I've recently studyed android by myself.
and I tried Using Fragment by following my Textbook
but I met an error even though I typed codes exactly the same as my textbook.

Can you guys explain to me what is wrong?

This is MainActivity.java

```
package com.example.ex_1;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public static class CounterFragment extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            // TODO Auto-generated method stub

            View root = inflater.inflate(R.layout.counterfragment, container, false);
            Button btnIncrease = (Button)root.findViewById(R.id.btnincrease);
            final TextView textCounter = (TextView)root.findViewById(R.id.txtcounter);
            btnIncrease.setOnClickListener(new Button.OnClickListener() {
                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    int count = Integer.parseInt(textCounter.getText().toString());
                    textCounter.setText(Integer.toString(count + 1));
                }

            });
            return root;
        }

    }
}

```

This is activity\_main.xml

```
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="${relativePackage}.${activityClass}" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="~~"/>
    <fragment 
        android:name="com.example.ex_1.MainActivity$CounterFragment"
        android:id="@+id/counterfragment"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

```

And the error is 

```
09-24 07:40:08.329: E/AndroidRuntime(1794): FATAL EXCEPTION: main
09-24 07:40:08.329: E/AndroidRuntime(1794): Process: com.example.ex_1, PID: 1794
09-24 07:40:08.329: E/AndroidRuntime(1794): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ex_1/com.example.ex_1.MainActivity}: android.view.InflateException: Binary XML file line #13: Error inflating class fragment
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.access$800(ActivityThread.java:144)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.os.Handler.dispatchMessage(Handler.java:102)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.os.Looper.loop(Looper.java:135)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.main(ActivityThread.java:5221)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at java.lang.reflect.Method.invoke(Native Method)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at java.lang.reflect.Method.invoke(Method.java:372)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
09-24 07:40:08.329: E/AndroidRuntime(1794): Caused by: android.view.InflateException: Binary XML file line #13: Error inflating class fragment
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:763)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:377)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Activity.setContentView(Activity.java:2144)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at com.example.ex_1.MainActivity.onCreate(MainActivity.java:19)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Activity.performCreate(Activity.java:5937)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
09-24 07:40:08.329: E/AndroidRuntime(1794):     ... 10 more
09-24 07:40:08.329: E/AndroidRuntime(1794): Caused by: android.app.Fragment$InstantiationException: Trying to instantiate a class com.example.ex_1.MainActivity$CounterFragment that is not a Fragment
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Fragment.instantiate(Fragment.java:606)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Fragment.instantiate(Fragment.java:582)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2108)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.app.Activity.onCreateView(Activity.java:5286)
09-24 07:40:08.329: E/AndroidRuntime(1794):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:733)
09-24 07:40:08.329: E/AndroidRuntime(1794):     ... 20 more
09-24 07:40:08.329: E/AndroidRuntime(1794): Caused by: java.lang.ClassCastException
09-24 07:40:08.329: E/AndroidRuntime(1794):     ... 25 more

```