我该如何正确地将一些Fragment放入mainActivity的FrameLayout中？

Question

我试图通过单击MainActivity中的按钮将片段放入MainActivity的FrameLayout中。它几乎可以工作，但是MainActivity的public class MainActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Button btn = findViewById(R.id.pushMeBtn); btn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { FragmentManager f_m = getSupportFragmentManager(); FragmentTransaction f_t = f_m.beginTransaction(); f_t.replace(R.id.container_layout, new Fragment1()).addToBackStack(null).commit(); } }); } } 的内容不会被Fragment内容代替，而是添加到其中。所以问题是：如何使其正确？

我的MainActivity类

<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=".MainActivity">

    <FrameLayout
        android:id="@+id/container_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/pushMeBtn"
            android:text="push me"
            android:layout_gravity="center"/>
    </FrameLayout>
</RelativeLayout>

我的activity_main.xml

public class Fragment1 extends Fragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment1, container,false);
    }
}

我的Fragment1类

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent"
    android:background="@color/colorPrimary">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="339dp"
        android:gravity="center"
        android:text="fragment1"
        android:textSize="25sp"/>
</RelativeLayout>

我的fragment.xml

{{1}}