Question

我正在制作一个虚假的通话应用程序，我可以选择快速拨打电话。我在quickCall()方法中拥有此选项的所有逻辑。

这里是MainActivity

的代码

public class MainActivity extends AppCompatActivity {

    public static final String LOG_TAG = "MainActivity";

    ImageView imageView;
    EditText number, name;
    Button setTimeButton;
    ImageButton imageButton;
    TimePickerDialog timePicker;
    long selectedTimeInMillis;
    String enteredName, enteredNumber;

    private static final int SELECT_IMAGE = 100;

    public static final int REQUEST_CODE_PI = 1001;

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

        PreferenceManager.setDefaultValues(this, R.xml.settings, false);

        imageView = findViewById(R.id.image_view);
        setTimeButton = findViewById(R.id.set_time);
        imageButton = findViewById(R.id.place_call_button);

        number = findViewById(R.id.number);
        name = findViewById(R.id.name);

        imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent galleryIntent = new Intent(Intent.ACTION_PICK);
                galleryIntent.setType("image/*");
                startActivityForResult(galleryIntent, SELECT_IMAGE);
            }
        });

        setTimeButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final Calendar calendar = Calendar.getInstance();
                int hour = calendar.get(Calendar.HOUR_OF_DAY);
                int minute = calendar.get(Calendar.MINUTE);
                timePicker = new TimePickerDialog(MainActivity.this, new TimePickerDialog.OnTimeSetListener() {
                    @Override
                    public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
                        calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                        calendar.set(Calendar.MINUTE, minute);
                        calendar.set(Calendar.SECOND, 0);
                        calendar.set(Calendar.MILLISECOND, 0);
                        selectedTimeInMillis = calendar.getTimeInMillis();

                        if (hourOfDay > 12) {
                            hourOfDay = hourOfDay - 12;
                        }

                        Toast.makeText(MainActivity.this, hourOfDay + ":" + minute, Toast.LENGTH_SHORT).show();

                        Log.v(LOG_TAG, "Selected time in millis:" + selectedTimeInMillis);
                    }
                }, hour, minute, false);
                timePicker.show();
            }
        });

        imageButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                enteredName = name.getText().toString().trim();
                enteredNumber = number.getText().toString().trim();
                if (enteredNumber.isEmpty()){
                    Toast.makeText(MainActivity.this, "Please enter  a number", Toast.LENGTH_LONG).show();
                    return;
                }
                Intent intent = new Intent(MainActivity.this, AlarmReciever.class);
                intent.putExtra("FAKE_NAME", enteredName);
                intent.putExtra("FAKE_NUMBER", enteredNumber);

                PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(), REQUEST_CODE_PI, intent, 0);

                AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
                if (alarmManager != null) {
                    alarmManager.set(AlarmManager.RTC_WAKEUP, selectedTimeInMillis, pendingIntent);
                    Toast.makeText(MainActivity.this, "Your call has been placed", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(MainActivity.this, "Error: something wrong", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.settings:
                Intent intent = new Intent(MainActivity.this, SettingsActivity.class);
                startActivity(intent);
                return true;

            case R.id.quick_call:
                quickCall();
                return true;

                default:
                return super.onOptionsItemSelected(item);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (resultCode == RESULT_OK) {
            try {
                Uri imageUri = data.getData();
                InputStream imageStream = null;
                if (imageUri != null) {
                    imageStream = getContentResolver().openInputStream(imageUri);
                }
                Bitmap selectedImage = BitmapFactory.decodeStream(imageStream);
                imageView.setImageBitmap(selectedImage);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
                Toast.makeText(this, "Something went wrong", Toast.LENGTH_SHORT).show();
            }

        } else {
            Toast.makeText(this, "You haven't picked any Image", Toast.LENGTH_SHORT).show();
        }
    }

    public void quickCall(){

        Calendar calendar = Calendar.getInstance();
        calendar.get(Calendar.HOUR_OF_DAY);
        calendar.get(Calendar.MINUTE);
        long millis = calendar.getTimeInMillis();

        Intent quickCallIntent = new Intent(MainActivity.this, AlarmReciever.class);

        PendingIntent quickCallPendingIntent = PendingIntent.getBroadcast(getApplicationContext(), REQUEST_CODE_PI, quickCallIntent, 0);

        AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
        if (alarmManager != null) {
            alarmManager.set(AlarmManager.RTC_WAKEUP, millis + 10000, quickCallPendingIntent);
            Toast.makeText(MainActivity.this, "Your call has been placed", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(MainActivity.this, "Error: something wrong", Toast.LENGTH_SHORT).show();
        }
    }
}

这是AlarmReceiver类

public class AlarmReciever extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        String getFakeName = intent.getStringExtra("FAKE_NAME");
        String getFakeNumber = intent.getStringExtra("FAKE_NUMBER");

        Intent fakeRinger = new Intent();
        fakeRinger.setClassName("com.example.mani.fakecall", "com.example.mani.fakecall.FakeRinger");
        fakeRinger.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        fakeRinger.putExtra("USER_FAKE_NAME", getFakeName);
        fakeRinger.putExtra("USER_FAKE_NUMBER", getFakeNumber);
        context.startActivity(fakeRinger);

        Log.v("Fake name is", getFakeName);
        Log.v("Fake number is", getFakeNumber);
    }
}

这是FakeRinger活动

public class FakeRinger extends AppCompatActivity {

    TextView displayName, displayNumber, displayCarrier;
    ImageButton alarmOffButton;
    String carrierName;
    ImageView displayImage;

    public static final int REQUEST_CODE = 1001;

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

        displayName = findViewById(R.id.display_name);
        displayNumber = findViewById(R.id.display_number);
        displayCarrier = findViewById(R.id.network_operator);
        displayImage = findViewById(R.id.display_image);

        TelephonyManager telephonyManager = (TelephonyManager) getSystemService(TELEPHONY_SERVICE);
        if (telephonyManager != null) {
            carrierName = telephonyManager.getNetworkOperatorName();
        }

        if (carrierName != null) {
            displayCarrier.setText(getResources().getString(R.string.incoming_call, carrierName));
        } else {
            displayCarrier.setText(getResources().getString(R.string.incoming_call));
        }

        Intent intent = getIntent();

        String userFakeName = intent.getExtras().getString("USER_FAKE_NAME");
        displayName.setText(userFakeName);

        String userFakeNumber = intent.getExtras().getString("USER_FAKE_NUMBER");
        displayNumber.setText(userFakeNumber);

        alarmOffButton = findViewById(R.id.hang_up_call);
        alarmOffButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(getApplicationContext(), AlarmReciever.class);
                PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(), REQUEST_CODE, intent, 0);
                AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
                stopService(intent);
                if (alarmManager != null) {
                    alarmManager.cancel(pendingIntent);
                }
            }
        });
    }
}

每当我点击快速通话选项，我的应用程序崩溃。这是我得到的错误 - java.lang.RuntimeException: Unable to start receiver com.example.mani.fakecall.AlarmReciever: java.lang.NullPointerException: println needs a message

Answer 1

当您尝试在LogCat中打印值时，如果值为null，则会收到错误消息：

java.lang.NullPointerException：println需要一条消息

所以你可以验证一个空值：

 Log.v("Fake name is", getFakeName!=null?getFakeName:"Not determinated");
 Log.v("Fake number is", getFakeNumber!=null?getFakeNumber:"Not determinated");

或只是

if(getFakeName != null){
   Log.v("Fake name is", getFakeName);
}
if(getFakeNumber != null){
    Log.v("Fake number is", getFakeNumber);
}

如果我们查看Log.v()的源代码，则消息需要String值（不是空值）：

public static int v(String tag, String msg, Throwable tr) {
    return println(LOG_ID_MAIN, VERBOSE, tag, msg + '\n' + getStackTraceString(tr));
}

Answer 2

只需在将值打印到logcat之前添加检查：

if(getFakeName != null)
    Log.v("Fake name is", getFakeName);
if(getFakeNumber != null)
    Log.v("Fake number is", getFakeNumber);

您需要将值传递给Log.v()，而不能null

Answer 3

检查您是否在AndroidManifest.xml

中声明了AlarmReciever

https://developer.android.com/guide/components/broadcasts.html#receiving_broadcasts

Android NullPointerException：println需要一条消息

3 个答案: