com.example.main cannot be cast to android.support.v4.app.Fragment

Question

Just following the basic android documentation on FragmentTabHost (top example - FragmentTabHost in an Activity) and received the following error:

10-21 02:30:07.409  26265-26265/com.example E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.ClassCastException: com.example.Main cannot be cast to android.support.v4.app.Fragment

What's strange is that I've followed everything properly and installed the necessary packages.

Main.java

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTabHost;

public class Main extends FragmentActivity {
    // Fragment TabHost as mTabHost
    private FragmentTabHost mTabHost;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        mTabHost = (FragmentTabHost)findViewById(android.R.id.tabhost);
        mTabHost.setup(this, getSupportFragmentManager(), R.id.realtabcontent);

        mTabHost.addTab(mTabHost.newTabSpec("tab1").setIndicator("Tab1"),
                Main.class, null);
        mTabHost.addTab(mTabHost.newTabSpec("tab2").setIndicator("Tab2"),
                ListNewItem.class, null);
        mTabHost.addTab(mTabHost.newTabSpec("tab3").setIndicator("Tab3"),
                Favourites.class, null);
        mTabHost.addTab(mTabHost.newTabSpec("tab4").setIndicator("Tab4"),
                Notifications.class, null);
    }
}

main.xml

Note: Intellij displays the following in the side-window when attempting to display a preview:

Rendering Problems Exception raised during rendering: No tab known for tag null

Library bug maybe?

<android.support.v4.app.FragmentTabHost
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@android:id/tabhost"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:orientation="vertical" >

        <TabWidget
                android:id="@android:id/tabs"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_weight="0"
                android:orientation="horizontal" />

        <FrameLayout
                android:id="@android:id/tabcontent"
                android:layout_width="0dp"
                android:layout_height="0dp"
                android:layout_weight="0" />

        <FrameLayout
                android:id="@+id/realtabcontent"
                android:layout_width="match_parent"
                android:layout_height="0dp"
                android:layout_weight="1" />
    </LinearLayout>
</android.support.v4.app.FragmentTabHost>

Manifest.xml

<activity android:name=".Main"
        android:label="@string/main"
        android:uiOptions="splitActionBarWhenNarrow" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
</activity>

Notifications.java (badly named fragment)

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

public class Favourites extends Fragment  {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View V = inflater.inflate(R.layout.favourites, container, false);

        return V;
    }
}

Does anyone know why I'm having the problems with both the rendering and why the class conversion isn't working?

Answer 1

Like what you see in the documentation we need to pass Fragment class, not FragmentActivity to the addTab() function.

in here you are passing Main.Class

mTabHost.addTab(mTabHost.newTabSpec("tab1").setIndicator("Tab1"),
                Main.class, null);

Which is a FragmentActivity Class not a Fragment

public class Main extends FragmentActivity 

See this part

mTabHost.addTab(mTabHost.newTabSpec("simple").setIndicator("Simple"),
                FragmentStackSupport.CountingFragment.class, null);

They are passing FragmentStackSupport.CountingFragment.class which is a Fragment

To make you more sure see this grepcode link of android source code for FragmentStackSupport.CountingFragment -> link

That will explain why you are getting java.lang.ClassCastException because you are passing wrong type of class.