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……