Accessing fragment method through activity

Question

I'm developing a kiosk app where people can walk to and order something.

I have a single activity with bunch of different fragments (order, review, pay, etc). Some replace each other, and some get added. The activity has a single fragment hardcoded R.id.fragmentContainer and the rest are programmatically added and tagged.

Now what I want is to have a function in my activity that calls one of the elements of the fragments (look at updateReceivedData()) but for some reason I'm not able to do so and I get cannot resolve method adjustPriceFunc.

I'm adding the code so someone could tell me what I'm doing wrong. The app would normally talk to some hardware so I took out a bunch of those details from the code to make it easier to read.

public class MainActivity extends FragmentActivity {
private final String TAG = MainActivity.class.getSimpleName();

List<WeakReference<Fragment>> fragList = new ArrayList<WeakReference<Fragment>>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    Log.d(TAG, "onCreate()");
    super.onCreate(savedInstanceState);
    setContentView(R.layout.backbone);
    android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
    android.support.v4.app.Fragment fragment = fm.findFragmentById(R.id.fragmentContainer);

    if (fragment == null) {
        fragment = new Fragment();
        fm.beginTransaction()
                .add(R.id.fragmentContainer, fragment, "SystemDownFragment")
                .addToBackStack(null)
                .commit();
    }
}

public void orderFunc() {
    Log.d(TAG, "orderFunc()");
    if(sendingLogFlag)      attemptSend(TAG + ":orderFunc()");

    for(int i = 0; i < getActiveFragments().size(); i++) {
        getSupportFragmentManager().beginTransaction().remove(getActiveFragments().get(i)).commit();
    }

    Fragment newFragment = new Fragment();
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.add(R.id.fragmentContainer, newFragment, "OrderFragment");
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    ft.commit();
}

public void checkoutFunc() {
    Log.d(TAG, "checkoutFunc()");
    if(sendingLogFlag)      attemptSend(TAG + ":checkoutFunc()");

    for(int i = 0; i < getActiveFragments().size(); i++) {
        getSupportFragmentManager().beginTransaction().remove(getActiveFragments().get(i)).commit();
    }

    Fragment newFragment = new Fragment();
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.add(R.id.fragmentContainer, newFragment, "CheckOutFragment");
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    ft.commit();
}

public void reviewFunc(){
    Log.d(TAG, "reviewFunc()");
    if(sendingLogFlag)      attemptSend(TAG + ":reviewFunc()");

    if(getActiveFragments().size() > 1){
        Fragment frag = getSupportFragmentManager().findFragmentByTag("ReviewFragment");
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_CLOSE);
        ft.remove(frag);
        ft.commit();
    }
    else {
        Fragment newFragment = new Fragment();
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        ft.add(R.id.fragmentContainer, newFragment, "ReviewFragment");
        ft.commit();
    }
    getSupportFragmentManager().executePendingTransactions();
}

public void payFunc(boolean enabled){
    Log.d(TAG, "payFunc()");
    if(sendingLogFlag)      attemptSend(TAG + ":payFunc()");

    if(!enabled){
        Fragment frag = getSupportFragmentManager().findFragmentByTag("PayFragment");
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_CLOSE);
        ft.remove(frag);
        ft.commit();
    }
    else {
        Fragment newFragment = new Fragment();
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        ft.add(R.id.fragmentContainer, newFragment, "PayFragment");
        ft.commit();
    }
    getSupportFragmentManager().executePendingTransactions();
}

public void doneFunc() {
    Log.d(TAG, "doneFunc()");

    for(int i = 0; i < getActiveFragments().size(); i++) {
        getSupportFragmentManager().beginTransaction().remove(getActiveFragments().get(i)).commit();
    }

    Fragment newFragment = new Fragment();
    FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
    ft.add(R.id.fragmentContainer, newFragment, "StartupFragment");
    ft.commit();
}

@Override
public void onAttachFragment (Fragment fragment) {
    fragList.add(new WeakReference(fragment));
}

public List<Fragment> getActiveFragments() {
    ArrayList<Fragment> ret = new ArrayList<Fragment>();
    for(WeakReference<Fragment> ref : fragList) {
        Fragment f = ref.get();
        if(f != null) {
            if(f.isVisible()) {
                ret.add(f);
            }
        }
    }
    return ret;
}

private void updateReceivedData() {
    Fragment frag = getSupportFragmentManager().findFragmentByTag("PayFragment");
                        frag.adjustPriceFunc();
}

Answer 1

There is few mistakes here in the code

• In orderFunc, checkoutFunc etc. add remove to the transaction and call commit once after the loop, like

  FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
  for(int i = 0; i < getActiveFragments().size(); i++) {
      transaction.remove(getActiveFragments().get(i));
  }
  transaction.commit();
  

• You get compilation error in updateReceivedData because Fragmentdoes not have adjustPriceFunc() method. You need either (cleaner approach) create interface with adjustPriceFunc() method, let your fragment implement it and then your updateReceivedData will look like follows:

  private void updateReceivedData() {
      InterfaceWithAdjustPriceMethod frag = (InterfaceWithAdjustPriceMethod) getSupportFragmentManager().findFragmentByTag("PayFragment");
      frag.adjustPriceFunc();
  }
  

Answer 2

You are trying to use method adjustPriceFunc() from class Fragment, which is not part of it.

Use this code, where MyFragment is your proper fragment (I assume it should be PayFragment).

private void updateReceivedData() {
    Fragment frag = getSupportFragmentManager().findFragmentByTag("PayFragment");
    if (frag instanceof MyFragment) {
        frag.adjustPriceFunc();  
    }                  
}

Answer 3

Storing reference to fragment is a bad practice, even if it is WeakReference.
Better use this way:

   Fragment fragment = getSupportFragmentManager().findFragmentByTag("tag");