Android網路下載圖片

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 1 package net.learn2develop.Networking; 2  3 import android.app.Activity; 4 import android.os.Bundle; 5  6 import java.io.IOException; 7 import java.io.InputStream; 8  9 import java.net.HttpURLConnection;10 import java.net.URL;11 import java.net.URLConnection;12 import android.util.Log;13 14 import android.widget.ImageView;15 import android.widget.Toast;16 import android.graphics.Bitmap;17 import android.graphics.BitmapFactory;18 import android.os.AsyncTask;19 public class NetworkingActivity extends Activity {20         21     ImageView img;    22     23     private InputStream OpenHttpConnection(String urlString) throws IOException24     {25         InputStream in = null;26         int response = -1;27                28         URL url = new URL(urlString); 29         URLConnection conn = url.openConnection();30                  31         if (!(conn instanceof HttpURLConnection))                     32             throw new IOException("Not an HTTP connection");        33         try{34             HttpURLConnection httpConn = (HttpURLConnection) conn;35             httpConn.setAllowUserInteraction(false);36             httpConn.setInstanceFollowRedirects(true);37             httpConn.setRequestMethod("GET");38             httpConn.connect();39             response = httpConn.getResponseCode();                 40             if (response == HttpURLConnection.HTTP_OK) {41                 in = httpConn.getInputStream();                                 42             }                     43         }44         catch (Exception ex)45         {46             Log.d("Networking", ex.getLocalizedMessage());47             throw new IOException("Error connecting");48         }49         return in;     50     }51     52     private Bitmap DownloadImage(String URL)53     {        54         Bitmap bitmap = null;55         InputStream in = null;        56         try {57             in = OpenHttpConnection(URL);58             bitmap = BitmapFactory.decodeStream(in);59             in.close();60         } catch (IOException e1) {61             Log.d("NetworkingActivity", e1.getLocalizedMessage());            62         }63         return bitmap;                64     }65         66 67     private class DownloadImageTask extends AsyncTask<String, Void, Bitmap> {68         protected Bitmap doInBackground(String... urls) {69             return DownloadImage(urls[0]);70         }71         72         protected void onPostExecute(Bitmap result) {73             ImageView img = (ImageView) findViewById(R.id.img);74             img.setImageBitmap(result);75         }76     }77 78 @Override79     public void onCreate(Bundle savedInstanceState) {80         super.onCreate(savedInstanceState);81         setContentView(R.layout.main);82         83         new DownloadImageTask().execute("http://www.mayoff.com/5-01cablecarDCP01934.jpg");84 }85 }

因為DownloadImage()方法是同步的——這意味著，在圖片下載完之前不會返回控制權——所以直接調用它會導致活動UI被凍結，使用AsyncTask允許在單獨的線程中執行背景工作，然後在UI線程中返回結果。

Android網路下載圖片