我的应用检查 onResume 中的日期,以查看是否需要调用 MainActivity 中名为 changeReminder 的方法。也就是说,如果日期与存储的日期不同,则调用 changeReminder(也从其他方法调用 changeReminder,例如刷新按钮)。 changeReminder 依次调用 Reminder 类,该类将在创建实例时创建新提醒。
现在,我要向应用程序添加闹钟、广播接收器和通知。因为更改提醒是从 MainActivity 调用的,所以我在 BroadcastReceiver 类中创建了该 Activity 的一个实例,但是因为提醒类需要上下文(它始终来自 MainActivity),所以它会引发错误。在这种情况下,有没有办法从广播接收器成功传递上下文?我想我在下面包含了相关代码,但如果需要我可以添加更多...
触发警报后的日志:
05-02 13:23:00.712 15511-15511/com.mycompany.dudesmyreminders I/System.out﹕ onReceive
05-02 13:23:00.722 15511-15511/com.mycompany.dudesmyreminders I/System.out﹕ start changeReminder
05-02 13:23:00.722 15511-15511/com.mycompany.dudesmyreminders I/System.out﹕ start Reminder
05-02 13:23:00.752 15511-15511/com.mycompany.dudesmyreminders E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.mycompany.dudesmyreminders, PID: 15511
java.lang.RuntimeException: Unable to start receiver com.mycompany.dudesmyreminders.ReminderReceiver: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2726)
at android.app.ActivityThread.access$1700(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:155)
at android.app.ActivityThread.main(ActivityThread.java:5696)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.sqlite.SQLiteDatabase android.content.Context.openOrCreateDatabase(java.lang.String, int, android.database.sqlite.SQLiteDatabase$CursorFactory, android.database.DatabaseErrorHandler)' on a null object reference
at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:267)
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:223)
at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:163)
at com.mycompany.dudesmyreminders.dbDataSource.open(dbDataSource.java:39)
at com.mycompany.dudesmyreminders.Reminder.<init>(Reminder.java:37)
at com.mycompany.dudesmyreminders.MainActivity.changeReminder(MainActivity.java:283)
at com.mycompany.dudesmyreminders.ReminderReceiver.onReceive(ReminderReceiver.java:23)
at android.app.ActivityThread.handleReceiver(ActivityThread.java:2712)
at android.app.ActivityThread.access$1700(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:155)
at android.app.ActivityThread.main(ActivityThread.java:5696)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
MainActivity onCreate 中的警报管理器:
//Alarm manager for notifications....
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.HOUR_OF_DAY, Calendar.getInstance().get(Calendar.HOUR_OF_DAY));
System.out.println("Hour = " + Calendar.getInstance().get(Calendar.HOUR_OF_DAY));
calendar.set(Calendar.MINUTE, Calendar.getInstance().get(Calendar.MINUTE) + 2);
System.out.println("Minute = " + Calendar.getInstance().get(Calendar.MINUTE));
calendar.set(Calendar.SECOND, 0);
Intent intent1 = new Intent(MainActivity.this, ReminderReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0,intent1, PendingIntent.FLAG_UPDATE_CURRENT);
AlarmManager am = (AlarmManager) MainActivity.this.getSystemService(MainActivity.ALARM_SERVICE);
am.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), AlarmManager.INTERVAL_DAY, pendingIntent);
广播接收器:
public class ReminderReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
// TODO: This method is called when the BroadcastReceiver is receiving
// an Intent broadcast.
//throw new UnsupportedOperationException("Not yet implemented");
System.out.println("onReceive");
MainActivity ma = new MainActivity();
ma.changeReminder(context);
String message = ma.getStoredPreference("CurrentMessage");
NewReminderNotification.notify(context,message,1);
}
}
主 Activity 中的 changeReminder:
public void changeReminder(Context context) {
System.out.println("start changeReminder");
Reminder reminder = new Reminder(this);
// Save the message to the Shared Preferences file
int altitude = getStoredPreferenceInt(SEEKBAR_CURRENT_INT);
savePreference("CurrentMessage", reminder.determineReminder(altitude));
savePreferenceInt(DBDATA_ID, (int) reminder.dbData.getId());
//populates the reminder dbData for current session
//DBDATA_ID is only changed in the line above
dbDataCurrentReminder = datasource.getDB_Row_FromID(dbRTable, (long) getStoredPreferenceInt(DBDATA_ID));
//display the message just saved
DisplaySavedMessage();
// save the current date to Preferences
saveDate();
setToggles(0);
}
提醒构造函数:
public Reminder(Context context) {
System.out.println("start Reminder");
ds = new dbDataSource(context);
ds.open();
DatabaseVersion = ds.DatabaseVersion;
}
最佳答案
您的代码存在一些问题。
MainActivity ma = new MainActivity();
首先,绝不自己创建Activity
、Service
或ContentProvider
的实例。这些只能由框架实例化,而不是你。这就是您的实例不起作用的原因。
其次,不要在主应用程序线程上执行磁盘 I/O 或网络 I/O,因为在 I/O 进行时您的 UI 将被卡住。 BroadcastReceiver
的 onReceive()
在主应用程序线程上被调用,而您正在尝试(徒劳地)在该线程上执行数据库 I/O。
Is there a way to successfully pass the context from the Broadcast Receiver in this case?
欢迎您将该方法设为静态
方法。
但是,更好的解决方案是将此代码移动到 IntentService
中。首先,它为您提供了一个安全的、受管理的后台线程来完成这项工作。其次,它与您应该使用的 WakefulBroadcastReceiver
一起工作,以确保设备可以保持唤醒状态足够长的时间,以便您执行此数据库 I/O。始终将 WakefulBroadcastReceiver
、我的 WakefulIntentService
或您自己的 WakeLock
与 RTC_WAKEUP
或 ELAPSED_REALTIME_WAKEUP
一起使用警报。
关于android - 从广播接收器调用电话时出现上下文错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/30006973/