public class MainActivity extends Activity {private ImageView image_load;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);this.image_load = (ImageView) this.findViewById(R.id.image_load);}public void download(View view) {String url = "http://litchiapi.jstv.com/Attachs/Top/11949/e650e0201de541d2ba91dca202b0fcfe.jpg";// 调用异步任务，执行网络访问，注意联网要权限new MyTask(this).execute(url);// 不用提示框时new MyTask()不加加入当前this，不用构造函数，}class MyTask extends AsyncTask<String, Void, byte[]> {/** //AsyncTask三个重要参数：Params: 是一个可变数组 //Progress:进度条，没有时写为void ,* //Result：结果参数，一般为byte[]数组*/private ProgressDialog pDialog;// 不用在布局文件配置这个对话框public MyTask(Context context) {// 创建提示对话框pDialog = new ProgressDialog(context);// 当前上下文的对话框pDialog.setTitle("提示");pDialog.setMessage("正在下载.....");pDialog.setIcon(R.drawable.ic_launcher);}// 主线程运行, 在doInBackground之前执行@Overrideprotected void onPreExecute() {super.onPreExecute();Log.i("MainActivity", "onPreExecute : "+ Thread.currentThread().getName());pDialog.show();// 在doInBackground之前执行，打开对话框}@Override// 在子线程中调用后台执行protected byte[] doInBackground(String... params) {Log.i("MainActivity", "onPostExecute : "+ Thread.currentThread().getName());String url = params[0];HttpClient client = new DefaultHttpClient();HttpGet get = new HttpGet(url);try {HttpResponse response = client.execute(get);if (response.getStatusLine().getStatusCode() == 200) {return EntityUtils.toByteArray(response.getEntity());}} catch (ClientProtocolException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}return null;}// onPostExecute在主线程中执行，在doInBackground后执行，进行UI更新操作@Overrideprotected void onPostExecute(byte[] result) {Log.i("MainActivity", "onPostExecute : "+ Thread.currentThread().getName());super.onPostExecute(result);if (result != null) {Bitmap bitmap = BitmapFactory.decodeByteArray(result, 0,result.length);image_load.setImageBitmap(bitmap);} else {Toast.makeText(MainActivity.this, "网络异常！", Toast.LENGTH_SHORT).show();}pDialog.dismiss();// 下载完关闭对话框}}
}
//布局
<ImageViewandroid:id="@+id/image_load"android:layout_width="wrap_content"android:layout_height="wrap_content" /><Buttonandroid:id="@+id/btn_load"android:layout_width="wrap_content"android:layout_height="wrap_content"android:onClick="download"android:layout_below="@+id/image_load"android:text="下载" />