android – 使用0 containerViewId添加片段

我编写了这段代码,但我看不到片段的布局.它显示一个空屏幕.

@Override
    protected void onCreate(Bundle savedInstanceStatE) {
        super.onCreate(savedInstanceStatE);
        setContentView(R.layout.activity_main);
        Fragment fragment = new TestFragment();
        Fragmenttransaction ft = getFragmentManager().begintransaction();
        ft.add(fragment,"test");
        ft.commit();
    } // onCreate

 public class TestFragment extends Fragment {

        @Nullable
        @Override
        public View onCreateView(LayoutInflater inflater,ViewGroup        container,Bundle savedInstanceStatE) {
            return inflater.inflate(R.layout.frag_layout,container,falsE);
        }
    } // TestFragment@H_675_10@