java - Android Crashlytics 空指针异常

Question

我试图理解为什么我得到 NullPointerException。

这是 Crashlytics 报告:

Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String co.roomapp.klassroom.sdk.model.KRPostEvent.getCoverThumbUrl()' on a null object reference
   at co.roomapp.klassroom.activity.KREventFormActivity.initUI + 150(KREventFormActivity.java:150)
   at co.roomapp.klassroom.activity.KREventFormActivity.onCreate + 101(KREventFormActivity.java:101)
   at android.app.Activity.performCreate + 7458(Activity.java:7458)
   at android.app.Activity.performCreate + 7448(Activity.java:7448)
   at android.app.Instrumentation.callActivityOnCreate + 1286(Instrumentation.java:1286)
   at android.app.ActivityThread.performLaunchActivity + 3409(ActivityThread.java:3409)
   at android.app.ActivityThread.handleLaunchActivity + 3614(ActivityThread.java:3614)
   at android.app.servertransaction.LaunchActivityItem.execute + 86(LaunchActivityItem.java:86)
   at android.app.servertransaction.TransactionExecutor.executeCallbacks + 108(TransactionExecutor.java:108)
   at android.app.servertransaction.TransactionExecutor.execute + 68(TransactionExecutor.java:68)
   at android.app.ActivityThread$H.handleMessage + 2199(ActivityThread.java:2199)
   at android.os.Handler.dispatchMessage + 112(Handler.java:112)
   at android.os.Looper.loop + 216(Looper.java:216)
   at android.app.ActivityThread.main + 7625(ActivityThread.java:7625)
   at java.lang.reflect.Method.invoke(Method.java)
   at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run + 524(RuntimeInit.java:524)
   at com.android.internal.os.ZygoteInit.main + 987(ZygoteInit.java:987)

有一个java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String co.roomapp.klassroom.sdk.model.KRPostEvent.getCoverThumbUrl()' on a null object reference.

但是你可以在我的类中看到实例是在实例化类时创建的 KRPostEvent event = new KRPostEvent();。

任何人都可以告诉我这个变量事件 coule 是如何变为 null 的？这可能是由于生命周期？应该是强引用，不是GC收集的。

public class KREventFormActivity extends BaseActivity implements EasyPermissions.PermissionCallbacks {

    ImageView btnCamera;
    ImageView imgCover;
    TextView btnNext;

    EditText txtEventTitle;
    EditText txtEventLocation;
    EditText txtEventStart;
    EditText txtEventEnd;

    EditText txtEventDescription;
    Button btnDelete;

    Date startDate;
    Date endDate;
    boolean editMode = false;
    KRPostEvent event = new KRPostEvent();
    KRPost post;
    KRKlass klass;

    final Calendar myCalendar = Calendar.getInstance();

    String filename;
    Bitmap savedImage;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_event_form);

        initVariables();
        initUI();
    }

    private void initVariables(){

        navigationHeaderView = (KRNavigationHeaderView) findViewById(R.id.navigationHeaderView);
        editMode = getIntent().getBooleanExtra("editMode",false);

        txtEventTitle = (EditText) findViewById(R.id.eventForm_txtEventTitle);
        txtEventLocation = (EditText) findViewById(R.id.eventForm_txtEventLocation);
        txtEventDescription = (EditText) findViewById(R.id.eventForm_txtEventDescription);
        txtEventStart = (EditText) findViewById(R.id.eventForm_txtEventStart);
        txtEventEnd = (EditText) findViewById(R.id.eventForm_txtEventEnd);

        btnNext = (TextView) findViewById(R.id.eventForm_btnNext);
        btnCamera = (ImageView) findViewById(R.id.eventForm_btnCamera);

        imgCover = (ImageView) findViewById(R.id.eventForm_imgCover);
        btnDelete =  findViewById(R.id.btnDelete);

        if(getIntent().hasExtra("event")) event = AppUtil.unserializeObject(getIntent().getStringExtra("event"), KRPostEvent.class);

        if(getIntent().hasExtra("klassID") && getIntent().hasExtra("postID")){
            KRKlass k = KRClient.getInstance().getKlasses().get(getIntent().getStringExtra("klassID"));
            post = k.getPosts().get(getIntent().getStringExtra("postID"));
        }
    }

    private void initUI(){

        navigationHeaderView.lblTitle.setText((editMode)?R.string.str_title_event_edit:R.string.str_title_event_new);

        if(NavigationContoller.getInstance().isRoot(navigationName,this)){
            navigationHeaderView.enableCloseButton();
        }
        navigationHeaderView.setListener(new KRNavigationHeaderViewListener() {
            @Override
            public void onBack() {
                KREventFormActivity.this.onBack();
            }
        });


        if(event.getCoverThumbUrl() != null){
            Glide.with(this).load(event.getCoverThumbUrl()).fitCenter().placeholder(R.drawable.classroom).fitCenter().error(R.drawable.classroom).fitCenter().dontAnimate().into(imgCover);

        }else{
            if(event.getCoverImage() != null){
                imgCover.setImageBitmap(event.getCoverImage());
            }
        }

        txtEventTitle.setText(event.getTitle());
        txtEventDescription.setText(event.getDescription());
        txtEventLocation.setText(event.getLocation());

        if(event.getStartDate() != null){
            startDate = event.getStartDate();
            txtEventStart.setText( DateUtil.convertDateToPrettyString(startDate));
        }


        if(event.getEndDate() != null){
            endDate = event.getEndDate();
            txtEventEnd.setText( DateUtil.convertDateToPrettyString(endDate));
        }

        final TimePickerDialog.OnTimeSetListener startTimePicker = new TimePickerDialog.OnTimeSetListener() {

            @Override
            public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
                myCalendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                myCalendar.set(Calendar.MINUTE, minute);
                myCalendar.set(Calendar.SECOND , 0);
                myCalendar.set(Calendar.MILLISECOND , 0);
                updateTextFieldStartDate();
            }
        };

        final DatePickerDialog.OnDateSetListener startDatePicker = new DatePickerDialog.OnDateSetListener() {
            @Override
            public void onDateSet(DatePicker view, int year, int monthOfYear,
                                  int dayOfMonth) {
                myCalendar.set(Calendar.YEAR, year);
                myCalendar.set(Calendar.MONTH, monthOfYear);
                myCalendar.set(Calendar.DAY_OF_MONTH, dayOfMonth);
                new TimePickerDialog(KREventFormActivity.this, startTimePicker, myCalendar
                        .get(Calendar.HOUR_OF_DAY), myCalendar.get(Calendar.MINUTE),
                        DateFormat.is24HourFormat(KREventFormActivity.this)).show();
            }
        };

        txtEventStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(startDate != null){
                    myCalendar.setTime(startDate);
                }
                new DatePickerDialog(KREventFormActivity.this, startDatePicker, myCalendar
                        .get(Calendar.YEAR), myCalendar.get(Calendar.MONTH),
                        myCalendar.get(Calendar.DAY_OF_MONTH)).show();
            }
        });

        final TimePickerDialog.OnTimeSetListener endTimePicker = new TimePickerDialog.OnTimeSetListener() {

            @Override
            public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
                myCalendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                myCalendar.set(Calendar.MINUTE, minute);
                myCalendar.set(Calendar.SECOND , 0);
                myCalendar.set(Calendar.MILLISECOND , 0);
                updateTextFieldEndDate();
            }
        };

        final DatePickerDialog.OnDateSetListener endDatePicker = new DatePickerDialog.OnDateSetListener() {
            @Override
            public void onDateSet(DatePicker view, int year, int monthOfYear,
                                  int dayOfMonth) {
                myCalendar.set(Calendar.YEAR, year);
                myCalendar.set(Calendar.MONTH, monthOfYear);
                myCalendar.set(Calendar.DAY_OF_MONTH, dayOfMonth);
                new TimePickerDialog(KREventFormActivity.this, endTimePicker, myCalendar
                        .get(Calendar.HOUR_OF_DAY), myCalendar.get(Calendar.MINUTE),
                        DateFormat.is24HourFormat(KREventFormActivity.this)).show();
            }
        };

        txtEventEnd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(endDate != null){
                    myCalendar.setTime(endDate);
                }
                new DatePickerDialog(KREventFormActivity.this, endDatePicker, myCalendar
                        .get(Calendar.YEAR), myCalendar.get(Calendar.MONTH),
                        myCalendar.get(Calendar.DAY_OF_MONTH)).show();
            }
        });


        btnDelete.setVisibility(post != null ? View.VISIBLE : View.GONE);

        btnDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                MessageDialog.showAlertMsg(KREventFormActivity.this, KREventFormActivity.this.getString(R.string.str_dialog_title_delete_post), KREventFormActivity.this.getString(R.string.str_dialog_content_delete_post), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        post.delete(new KRApiHandler(){
                            @Override
                            public void onSuccess() {
                                NavigationContoller.getInstance().dismiss(navigationName,KREventFormActivity.this);
                            }
                        });
                    }
                }, new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                    }
                });
            }
        });
        txtEventStart.setInputType(InputType.TYPE_NULL);
        txtEventEnd.setInputType(InputType.TYPE_NULL);

        txtEventTitle.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {

            }

            @Override
            public void afterTextChanged(Editable s) {
                KREventFormActivity.this.checkValid();
            }
        });

        btnNext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                saveEvent();
            }
        });

        btnCamera.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addImage();
            }
        });

        checkValid();
    }

    private void onBack(){
        setResult(RESULT_CANCELED);
        NavigationContoller.getInstance().pop(navigationName,this);
        overridePendingTransition(R.anim.noanim, R.anim.slide_up_leave);
    }

    private void checkValid(){
        if(txtEventTitle.getText().toString().trim().isEmpty() || startDate == null || endDate == null){
            btnNext.setVisibility(View.GONE);
        }else{
            btnNext.setVisibility(View.VISIBLE);
        }
    }

    private void updateTextFieldStartDate(){
        checkValid();
        startDate = myCalendar.getTime();
        txtEventStart.setText( DateUtil.convertDateToPrettyString(startDate));
        checkValid();
    }

    private void updateTextFieldEndDate(){
        checkValid();
        endDate = myCalendar.getTime();
        txtEventEnd.setText( DateUtil.convertDateToPrettyString(endDate));
        checkValid();
    }

    private void saveEvent(){

        event.setTitle(txtEventTitle.getText().toString().trim());
        if(txtEventLocation.getText() != null) event.setLocation(txtEventLocation.getText().toString().trim());
        if(txtEventDescription.getText() != null) event.setDescription(txtEventDescription.getText().toString().trim());
        if(startDate != null) event.setStartDate(startDate);
        if(endDate != null) event.setEndDate(endDate);
        if(savedImage != null) event.setCoverImage(savedImage);

        if(post != null){

            MessageDialog.showAlertMsg(this, getString(R.string.app_name), getString(R.string.remind_update_post),R.string.str_label_yes, R.string.str_label_no, new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    _finish(true);
                }
            }, new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialogInterface, int i) {
                    _finish(false);
                }
            });

        }else{
            Intent intent = new Intent();
            intent.putExtra("event", event);
            setResult(RESULT_OK,intent);

            NavigationContoller.getInstance().pop(navigationName,this);
        }
    }

    private void _finish(boolean remind){

        if(remind){
            post.setRemindType(KRPostType.event);
        }else{
            post.setRemindType(null);
        }
        post.setEvent(event);
        if(post.getEvent() != null && post.getEvent().getCoverImage() != null){
            ProgressDlg.showProgressProcess(this,getString(R.string.str_guide_upload_event));
            ProgressDlg.pd.setMax(100);
        }

        btnNext.setEnabled(false);

        post.send(null, new KRApiHandler(){

            @Override
            public void onSuccess() {
                ProgressDlg.closeprocess(KREventFormActivity.this);
                NavigationContoller.getInstance().pop(navigationName,KREventFormActivity.this);
            }

            @Override
            public void onError(KRException e) {
                ProgressDlg.closeprocess(KREventFormActivity.this);
                btnNext.setEnabled(true);
                MessageDialog.showAlertMsg(KREventFormActivity.this, getString(R.string.str_title_error), e.getMessage());
            }

            @Override
            public void onProgress(final long bytesWritten, final long totalSize) {
                KREventFormActivity.this.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        //ProgressDlg.pd.setMax((int)totalSize);
                        if(ProgressDlg.pd != null){
                            int prg = (int)(bytesWritten*1.0/totalSize*100);
                            ProgressDlg.pd.setProgress(0);
                            ProgressDlg.pd.setProgress(prg);
                        }

                    }
                });
            }
        });
    }

    private void addImage(){
        showTakePhotosDialog();

    }

    private void showTakePhotosDialog() {
        String[] perms = {Manifest.permission.CAMERA,Manifest.permission.READ_EXTERNAL_STORAGE,Manifest.permission.WRITE_EXTERNAL_STORAGE};
        if(EasyPermissions.hasPermissions(this,perms)){
            final CharSequence[] items = {this.getString(R.string.str_label_gallery), this.getString(R.string.str_label_camera), this.getString(R.string.str_label_cancel)};
            final AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setTitle(this.getString(R.string.str_guide_picture));
            builder.setItems(items, new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int item) {
                    if (items[item] == getString(R.string.str_label_gallery)) {
                        chooseFromGallery();
                    }
                    if (items[item] == getString(R.string.str_label_camera)) {
                        takePhoto();
                    }
                    if (items[item] == getString(R.string.str_label_cancel)) {
                        builder.setCancelable(true);
                    }
                }
            });
            AlertDialog alert = builder.create();
            alert.show();
        }else{
            EasyPermissions.requestPermissions(this,this.getString(R.string.str_guide_permission_camera),Constants.kPERMISSION_CAMERA_STORAGE,perms);
        }
    }

    private void chooseFromGallery(){
        Intent intent = new Intent();
        intent.setType("image/*");
        intent.setAction(Intent.ACTION_GET_CONTENT);
        this.startActivityForResult(intent, Constants.kGALLERY);
    }

    public void takePhoto() {

        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        filename = "IMG-" + (new Date()).getTime()+".jpg";
        intent.putExtra(MediaStore.EXTRA_OUTPUT, AppUtil.CacheUrifromFilename(this,filename));
        this.startActivityForResult(intent, Constants.kCAMERA);
    }


    //Delegate Photo
    public void didFinishTakingPicture(){
        Uri selectedImage = AppUtil.CacheUrifromFilename(this,filename);

        File source = AppUtil.getFile(KREventFormActivity.this,selectedImage);
        File f = AppUtil.moveImageToDir(KREventFormActivity.this, "Klassroom", source, KRUtils.getFlagForKey(Constants.FLAG_KEEP_LOCAL,true));

        String n = "TMP-"+f.getName();
        CropImage.activity(Uri.fromFile(f)).setGuidelines(CropImageView.Guidelines.ON).setOutputCompressQuality(80).setOutputUri(AppUtil.CacheUrifromFilename(this,n)).start(this);

    }

    public void didSelectImagesFromGallery(Uri fileuri){
        if("content".equalsIgnoreCase(fileuri.getScheme())){
            String mimeType = getContentResolver().getType(fileuri);

            if(mimeType.contains("image")) {
                Cursor returnCursor = getContentResolver().query(fileuri, null, null, null, null);
                returnCursor.moveToFirst();
                int nameIndex = returnCursor.getColumnIndex(OpenableColumns.DISPLAY_NAME);
                String fileName = returnCursor.getString(nameIndex);
                try {
                    InputStream is = this.getContentResolver().openInputStream(fileuri);
                    byte[] bytesArray = IOUtils.toByteArray(is);
                    KRFile f1 = new KRFile();
                    f1.setFileName(fileName);
                    f1.setMimeType("image");
                    f1.setData(bytesArray);

                    File f = f1.toFile();
                    String n = "TMP-"+f.getName();
                    CropImage.activity(Uri.fromFile(f)).setGuidelines(CropImageView.Guidelines.ON).setOutputCompressQuality(80).setOutputUri(AppUtil.CacheUrifromFilename(this,n)).start(this);

                } catch (Exception e) {

                }
            }else{
                MessageDialog.showAlertMsg(this,getString(R.string.app_name),getString(R.string.str_dialog_content_cantimportfile));
            }

        }else{
            File f = AppUtil.getFile(this,fileuri);

            if(f.exists()) {
                String[] acceptedmim = {"jpg","jpeg","png"};
                boolean c = false;
                for(String s:acceptedmim){
                    if(FilenameUtils.getExtension(f.getPath()).toLowerCase().contains(s)){
                        c = true;
                    }
                }
                if(c) {
                    String n = "TMP-"+f.getName();
                    CropImage.activity(Uri.fromFile(f)).setGuidelines(CropImageView.Guidelines.ON).setOutputCompressQuality(80).setOutputUri(AppUtil.CacheUrifromFilename(this,n)).start(this);
                }else{
                    MessageDialog.showAlertMsg(this,getString(R.string.app_name),getString(R.string.str_dialog_content_cantimportfile));
                }
            }
        }
    }

    public void didEditPhoto(final Uri imageUri)
    {

        new AsyncTask<Integer, Void, Void>() {
            @Override
            protected Void doInBackground(Integer... params) {
                File f = AppUtil.getFile(KREventFormActivity.this,imageUri);
                try {
                    if(f != null && f.exists()) {
                        savedImage = Glide.with(KREventFormActivity.this).load(f).asBitmap().fitCenter().into(1280, 1280).get();

                        filename = null;

                        KREventFormActivity.this.runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                imgCover.setImageBitmap(savedImage);
                            }
                        });
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }

                return null;
            }
        }.execute();

    }


    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (resultCode != Activity.RESULT_OK) {
            return;
        }
        switch (requestCode) {
            case Constants.kCAMERA:
                didFinishTakingPicture();
                break;
            case Constants.kGALLERY:
                didSelectImagesFromGallery(data.getData());
                break;
            case CropImage.CROP_IMAGE_ACTIVITY_REQUEST_CODE:
                CropImage.ActivityResult result = CropImage.getActivityResult(data);
                if (resultCode == RESULT_OK) {
                    didEditPhoto(result.getUri());
                } else if (resultCode == CropImage.CROP_IMAGE_ACTIVITY_RESULT_ERROR_CODE) {
                    Exception error = result.getError();
                }
                break;
            default:
                break;
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        EasyPermissions.onRequestPermissionsResult(requestCode,permissions,grantResults,this);
    }

    @Override
    public void onPermissionsGranted(int requestCode, List<String> perms) {
        if(requestCode == Constants.kPERMISSION_CAMERA_STORAGE){
            showTakePhotosDialog();
        }
    }

    @Override
    public void onPermissionsDenied(int requestCode, List<String> perms) {

    }
}

Answer 1

是的，你把它声明为

KRPostEvent event = new KRPostEvent();

但是这个调用:

if(getIntent().hasExtra("event")) 
    event = AppUtil.unserializeObject(getIntent().getStringExtra("event"), KRPostEvent.class);

将为您的 event 变量重新分配一个新值。在你的例子中，一个 null。