如何将ios7 UIPickerView格式化为仅显示3个选项?例如，一个在主动选择之上，一个在主动选择之下?

I want to format the iOS 7 UIPickerView to display only three choices. I.e. one above and one below the selected option. I would also like to format the text to be smaller than the default. How do I achieve this?I want to format the iOS 7 UIPickerView to disp