错误：The method replace(int, Fragment) in the type FragmentTransaction is not applicable for the arguments (int, MyFragment)

Fragment newfragment =new MyFragment();
fragmentTransaction.replace(R.layout.activity_main,newfragment ).commit();

提示错误：The method replace(int, Fragment) in the type FragmentTransaction is not applicable for the arguments (int, MyFragment)

妈蛋，找了好久！一直以为子类对象不能赋值给父类引用。这部科学啊！

错误代码：

package com.example.testforfragment;

import android.os.Bundle;

import android.app.Activity;

import android.app.FragmentManager;

import android.app.FragmentTransaction;

import android.support.v4.app.Fragment;

import android.support.v4.app.Fragment.*;

import android.view.Menu;

public class MainActivity extends Activity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        FragmentManager fragmentManager = getFragmentManager();

        FragmentTransaction  fragmentTransaction = fragmentManager.beginTransaction();

        Fragment newfragment =new MyFragment();

        fragmentTransaction.replace(R.layout.activity_main,newfragment ).commit();

    }

    @Override

    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.

        getMenuInflater().inflate(R.menu.main, menu);

        return true;

    }

}

修改：

package com.example.testforfragment;

import android.os.Bundle;

import android.app.Activity;

import android.support.v4.app.Fragment;

import android.support.v4.app.FragmentActivity;

import android.support.v4.app.FragmentManager;

import android.support.v4.app.FragmentTransaction;

import android.view.Menu;

public class MainActivity extends FragmentActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        FragmentManager fragmentManager = getSupportFragmentManager();

        FragmentTransaction  fragmentTransaction = fragmentManager.beginTransaction();

        Fragment newfragment =new MyFragment();

        fragmentTransaction.replace(R.layout.activity_main,newfragment ).commit();

    }

    @Override

    public boolean onCreateOptionsMenu(Menu menu) {

        // Inflate the menu; this adds items to the action bar if it is present.

        getMenuInflater().inflate(R.menu.main, menu);

        return true;

    }

}

1.导入的包

2.extends

3.getSurpport……