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我是 Android 编程新手，现在我正在开发一个应用程序来提醒我讲座的日程安排。例如，讲座从 12:30 开始，到 1:30 pm 结束。该应用程序将在该日期通知我，并将我的手机设置为静音模式。我的应用程序现在运行良好，但问题是在讲座结束后，应用程序应该将手机调回正常模式。我的 main_activity 代码：

 public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ring(12,21,0);
    ring(12,30,1);

}
public void ring (int h,int m,int mode){
/** This intent invokes the activity DemoActivity, which in turn opens the AlertDialog window */
Intent i = new Intent("in.wptrafficanalyzer.servicealarmdemo.demoactivity");
    i.putExtra("mode",mode);

/** Creating a Pending Intent */
PendingIntent operation = PendingIntent.getActivity(getBaseContext(), 0, i, Intent.FLAG_ACTIVITY_NEW_TASK);

/** Getting a reference to the System Service ALARM_SERVICE */
AlarmManager alarmManager = (AlarmManager) getBaseContext().getSystemService(ALARM_SERVICE);



int year = Calendar.getInstance().get(Calendar.YEAR);
int month = Calendar.getInstance().get(Calendar.MONTH);
int day = Calendar.getInstance().get(Calendar.DAY_OF_MONTH);
int hour = h;
int minute = m;

/** Creating a calendar object corresponding to the date and time set by the user */
GregorianCalendar calendar = new GregorianCalendar(year,month,day, hour, minute);

/** Converting the date and time in to milliseconds elapsed since epoch */
long alarm_time = calendar.getTimeInMillis();

/** Setting an alarm, which invokes the operation at alart_time */
alarmManager.set(AlarmManager.RTC_WAKEUP  , alarm_time , operation);

/** Alert is set successfully */
Toast.makeText(getBaseContext(), "Alarm is set successfully",Toast.LENGTH_SHORT).show();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}
}

我的演示活动代码：

public class DemoActivity extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {        
    super.onCreate(savedInstanceState); 

    /** Creating an Alert Dialog Window */
    AlertDemo alert = new AlertDemo();

    /** Opening the Alert Dialog Window */
    alert.show(getSupportFragmentManager(), "AlertDemo");
}
}

我的问题出在 AlertDemo 代码中：

public Dialog onCreateDialog(Bundle savedInstanceState) {
    am = (AudioManager) getActivity().getBaseContext().getSystemService(Context.AUDIO_SERVICE);

    Intent i = this.getActivity().getIntent();
    int info = this.getActivity().getIntent().getIntExtra("mode", 0);
    if (info == 0) {
        /** Turn Screen On and Unlock the keypad when this alert dialog is displayed */
        getActivity().getWindow().addFlags(LayoutParams.FLAG_TURN_SCREEN_ON | LayoutParams.FLAG_DISMISS_KEYGUARD);
        /** Creating a alert dialog builder */
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());

        /** Setting title for the alert dialog */
        builder.setTitle("Alarm");

        /** Setting the content for the alert dialog */
        builder.setMessage("An Alarm by AlarmManager");
        Uri uri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_ALARM);
        final Ringtone ringtone = RingtoneManager.getRingtone(getContext(), uri);
        ringtone.play();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                am.setRingerMode(AudioManager.RINGER_MODE_SILENT);
            }
        }, 300000);

        /** Defining an OK button event listener */
        builder.setPositiveButton("OK", new OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                /** Exit application on click OK */
                getActivity().finish();
                ringtone.stop();
            }
        });

        /** Creating the alert dialog window */
        return builder.create();
    }
    else
        am.setRingerMode(AudioManager.RINGER_MODE_NORMAL);
}

当我添加语句“return null”时，问题是缺少返回语句出现此错误（应用程序已停止）：

java.lang.RuntimeException: Unable to start activity ComponentInfo{in.wptrafficanalyzer.servicealarmdemo/in.wptrafficanalyzer.servicealarmdemo.DemoActivity}: java.lang.NullPointerException
                                                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
                                                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
                                                                                     at android.app.ActivityThread.access$600(ActivityThread.java:128)
                                                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
                                                                                     at android.os.Handler.dispatchMessage(Handler.java:99)
                                                                                     at android.os.Looper.loop(Looper.java:137)
                                                                                     at android.app.ActivityThread.main(ActivityThread.java:4517)
                                                                                     at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                     at java.lang.reflect.Method.invoke(Method.java:511)
                                                                                     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
                                                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
                                                                                     at dalvik.system.NativeStart.main(Native Method)
4

2 回答 2

0

如果您返回 null，则您的警报对象为 null。然后你继续要求在这个对象上执行“show”方法，因此出现空指针异常。由于您在 DemoActivity 的“onCreate”方法中执行此操作，因此您的活动无法启动。尝试在创建警报之前事先决定是否显示对话框。然后只在模式合适时创建（并显示）警报（顺便说一下，Java 有布尔值，你为什么使用整数？）。

于 2018-06-07T13:40:26.470 回答
0

不要在onCreateDialog方法上做决定。删除if-else块onCreateDialog

public class DemoActivity extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    am = (AudioManager) getActivity().getBaseContext().getSystemService(Context.AUDIO_SERVICE);

    Intent i = this.getActivity().getIntent();
    int info = this.getActivity().getIntent().getIntExtra("mode", 0);
    if (info == 0) {
        AlertDemo alert = new AlertDemo();

        /** Opening the Alert Dialog Window */
        alert.show(getSupportFragmentManager(), "AlertDemo");
    } else
        am.setRingerMode(AudioManager.RINGER_MODE_NORMAL);
}

}

于 2018-06-07T13:45:40.893 回答