Fragment跳转问题

为什么用第一次使用replace转换Fragment的时候会出现空白页,要多点一次才出现需要的Fragment

MainActivity的代码如下：

package com.example.imooc.shopping;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.LinearLayout;

import com.example.imooc.shopping.Fragment.MainFragment;
import com.example.imooc.shopping.Fragment.MeFragment;
import com.example.imooc.shopping.Fragment.ShopFragment;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    protected MainFragment mainFragment=new MainFragment();
    protected MeFragment meFragment=new MeFragment();
    protected ShopFragment shopFragment=new ShopFragment();

    protected LinearLayout menuMain,menuMe,menuShop;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.getSupportFragmentManager().beginTransaction()
                .add(R.id.container_content,mainFragment)
                .add(R.id.container_content,meFragment).hide(meFragment)
                .add(R.id.container_content,shopFragment).hide(shopFragment)
                .commit();
        intent();
    }


    private void intent() {
        menuMain=this.findViewById(R.id.menu_main);
        menuMain.setOnClickListener(this);
        menuMe=this.findViewById(R.id.menu_me);
        menuMe.setOnClickListener(this);
        menuShop=this.findViewById(R.id.menu_shop);
        menuShop.setOnClickListener(this);

    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.menu_main:
                this.getSupportFragmentManager().beginTransaction()
                        .replace(R.id.container_content,mainFragment).commit();
                break;
            case R.id.menu_me:
                this.getSupportFragmentManager().beginTransaction()
                        .replace(R.id.container_content,meFragment).commit();
                break;
            case R.id.menu_shop:
                this.getSupportFragmentManager().beginTransaction()
                        .replace(R.id.container_content,shopFragment).commit();
                break;
        }
    }
}

还有我看提问里面有老师说可以用FragmentList来帮助使用show，hide来显示Fragment，需要遍历FragmentList来判断Fragment是否展示或隐藏，那怎么判断它是展示还是隐藏，这些都没接触过啊，具体是需要怎么写？