Android 从保存位置检索文件时出现NullPointerException

我正在构建一个Android应用程序，它可以拍照，然后立即进入屏幕。我不知道如何在不降级的情况下传递图像（例如，如果我将其打包），因此我决定保存图像并将其从卡中取出

现在，当我试图将图像恢复到新的裁剪视图中时，该视图正好位于摄影机视图之后，应用程序会在下面代码中指示的行上抛出一个空指针异常。图像实际上设置在Pictures/MyApp/IMG_APP.jpg，其中“Pictures”是我的默认图片目录

public Bitmap getImage() {
    Bitmap toReturn = null;

    File root = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
    ImageView IV = (ImageView) findViewById(R.id.crop_view);
    toReturn = BitmapFactory.decodeFile(root+"/MyApp/IMG_APP.jpg");
    IV.setImageBitmap(toReturn);
    return toReturn;// TODO Fix this line. It is breaking here with a null pointer exception.
}

下面是保存图片的代码。我已经确认它是通过在另一个应用程序中检查实际sd卡保存的

    void onPictureJpeg(byte[] bitmapdata, Camera camera) {
        int i = bitmapdata.length;
        Log.d(TAG, String.format("bytes = %d", i));

        File f = IMGP_Photo_Handler.generateTimeStampPhotoFile();

        try {
            OutputStream outputStream = new BufferedOutputStream(new FileOutputStream(f));
            outputStream.write(bitmapdata);
            outputStream.flush();
            outputStream.close();
            exceptionCaught = false;

        } catch (Exception e) {
            Log.e(TAG, "Error accessing photo output file:" + e.getMessage());
            Toast
              .makeText(IMGP_Camera.this, "Cannot save file. \nPlease mount an external SD Card", Toast.LENGTH_LONG)
              .show();
            exceptionCaught = true;// To get this to not start the next intent if the file save doesn't work.
        }

        if(!exceptionCaught){
        sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED,
                Uri.parse("file://" + Environment.getExternalStorageDirectory())));

        Intent intent = new Intent();
        intent.setClass(IMGP_Camera.this, IMGP_Crop.class);
        intent.putExtra("po","3265695");
        startActivity(intent);
        }
        finish();

    }

最后是我的照片处理程序：

    public static Uri photoFileUri = null;

    public static File getPhotoDirectory()  {
        File outputDir = null;
        String externalStorageState = Environment.getExternalStorageState();
        if (externalStorageState.equals(Environment.MEDIA_MOUNTED)) {
            File pictureDir =
                Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
            outputDir = new File(pictureDir, "MyApp");
            if(!outputDir.exists())  {
                if(!outputDir.mkdirs()) {
                    String message = "Failed to create directory:" + outputDir.getAbsolutePath();
                    Log.e(TAG, message);
                    outputDir = null;
                }
            }
        }

        return outputDir;
    }

    public static File generateTimeStampPhotoFile() {
        File photoFile = null;
        File outputDir = getPhotoDirectory();

        if (outputDir != null) {
            String photoFileName =  "IMG_APP.jpg";
            photoFile = new File(outputDir, photoFileName);
        }

        return photoFile;
    }

    public static Uri generateTimeStampPhotoFileUri() {
        photoFileUri = null;
        File photoFile = generateTimeStampPhotoFile() ;

        if (photoFile != null) {
            photoFileUri = Uri.fromFile(photoFile);
        }

        return photoFileUri;
    }

    public static Uri getFile(){
        return photoFileUri;
    }

---

我通过在一个额外的文件中传递照片和uri的路径解决了这个问题：

String photoFileName =  "IMG_TQL.jpg";
photoFile = new File(outputDir, photoFileName);
photoFilePath = photoFile.getAbsolutePath();


Intent intent = new Intent();
intent.setClass(IMGP_Camera.this, IMGP_Crop.class);
intent.putExtra("path", path);
intent.putExtra("uri", uri);
startActivity(intent);

---

我通过在一个额外的文件中传递照片和uri的路径解决了这个问题：

String photoFileName =  "IMG_TQL.jpg";
photoFile = new File(outputDir, photoFileName);
photoFilePath = photoFile.getAbsolutePath();


Intent intent = new Intent();
intent.setClass(IMGP_Camera.this, IMGP_Crop.class);
intent.putExtra("path", path);
intent.putExtra("uri", uri);
startActivity(intent);

---

您是否添加了这些权限

读取外部存储

或

写入外部存储

？因为从API 16开始，如果您的设备上启用了保护USB存储，那么如果没有这些权限之一，您将无法访问外部存储。是的，我添加了读取外部存储您是否添加了这些权限

READ\u external\u storage

或

WRITE\u external\u storage

？因为从API 16开始，如果您的设备上启用了保护USB存储，那么如果没有这些权限，您将无法访问外部存储。是的，我已添加了读取外部存储