无法将java.lang.ClassCastException强制转换为android.app.Fragment

Question

我有MainActivity类，该类具有实例化ApplicationBar的方法，所有其他Activity都从此MainActivity继承，因此他们可以使用此方法。

但是我还有一个MapHolder类，它必须从FragmentActivity扩展，因为在xml中它使用一个fragment来显示地图。 问题是，如果我从FragmentActivity扩展它，我将无法显示ApplicationBar选项卡；如果从MainActivity扩展它，则无法显示地图，并且会出现此错误：

LogCat Output:

    09-29 17:52:10.107: E/GooglePlayServicesUtil(3788): Google Play services is invalid. Cannot recover.
09-29 17:52:43.536: E/AndroidRuntime(3832): FATAL EXCEPTION: main
09-29 17:52:43.536: E/AndroidRuntime(3832): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mydomain.myproj/com.mydomain.myproj.MapHolder }: android.view.InflateException: Binary XML file line #2: Error inflating class fragment
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.os.Looper.loop(Looper.java:137)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.ActivityThread.main(ActivityThread.java:5103)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at java.lang.reflect.Method.invokeNative(Native Method)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at java.lang.reflect.Method.invoke(Method.java:525)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at dalvik.system.NativeStart.main(Native Method)
09-29 17:52:43.536: E/AndroidRuntime(3832): Caused by: android.view.InflateException: Binary XML file line #2: Error inflating class fragment
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:713)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.view.LayoutInflater.inflate(LayoutInflater.java:469)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:267)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.Activity.setContentView(Activity.java:1895)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at com.mydomain.myproj.MapHolder .onCreate(MapHolder .java:19)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.Activity.performCreate(Activity.java:5133)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
09-29 17:52:43.536: E/AndroidRuntime(3832):     ... 11 more
09-29 17:52:43.536: E/AndroidRuntime(3832): Caused by: java.lang.ClassCastException: com.google.android.gms.maps.SupportMapFragment cannot be cast to android.app.Fragment
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.Fragment.instantiate(Fragment.java:585)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.Fragment.instantiate(Fragment.java:560)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.app.Activity.onCreateView(Activity.java:4738)
09-29 17:52:43.536: E/AndroidRuntime(3832):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:689)
09-29 17:52:43.536: E/AndroidRuntime(3832):     ... 20 more

Answer 1

您正在尝试将SupportMapFragment转换为本地API级别11 android.app.Fragment 。 那不管用。 或者：

• 将您的android:minSdkVersion设置为11或更高版本，并使用MapFragment代替SupportMapFragment ，或者

• 将您的SupportMapFragment投射为android.support.v4.app.Fragment

问题是，如果我从FragmentActivity扩展它，我将无法显示ApplicationBar选项卡

该操作栏已添加到API级别11中的Android。如果您希望在较旧版本的Android上使用操作栏，则需要使用backport，即Android支持包中的 ActionBarSherlock或AppCompat backport 。

Answer 2

如果您使用的是com.google.android.gms.maps.SupportMapFragment，则您的活动必须扩展android.support.v4.app.FragmentActivity而不是android.app.Activity