Activity_or_Fragment.java

private static final int PICK_PHOTO_FOR_AVATAR = 0;

public void pickImage() {
  Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
  intent.setType("image/*");
  startActivityForResult(intent, PICK_PHOTO_FOR_AVATAR);
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == PICK_PHOTO_FOR_AVATAR && resultCode == Activity.RESULT_OK) {
        if (data == null) {
            //Display an error
            return;
        }
        InputStream inputStream = context.getContentResolver().openInputStream(data.getData());
        //Now you can do whatever you want with your inpustream, save it as file, upload to a server, decode a bitmap...
    }
}