android - 为什么我的Android应用程序中出现 “unfortunately myapp has stopped”？

Question

在我的应用程序中单击图像按钮时，我总是收到消息:“不幸的是，myapp已停止”。问题是什么？？？

这是我的代码。单击图像按钮将调用showImageDialog方法:

public class ReminderEditActivity extends Activity {

//
// Private instance variables
//
private Button mDateButton;
private Calendar mCalendar;
private Button mTimeButton;
private EditText mTitleText;
private EditText mBodyText;
private Button mConfirmButton;

private RemindersDbAdapter mDbHelper;
private ImageAdapter mImageHelper;

private Long mRowId;
private Long mImageRowId;

private ImageButton mImageButton;

private Uri mImageCaptureUri;

public String imageFilePath;


//
// Private constants
//
private static final int DATE_PICKER_DIALOG = 0;
private static final int TIME_PICKER_DIALOG = 1;
private static final String DATE_FORMAT = "dd-MM-yyyy";
private static final String TIME_FORMAT = "kk:mm";

public static final String DATE_TIME_FORMAT = "dd-MM-yyyy kk:mm:ss";

private static final int PICK_FROM_CAMERA = 1;
private static final int PICK_FROM_FILE = 2;


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

    // Instantiate mDbHelper and mImageHelper
    mDbHelper = new RemindersDbAdapter(this);
    mImageHelper = new ImageAdapter(this);

    setContentView(R.layout.reminder_edit);

    //
    // Instantiate instance variables
    //
    mTimeButton = (Button)findViewById(R.id.reminder_time);
    mCalendar = Calendar.getInstance();
    mDateButton = (Button)findViewById(R.id.reminder_date);
    mConfirmButton = (Button)findViewById(R.id.confirm);
    mTitleText = (EditText)findViewById(R.id.title);
    mBodyText = (EditText)findViewById(R.id.body);

    mImageButton =(ImageButton)findViewById(R.id.image);

    //Checks whether mRowId contains any values.
    mRowId = savedInstanceState != null ? savedInstanceState.getLong(RemindersDbAdapter.KEY_ROWID) : null;
    mImageRowId = savedInstanceState != null ? savedInstanceState.getLong(ImageAdapter.KEY_ROWID) : null;

    registerButtonListenerandSetDefaultText();
}

//
// Sets the row id from the intent. If mRowId is null its content is null.
//
private void setRowIdFromIntent() {
    if(mRowId == null) {
        Bundle extras = getIntent().getExtras();
        mRowId = extras != null ? extras.getLong(RemindersDbAdapter.KEY_ROWID) : null;
    }
}

//
// Executed on pause.
//
@Override
protected void onPause() {
    super.onPause();
    mDbHelper.close();
    mImageHelper.close();
}

//
// Executed on resume
//
@Override
protected void onResume() {
    super.onResume();
    mDbHelper.open();
    mImageHelper.open();
    setRowIdFromIntent();
    populateFields();
    populateImageField();
}

//
// Register the Date, Time and Save Button and set the default text
//
private void registerButtonListenerandSetDefaultText() {

    mDateButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            showDialog(DATE_PICKER_DIALOG); 
        }
    });

    mTimeButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            showDialog(TIME_PICKER_DIALOG);
        }
    });

    mConfirmButton.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            saveState();
            setResult(RESULT_OK);
            Toast.makeText(ReminderEditActivity.this, getString(R.string.task_saved_message), Toast.LENGTH_SHORT).show();
            finish();
        }
    }); 

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

    updateDateButtonText();
    updateTimeButtonText(); 
}


private void showImageDialog() {
    final String [] items = new String [] {"From Camera", "From SD Card"};
    ArrayAdapter<String> adapter = new ArrayAdapter<String> (this, android.R.layout.select_dialog_item,items);
    AlertDialog.Builder builder = new AlertDialog.Builder(this);

    builder.setTitle("Select Image");
    builder.setAdapter( adapter, new DialogInterface.OnClickListener() {
        public void onClick( DialogInterface dialog, int item ) {
            if (item == 0) {
                Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                File file = new File(Environment.getExternalStorageDirectory(),
                                    "tmp_avatar_" + String.valueOf(System.currentTimeMillis()) + ".jpg");
                mImageCaptureUri = Uri.fromFile(file);

                try {
                    intent.putExtra(android.provider.MediaStore.EXTRA_OUTPUT, mImageCaptureUri);
                    intent.putExtra("return-data", true);

                    startActivityForResult(intent, PICK_FROM_CAMERA);
                } catch (Exception e) {
                    e.printStackTrace();
                }

                dialog.cancel();
            } else {
                Intent intent = new Intent();

                intent.setType("image/*");
                intent.setAction(Intent.ACTION_GET_CONTENT);

                startActivityForResult(Intent.createChooser(intent, "Complete action using"), PICK_FROM_FILE);
            }
        }
    } );

    final AlertDialog dialog = builder.create();
    dialog.show();
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
       if(requestCode == PICK_FROM_FILE && data != null && data.getData() != null) {
           Uri uri = data.getData();
           if(uri != null) {
              Cursor cursor = getContentResolver().query(uri, new String[] {   
                                       android.provider.MediaStore.Images.ImageColumns.DATA}, 
                                       null, null, null);
                    cursor.moveToFirst();
                    String imageFilePath = cursor.getString(0);             
                    cursor.close();

                    if(imageFilePath != null) {
                            // Do whatever you want like decode it into a Bitmap
                            Bitmap bitmap = BitmapFactory.decodeFile(imageFilePath);
                            mImageButton.setImageBitmap(bitmap);
                            // Or.. store it somewhere in your local db  
                        }
           }
       }
    }


//
// If mRowId is not null (it contains value and we want to edit the task)
// this method is called.
//
private void populateFields() {
    if (mRowId != null) {
        Cursor reminder = mDbHelper.fetchReminder(mRowId);
        startManagingCursor(reminder);
        mTitleText.setText(reminder.getString(reminder.getColumnIndexOrThrow(RemindersDbAdapter.KEY_TITLE)));
        mBodyText.setText(reminder.getString(reminder.getColumnIndexOrThrow(RemindersDbAdapter.KEY_BODY)));


        SimpleDateFormat dateTimeFormat = new SimpleDateFormat(DATE_TIME_FORMAT);
        Date date = null;
        try {
            String dateString = reminder.getString(reminder.getColumnIndexOrThrow(RemindersDbAdapter.KEY_DATE_TIME));
            date = dateTimeFormat.parse(dateString);
            mCalendar.setTime(date);
        } catch (ParseException e) {
            Log.e("ReminderEditActivity", e.getMessage(), e);
        }
    } 

    updateDateButtonText();
    updateTimeButtonText();
}

private void populateImageField() {
    if (mImageRowId != null) {
        Cursor reminderImage = mImageHelper.fetchReminder(mImageRowId);
        startManagingCursor(reminderImage);
        String imagePath = reminderImage.getString(reminderImage.getColumnIndexOrThrow(ImageAdapter.KEY_IMAGE));

        Bitmap bitmap = BitmapFactory.decodeFile(imagePath);
        mImageButton.setImageBitmap(bitmap);

    }
}


//
// Saves the state so that it can be restored.
//
@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putLong(RemindersDbAdapter.KEY_ROWID, mRowId);

}

//
// Saves the content by communicating with the RemindersDbAdapter.
//
private void saveState() {
    String title = mTitleText.getText().toString();
    String body = mBodyText.getText().toString();

    SimpleDateFormat dateTimeFormat = new SimpleDateFormat(DATE_TIME_FORMAT);
    String reminderDateTime = dateTimeFormat.format(mCalendar.getTime());

    // Creates a new reminder if the value is null.
    if (mRowId == null) {
        long id = mDbHelper.createReminder(title, body, reminderDateTime);
        if (id > 0) {
            mRowId = id;

        } 
    // Updates the reminder if the content is not null.     
    } else {
        mDbHelper.updateReminder(mRowId, title, body, reminderDateTime);
    }
}

//
// Opens up an alert dialog box and asks the user if he wants to discard his task.
//
@Override
public void onBackPressed() {
    AlertDialog.Builder builder = new AlertDialog.Builder(ReminderEditActivity.this);
    builder.setMessage("Are you sure you want to discard your task?");
            builder.setTitle("Are you sure?");
            builder.setCancelable(false);
            builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int id) {
                    Intent j = new Intent(((Dialog)dialog).getContext(), ReminderListActivity.class);
                    startActivity(j);
                    return;

                }
            });

            builder.setNegativeButton("No", new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int id) {
                    dialog.cancel();

                }
            });
            builder.create().show();        
}

//
// When creating a dialog box, it either shows up a date or time picker.
//
@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
        case DATE_PICKER_DIALOG:
            return showDatePicker();
        case TIME_PICKER_DIALOG:
            return showTimePicker();
    }
    return super.onCreateDialog(id);
}

//
// Creates the date picker dialog box.
//
private DatePickerDialog showDatePicker() {
    DatePickerDialog datePicker = new DatePickerDialog(ReminderEditActivity.this, new DatePickerDialog.OnDateSetListener() {

        @Override
        public void onDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth) {
            mCalendar.set(Calendar.YEAR, year);
            mCalendar.set(Calendar.MONTH, monthOfYear);
            mCalendar.set(Calendar.DAY_OF_MONTH, dayOfMonth);
            updateDateButtonText();
        }
    }, mCalendar.get(Calendar.YEAR), mCalendar.get(Calendar.MONTH), mCalendar.get(Calendar.DAY_OF_MONTH));
    return datePicker;
}

//
// Creates the time picker dialog box.
//
private TimePickerDialog showTimePicker() {
    TimePickerDialog timePicker = new TimePickerDialog(ReminderEditActivity.this, new TimePickerDialog.OnTimeSetListener() {

        @Override
        public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
            mCalendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
            mCalendar.set(Calendar.MINUTE, minute);
            updateTimeButtonText();
        }
    }, mCalendar.get(Calendar.HOUR_OF_DAY), mCalendar.get(Calendar.MINUTE), true);
    return timePicker;
}

//
// Updates the Date Button text.
//
private void updateDateButtonText() {
    SimpleDateFormat dateFormat = new SimpleDateFormat(DATE_FORMAT);
    String dateForButton = dateFormat.format(mCalendar.getTime());
    mDateButton.setText(dateForButton);
}

//
// Updates the Time Button text.
//
private void updateTimeButtonText() {
    SimpleDateFormat timeFormat = new SimpleDateFormat(TIME_FORMAT);
    String timeForButton = timeFormat.format(mCalendar.getTime());
    mTimeButton.setText(timeForButton);
}

}

这是LogCat:

05-30 22:09:06.726: E/AndroidRuntime(628): FATAL EXCEPTION: main
05-30 22:09:06.726: E/AndroidRuntime(628): java.lang.RuntimeException: Unable to pause activity {com.ndroidstudios.android.taskreminder/com.ndroidstudios.android.taskreminder.ReminderEditActivity}: java.lang.NullPointerException
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2706)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2662)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:2640)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.ActivityThread.access$800(ActivityThread.java:123)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1154)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.os.Handler.dispatchMessage(Handler.java:99)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.os.Looper.loop(Looper.java:137)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.ActivityThread.main(ActivityThread.java:4424)
05-30 22:09:06.726: E/AndroidRuntime(628):  at java.lang.reflect.Method.invokeNative(Native Method)
05-30 22:09:06.726: E/AndroidRuntime(628):  at java.lang.reflect.Method.invoke(Method.java:511)
05-30 22:09:06.726: E/AndroidRuntime(628):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-30 22:09:06.726: E/AndroidRuntime(628):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-30 22:09:06.726: E/AndroidRuntime(628):  at dalvik.system.NativeStart.main(Native Method)
05-30 22:09:06.726: E/AndroidRuntime(628): Caused by: java.lang.NullPointerException
05-30 22:09:06.726: E/AndroidRuntime(628):  at com.ndroidstudios.android.taskreminder.ReminderEditActivity.onSaveInstanceState(ReminderEditActivity.java:345)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.Activity.performSaveInstanceState(Activity.java:1113)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1185)
05-30 22:09:06.726: E/AndroidRuntime(628):  at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2688)
05-30 22:09:06.726: E/AndroidRuntime(628):  ... 12 more

这是我的 list 文件:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.ndroidstudios.android.taskreminder"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk android:minSdkVersion="4" android:targetSdkVersion="8" />

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:name=".ReminderListActivity"
        android:label="@string/app_name"
        android:configChanges="orientation|keyboardHidden" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity
        android:name=".ReminderEditActivity"
        android:label="@string/app_name" />
    <activity 
        android:name=".ImageAdapter"
        android:label="@string/app_name" />    
</application>

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera.autofocus" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

Answer 1

第345行的ReminderEditActivity具有空对象。我不确定代码中的哪一行会导致没有行号