Android - 确认ImageView的图片是否加载成功

判断ImageView图片是否存在，未加载成功，就显示默认图片。 

if (mPhotoView.getDrawable() == null) {  //            Toast.makeText(getActivity(), "图片加载失败", Toast.LENGTH_SHORT).show();              mPhotoView.setImageDrawable(getResources().getDrawable(R.drawable.icon_default_user_photo));          }

Android中Bitmap, Drawable, Byte,ID之间的转化

1.  Bitmap 转化为 byte

ByteArrayOutputStream out = new ByteArrayOutputStream();  bitmap.compress(Bitmap.CompressFormat.PNG, 100, out);  byte[] array= out.toByteArray();

2. byte转化为bitmap

Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);

3. bitmap转化为Drawable

Drawable drawable = new FastBitmapDrawable(bitmap);

4. Drawable转化为bitmap
a. BitmapDrawable, FastBitmapDrawable直接用getBitmap
b. 其他类型的Drawable用Canvas画到一个bitmap上

Canvas canvas = new Canvas(bitmap)        drawable.draw(canvas)

5.id转化graphic.drawable

Drawable drawable = activity.getResources().getDrawable(R.drawable.icon);

6.id转化成Bitmap

Bitmap bitmap = BitmapFactory. decodeResource (Resources   res, int id)