activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" > <Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_centerHorizontal="true" android:text="下载网络图片" /> <ImageView android:id="@+id/imageView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:src="@drawable/ic_launcher" /></RelativeLayout>
MainActivity
package com.example.android_asytask_download;import java.io.ByteArrayOutputStream;import java.io.InputStream;import org.apache.http.HttpEntity;import org.apache.http.HttpResponse;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.R.integer;import android.app.Activity;import android.app.ProgressDialog;import android.content.Entity;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.view.Menu;import android.view.View;import android.widget.Button;import android.widget.ImageView;public class MainActivity extends Activity { private Button button; private ImageView imageView; private ProgressDialog progressDialog; private final int IS_END = 1; private String image_path = "http://a.hiphotos.baidu.com/image/w%3D2048/sign=7610c70c5143fbf2c52ca1238446cb80/d4628535e5dde71120a3a1f2a5efce1b9d166145.jpg"; private Handler handler = new Handler() { @Override public void handleMessage(android.os.Message msg) { byte[] data = (byte[]) msg.obj; Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length); imageView.setImageBitmap(bitmap); if(msg.what==IS_END) { progressDialog.dismiss(); } }; }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); button = (Button) this.findViewById(R.id.button1); imageView = (ImageView) this.findViewById(R.id.imageView1); progressDialog = new ProgressDialog(this); progressDialog.setTitle("提示"); progressDialog.setMessage("正在下载，请稍后..."); progressDialog.setCancelable(false);// 点击不会失去焦点，直到下载结束 button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View arg0) { // TODO Auto-generated method stub new Thread(new MyThread()).start(); progressDialog.show(); } }); } public class MyThread implements Runnable { @Override public void run() { // 线程耗时部分的主体操作 HttpClient httpClient = new DefaultHttpClient(); HttpGet httpGet = new HttpGet(image_path); try { HttpResponse httpResponse = httpClient.execute(httpGet);// 执行http操作 if (httpResponse.getStatusLine().getStatusCode() == 200) { byte[] data = EntityUtils.toByteArray(httpResponse .getEntity()); // 一般实例化消息对象不用new Message()，而是通过Message.obtain() Message message = Message.obtain(); message.obj = data; message.what = IS_END; handler.sendMessage(message);// handler对象发送消息 } } catch (Exception e) { // TODO: handle exception } } } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; }}
1.Handler对象负责发送消息和处理消息
2.Message消息对象实例化使用Message message = Message.obtain();