关于Android Studio制作的闹钟有时无法响铃的问题

参考网络上的一些教程制作的闹钟，为什么有时候无法响铃？辛苦大家帮忙看一下，指出一下问题。

package com.example.clock3;

import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.app.AlarmManager;
import android.app.DatePickerDialog;
import android.app.PendingIntent;
import android.app.TimePickerDialog;
import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.DatePicker;
import android.widget.TextView;
import android.widget.TimePicker;
import android.widget.Toast;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity {
    private Button btnStart, btnStop;
    private TextView tvInfo;
    private PendingIntent pendingIntent;
    private AlarmManager alarmManager;
    private Calendar calendar = Calendar.getInstance();

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

        btnStart = findViewById(R.id.btnStart);
        btnStop = findViewById(R.id.btnStop);
        tvInfo = findViewById(R.id.tvInfo);
        alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);

        Intent intent = new Intent(MainActivity.this, ClockActivity.class);
        pendingIntent = PendingIntent.getActivity(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

        btnStart.setOnClickListener(new View.OnClickListener() {
            @RequiresApi(api = Build.VERSION_CODES.KITKAT)
            @Override
            public void onClick(View v) {

                calendar.setTimeInMillis(System.currentTimeMillis());

                final Calendar currentTime = Calendar.getInstance();//用于存放时间选择器中的默认时间(当前时间)
                new TimePickerDialog(MainActivity.this, new TimePickerDialog.OnTimeSetListener() {
                    @RequiresApi(api = Build.VERSION_CODES.KITKAT)
                    @SuppressLint("SetTextI18n")
                    @Override
                    public void onTimeSet(TimePicker view, int hourOfDay, int minute) {
//                        long sysTime=System.currentTimeMillis();//取出当前的时间毫秒值。
                        calendar.set(Calendar.HOUR, hourOfDay);
                        calendar.set(Calendar.MINUTE, minute);
                        calendar.set(Calendar.SECOND, 0);
                        calendar.set(Calendar.MILLISECOND, 0);
//                        long selTime=calendar.getTimeInMillis();//取出设置时间的毫秒值。
//                        if(sysTime>selTime){
//                            c.add(Calendar.DAY_OF_MONTH,1);
//                        }
                        if (minute < 10) {
                            if (hourOfDay < 10) {
                                tvInfo.append("0" + hourOfDay + ":0" + minute);
                            } else {
                                tvInfo.append(hourOfDay + ":0" + minute);
                            }
                        } else {
                            if (hourOfDay < 10) {
                                tvInfo.append("0" + hourOfDay + ":" + minute);
                            } else {
                                tvInfo.append(hourOfDay + ":" + minute);
                            }
                        }
                        Toast.makeText(MainActivity.this, (int) (calendar.getTimeInMillis() / (1000 * 60)), Toast.LENGTH_LONG).show();
                    }
                }, currentTime.get(Calendar.HOUR_OF_DAY), currentTime.get(Calendar.MINUTE), true).show();

                new DatePickerDialog(MainActivity.this, new DatePickerDialog.OnDateSetListener() {
                    @RequiresApi(api = Build.VERSION_CODES.KITKAT)
                    @Override
                    public void onDateSet(DatePicker view, int year, int month, int dayOfMonth) {
                        String text = year + "年" + (month + 1) + "月" + dayOfMonth + "日";
                        Toast.makeText(MainActivity.this, text, Toast.LENGTH_SHORT).show();
                        calendar.set(Calendar.YEAR, year);
                        calendar.set(Calendar.MONTH, month + 1);
                        calendar.set(Calendar.DAY_OF_MONTH, dayOfMonth);
                        tvInfo.setText("你设置的闹钟时间为：" + year + "年" + (month + 1) + "月" + dayOfMonth + "日");
                    }
                }
                        , currentTime.get(Calendar.YEAR)
                        , currentTime.get(Calendar.MONTH)
                        , currentTime.get(Calendar.DAY_OF_MONTH)).show();
                alarmManager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
            }
        });

        btnStop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                alarmManager.cancel(pendingIntent);
                tvInfo.setText("你未设置闹钟");
            }
        });
    }
}

本文地址：https://blog.csdn.net/weixin_45877890/article/details/108126908