cannot be cast to android.app.Fragment

08-15 17:54:59.948: E/AndroidRuntime(28238): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.xuzhi.fragment/com.xuzhi.fragment.FragmentDemoActivity}: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.ActivityThread.access$600(ActivityThread.java:139)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.os.Handler.dispatchMessage(Handler.java:99)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.os.Looper.loop(Looper.java:154)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.ActivityThread.main(ActivityThread.java:4945)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at java.lang.reflect.Method.invokeNative(Native Method)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at java.lang.reflect.Method.invoke(Method.java:511)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at dalvik.system.NativeStart.main(Native Method)
08-15 17:54:59.948: E/AndroidRuntime(28238): Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:697)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.view.LayoutInflater.rInflate(LayoutInflater.java:739)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:269)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.Activity.setContentView(Activity.java:1885)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at com.xuzhi.fragment.FragmentDemoActivity.onCreate(FragmentDemoActivity.java:31)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.Activity.performCreate(Activity.java:4531)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	... 11 more
08-15 17:54:59.948: E/AndroidRuntime(28238): Caused by: java.lang.ClassCastException: com.xuzhi.fragment.FragmentDemoActivity$TitlesFragment cannot be cast to android.app.Fragment
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.Fragment.instantiate(Fragment.java:597)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.Fragment.instantiate(Fragment.java:572)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.app.Activity.onCreateView(Activity.java:4296)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:673)
08-15 17:54:59.948: E/AndroidRuntime(28238): 	... 21 more

使用Frangment出现这个错误，是因为，导包时使用的是android-support-v4.jar，应当换成系统的api；具体原因不清楚；

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.ListFragment;

上面的出错；

import android.app.Fragment;
import android.app.FragmentTransaction;
import android.app.ListFragment;