Android InflateException Error Inflating Class Fragment FATAL EXCEPTION: Main

Question

I lost at least 3 hours to search for solution for this and no result... Can you please tell me what's the problem and how can I fix it?

activity layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/background2"
    tools:context="com.example.try.Sigiture"
    tools:ignore="MergeRootFrame" >


    <fragment 
        android:name="com.example.try.PlaceholderFragment"
        android:id="@+id/fragment1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true" />

</RelativeLayout>

fragment layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/fragment"
    android:layout_width="20dp"
    android:layout_height="20dp"
    android:background="@drawable/sign_field"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    tools:context="com.example.try.Sigiture$PlaceholderFragment" >

</RelativeLayout>

activity class:

import android.app.Activity;
import android.os.Bundle;

public class Sigiture extends Activity {

    private PlaceholderFragment placeholderFragment;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sigiture);
    }   
}

fragment class:

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;

public class PlaceholderFragment extends Fragment implements OnClickListener {
    public PlaceholderFragment() {

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_sigiture, container, false);
    }   

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        Log.d("Fragmend", "Click");
    }
}

And this is what is said in the LogCat:

07-08 18:55:28.772: W/dalvikvm(872): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
07-08 18:55:28.852: E/AndroidRuntime(872): FATAL EXCEPTION: main
07-08 18:55:28.852: E/AndroidRuntime(872): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.try/com.example.try.Sigiture}: android.view.InflateException: Binary XML file line #11: Error inflating class fragment
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.os.Handler.dispatchMessage(Handler.java:99)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.os.Looper.loop(Looper.java:137)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.ActivityThread.main(ActivityThread.java:5041)
07-08 18:55:28.852: E/AndroidRuntime(872):  at java.lang.reflect.Method.invokeNative(Native Method)
07-08 18:55:28.852: E/AndroidRuntime(872):  at java.lang.reflect.Method.invoke(Method.java:511)
07-08 18:55:28.852: E/AndroidRuntime(872):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-08 18:55:28.852: E/AndroidRuntime(872):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-08 18:55:28.852: E/AndroidRuntime(872):  at dalvik.system.NativeStart.main(Native Method)
07-08 18:55:28.852: E/AndroidRuntime(872): Caused by: android.view.InflateException: Binary XML file line #11: Error inflating class fragment
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:704)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
07-08 18:55:28.852: E/AndroidRuntime(872):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:270)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.Activity.setContentView(Activity.java:1881)
07-08 18:55:28.852: E/AndroidRuntime(872):  at com.example.try.Sigiture.onCreate(Sigiture.java:13)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.Activity.performCreate(Activity.java:5104)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-08 18:55:28.852: E/AndroidRuntime(872):  ... 11 more
07-08 18:55:28.852: E/AndroidRuntime(872): Caused by: java.lang.ClassCastException: com.example.try.PlaceholderFragment cannot be cast to android.app.Fragment
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.Fragment.instantiate(Fragment.java:585)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.Fragment.instantiate(Fragment.java:560)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.app.Activity.onCreateView(Activity.java:4709)
07-08 18:55:28.852: E/AndroidRuntime(872):  at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:680)
07-08 18:55:28.852: E/AndroidRuntime(872):  ... 21 more

I found some answers but they didn't help. Please give me your support. I'm working with fragments for the first time and I know they are important and I need to learn how to use them.

Answer 1

Changing the <android.support.v4.app.Fragment... in your xml file from <Fragment... might just do the Trick

As in the PlaceHolderFragment you are using v4 support and in XML you use the direct Fragment from android.app.Fragment and hence the exception