做闹钟，为什么我的日历是空的？

Question

今年夏天，为了学习app开发，我已经决定在Android工作室做一个闹钟，事先没有太多Java或OOP方面的知识。

我试图使用TimePickerDiaglog获取用户对警报的输入，然后将该时间存储在Calendar实用程序中，这样我就可以使用警报管理器设置一个挂起的意图。

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();
            }
        });
    }}

不幸的是，我收到一个NullPointerException，这意味着我的日历设置不正确，当我与AlarmManager一起使用时，它是空的？

java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Calendar.getTimeInMillis()' on a null object reference
                                                                                at xxxxxx.englishalarmclock.AlarmParameters$2.onClick(AlarmParameters.java:95)

所以我想问题归结为我在TimePickerDialog中说这些的地方。

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

我试着在BTN_SET_ALARM.SetonClickListener中设置日历...但是我不知道在TimePickerDialog东西之外如何使用int selectedHour/minute（onTimeSet（）的参数）。当我尝试在onTimeSet（）内设置selectedHour/minute的公共变量时，它说这是不允许的。

所以，最后我有三个问题：

1.当我在onTimeSet（）中设置选定的小时/分钟值时，为什么日历没有收到这些值？

2.为什么我“不允许”在onTimeSet（）中设置一个公共变量？

3.如何使用onTimeSet（）之外的SelectedHour/Minute变量？

谢谢你抽出时间！

还有，如果你看到我还有什么不对的地方，或者我可以做得更好，请告诉我！我是来学习的！\(••)/

Answer 1

重新声明mCurrentTime。只需删除final Calendar行的final CalendarmcurrentTime=Calendar.getInstance（）；