字符串连接不是路径结合起来的好方法。这是更好地使用文件构造：

String concatenation isn't a good way to combine paths. It is better to use the File constructor :

File directory = new File(extStorageDirectory, "myFolder");
File fileInDirectory = new File(directory, files[which]);
Bitmap bitmap = BitmapFactory.decodeFile(fileInDirectory.getAbsolutePath());