BubbleSeekBar NullPointterException

java.lang.NullPointerException at com.xw.repo.BubbleSeekBar.onMeasure(BubbleSeekBar.java) at android.view.View.measure(View.java:16555) at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719) at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455) at android.view.View.measure(View.java:16555) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5147) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1430) at android.widget.LinearLayout.measureVertical(LinearLayout.java:716) at android.widget.LinearLayout.onMeasure(LinearLayout.java:609) at android.view.View.measure(View.java:16555) at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719) at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455) at android.view.View.measure(View.java:16555) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1999) at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1171) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1356) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1058) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5974) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:780) at android.view.Choreographer.doCallbacks(Choreographer.java:593) at android.view.Choreographer.doFrame(Choreographer.java:562) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:766) at android.os.Handler.handleCallback(Handler.java:733) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5315) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:864) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:680) at dalvik.system.NativeStart.main(Native Method)