上篇文章寫到了簡單的文件下載的功能，這里再簡單的添加一個功能（顯示下載進度）。代碼方面改變不大，只是運用了AsyncTask的onProgressUpdate函數，不過下載圖片的代碼得要用另外一種方式寫了。 ~~~ 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.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 ProgressDialog dia; @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); dia = new ProgressDialog(this); dia.setTitle("提示信息"); dia.setMessage("正在下載..."); dia.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub new myTask().execute(path); } }); } private class myTask extends AsyncTask<String, Integer, Bitmap> { @Override protected void onPreExecute() { // TODO Auto-generated method stub super.onPreExecute(); dia.show(); } @Override protected void onProgressUpdate(Integer... values) { // TODO Auto-generated method stub super.onProgressUpdate(values); dia.setProgress(values[0]); } @Override protected Bitmap doInBackground(String... params) { // TODO Auto-generated method stub Bitmap bitmap = null; ByteArrayOutputStream outputStream = new ByteArrayOutputStream(); InputStream inputStream = null; HttpClient httpClient = new DefaultHttpClient(); HttpGet httpGet = new HttpGet(params[0]); try { HttpResponse httpResponse = httpClient.execute(httpGet); if (httpResponse.getStatusLine().getStatusCode() == 200) { long total_length = httpResponse.getEntity() .getContentLength(); int has_read = 0; int total_read = 0; byte[] data = new byte[1024]; inputStream = httpResponse.getEntity().getContent(); while ((has_read = inputStream.read(data)) != -1) { total_read += has_read; outputStream.write(data, 0, has_read); int value = (int) (total_read / (float) total_length * 100); publishProgress(value); } byte[] result = outputStream.toByteArray(); bitmap = BitmapFactory.decodeByteArray(result, 0, result.length); } } catch (ClientProtocolException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } return bitmap; } @Override protected void onPostExecute(Bitmap result) { // TODO Auto-generated method stub super.onPostExecute(result); iv.setImageBitmap(result); dia.dismiss(); } } } ~~~