制作闹钟，为什么我的日历为空？

Question

今年夏天，为了学习应用程序开发，我决定在 Android Studio 中制作一个闹钟，而没有太多 Java 或 OOP 的先验知识。

我正在尝试使用 TimePickerDiaglog 获取用户对警报的输入，然后将该时间存储在日历实用程序中，这样我就可以使用警报管理器设置待定意图。

public class AlarmParameters extends AppCompatActivity {
    EditText time;
    Button btn_set_alarm;
    TimePickerDialog mTimePicker;
    Calendar mcurrentTime;
    AlarmManager alarmManager;
    private PendingIntent pending_intent;
    private AlarmReceiver alarm;

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

        //match ids
        btn_set_alarm = (Button) findViewById(R.id.parameters_btn_set_alarm);
        time = (EditText) findViewById(R.id.time_box_text);

        //remove pesky keyboard
        time.setInputType(InputType.TYPE_NULL);

        // perform click event listener on edit text
        time.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //retrieve current time
                final Calendar mcurrentTime = Calendar.getInstance();
                int hour = mcurrentTime.get(Calendar.HOUR_OF_DAY);
                int minute = mcurrentTime.get(Calendar.MINUTE);

                mTimePicker = new TimePickerDialog(AlarmParameters.this, new TimePickerDialog.OnTimeSetListener() {
                    @Override
                    public void onTimeSet(TimePicker timePicker, int selectedHour, int selectedMinute) {
                        //adds the 0, like : 10:6 AM --> 10:06 AM
                        if(selectedMinute<10){
                            time.setText(selectedHour + ":0" + selectedMinute);
                        }
                        else {
                            time.setText(selectedHour + ":" + selectedMinute);
                        }

                        //store time picked in the calendar
                        mcurrentTime.set(Calendar.HOUR_OF_DAY, selectedHour);
                        mcurrentTime.set(Calendar.MINUTE, selectedMinute);

                        // no seconds in the calendar
                        mcurrentTime.add(Calendar.SECOND, 0);
                    }
                }, hour, minute, true);//Yes 24 hour time

                //more settings for dialog window
                mTimePicker.setTitle("Select Time");
                mTimePicker.show();
            }
        });

        //actions when you hit the set alarm text
        btn_set_alarm.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //get the time of the alarm set from text box
                String alarm_set_string = String.valueOf(time.getText());

                //add that alarm to list of alarms on first page
                MainActivity.ALARMARRAY.add(alarm_set_string);

                //create intent to send to alarmReceiver
                final Intent myIntent = new Intent(AlarmParameters.this, AlarmReceiver.class);

                //set up alarm manager
                alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);

                //make the myIntent a pending intent?
                pending_intent = PendingIntent.getBroadcast(AlarmParameters.this, 0, myIntent, PendingIntent.FLAG_UPDATE_CURRENT);

                //tell alarmManager to send the pending intent at the time selected by the timepicker (in calendar now)
                alarmManager.set(AlarmManager.RTC_WAKEUP, mcurrentTime.getTimeInMillis(), pending_intent);//error here

                Log.e("BUTTON", "alarm set");
                finish();
            }
        });
    }}

很遗憾，我收到了一个 NullPointerException，这意味着我的日历设置不正确，当我使用 AlarmManager 时它为空？

java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Calendar.getTimeInMillis()' on a null object reference
                                                                                at xxxxxx.englishalarmclock.AlarmParameters.onClick(AlarmParameters.java:95)

所以我认为问题归结为我在 TimePickerDialog 中说这个的地方。

//store time picked in the calendar
mcurrentTime.set(Calendar.HOUR_OF_DAY, selectedHour);
mcurrentTime.set(Calendar.MINUTE, selectedMinute);

我尝试这样做，在 btn_set_alarm.setOnclickListener... 内部设置日历，但我不知道如何在外部时使用 int selectedHour/Minute（onTimeSet() 的参数） TimePickerDialog 的东西。当我尝试在 onTimeSet() 中设置 selectedHour/Minute 的 public 变量时，它说这是不允许的。

所以，最后我有 3 个问题：

1.当我在 onTimeSet() 中设置它们时，为什么我的日历没有收到 selectedHour/Minute 值？

2。为什么我 "not allowed" 在 onTimeSet() 中设置一个 public 变量？

3。我将如何在 onTimeSet() 之外使用 selectedHour/Minute 变量？

感谢您的宝贵时间！

--另外，如果您发现我做错了什么或者我可以做得更好，请告诉我！我是来学习的！ \(•◡•) /

Answer 1

您重新声明了 mCurrentTime。只需删除第 final Calendar mcurrentTime = Calendar.getInstance();

行的 final Calendar