//静态引用fragment必须要加这一句

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import android.view.Window;

public class MainActivityextends AppCompatActivity {

@Override

    protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

//静态引用fragment必须要加这一句

        requestWindowFeature(Window.FEATURE_NO_TITLE);

setContentView(R.layout.activity_main);

}

}