Android异步处理系列文章四篇之二 使用AsyncTask异步更新UI界面

 1 package com.zhuozhuo;
 2 
 3 
 4 import org.apache.http.HttpResponse;
 5 import org.apache.http.client.HttpClient;
 6 import org.apache.http.client.methods.HttpGet;
 7 import org.apache.http.impl.client.DefaultHttpClient;
 8 
 9 import android.app.Activity;
10 import android.graphics.Bitmap;
11 import android.graphics.BitmapFactory;
12 import android.os.AsyncTask;
13 import android.os.Bundle;
14 import android.view.View;
15 import android.view.View.OnClickListener;
16 import android.widget.Button;
17 import android.widget.ImageView;
18 import android.widget.ProgressBar;
19 import android.widget.Toast;
20 
21 public class AsyncTaskActivity extends Activity {
22     
23     private ImageView mImageView;
24     private Button mButton;
25     private ProgressBar mProgressBar;
26     
27     @Override
28     public void onCreate(Bundle savedInstanceState) {
29         super.onCreate(savedInstanceState);
30         setContentView(R.layout.main);
31         
32         mImageView= (ImageView) findViewById(R.id.imageView);
33         mButton = (Button) findViewById(R.id.button);
34         mProgressBar = (ProgressBar) findViewById(R.id.progressBar);
35         mButton.setOnClickListener(new OnClickListener() {
36             
37             @Override
38             public void onClick(View v) {
39                 GetCSDNLogoTask task = new GetCSDNLogoTask();
40                 task.execute("http://csdnimg.cn/www/images/csdnindex_logo.gif");
41             }
42         });
43     }
44     
45     class GetCSDNLogoTask extends AsyncTask<String,Integer,Bitmap> {//继承AsyncTask
46 
47         @Override
48         protected Bitmap doInBackground(String... params) {//处理后台执行的任务，在后台线程执行
49             publishProgress(0);//将会调用onProgressUpdate(Integer... progress)方法
50             HttpClient hc = new DefaultHttpClient();
51             publishProgress(30);
52             HttpGet hg = new HttpGet(params[0]);//获取csdn的logo
53             final Bitmap bm;
54             try {
55                 HttpResponse hr = hc.execute(hg);
56                 bm = BitmapFactory.decodeStream(hr.getEntity().getContent());
57             } catch (Exception e) {
58                 
59                 return null;
60             }
61             publishProgress(100);
62             //mImageView.setImageBitmap(result); 不能在后台线程操作ui
63             return bm;
64         }
65         
66         protected void onProgressUpdate(Integer... progress) {//在调用publishProgress之后被调用，在ui线程执行
67             mProgressBar.setProgress(progress[0]);//更新进度条的进度
68          }
69 
70          protected void onPostExecute(Bitmap result) {//后台任务执行完之后被调用，在ui线程执行
71              if(result != null) {
72                  Toast.makeText(AsyncTaskActivity.this, "成功获取图片", Toast.LENGTH_LONG).show();
73                  mImageView.setImageBitmap(result);
74              }else {
75                  Toast.makeText(AsyncTaskActivity.this, "获取图片失败", Toast.LENGTH_LONG).show();
76              }
77          }
78          
79          protected void onPreExecute () {//在 doInBackground(Params...)之前被调用，在ui线程执行
80              mImageView.setImageBitmap(null);
81              mProgressBar.setProgress(0);//进度条复位
82          }
83          
84          protected void onCancelled () {//在ui线程执行
85              mProgressBar.setProgress(0);//进度条复位
86          }
87         
88     }
89     
90 
91 }

1 <?xml version="1.0" encoding="utf-8"?>
2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
3     android:orientation="vertical" android:layout_width="fill_parent"
4     android:layout_height="fill_parent">
5     <ProgressBar android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/progressBar" style="?android:attr/progressBarStyleHorizontal"></ProgressBar>
6     <Button android:id="@+id/button" android:text="下载图片" android:layout_width="wrap_content" android:layout_height="wrap_content"></Button>
7     <ImageView android:id="@+id/imageView" android:layout_height="wrap_content"
8         android:layout_width="wrap_content" />
9 </LinearLayout>

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
 3       package="com.zhuozhuo"
 4       android:versionCode="1"
 5       android:versionName="1.0">
 6     <uses-sdk android:minSdkVersion="10" />
 7 <uses-permission android:name="android.permission.INTERNET"></uses-permission>
 8     <application android:icon="@drawable/icon" android:label="@string/app_name">
 9         <activity android:name=".AsyncTaskActivity"
10                   android:label="@string/app_name">
11             <intent-filter>
12                 <action android:name="android.intent.action.MAIN" />
13                 <category android:name="android.intent.category.LAUNCHER" />
14             </intent-filter>
15         </activity>
16 
17     </application>
18 </manifest>