button.contentHorizontalAlignment =UIControlContentHorizontalAlignmentLeft;button.contentHorizontalAlignment =UIControlContentHorizontalAlignmentRight; //枚举类型typedef NS_ENUM(NSInteger, UIControlContentHorizontalAlignment) {    UIControlContentHorizontalAlignmentCenter = 0,    UIControlContentHorizontalAlignmentLeft   = 1,    UIControlContentHorizontalAlignmentRight  = 2,    UIControlContentHorizontalAlignmentFill   = 3,};