IOS UILabel垂直顶部，中间，底部对齐

最新推荐文章于 2017-11-14 18:27:00 发布

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#UILabel #IOS UILabel #UILabel VerticalAlig #UILabel 垂直居中 #UILabel扩展

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本文介绍如何创建一个名为MyLabel的自定义UILabel子类，实现垂直顶部、中间和底部对齐的功能。

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在IOS中默认的UILabel中的文字是正能是居中对齐的，在应用的时候，我们可能会用到顶部或者底部对齐，下面我们就来实现UILabel的顶部，底部对齐，

首先新建一个类MyLabel继承自UILabel,代码如下

#import <UIKit/UIKit.h>

typedef enum
{
    VerticalAlignmentTop=0,
    VerticalAlignmentMiddle,//default
    VerticalAlignmentBottom,
    
}VerticalAlignment;

@interface MyLabel : UILabel
{
    @private
    VerticalAlignment _verticalAlignment;
}

@property(nonatomic)VerticalAlignment verticalAlignment;

@end

实现代码如下

#import "MyLabel.h"

@implementation MyLabel

@synthesize verticalAlignment=_verticalAlignment;

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.verticalAlignment=VerticalAlignmentMiddle;
    }
    return self;
}
-(void)setVerticalAlignment:(VerticalAlignment)verticalAlignment
{
    _verticalAlignment=verticalAlignment;
    [self setNeedsDisplay];//重绘一下
}

-(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 VerticalAlignmentMiddle:
            textRect.origin.y=bounds.origin.y+(bounds.size.height-textRect.size.height)/2.0;
            break;
        case VerticalAlignmentBottom:
            textRect.origin.y=bounds.origin.y+bounds.size.height-textRect.size.height;
            break;
        default:
            textRect.origin.y=bounds.origin.y+(bounds.size.height-textRect.size.height)/2.0;
            break;
    }
    return textRect;
}
-(void)drawTextInRect:(CGRect)rect
{
    CGRect actualRect=[self textRectForBounds:rect limitedToNumberOfLines:self.numberOfLines];//重新计算位置
    [super drawTextInRect:actualRect];
}

@end

在调用的时候首先引入MyLabel,调用代码如下：

MyLabel *lbl = [[MyLabel alloc] initWithFrame:CGRectMake(20, 20, 150, 300)];
   
    lbl.textAlignment = UITextAlignmentCenter;
    lbl.textColor = [UIColor redColor];
    lbl.lineBreakMode = UILineBreakModeWordWrap;
    lbl.numberOfLines = 0;
    lbl.text=@"My Content";
    [lbl setVerticalAlignment:VerticalAlignmentMiddle];
    [self.view addSubview:lbl];