Android中Activity未启动时能否运行Java代码实现后台闹钟功能

Android系统自带的AlarmManager服务专门处理定时触发任务，就算应用未启动、进程被杀也能正常触发，完全符合你的需求，不需要自己维护循环检查时间的逻辑，具体实现步骤如下：

步骤1：修正并改造DateTimeAlarm类 #

你代码里的bool是其他语言的写法，Java中对应boolean，同时实现Parcelable接口方便组件间传参：

import android.os.Parcel;
import android.os.Parcelable;

public class DateTimeAlarm implements Parcelable {
    public int day;
    public int hour;
    public int minute;
    public boolean alarmed = false;

    public DateTimeAlarm(int day, int hour, int minute) {
        this.day = day;
        this.hour = hour;
        this.minute = minute;
    }

    protected DateTimeAlarm(Parcel in) {
        day = in.readInt();
        hour = in.readInt();
        minute = in.readInt();
        alarmed = in.readByte() != 0;
    }

    public static final Creator<DateTimeAlarm> CREATOR = new Creator<DateTimeAlarm>() {
        @Override
        public DateTimeAlarm createFromParcel(Parcel in) {
            return new DateTimeAlarm(in);
        }

        @Override
        public DateTimeAlarm[] newArray(int size) {
            return new DateTimeAlarm[size];
        }
    };

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(day);
        dest.writeInt(hour);
        dest.writeInt(minute);
        dest.writeByte((byte) (alarmed ? 1 : 0));
    }
}

步骤2：新建广播接收器放置你的业务逻辑 #

广播接收器可以在应用未启动的状态下被系统唤起，你原来的时间校验、Alarm()函数逻辑都放在这里即可：

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import java.util.Calendar;

public class AlarmTriggerReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // 获取你设置闹钟时传入的目标时间参数
        DateTimeAlarm targetTime = intent.getParcelableExtra("target_alarm");
        if (targetTime == null) return;

        // 系统触发广播时再做一次时间校验，匹配你的原有逻辑
        Calendar current = Calendar.getInstance();
        int currentDay = current.get(Calendar.DAY_OF_WEEK); // 注意Calendar默认周日为1，如果你是自定义的day计数规则自行对应转换
        int currentHour = current.get(Calendar.HOUR_OF_DAY);
        int currentMinute = current.get(Calendar.MINUTE);

        if (!targetTime.alarmed && currentDay == targetTime.day 
            && currentHour == targetTime.hour 
            && currentMinute >= targetTime.minute) {
            targetTime.alarmed = true;
            // 执行你的闹钟业务逻辑
            Alarm();
        }
    }

    private void Alarm() {
        // 把你原来Alarm()函数的逻辑（响铃、弹通知、跳转页面等）写在这里
    }
}

步骤3：在AndroidManifest.xml中注册广播接收器 #

不注册的话系统无法找到对应的接收器，在<application>标签内添加以下代码：

<receiver
    android:name=".AlarmTriggerReceiver"
    android:exported="false" />

步骤4：用户设置闹钟时调用AlarmManager注册定时任务 #

这段代码放在你设置闹钟的交互逻辑里即可（比如用户点击「保存闹钟」按钮的回调中）：

import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import java.util.Calendar;

public void setAlarm(Context context, DateTimeAlarm targetTime) {
    AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
    Intent intent = new Intent(context, AlarmTriggerReceiver.class);
    intent.putExtra("target_alarm", targetTime);

    // 计算闹钟触发的时间戳
    Calendar calendar = Calendar.getInstance();
    calendar.set(Calendar.DAY_OF_WEEK, targetTime.day);
    calendar.set(Calendar.HOUR_OF_DAY, targetTime.hour);
    calendar.set(Calendar.MINUTE, targetTime.minute);
    calendar.set(Calendar.SECOND, 0);

    // 如果设置的时间已经过了，自动顺延一周（如果是单次闹钟可自行判断提示用户）
    if (calendar.before(Calendar.getInstance())) {
        calendar.add(Calendar.DATE, 7);
    }

    // 每个闹钟要生成唯一的requestCode，避免覆盖
    int requestCode = targetTime.day * 10000 + targetTime.hour * 100 + targetTime.minute;
    PendingIntent pendingIntent = PendingIntent.getBroadcast(
        context,
        requestCode,
        intent,
        PendingIntent.FLAG_UPDATE_CURRENT | PendingIntent.FLAG_IMMUTABLE
    );

    // 设置闹钟，RTC_WAKEUP参数表示就算设备休眠也会唤醒触发
    alarmManager.setExactAndAllowWhileIdle(
        AlarmManager.RTC_WAKEUP,
        calendar.getTimeInMillis(),
        pendingIntent
    );
}

补充注意事项 #

• Android 6.0及以上的低电耗模式会限制普通闹钟触发，使用setExactAndAllowWhileIdle可以保证在低电耗模式下也能正常触发
• 如果是单次闹钟，触发后记得调用alarmManager.cancel(pendingIntent)取消定时任务，避免重复触发
• 如果需要闹钟触发时打开Activity，在Alarm()方法里加启动Activity的Intent即可，注意要添加FLAG_ACTIVITY_NEW_TASK标记

内容的提问来源于stack exchange，提问作者Erfan Games