Hide/Show Button in Fragment from Activity

Question

i am trying to hide/show Button in fragment from Activity but it give me following exception.

android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.

Home Activity

 public class HomeActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        CategoryFragment frag=(CategoryFragment) activity.getSupportFragmentManager() 
                                  .findFragmentByTag("cat_frag");
        Button newDesigns= (Button) frag.getView().findViewById(R.id.new_designs);
        newDesigns.setVisibility(View.VISIBLE);
     }
 }

Category Fragment

 public class CategoryFragment extends Fragment{
    Button newDesigns;
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.fragment_category, null);
        newDesigns= (Button) v.findViewById(R.id.new_designs);
   }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#CCCCCC">

    <TextView
        android:id="@+id/list_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:background="@drawable/shape_logo_bg"
        android:gravity="center"
        android:padding="5dp"
        android:textColor="@android:color/white"
        android:textSize="18sp" />

    <Button
        android:id="@+id/new_designs"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/list_name"
        android:background="@color/edit_button_color"
        android:padding="10dp"
        android:text="@string/new_designs"
        android:textColor="@color/btn_text_color"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="5dp"
        android:visibility="gone"
        />
</RelativeLayout>

Code is too large to be posted here. Thats why i have only posted the code where i am finding an issue.

I am able to get newDesigns BUTTON instance.What is shocking for me is if try to play with button instance (VISIBLE/GONE) it gives me above mentioned exception.

Help is appreciated.

Answer 1

You shouldn't play with a view of the Fragment while you are in a Activity directly. You will not know what the view's state will be and this can potentially lead to issues you can't even think of(beleive me i faced many). To interact with the activity's views, make an interface:

public interface AccessFragmentViews{
  public void setVisibilityForButton(boolean bool);
  //any other methods that you need
}

Now implement this inside the fragment class and override the method.

class YourFragment implements AccessFragmentViews{

. 
.

    public void serVisibilityForButton(boolean shouldHide){
       if(shouldHide){
           yourButton.setVisibility(View.GONE);
       }else{
           yourButton.setVisibility(View.VISIBLE);
       }
    }
}

Now you can interact safely with the views of the fragment within a activity using this interface. Make sure that the fragment is alive before doing so though ;) accessing child's view are prone to WindowLeakedExceptions and illegalstateexceptions

In the activity use it as follows:

you can get the fragment reference by either finding it by its tag or by using the reference you used to create the fragment

//NOTE: it is very very dangerous to do the accessing on a fragment views from an activity

//first the alive check then the logic 

if(yourFragmentReference!=null){
((AccessFragmentViews)yourFragmentReference).setVisibilityForButton(true);// or false if you want to make it visible
}

Answer 2

Add a method in your fragment class

public void changeButtonVisibility(boolean visibility){
  if(visibility){
    newDesigns.setVisibility(View.VISIBLE);
  }else{
    newDesigns.setVisibilty(View.GONE);
  }
}

and in your activity class

add this line

 public class HomeActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home);
        CategoryFragment frag=(CategoryFragment) activity.getSupportFragmentManager() 
                                  .findFragmentByTag("cat_frag");
        frag.changeButtonVisibility(true);
     }
 }