Swift环境下实现UILabel居上 居中 居下对齐

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) 2013 yexiaozi_007. All rights reserved.//#import <UIKit/UIKit.h>typedef enum{    VerticalAlignmentTop = 0, // default    VerticalAlignmentMiddle,    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) 2013 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