来自其他活动的Android调用方法

Question

I have read a bunch of posts,articles and everything but i cant get a solution.. i make an android app.. i start the first activity(first class). then i have a button for the second activity which i load it like this:

Intent i=new Intent(firstactivity.this,secondactivity.class);
startActivity(i);

in the second activity on click event to a button i want to call one method from the first activity:

firstactivity f1= new firstactivity();
f1.MyMethod("my string goes here")

when i run this the application crashes..i tried the try catch exeption and i printed to exeption which is one error for null... i cant get it to work.....

thanks in advance!

PS is there any way to start the second activity and update some values (in a textview) in the layout of the first activity?not update it only on load but also have a timer for example in the second activity and every 5 seconds settext to a textview in the layout of the first activity.. any solution(either this or what i asked above about the method) would be appreciated

Answer 1

Try to use intents to communicate between activity

either via the onNewIntent:

@Override
protected void onNewIntent(Intent intent) {
    setIntent(intent);
    handleIntent(intent);
}

private void handleIntent(Intent intent) {
    if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
      String query = intent.getStringExtra(SearchManager.QUERY);
      if (query == null) {
          query = intent.getData().toString();
      }
      doMySearch(query);
    }
}

or use a listener.

class ActivityA implements Activity {

    // Nested 'listener'
    protected class TitleBarListener extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(NEW_TITLE_INTENT))
            {
                intent.getStringExtra(NEW_TITLE_TEXT_VALUE));
            }
        }
    }

    TitleBarListener mListener;

    // then create and register
    mListener = new TitleBarListener();
    registerReceiver(mListener, new IntentFilter(NEW_TITLE_INTENT));

be sure to add the intents to the android.xml

    <intent-filter>
    <action android:name="android.intent.action.SEARCH"/>
    <action android:name="com.mypackage.changeTitle"/> 
</intent-filter>

then you should be able to broadcast / send intent to that activity

   Intent i = new Intent(AccountMainView.NEW_TITLE_INTENT);
   getActivity().sendBroadcast(i);


   // or if you activity is singleTop and you're using the onNewIntent:
   Intent i=new Intent(this,MainActivity.class);
   i.putExtra("methodName","Mymethod");//goes to previous Intent
   startActivity(i);//will trigger only Mymethod in MainActivity

Answer 2

I think that your approach is not good. what kind of method do you want to run in the first Activity ? and what is the point in doing that if your Activity is not in use by the user at the moment?

what you should do is to define your actions as part of your onResume() method of the first Activity and place their the method/s you want to run, following that just pas a Bundle or an Extra from you second Activity to the first one to determine what action should be taken.

Answer 3

Create an Interface, implement that interface in the first activity, and then call the instanciated methods from the second activity.

You can pass the instantiated interface object in the intent when starting the second activity.