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Accepted
Mario López Batres
Asked: 2020-01-14 12:55:14 +0800 CST 2020-01-14 12:55:14 +0800 CST

How to communicate an activity with a fragment

  • 772

I would like to know how to access the variables of an activity from its fragment.

I will give an example to clarify my doubt:

Suppose I have an activity with a global variable called ventanaFragmentoAbierta, and I want when the fragment opens one of its layouts it puts its value to trueand the activity finds out in real time (I'd like to work on onBackPressed()it based on this).

java

3 Answers

  1. Best Answer

    In Activityit you define your method to modify the variable:

    public void setVariable(boolean valor){
   ventanaFragmentoAbierta = valor;
}

    and you access it from Fragmentit like this:

    ((TuActivity)getActivity()).setVariable(true);

    It is done this way since defining a public variable in one Activitycan lead to problems if you have another Activity with the same public variable, you must ensure access to the Class method to modify its variable.

    • 4

  2. define an interface

    In your fragment you define an interface and make it throw an exception if the activity does not implement it

     // Tu Activity deberá implementar esta interfaz
public interface OnVarChangedFromFragment {
    public void onChangeVar();
}

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    // De esta forma te aseguras que la activity tenga la interfaz
    // Sino saltará una excepción
    try {
        mCallback = (OnVarChangedFromFragment) activity;
    } catch (ClassCastException e) {
        throw new ClassCastException(activity.toString()
                + " debes implementar OnVarChangedFromFragment");
    }
}

    When you need to notify your activity you call your fragment's interface like this:

    mCallback.onChangeVar();

    On the other hand your activity will implement the interface

    public static class MainActivity extends Activity
        implements OnVarChangedFromFragment

    And when your fragment calls the method you do what you want in your activity, which will be notified

    More info: https://developer.android.com/training/basics/fragments/communicating.html#Implement

    • 0

  3. To access a variable of an activity from a fragment as you call it, I would tell you that it is wrong. I mean that what you are really looking for is to obtain a variable from a class, for this you only have to add staticto the variable that you want to access from another class for example...

    public class Ejemplo {
public static int str_casa = -1;

    you have to initialize since calling another class will get the value unless it has been altered in the course. Now to call from another class you would just have to do this.

    Ejemplo.str_casa

    and so you would get the value of that variable

    • -1