android - 无法在android应用程序中创建文件类

Question

我正在尝试制作一个应用程序，它可以捕获图片，然后将其保存在特定文件夹中。问题是我无法让文件类工作。

public class startScreen extends Activity {

private static final int CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE = 100;
public Uri picUri;

public void makeFlash(View startScreen) {
    startCameraActivity();
}

protected void startCameraActivity() {

    // create Intent to take a picture and return control to the calling
    // application
    Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

    picUri = getOutputMediaFileUri(1); // create a file to save the image
    intent.putExtra(MediaStore.EXTRA_OUTPUT, picUri); // set the image file
                                                        // name

    // start the image capture Intent
    startActivityForResult(intent, CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE);

}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_start_screen);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_start_screen, menu);
    return true;
}

private static Uri getOutputMediaFileUri(int type){
      return Uri.fromFile(getOutputMediaFile(type));
}

private static File getOutputMediaFile(int type) {
    if (Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED)) {

        File mediaStorageDir = new File(Environment.getExternalStorageDirectory()
                + "/SnapFlash", "SnapFlash");

        // Create the storage directory if it does not exist
        if (!mediaStorageDir.exists()) {
            if (!mediaStorageDir.mkdirs()) {
                Log.d("MyCameraApp", "failed to create directory");
                return null;
            }
        }

        // Create a media file name
        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss")
                .format(new Date());
        File mediaFile;
        if (type == 1) {
            mediaFile = new File(mediaStorageDir.getPath() + File.separator
                    + "SF_" + timeStamp + ".jpg");
        } else {
            return null;
        }

        return mediaFile;
    } else{
        return null;
    }

}

}

在调试时，它看起来好像从未设置过 mediaStorageDir。相机确实运行，但图片保存在默认图片文件夹中。