Set state of BottomSheetDialogFragment to expanded

Question

"Note that you cannot call the method before view layouts."

The above text is the clue.

Dialogs have a listener that is fired once the dialog is shown. The dialog cannot be shown if it isn't laid out.

So, in the onCreateDialog() of your modal bottom sheet (BottomSheetFragment), just before returning the dialog (or anywhere, once you have a reference to the dialog), call:

// This listener's onShow is fired when the dialog is shown
dialog.setOnShowListener(new DialogInterface.OnShowListener() {
    @Override
    public void onShow(DialogInterface dialog) {

        // In a previous life I used this method to get handles to the positive and negative buttons
        // of a dialog in order to change their Typeface. Good ol' days.

        BottomSheetDialog d = (BottomSheetDialog) dialog;
        
        // This is gotten directly from the source of BottomSheetDialog
        // in the wrapInBottomSheet() method
        FrameLayout bottomSheet = (FrameLayout) d.findViewById(android.support.design.R.id.design_bottom_sheet);

        // Right here!
        BottomSheetBehavior.from(bottomSheet)
            .setState(BottomSheetBehavior.STATE_EXPANDED);
    }
});

In my case, my custom BottomSheet turned out to be:

@SuppressWarnings("ConstantConditions")
public class ShareBottomSheetFragment extends AppCompatDialogFragment {

    @NonNull @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        BottomSheetDialog dialog =
                new BottomSheetDialog(getActivity(), R.style.Haute_Dialog_ShareImage);

        dialog.setContentView(R.layout.dialog_share_image);

        dialog.findViewById(R.id.cancel).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                dismiss();
            }
        });

        dialog.setOnShowListener(new DialogInterface.OnShowListener() {
            @Override
            public void onShow(DialogInterface dialog) {
                BottomSheetDialog d = (BottomSheetDialog) dialog;

                FrameLayout bottomSheet = (FrameLayout) d.findViewById(android.support.design.R.id.design_bottom_sheet);
                BottomSheetBehavior.from(bottomSheet).setState(BottomSheetBehavior.STATE_EXPANDED);
            }
        });

        SwitchCompat switchview = (SwitchCompat) dialog.findViewById(R.id.switchview);
        switchview.setTypeface(FontCache.get(dialog.getContext(), lookup(muli, NORMAL)));

        return dialog;
    }
}

Let me know if this helps.

UPDATE

Note that you can also override BottomSheetDialogFragment as:

public class SimpleInitiallyExpandedBottomSheetFragment extends BottomSheetDialogFragment {

    @NonNull @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        BottomSheetDialog dialog = (BottomSheetDialog) super.onCreateDialog(savedInstanceState);

        dialog.setOnShowListener(new DialogInterface.OnShowListener() {
            @Override
            public void onShow(DialogInterface dialog) {
                BottomSheetDialog d = (BottomSheetDialog) dialog;

                FrameLayout bottomSheet = (FrameLayout) d.findViewById(android.support.design.R.id.design_bottom_sheet);
                BottomSheetBehavior.from(bottomSheet).setState(BottomSheetBehavior.STATE_EXPANDED);
            }
        });

        // Do something with your dialog like setContentView() or whatever
        return dialog;
    }
}

But I really don't see why anyone would want to do that as the base BottomSheetFragment doesn't do anything other than return a BottomSheetDialog.

UPDATE FOR ANDROIDX

When using AndroidX, the resource previously found at android.support.design.R.id.design_bottom_sheet can now be found at com.google.android.material.R.id.design_bottom_sheet.

efeturi's answer is great, however, if you want to use onCreateView() to create your BottomSheet, as opposed to going with onCreateDialog(), here is the code you will need to add under your onCreateView() method:

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    getDialog().setOnShowListener(new DialogInterface.OnShowListener() {
        @Override
        public void onShow(DialogInterface dialog) {
            BottomSheetDialog d = (BottomSheetDialog) dialog;
            View bottomSheetInternal = d.findViewById(android.support.design.R.id.design_bottom_sheet);
            BottomSheetBehavior.from(bottomSheetInternal).setState(BottomSheetBehavior.STATE_EXPANDED);
        }
    });
    return inflater.inflate(R.layout.your_bottomsheet_content_layout, container, false);
}

A simplistic and elegant solution:

BottomSheetDialogFragment could be subclassed to address this:

class NonCollapsableBottomSheetDialogFragment extends BottomSheetDialogFragment {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        final BottomSheetDialog dialog = (BottomSheetDialog) super.onCreateDialog(savedInstanceState);

        dialog.setOnShowListener(new DialogInterface.OnShowListener() {
            @Override
            public void onShow(DialogInterface dialog) {
                FrameLayout bottomSheet = bottomSheetDialog.findViewById(com.google.android.material.R.id.design_bottom_sheet);

                BottomSheetBehavior behavior = BottomSheetBehavior.from(bottomSheet);
                behavior.setSkipCollapsed(true);
                behavior.setState(BottomSheetBehavior.STATE_EXPANDED);
            }
        });
        return dialog;
    }
}

So extend this class instead of BottomSheetDialogFragment to create your own bottom sheet.

Note

Change com.google.android.material.R.id.design_bottom_sheet to android.support.design.R.id.design_bottom_sheet if your project uses old Android support libraries.

I think those above is better. Sadly I did not find those solution before I had solved. But write my solution. quite similar to all.

==================================================================================

I face the same issue. This is what I solved. The Behavior is hidden in BottomSheetDialog, which is available to get the behavior If you would like not to change your parent layout to be CooridateLayout, you can try this.

STEP 1: customize the BottomSheetDialogFragment

open class CBottomSheetDialogFragment : BottomSheetDialogFragment() {
   //wanna get the bottomSheetDialog
   protected lateinit var dialog : BottomSheetDialog 
   override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
      dialog = super.onCreateDialog(savedInstanceState) as BottomSheetDialog
      return dialog
   }

   //set the behavior here
   fun setFullScreen(){
      dialog.behavior.state = BottomSheetBehavior.STATE_EXPANDED
   }
}

STEP 2: make your fragment extend this customized fragment

class YourBottomSheetFragment : CBottomSheetDialogFragment(){
    
   //make sure invoke this method after view is built
   //such as after OnActivityCreated(savedInstanceState: Bundle?)
   override fun onStart() {
      super.onStart()
      setFullScreen()//initiated at onActivityCreated(), onStart()
   }
}