本文实例讲述了Android使用AsyncTask实现多线程下载的方法。分享给大家供大家参考，具体如下：
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public class MainActivity extends Activity implements OnClickListener {
private Button btn1, btn2, btn3;
private ProgressBar progressBar1, progressBar2, progressBar3;
private ImageView img1, img2, img3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initListener();
}
/**
* 初始化监听器
*/
private void initListener() {
btn1.setOnClickListener(this);
btn2.setOnClickListener(this);
btn3.setOnClickListener(this);
}
/**
*
* 初始化控件
*/
private void initView() {
btn1 = (Button) findViewById(R.id.btn1);
btn2 = (Button) findViewById(R.id.btn2);
btn3 = (Button) findViewById(R.id.btn3);
progressBar1 = (ProgressBar) findViewById(R.id.progressbar1);
progressBar2 = (ProgressBar) findViewById(R.id.progressbar2);
progressBar3 = (ProgressBar) findViewById(R.id.progressbar3);
img1 = (ImageView) findViewById(R.id.img1);
img2 = (ImageView) findViewById(R.id.img2);
img3 = (ImageView) findViewById(R.id.img3);
}
@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;
}
@Override
public void onClick(View arg0) {
// 点击按钮模拟下载
MyDownloadAsy down = new MyDownloadAsy();
down.execute(IMG_URI, arg0.getId() + "");
}
/**
* 1.Params，传递给后台任务的参数类型。
*
* 2.Progress，后台计算执行过程中，进步单位（progress units）的类型。（就是后台程序已经执行了百分之几了。）
*
* 3.Result， 后台执行返回的结果的类型。
*/
class MyDownloadAsy extends AsyncTask<String, Integer, Bitmap> {
private static final String TAG = "asy";
private int clickBtn = 0;
private void i(String object) {
Log.i(TAG, object);
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
i("準備運行線程");
progressBar1.setProgress(0);// 进度条复位
progressBar2.setProgress(0);// 进度条复位
progressBar3.setProgress(0);// 进度条复位
}
@Override
protected Bitmap doInBackground(String... arg0) {
switch (Integer.parseInt(arg0[1])) {
case R.id.btn1:
clickBtn = 1;
break;
case R.id.btn2:
clickBtn = 2;
break;
case R.id.btn3:
clickBtn = 3;
break;
default:
break;
}
i("正在后台执行");
publishProgress(0);
// 下载图片
HttpClient hc = new DefaultHttpClient();
// 等待2s
sleepWait();
publishProgress(50);
HttpGet hg = new HttpGet(arg0[0]);// 获取jb51的logo
final Bitmap bm;
try {
HttpResponse hr = hc.execute(hg);
bm = BitmapFactory.decodeStream(hr.getEntity().getContent());
} catch (Exception e) {
return null;
}
sleepWait();
publishProgress(100);
// mImageView.setImageBitmap(result); 不能在后台线程操作ui
return bm;
}
/**
* 等待2s钟
*/
private void sleepWait() {
try {
Thread.sleep(2000);
} catch (InterruptedException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
protected void onProgressUpdate(Integer... values) {
// 动态更新
i("進度更新");
switch (clickBtn) {
case 1:
progressBar1.setProgress(values[0]);// 更新进度条的进度
break;
case 2:
progressBar2.setProgress(values[0]);// 更新进度条的进度
break;
case 3:
progressBar3.setProgress(values[0]);// 更新进度条的进度
break;
default:
break;
}
}
protected void onPostExecute(Bitmap result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
i("线程执行完成");
if (result != null) {
i("下载图片成功");
switch (clickBtn) {
case 1:
img1.setImageBitmap(result);
break;
case 2:
img2.setImageBitmap(result);
break;
case 3:
img3.setImageBitmap(result);
break;
default:
break;
}
} else {
i("下载图片失败");
}
}
@Override
protected void onCancelled() {
// TODO Auto-generated method stub
super.onCancelled();
i("取消线程");
switch (clickBtn) {
case 1:
progressBar1.setProgress(0);// 进度条复位
break;
case 2:
progressBar2.setProgress(0);// 进度条复位
break;
case 3:
progressBar3.setProgress(0);// 进度条复位
break;
default:
break;
}
}
}
}
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xml:
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<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TableLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_centerHorizontal="true" >
<TableRow>
<Button
android:id="@+id/btn1"
android:text="@string/btn1" />
<ProgressBar
android:id="@+id/progressbar1"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<ImageView
android:id="@+id/img1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="@id/img1"
android:src="@drawable/ic_launcher" />
</TableRow>
<TableRow>
<Button
android:id="@+id/btn2"
android:text="@string/btn2" />
<ProgressBar
android:id="@+id/progressbar2"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<ImageView
android:id="@+id/img2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="@id/img2"
android:src="@drawable/ic_launcher" />
</TableRow>
<TableRow>
<Button
android:id="@+id/btn3"
android:text="@string/btn3" />
<ProgressBar
android:id="@+id/progressbar3"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<ImageView
android:id="@+id/img3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:contentDescription="@id/img3"
android:src="@drawable/ic_launcher" />
</TableRow>
</TableLayout>
</RelativeLayout>
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AndroidManifast:
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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.xunfang.asynctackdemo"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="10"
android:targetSdkVersion="10" />
<!-- 访问网络的权限 -->
<uses-permission android:name="android.permission.INTERNET" >
</uses-permission>
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.xunfang.asynctackdemo.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
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希望本文所述对大家Android程序设计有所帮助。