首先在Xcode中新建.h文件，将以下代码复制进去
//// myUILabel.h// //// Created by yexiaozi_007 on 3/4/13.// Copyright (c) yexiaozi_007. All rights reserved.//#import <UIKit/UIKit.h>typedef enum{VerticalAlignmentTop = 0, // defaultVerticalAlignmentMiddle,VerticalAlignmentBottom,} VerticalAlignment;@interface myUILabel : UILabel{@privateVerticalAlignment _verticalAlignment;}@property (nonatomic) VerticalAlignment verticalAlignment;@end
再新建一个.m文件，拷入以下代码
//// myUILabel.m// //// Created by yexiaozi_007 on 3/4/13.// Copyright (c) yexiaozi_007. All rights reserved.//#import "myUILabel.h"@implementation myUILabel@synthesize verticalAlignment = verticalAlignment_;- (id)initWithFrame:(CGRect)frame {if (self = [super initWithFrame:frame]) {self.verticalAlignment = VerticalAlignmentMiddle;}return self;}- (void)setVerticalAlignment:(VerticalAlignment)verticalAlignment {verticalAlignment_ = verticalAlignment;[self setNeedsDisplay];}- (CGRect)textRectForBounds:(CGRect)bounds limitedToNumberOfLines:(NSInteger)numberOfLines {CGRect textRect = [super textRectForBounds:bounds limitedToNumberOfLines:numberOfLines];switch (self.verticalAlignment) {case VerticalAlignmentTop:textRect.origin.y = bounds.origin.y;break;case VerticalAlignmentBottom:textRect.origin.y = bounds.origin.y + bounds.size.height - textRect.size.height;break;case VerticalAlignmentMiddle:// Fall through.default:textRect.origin.y = bounds.origin.y + (bounds.size.height - textRect.size.height) / 2.0;}return textRect;}-(void)drawTextInRect:(CGRect)requestedRect {CGRect actualRect = [self textRectForBounds:requestedRect limitedToNumberOfLines:self.numberOfLines];[super drawTextInRect:actualRect];}@end
如果这是你导入的第一个.m文件Xcode会提示你要不要创建Bridging-Header，选Ok
在新创建的Bridging-Header文件里拷入下方代码
#import "myUILabel.h"
然后打开你的StoryBoard，点选你想要更改对齐方式的Label，将其Class改为myUILabel，示意图如下
然后右键拖动Label或者按住Control键左键拖动连线到Label所在的父View的Class中生成Outlet，如果之前已经连线好，则改完Custom Class后，将连线生成代码中的UILabel改为myUILabel，示意图如下
然后就可以调用该label的类方法
label.verticalAlignment = VerticalAlignmentBottom
按上方代码可以实现居下对其，居中 居上 分别将代码中的Bottom改为Middle和Top，默认为居上
