String imageUri = "http://site.com/image.png"; // 网络图片  
String imageUri = "file:///mnt/sdcard/image.png"; //SD卡图片  
String imageUri = "content://media/external/audio/albumart/13"; // 媒体文件夹  
String imageUri = "assets://image.png"; // assets  
String imageUri = "drawable://" + R.drawable.image; //  drawable文件