System services not available to Activities before onCreate()错误解决方法

错误信息：

11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: FATAL EXCEPTION: main
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.atmu.materialdesign.mcsm/com.atmu.mcsm.ui.activity.FwssActivity}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2219)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.access$700(ActivityThread.java:159)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:99)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.os.Looper.loop(Looper.java:176)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5419)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:525)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.Activity.getSystemService(Activity.java:4712)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.view.LayoutInflater.from(LayoutInflater.java:212)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at com.atmu.mcsm.ui.adpter.SpinnerAdapter.<init>(SpinnerAdapter.java:30)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at com.atmu.mcsm.ui.activity.FwssActivity.<init>(FwssActivity.java:26)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at java.lang.Class.newInstanceImpl(Native Method)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at java.lang.Class.newInstance(Class.java:1130)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2210)
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.access$700(ActivityThread.java:159) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.os.Handler.dispatchMessage(Handler.java:99) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.os.Looper.loop(Looper.java:176) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:5419) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at java.lang.reflect.Method.invokeNative(Native Method) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at java.lang.reflect.Method.invoke(Method.java:525) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862) 
11-05 12:11:45.439 11428-11428/com.atmu.materialdesign.mcsm E/AndroidRuntime: at dalvik.system.NativeStart.main(Native Method) 

原因：Activity中的一个类变量的构造函数需要激活系统服务。而这个类变量的实例化是直接在Activity类里面，而不是在OnCreate函数里面。

解决方法：把Activity中类变量的实例化工作放到Activity的OnCreate函数里面。