我有一个有buy按钮的列表，点击此按钮我想进行应用内购买。
我已经在我的片段中创建了一个接口和一个函数，但是我收到了以下错误。
05-11 11:02:03.224: E/AndroidRuntime(2999): FATAL EXCEPTION: main
05-11 11:02:03.224: E/AndroidRuntime(2999): java.lang.ClassCastException: com.chinese.flashcard.ShopActivity cannot be cast to com.chinese.flashcard.TestAdapter$IABHelperProvider
05-11 11:02:03.224: E/AndroidRuntime(2999): at com.chinese.flashcard.TestAdapter.getView(TestAdapter.java:82)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.widget.AbsListView.obtainView(AbsListView.java:2177)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.widget.ListView.makeAndAddView(ListView.java:1840)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.widget.ListView.fillDown(ListView.java:675)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.widget.ListView.fillFromTop(ListView.java:736)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.widget.ListView.layoutChildren(ListView.java:1655)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.widget.AbsListView.onLayout(AbsListView.java:2012)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.view.View.layout(View.java:14289)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.view.ViewGroup.layout(ViewGroup.java:4562)
05-11 11:02:03.224: E/AndroidRuntime(2999): at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076)