Android cannot be cast to android.app.Fragment

10-21 17:33:45.171: E/AndroidRuntime(7644): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.yw.myapiupdate/com.yw.myapiupdate.fragment.MyFragmentActivity}: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2077)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2104)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.ActivityThread.access$600(ActivityThread.java:134)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.os.Looper.loop(Looper.java:154)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.ActivityThread.main(ActivityThread.java:4624)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at java.lang.reflect.Method.invokeNative(Native Method)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at java.lang.reflect.Method.invoke(Method.java:511)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at dalvik.system.NativeStart.main(Native Method)
10-21 17:33:45.171: E/AndroidRuntime(7644): Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class fragment
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:699)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:741)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.view.LayoutInflater.inflate(LayoutInflater.java:491)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:254)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.Activity.setContentView(Activity.java:1837)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at com.yw.myapiupdate.fragment.MyFragmentActivity.onCreate(MyFragmentActivity.java:13)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.Activity.performCreate(Activity.java:4479)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1050)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2041)
10-21 17:33:45.171: E/AndroidRuntime(7644):     ... 11 more
10-21 17:33:45.171: E/AndroidRuntime(7644): Caused by: java.lang.ClassCastException: com.yw.myapiupdate.fragment.FragmentRed cannot be cast to android.app.Fragment
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.Fragment.instantiate(Fragment.java:574)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.Fragment.instantiate(Fragment.java:549)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.app.Activity.onCreateView(Activity.java:4249)
10-21 17:33:45.171: E/AndroidRuntime(7644):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:675)
10-21 17:33:45.171: E/AndroidRuntime(7644):     ... 21 more

原因：在导入支持Fragment包时，导入了系统识别不了的包。（import android.support.v4.app.Fragment;）

解决办法：将上述的包换成系统包就行了（import android.app.Fragment;）在导入系统包时注意了一定要添加上支持最新api（@SuppressLint("NewApi")）

至于为什么要这样做暂时还没查出来。知道的朋友 别忘了分享一下哈。