Cannot convert from android.support.v4.app.Fragment to android.app.Fragment

Question

I'm doing my first Android app, and wanted to get straight into the ICS API. I have so far created an app using an ActionBar, with swipeable tabs using Viewpager and Fragments.

I do however experience some errors that I keep returning to.

Depending on how I implement it, it always keep going back to an "Type mismatch" error: "cannot convert from android.support.v4.app.Fragment to android.app.Fragment". I have tried removing all import references to either, and this error appears when I only use android.support.v4.app.Fragment in TabListener, FragmentActivity and my two Fragments.

The error occurs in my TabListener:

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.Activity;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.ViewPager;
import android.util.Log;

public class TabListener implements ActionBar.TabListener {
    private android.app.Fragment fragment;
    private Activity activity;
    private ViewPager pager;
    private FragmentTransaction ft;

    public TabListener(Activity activity, Fragment fragment, ViewPager pager) {
        this.activity = activity;
        this.fragment = fragment;
        this.pager = pager;
    }

    @Override
    public void onTabSelected(Tab tab, android.app.FragmentTransaction ft){     
        if (fragment == null) {
            ft.add(fragment, null);
        } else {
            ft.attach(fragment);
        }
    }

    @Override
    public void onTabReselected(Tab tab, android.app.FragmentTransaction ft){
        // TODO Auto-generated method stub
    }

    @Override
    public void onTabUnselected(Tab tab, android.app.FragmentTransaction ft){
        // TODO Auto-generated method stub  
    }
}

By removing "android.app.FragmentTransaction ft", replacing it with just "FragmentTransaction ft", the problem goes awawy. Then new problems arise:

The method onTabReselected(ActionBar.Tab, FragmentTransaction) of type TabListener must override or implement a supertype method TabListener.java

The method onTabSelected(ActionBar.Tab, FragmentTransaction) of type TabListener must override or implement a supertype method TabListener.java

The method onTabUnselected(ActionBar.Tab, FragmentTransaction) of type TabListener must override or implement a supertype method TabListener.java

The type TabListener must implement the inherited abstract method ActionBar.TabListener.onTabReselected(ActionBar.Tab, FragmentTransaction) TabListener.java

The type TabListener must implement the inherited abstract method ActionBar.TabListener.onTabSelected(ActionBar.Tab, FragmentTransaction) TabListener.java

The type TabListener must implement the inherited abstract method ActionBar.TabListener.onTabUnselected(ActionBar.Tab, FragmentTransaction) TabListener.java

Whats going on here?

As you may understand, I'm new to Java and Android development. I feel like I'm pretty close, but I'm not able to solve this problem. I don't understand why it want to "convert from android.support.v4.app.Fragment to android.app.Fragment when I'm not even importing android.app.Fragment anywhere.

I guess it's related to using the compatibility package. (Do I have to use this package at all when creating an app for the newest version of the SDK?)

Solution 1

Try to use getSupportFragmentManager() instead getFragmentManager()

Solution 2

Whats going on here?

While the Android Support package gives you a backwards-compatible Fragment implementation, the ActionBar is not part of the Android Support package. Hence, ActionBar.TabListener is expecting native API Level 11 Fragment objects. Consider using ActionBarSherlock to have both an action bar and Android Support fragments.

but then I'm left with another problem in my FragmentPagerAdapter

The FragmentPagerAdapter in the Android Support package is a bit messy -- it wants API Level 11 Fragment objects, not Android Support Fragment objects. However, you can clone the source to FragmentPagerAdapter (source is in your SDK) and create your own implementation that uses the support.v4 flavor of Fragment and kin.

Solution 3

This solution works for me

replace

public class MyFragment extends Fragment{
}

with

public class MyFragment extends android.support.v4.app.Fragment{
}

and also replace import

import android.app.Fragment;

with

import android.support.v4.app.Fragment;

Solution 4

I know that it has been too late to answer this question but it might help someone with the same problem.

Go to your java folder and click on your fragment's activity.

In the imports, replace import android.app.Fragment; with

import android.support.v4.app.Fragment;

Keep the code in the MainActivity intact and this should help resolve the issue.

Note: If it doesn't work at once, don't worry. Build > Rebuild project.

View more solutions

Comments

[Kjell-Bear]

I understand. I have tried removing the need to use the support package, but then I'm left with another problem in my FragmentPagerAdapter - which I can't import as "android.app.FragmentPagerAdapter". >The return type is incompatible with FragmentPagerAdapter.getItem(int) MainFragmentActivity.java It tries here to return fragment, which is Fragment mFragment = LatestFragment.newInstance(position);

[CommonsWare]

It is perfectly reasonable to have a build target of API Level 11 or higher and use the Android Support package.

[Jave]

@CommonsWare: I was under the impression that the support package (v4) was built on features from API level 11 (the v13 package slipped my mind), but in op's case, when he develops for ICS (API>13), the contents of the packages should be supported without additional packages, or am I wrong?

[CommonsWare]

@Jave: Well, I can't quite follow everything the OP wrote. :-) If you are only deploying to API Level 11 and higher, you can use the native Fragment implementation supplied by API Level 11. If you are deploying to older devices, you need to use the Android Support package, regardless of your build target. It's entirely possible to want an ICS build target for selective things (e.g., CalendarContract) that can be bypassed on older devices, yet still want to use the Android Support package for fundamental stuff that needs to be fully backwards-compatible.

[Kjell-Bear]

Cloning the FragmentPagerAdapter, and asking it to use android.app.Fragment/import android.app.FragmentManager/import android.app.FragmentTransaction seems to have worked.. No errors this time! Thanks

[Jave]

@CommonsWare: Then I am with you there, My assumption was that OP was targeting and deploying on API level >13.

[Kjell-Bear]

I was being a bit unclear, mainly because of being new to this, and bad language. I am targeting > 13

[MattF]

SLekvak, does your implementation work on api 11 and lower devices, or just on api 13+?

[Newts]

I try this TutViewerFragment viewer = (TutViewerFragment)getSupportFragmentManager().findFragmentB‌​yId(R.id.tutview_fra‌​gment); but shows error "cannot cast from fragment to TutView Fragment"

[gayavat]

what is parent of TutViewerFragment?

[Newts]

its extends from FragmentActivity

[Mazen Kasser]

@gayavat, why when I use getSupportFragmentManager(); Android Studio says undefined!

[gayavat]

may be it helps stackoverflow.com/questions/13212353/…

[Admin]

@gayavat hi. I am stuck at same problem. But i need to implement ViewPager in Fragment,not Activity. What should i do??