android.content.Context.getPackageName()' 在空对象引用上，当试图通过 java class 访问 activity 中的方法时

Question

我是运行一个基本的实时人脸检测应用程序，我正在计算它在 FaceDetectionProcessor.java class 中检测到人脸的次数（以此作为参考 - -> https://github.com/firebase/quickstart-android/tree/master/mlkit/app/src/main/java/com/google/firebase/samples/apps/mlkit/java ) 并且在特定的计数值下，它使用 FaceDetectionProcessor.java 对象调用一个方法来启动一个新的 activity 并在那里创建一个 Activity 的对象崩溃。

试过FaceDetectActivity.this，简单地说，getApplicationContext()，甚至是一个全局上下文对象，它在 FaceDetectActivity[=17 的 onCreate() 中将其值设置为 "this" =]

public class FaceDetectActivity extends AppCompatActivity implements ActivityCompat.OnRequestPermissionsResultCallback,CompoundButton.OnCheckedChangeListener{
    private static final String FACE_DETECTION = "Face Detection";
    private static final String TAG = "LivePreviewActivity";
    private static final int PERMISSION_REQUESTS = 1;
    private CameraSource cameraSource = null;
    private CameraSourcePreview preview;
    private GraphicOverlay graphicOverlay;
    private String selectedModel = FACE_DETECTION;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
.
.
.
.
}


private void createCameraSource(String model) {
        // If there's no existing cameraSource, create one.
        if (cameraSource == null) {
            cameraSource = new CameraSource(this, graphicOverlay);
        }
        try {
            switch (model) {
                case FACE_DETECTION:
                    Log.i(TAG, "Using Face Detector Processor");
                    cameraSource.setMachineLearningFrameProcessor(new FaceDetectionProcessor());
                    break;
                default:
                    Log.e(TAG, "Unknown model: " + model);
            }
        } catch (Exception e) {
            Log.e(TAG, "can not create camera source: " + model);
        }
    }

public void alertAndMove(){
        Intent i=new Intent(FaceDetectActivity.this,SelectingParty.class);
        startActivity(i);
    }

public class FaceDetectionProcessor extends VisionProcessorBase<List<FirebaseVisionFace>> {
    int count=0;

    private static final String TAG = "FaceDetectionProcessor";

    private final FirebaseVisionFaceDetector detector;

    public FaceDetectionProcessor() {
        FirebaseVisionFaceDetectorOptions options =
                new FirebaseVisionFaceDetectorOptions.Builder()
                        .setClassificationMode(FirebaseVisionFaceDetectorOptions.ALL_CLASSIFICATIONS)
                        .enableTracking()
                        .build();

        detector = FirebaseVision.getInstance().getVisionFaceDetector(options);
    }

    .
    .
    .
    . 
    . 
    .
    .

    @Override
    protected void onSuccess(
            @NonNull List<FirebaseVisionFace> faces,
            @NonNull FrameMetadata frameMetadata,
            @NonNull GraphicOverlay graphicOverlay) {
        graphicOverlay.clear();
        for (int i = 0; i < faces.size(); ++i) {
            FirebaseVisionFace face = faces.get(i);
            FaceGraphic faceGraphic = new FaceGraphic(graphicOverlay);
            graphicOverlay.add(faceGraphic);
            faceGraphic.updateFace(face, frameMetadata.getCameraFacing());
            Log.d(TAG, "onSuccess: Face detected and count= "+count);
            count++;
            if(count>=15)
                new FaceDetectActivity().alertAndMove();
        }
    }

    @Override
    protected void onFailure(@NonNull Exception e) {
        Log.e(TAG, "Face detection failed " + e);
    }
}

调用 new FaceDetectActivity().alertAndMove() 时，应用程序在 alertAndMove() 行 Intent i=new Intent(FaceDetectActivity.this,...... )

这种情况最令人沮丧的是，相同的逻辑在相同的代码上运行，在我朋友的笔记本电脑上，我最初测试了逻辑。

Answer 1

在 FaceDetectActivity 中，我将 Intent 和上下文发送到 FaceDetectionProcessor.java:

case FACE_DETECTION:
                    Log.i(TAG, "Using Face Detector Processor");
                    Intent i=new Intent( this,SelectingParty.class);
                    cameraSource.setMachineLearningFrameProcessor(new FaceDetectionProcessor(this,i));
                    break;

并且在 FaceDetectionProcessor.java 的构造函数中我初始化了实例 Context obj 和 Intent 意图如下：

public FaceDetectionProcessor(Context obj, Intent intent) {
        this.obj=obj;
        this.intent=intent;
.
.
.

最后在 FaceDetectionProcessor.java 的 onSuccess 方法中我做了：

if(count>=15){
                obj.startActivity(intent);
            }

就是这样！但是我仍然无法关闭以前的活动，任何建议我如何实现的评论都会有很大帮助！ P.S。我尝试了 CLEAR_TASK、CLEAR_TOP、NEW_TASK，没有用，但我可能遗漏了一些东西。

android.content.Context.getPackageName()' 在空对象引用上，当试图通过 java class 访问 activity 中的方法时

android.content.Context.getPackageName()' on a null object reference, when trying to access a method in an activity through a java class

java

android-intent

firebase

firebase-mlkit