类型不匹配：无法从android.support.v4.app.Fragment转换为android.app.Fragment

Question

I'm having problem with different versions of Fragment related classes.

In Eclipse, in the Project Properties > Java Build Path > Libraries, I have:
android-support-v4.jar
android-support-v7-appcompart.jar

There are a few questions discussing similar problems, but they seem to have left me more confused. How do I fix this?

MainActivity.java

public class MainActivity extends FragmentActivity implements ActionBar.TabListener {

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
             ....
        mAdapter = new TabsPagerAdapter(this.getSupportFragmentManager());

        Fragment myFragment = mAdapter.getItem(MY_TAB); // error here

        FragmentManager fragmentManager = getFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.add(resources.getInteger(R.id.pager), myFragment, resources.getString(R.string.my_fragment));
          ...
     }

TabPageAdapter.java

public class TabsPagerAdapter extends FragmentPagerAdapter {

    public TabsPagerAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);
    }

    @Override
    public Fragment getItem(int index) {
      ...
    }
}

Edit (responding to comments). This is the confusion.

In MainActivity, I had:

import android.app.Fragment

Changing it to:

import android support.v4.app.Fragment;

causes this error:
The method add(int, android.app.Fragment, java.lang.String) in the type FragmentTransaction is not applicable for the arguments (int, android.support.v4.app.Fragment, java.lang.String) on this line:

fragmentTransaction.add(resources.getInteger(R.id.pager), permitsFragment, resources.getString(R.string.mys_fragment));

Changing to use the support fragment manager causes this error:
Type mismatch: cannot convert from android.support.v4.app.FragmentManager to android.app.FragmentManager on this line:

FragmentManager fragmentManager = getSupportFragmentManager();

So if I change all imports to v4:

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;

then I get errors on onTabReselected, onTabSelected, onTabUnselected saying:
The method onTabUnselected(ActionBar.Tab, FragmentTransaction) of type MainActivity must override or implement a supertype method
There doesn't appear to a v4 version of ActionBar.

Answer 1

You should either use Components from Support package or none.

So it applies to FragmentManager and Fragment.

Answer 2

I often get this and the most probable reason is wrong Fragment import which happens if you create a Fragment using the inbuilt android studio method. (Right Click => New => Fragment or something similar)

You must be doing

import android.app.Fragment

Change that to

import android.support.v4.app.Fragment

and then use getSupportFragmentManager() whenever dealing with fragments.