@property (strong, nonatomic) IBOutlet UISlider *slider; 这行提示错误如下： Illegal redeclaration of property in class extension ‘XXViewController’(attribute must be 'readwrite', while its primary must be 'readonly')

[Tonyhark]

learning 1 第六篇

照着文档输入代码，出现错误：

@Property (strong, nonatomic) IBOutlet UISlider *slider;
这行提示错误如下：
Illegal redeclaration of property in class extension ‘XXViewController’(attribute must be 'readwrite', while its primary must be 'readonly')

xcode 7 mac OS X 10.11.1