无法在react nativeOptions headerRight中设置事件处理程序

I'm new to react native. I am trying to setup a event handler to react-navgation. I using navigationOptioins-> headerRight-> icon and trying to set a _BananaButton to handle onPress event. But it is not working. Clicking on icon does not do anything. The same event handler is working in the TouchableHighlight button but not in the header.I'm new to react native. I am trying to setup a