How to create a simple DialogFragment

ExampleDialogFragment.java

public class ExampleDialogFragment extends DialogFragment {

    public static ExampleDialogFragment newInstance() {
        return new ExampleDialogFragment();
    }

    @NonNull
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        Dialog dialog = new Dialog(getActivity());
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        return dialog;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.dialog_fragment_example, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
    }

    @Override
    public void onStart() {
        super.onStart();
        getDialog().getWindow().setLayout(
                WindowManager.LayoutParams.MATCH_PARENT,
                WindowManager.LayoutParams.WRAP_CONTENT
        );
    }

}

SomeActivity.java

public class SomeActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //This is what you are looking for
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        Fragment prev = getSupportFragmentManager().findFragmentByTag("yourTag");
        if (prev != null) {
            ft.remove(prev);
        }
        ft.addToBackStack(null);

        DialogFragment dialogFragment = ExampleDialogFragment.newInstance();
        dialogFragment.show(ft, "yourTag");
    }
}

Dialogs cheat sheet https://gist.github.com/cutiko/348d5dee496d7abfd022d8a2e81ec812