如何在android列表中的imageview中设置默认图片？

Question

我想在结果为空时显示默认图片，这是我的尝试：

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;
                }
            }
        }

使用getBitmapFromURL的类：

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

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

在ListAdapter 中执行RetrievePic 类：

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);

当图片为空时，它不显示任何内容，但应该显示默认图片R.drawable.p3_books。感谢您的帮助。

Answer 1

你想做的是在你的适配器的getView()方法的实现中，像这样，

...
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();

这样，默认设置。如果您碰巧得到网络结果，请更改默认值。

Answer 2

你可以试试这个：

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

Answer 3

为什么不在xml中设置item的默认图片，然后result不为null时会替换默认图片

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

编辑：

        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);
                                }
                            });

        }
}