Android：MainActivity 中的方法工作正常，运行 MainActivity 中通过 BroadcastReceiver 的相同方法 class 给出空指针

Question

所以我的 MainActivity 中有这个方法，它正常工作。

public void DailyQuoteDatabaseAccess(){

SQLiteOpenHelper sqLiteOpenHelper = new SQLiteAssetHelper(this, DATABASE_NAME, null, DATABASE_VERSION);
SQLiteDatabase SqlDb = sqLiteOpenHelper.getReadableDatabase();
String rawQuery = "SELECT * FROM dailyQuoteTable ORDER BY RANDOM() LIMIT 1";
Cursor cursor = SqlDb.rawQuery(rawQuery, null);
DailyQuoteCursorAdapter DQCursorAdapter = new DailyQuoteCursorAdapter(this, cursor);
this.mDailyQuoteListView.setAdapter(DQCursorAdapter);
}

然而，当我尝试从我的 BroadcastReceiver class 运行它时，它被访问但应用程序崩溃并且我在 log 中收到以下错误猫:

Process: com.myapps.dailyquotes, PID: 15024
java.lang.RuntimeException: Error receiving broadcast Intent { act=android.net.conn.CONNECTIVITY_CHANGE flg=0x4000010 (has extras) } in com.myapps.dailyquotes.TodaysQuoteAlarmReceiver@d63089d
at android.app.LoadedApk$ReceiverDispatcher$Args.lambda$-android_app_LoadedApk$ReceiverDispatcher$Args_52497(LoadedApk.java:1323)
at android.app.-$Lambda$aS31cHIhRx41653CMnd4gZqshIQ.$m(Unknown Source:4)
at android.app.-$Lambda$aS31cHIhRx41653CMnd4gZqshIQ.run(Unknown Source:39)
at android.os.Handler.handleCallback(Handler.java:790)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:152)
at com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:109)
at com.readystatesoftware.sqliteasset.SQLiteAssetHelper.<init>(SQLiteAssetHelper.java:129)
at com.myapps.dailyquotes.MainActivity.DailyQuoteDatabaseAccess(MainActivity.java:403)

这是我的 BroadcastReceiver class:

package com.myapps.dailyquotes;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class TodaysQuoteAlarmReceiver  extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
MainActivity mainActivity = new MainActivity();
mainActivity.DailyQuoteDatabaseAccess();

}
}

它在MainActivity中的DailyQuoteDatabaseAccess方法中突出显示的行是这一行：

SQLiteOpenHelper sqLiteOpenHelper = new SQLiteAssetHelper(this, DATABASE_NAME, null, DATABASE_VERSION);

我在 MainActivity onCreate 中调用它...它链接到 TodaysQuoteAlarmReceiver：

 public void AlarmForQuote() {

    Calendar calendar = Calendar.getInstance();

    calendar.setTimeInMillis(System.currentTimeMillis());
    calendar.set(Calendar.HOUR_OF_DAY, 21);
    calendar.set(Calendar.MINUTE, 28);

    Calendar cur = Calendar.getInstance();

    if (cur.after(calendar)) {
        calendar.add(Calendar.DATE, 1);
    }

    mTodaysQuoteIntent = new Intent(this, 
 TodaysQuoteAlarmReceiver.class);
    int ALARM_ID = 10000;
    mTodaysQuotePendingIntent = PendingIntent.getBroadcast(
            this.getApplicationContext(), ALARM_ID, mTodaysQuoteIntent, 
 PendingIntent.FLAG_UPDATE_CURRENT);

    mNewTodaysQuote = (AlarmManager) getSystemService(ALARM_SERVICE);

    mNewTodaysQuote.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
            AlarmManager.INTERVAL_DAY, mTodaysQuotePendingIntent);

}

Answer 1

Activity 类 in Android 永远不会使用 new 运算符创建。它们是由系统在实现意图时创建的。如果您按照自己的方式创建 activity，它将没有正确的上下文集。这就是为什么在创建 SQLiteAssetHelper 时，您会得到一个空指针。

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