关于 Fragment 不显示的问题

[一支万宝路]

ViewActivity.java ：

public class ViewActivity extends AppCompatActivity {


    private MainFragment mainFragment;

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

        //实例化MainFragment
        mainFragment = new MainFragment();
        //将Fragment添加到container中
        getSupportFragmentManager().beginTransaction().add(R.id.fl_container,mainFragment).commitAllowingStateLoss();
    }
}

与它关联的xml文件， activity_view.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Fragment.ViewActivity">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="activity_view"
        android:textSize="20dp"
        android:id="@+id/tv_4"
        android:textColor="#000"/>

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/tv_4"
        android:id="@+id/fl_container" />

</RelativeLayout>

创建的 MainFragment 类

public class MainFragment extends Fragment {
    private TextView tv_3;
    private View view;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        view = inflater.inflate(R.layout.main_fragment,container,false);
        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        tv_3 = (TextView) view.findViewById(R.id.tv_3);
    }
}

与它关联的xml文件，main_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="主页"
        android:gravity="center"
        android:textSize="50dp"
        android:textColor="#000"
        android:id="@+id/tv_3"/>

</LinearLayout>

代码的情况就是这样，但是 FrameLayout 那一部分显示不出来


有没有大佬能帮我看下怎么解决这个问题啊啊啊啊

[闫文敬]

你的整体逻辑没问题，beginTransaction().add(),已经添加到事务里了，但是你仅仅是添加，没有调用show()方法，改为beginTransaction().add(xxx).show(xxx)即可