如何讓viewId用于另一個類？

我想創建一個類來處理ProgressBar。但是我找不到傳輸viewId的方法，這會導致空指針錯誤。

這是Helper類：

public class HelperProgressBar {
ProgressBar progressBar;
Activity activity;
int ID;

public HelperProgressBar(Activity activity, int ID) {
    this.activity = activity;
    this.ID = ID;
    progressBar.findViewById(ID);
}

public void showProgressBar(){
    progressBar.setVisibility(View.VISIBLE);
    activity.getWindow().setFlags(
            WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE,
            WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE);
}

public void hideProgressBar(){
    activity.getWindow().clearFlags(
            WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE);
}}

我這樣稱呼它：

HelperProgressBar helperProgressBar = new HelperProgressBar(getApplicationContext(), progressBar.getId());