一個消息隊列（在loop()函數里面） Message.obtain可回收的獲取Message對象（這樣就不用多次new對象） Handler通過sendMessage來把Message進行消息隊列的入隊，并且把Message的target（也就是對應的Handler綁定為自己） 當消息隊列循環到相應的Message的時候，會調用Message綁定的Handler的dispatchMessage函數，該函數會調用handleMessage函數，也就是用戶實現的handleMessage函數。Handler可以綁定多個Message，通過Message.what來識別身份。 --------源碼所得，2014/ 9/ 9 修改