【OBJC类扩展之定位】
#import <UIKit/UIKit.h> @interface UIView (Positioning) - (void)centerInRect:(CGRect)rect;- (void)centerVerticallyInRect:(CGRect)rect;- (void)centerHorizontallyInRect:(CGRect)rect; - (void)centerInSuperView;- (void)centerVerticallyInSuperView;- (void)centerHorizontallyInSuperView; - (void)centerHorizontallyBelow:(UIView *)view padding:(CGFloat)padding;- (void)centerHorizontallyBelow:(UIView *)view; @end#import "UIView+Positioning.h"#import "UIView+Size.h" @implementation UIView (Positioning) //针对给定的坐标系居中- (void)centerInRect:(CGRect)rect;{ //如果参数是小数，则求最大的整数但不大于本身. //CGRectGetMidX获取中心点的X轴坐标 [self setCenter:CGPointMake(floorf(CGRectGetMidX(rect)) + ((int)floorf([self width]) % 2 ? .5 : 0) , floorf(CGRectGetMidY(rect)) + ((int)floorf([self height]) % 2 ? .5 : 0))];} //针对给定的坐标系纵向居中- (void)centerVerticallyInRect:(CGRect)rect;{ [self setCenter:CGPointMake([self center].x, floorf(CGRectGetMidY(rect)) + ((int)floorf([self height]) % 2 ? .5 : 0))];} //针对给定的坐标系横向居中- (void)centerHorizontallyInRect:(CGRect)rect;{ [self setCenter:CGPointMake(floorf(CGRectGetMidX(rect)) + ((int)floorf([self width]) % 2 ? .5 : 0), [self center].y)];} //相对父视图居中- (void)centerInSuperView;{ [self centerInRect:[[self superview] bounds]];}- (void)centerVerticallyInSuperView;{ [self centerVerticallyInRect:[[self superview] bounds]];}- (void)centerHorizontallyInSuperView;{ [self centerHorizontallyInRect:[[self superview] bounds]];} //同一父视图的兄弟视图水平居中- (void)centerHorizontallyBelow:(UIView *)view padding:(CGFloat)padding;{ // for now, could use screen relative positions. NSAssert([self superview] == [view superview], @"views must have the same parent"); [self setCenter:CGPointMake([view center].x, floorf(padding + CGRectGetMaxY([view frame]) + ([self height] / 2)))];} - (void)centerHorizontallyBelow:(UIView *)view;{ [self centerHorizontallyBelow:view padding:0];} @end