在onActivityResult上的null指針異常

Question

我有一個具有Tablayout + Viewpager組合的活動，它們一起托管了四個片段，其中一個片段是我使用Intent打開相機並在那里解析結果。

有時當我在onActivityResults上解析結果時，我會收到NullPointerException

這是代碼

public class CheckInFragment extends BaseFragment implements CheckInPresenterView {

    private CameraIntegrator cameraIntegrator;

    private ImageCallback cameraResultCallback = new ImageCallback() {
        @Override
        public void onResult(int requestedBy, Result result) {

            if (requestedBy == RequestSource.SOURCE_CAMERA) {
                ...
            }
        }
    };


    private void openCamera() {

        // Permission Check Shifted To Attendance Activity
        if (cameraIntegrator == null) {
            cameraIntegrator = new CameraIntegrator(this);
            cameraIntegrator.setImageDirectoryName(GlobalConstants.IMAGE_FOLDER_NAME);
            cameraIntegrator.setRequiredImageSize(ImagesSizes.OPTIMUM_MEDIUM);
        }

        try {
            cameraIntegrator.initiateCapture();
        } catch (NoCameraAppFoundException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onActivityResult(final int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == Activity.RESULT_OK) {
            if (requestCode == CameraIntegrator.REQUEST_IMAGE_CAPTURE)
                cameraIntegrator.parseResults(requestCode, resultCode, data, cameraResultCallback); //Null Pointer Exception here sometimes
        }
    }
}

Crashlytics日志：

Fatal Exception: java.lang.RuntimeException: Unable to resume activity {com.xxx.AttendanceActivity}: java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=65537, result=-1, data=null} to activity {com.xxx.AttendanceActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.xxx.CameraIntegrator.parseResults(int, int, android.content.Intent, com.xxx.camera.ImageCallback)' on a null object reference
       at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3513)

有人可以解釋為什么有時候我使cameraIntegrator為null嗎？

是因為此代碼在父級活動中嗎？

    ViewPagerGeneralAdapter viewPagerAdapter = setupViewPager(viewPager);
    tabLayout.setupWithViewPager(viewPager);

    viewPager.setOffscreenPageLimit(viewPagerAdapter.getCount()); <---

我該如何重現此錯誤？

Answer 1

cameraIntegrator在片段的onResume()方法中初始化cameraIntegrator 。 問題是，如果重新創建了片段（例如，從其他活動返回時），則可能不會調用openCamera()方法，因此cameraIntegrator將永遠不會初始化，並且為null。

嘗試這個。

@override
public void onResume(){
    super.onResume();
    initializeCameraIntegrator();
}


private void initializeCameraIntegrator(){
    if (cameraIntegrator == null) {
        cameraIntegrator = new CameraIntegrator(this);
        cameraIntegrator.setImageDirectoryName(GlobalConstants.IMAGE_FOLDER_NAME);
        cameraIntegrator.setRequiredImageSize(ImagesSizes.OPTIMUM_MEDIUM);
    }
}

private void openCamera() {
    try {
        cameraIntegrator.initiateCapture();
    } catch (NoCameraAppFoundException e) {
        e.printStackTrace();
    }
}