如何在Android中設置列表中的默認圖片？

Question

我想顯示的默認PIC當結果爲空，這裏是我的嘗試：

getBitmapFromURL和使用它的類：

public static Bitmap getBitmapFromURL(String src) { 
     try { 
      URL url = new URL(src); 
      HttpURLConnection connection = (HttpURLConnection) url.openConnection(); 
      connection.setDoInput(true); 
      connection.connect(); 
      InputStream input = connection.getInputStream(); 
      Bitmap myBitmap = BitmapFactory.decodeStream(input); 
      connection.disconnect(); 
      return myBitmap; 
     } catch (IOException e) { 
//   tasvirdimg.setImageResource(R.drawable.p3_books); 
      e.printStackTrace(); 
      return null; 
     } 
    } 
} 
class RetrievePic extends AsyncTask<String, String, Bitmap>{ 

    @Override 
    protected Bitmap doInBackground(String... urls) { 
     String url = urls[0]; 
     return JSONCommands.getBitmapFromURL(url); 
    } 

} 

執行類ListAdapter：

//  tasvirlimg.setImageResource(R.drawable.p3_books); 
     RetrievePic retPic = new RetrievePic(); 
     retPic.execute(JSONCommands.firstURL + MainActivity.books_array.get(position).tasvir); 
     Bitmap img = null; 
     try { 
      img = retPic.get(); 
     } catch (InterruptedException e) { 
      // TODO Auto-generated catch block 
      tasvirlimg.setImageResource(R.drawable.p3_books); 
      e.printStackTrace(); 
     } catch (ExecutionException e) { 
      // TODO Auto-generated catch block 
      tasvirlimg.setImageResource(R.drawable.p3_books); 
      e.printStackTrace(); 
     } 

     tasvirlimg.setImageBitmap(img); 

當書籍圖片爲空時，它不顯示任何東西，但我想顯示默認圖片來源R.drawable.p3_books。請幫忙。謝謝。

Answer 1

你可以試試這個：

if(img == null) 
{ 
    tasvirlimg.setImageDrawable(R.drawable.p3_books); 
} 
else 
{ 
    tasvirlimg.setImageBitmap(img); 
} 

Answer 2

爲什麼不設置項目的默認PIC在XML，然後默認PIC會被替換時，結果是不爲空

<ImageView 
    ... 
     android:src="@drawable/p3_books" 
     /> 

編輯：

 class RetrievePic extends AsyncTask<String, String, Bitmap>{ 

    final image = (ImageView) findViewById(R.id.limg_tasvir); 

      @Override 
      protected Bitmap doInBackground(String... urls) { 
       String url = urls[0]; 
       return JSONCommands.getBitmapFromURL(url); 
      } 

      @Override 
        protected void onPreExecute() { 
         runOnUiThread(new Runnable() { 
           @Override 
           public void run() { 
         image.setBackgroundResource(R.drawable.p3_books); 
           } 
          }); 

     } 
} 

Answer 3

你想要做的是在你實現你的適配器的getView()方法，somethi ng這樣，

... 
final imageView = ...; 
imageView.setImageBitmap(defaultBitmap); 
new AsyncTask<Void,Void,Bitmap>() { 
    public Bitmap doInBackground(Void... params) { 
    // get bitmap from `net, or return null if failure 
    } 

    public void onPostExecute(Bitmap result) { 
    if (result != null) { 
     imageView.setBitmap(result); 
    } 
    } 
}.execute(); 

這樣，默認設置。如果您碰巧遇到網絡結果，請更改默認值。