设置background（背景）的函数：
imageview.setBackgroundReource(int resid)
imageview.setBackground(Drawable background)
imageview.setBackgroundColor(int color)
imageview.setBackgroundDrawable(Drawable background) //This method was deprecated in API level 16. use setBackground(Drawable) instead
设置src（前景）的函数：
imageview.setImageDrawable(Drawable drawable);
imageview.setImageBitmap(Bitmap bm);
imageview.setImageResource(int resId);
