java reflection - آموزش جدید

سلام دوستان . مشکل من اینه که توی کلاس UAppcompatActivity، بلاک try  اجرا نمیشه، لاگ گرفتم و تا یک خط قبلش مشکلی نداره اما اون خط مشکل داره و وقتی هم میره توی catch  برنامه فورس کلوز میشه 

public class UAppCompatActivity extends AppCompatActivity {

  @Override
  public void onCreate(Bundle savedInstanceState, PersistableBundle persistentState) {
    super.onCreate(savedInstanceState, persistentState);
  }

  @Override
  protected void onResume() {
    super.onResume();

    UBase.setCurrentActivity(this);
  }


  public static class Founder {
    private final Activity activity;
    private int[] features;
    private boolean noTitlebar;
    private boolean noActionbar;
    private boolean fullscreen;
    private int layoutId;
    private Object ui;

    public Founder(Activity activity) {
      this.activity = activity;
    }

    public Founder requestFeatures(int... features) {
      this.features = features;
      return this;
    }

    public Founder noTitlebar() {
      this.noTitlebar = true;
      return this;
    }

    public Founder noActionbar() {
      this.noActionbar = true;
      return this;
    }

    public Founder fullscreen() {
      this.fullscreen = true;
      return this;
    }

    public Founder contentView(@LayoutRes int layoutResID) {
      this.layoutId = layoutResID;
      return this;
    }

    public Founder extractUi(Object ui) {
      this.ui = ui;
      return this;
    }

    public Founder build() {
      for (int feature: this.features) {
        activity.getWindow().requestFeature(feature);
      }

      if (noTitlebar) {
        activity.getWindow().requestFeature(Window.FEATURE_NO_TITLE);
      }

      if (fullscreen) {
        activity.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
      }

      if (noActionbar) {
        activity.getWindow().requestFeature(Window.FEATURE_ACTION_BAR);

        {
          ActionBar actionBar = activity.getActionBar();
          if (actionBar != null) {
            actionBar.hide();
          }
        }

        if (activity instanceof AppCompatActivity) {
          AppCompatActivity castedActivity = (AppCompatActivity) activity;
          android.support.v7.app.ActionBar actionBar = castedActivity.getSupportActionBar();
          if (actionBar != null) {
            actionBar.hide();
          }
        }
      }

      activity.setContentView(layoutId);

      // reflect ui elements

        Class clazz = ui.getClass();
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
          String name = field.getName();
          Class type = field.getType();
          if (name.contains("$")) {
            continue;
          }

          int id = UBase.get().getResources().getIdentifier(name, "id", UBase.get().getPackageName());
          try {
            field.set(ui, activity.findViewById(id));
            
          } catch (IllegalAccessException e) {
            e.printStackTrace();

          }
        }


      return this;
    }
  }
}

کد main activity:

public class MainActivity extends UAppCompatActivity {

  private Ui ui;

  private class Ui {
    TextView txtview;
  }

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    ui = new Ui();

    new Founder(this)
      .requestFeatures()
      .noTitlebar()
      .noActionbar()
      .fullscreen()
      .contentView(R.layout.activity_main)
      .extractUi(ui)
      .build();

    ui.txtview.setText("My Name is Hello World after Reflection!");
  }
}

از این خط، خطای nullPointerException  میگیره

ui.txtview.setText("My Name is Hello World after Reflection!");

اینم خطی که تو کد اول اجرا نمیشه

            field.set(ui, activity.findViewById(id));