下載的png文件不可讀

Question

我已經通過服務下載了一些png文件，現在我正在嘗試使用它們。他們進入用戶的SD卡。我已驗證每個文件都在卡上。但是，當我嘗試將它們中的任何一個設置爲ImageView時，我會得到空白區域。

因此，我通過手動嘗試使用手機的圖片查看器在手機上顯示它們，發現文件完好無損。沒有任何文件會打開。我想知道的是，如果我在下載需要發生的文件以使它們可以看作png文件（或位圖文件）後缺少任何步驟。這裏是我服務的代碼，我用它來下載文件：

public class DownloadPicture extends IntentService { 

    private int result = Activity.RESULT_CANCELED; 
    public static final String FILENAME = "filename"; 
    public static final String FILEPATH = "filepath"; 
    public static final String RESULT = "result"; 
    public static final String NOTIFICATION "com.mydomain.myapp.MyBroadcastReceiver"; 

    public DownloadPicture() { 
     super("DownloadPicture"); 
    } 

    public DownloadPicture(String name) { 
     super(name); 
    } 

    @Override 
    protected void onHandleIntent(Intent intent) { 

     String fileName = intent.getStringExtra(FILENAME); 
     String urlPath = this.getResources().getString(R.string.imagesURL) + fileName; 
     System.err.println("starting download of: " + fileName); 
     System.err.println(urlPath); 
     File output = new File(Environment.getExternalStorageDirectory(), fileName); 
     if (output.exists()) {output.delete();} 

     InputStream stream = null; 
     FileOutputStream fos = null; 
     try { 
      URL url = new URL(urlPath); 
      stream = url.openConnection().getInputStream(); 
      InputStreamReader reader = new InputStreamReader(stream); 
      fos = new FileOutputStream(output.getPath()); 
      int next = -1; 
      while ((next = reader.read()) != -1) { 
      fos.write(next); 
      } 

      //Maybe I need to do something else here???? 

      // Successful finished 
      result = Activity.RESULT_OK; 

     } catch (Exception e) { 
      e.printStackTrace(); 
     } finally { 
      if (stream != null) { 
      try { 
       stream.close(); 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } 
      } 
      if (fos != null) { 
      try { 
       fos.close(); 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } 
      } 
     } 

     publishResults(output.getName(), output.getAbsolutePath(), result); 
    } 
} 

Answer 1

不要使用InputStreamReader它會改變字節流的字符流。 http://docs.oracle.com/javase/6/docs/api/java/io/InputStreamReader.html

在你的情況的圖像必須保留的字節流，所以你可以只使用由URL對象返回的InputStream：

while ((next = stream.read()) != -1) { 
    fos.write(next); 
}