Android:如何使findViewById(R.id.xxx)在从View类继承/扩展的类中工作？

<com.example.myapplication.MyCustomViewGroup
    android:id="@+id/my_custom_view_group"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

   <Button
        android:id="@+id/button_inside_custom_view_group"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Button inside Custom ViewGroup" />

</com.example.myapplication.MyCustomViewGroup>

package com.example.myapplication;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.widget.Button;
import android.widget.RelativeLayout;

public class MyCustomViewGroup extends RelativeLayout {

    public MyCustomViewGroup(Context context) {
        super(context);
        init(context);
    }

    public MyCustomViewGroup(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public MyCustomViewGroup(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    private void init(Context context) {
        View.inflate(context, R.layout.activity_main, this);

        Button buttonInsideCustomViewGroup = findViewById(R.id.button_inside_custom_view_group);
        buttonInsideCustomViewGroup.setText("Button inside Custom ViewGroup (modified)");
    }
}