How to use getSystemService in a non-activity class?

问题

I am building an application which triggers an alarm via AlarmManager.

I would like to be able to call the Alarm via it's own non-activity class, but since I am not extending Activity, I don't appear to have any 'context'. This concept confuses me, and I've read the sdk docs.

How would I go about using:

alarmTest = (AlarmManager)getSystemService(Context.ALARM_SERVICE);

in my non-activty class?

Also, I'm assuming getting context will allow me to use SharedPrefs and Intents in my non-activity class as well?

回答1:

You can pass the context to the non-activity class which is the preferred way or you could encapsulate the base context of the application to a singleton which would allow you to access the context anywhere within the application. At some cases this might be a good solution but in others its certainly not a good one.

Anyway, if you want to trigger an alarm via the AlarmManager I'm pretty sure the alarm should inherit from a Service or better yet from IntentService and in such cases you have access to the context via this.getBaseContext() or this.getApplicationContext()

回答2:

Service and Activity inherit from Context - so when you are calling getSystemService in these classes, you are really calling super.getSystemService.

If you want to have a Context available in another class, you can pass one as an argument to a method of that class, keep a reference to it, etc.

Edit: Code sample. But seriously, it is extremely basic - if you understand inheritance and methods.

class MyActivity extends Activity { // Activity extends Context, so MyActivity also extends Context
  void someMethod() {
    MyOtherClass.useStaticContext(this);
    MyOtherClass instance = new MyOtherClass();
    instance.useInstanceContext(this.getApplicationContext());
  }
}
class MyOtherClass {
  static void useStaticContext(Context context) {
  }
  void useInstanceContext(Context context) {
  }
}

回答3:

You can try the following, it allows you to get the current context the view is running through.

alarmTest = (AlarmManager)this.getContext().getSystemService(Context.ALARM_SERVICE);

回答4:

You need to pass a context into the non-activity class.

来源：https://stackoverflow.com/questions/4141555/how-to-use-getsystemservice-in-a-non-activity-class

标签

android

android-context