UILabel文本垂直顶部对齐的方法

也不知道为什么UILabel本身没有提供文本垂直顶部对齐的方法，真的有点晕。我们创建一个简单的UILabel来看看：

[box type="info"]

UILabel *myLabel = [[UILabel alloc]initWithFrame:CGRectMake(10, 10, 300, 100)];

[myLabel setText:@"苹果iOS(iphone Operation System)是由苹果公司开发的手持设备操作系统。苹果公司最早于2007年1月9日的Macworld大会上公布这个系统，最初是设计给iPhone使用的"];

[myLabel setFont:[UIFont fontWithName:@"Arial" size:14.0]];

[myLabel setBackgroundColor:[UIColor blueColor]];

[myLabel setTextColor:[UIColor whiteColor]];

[self.view addSubview:myLabel];

[/box]

在ios模拟器上看到的效果如下图：

这显然不是我们要的效果，我们再添加一行代码：

myLabel.numberOfLines = 0;

结果是：

显示有点正常了，但如何使文字顶部对齐呢？

实现代码：

[box type="info"]

UILabel *myLabel = [[UILabel alloc]init];//WithFrame:CGRectMake(10, 10, 300, 100)];

UIFont *strFont = [UIFont fontWithName:@"Arial" size:14.0];

[myLabel setFont:strFont];

[myLabel setBackgroundColor:[UIColor blueColor]];

[myLabel setTextColor:[UIColor whiteColor]];

myLabel.numberOfLines = 0;

CGSize maximumSize = CGSizeMake(300, 999);

NSString *string = @”苹果iOS(iphone Operation System)是由苹果公司开发的手持设备操作系统。苹果公司最早于2007年1月9日的Macworld大会上公布这个系统，最初是设计给iPhone使用的”;

CGSize stringSize = [string sizeWithFont:strFont

constrainedToSize:maximumSize

lineBreakMode:myLabel.lineBreakMode];

[myLabel setText:string];

CGRect strFrame = CGRectMake(10, 10, 300, stringSize.height);

myLabel.frame = strFrame;

[self.view addSubview:myLabel];

[/box]

运行结果如下图：

盆友们，如果有更好的方法使UILabel垂直顶部对齐，一定要分享出来哦

在iOS中默认的UILabel中的文字在竖直方向上只能居中对齐，从UILabel继承了一个新类，实现了居上对齐，居中对齐，居下对齐。具体如下：

//
//  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
{
@private
VerticalAlignment _verticalAlignment;
}

@property (nonatomic) VerticalAlignment verticalAlignment;

@end

//
//  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

在使用时：

lbl_mylabel = [[myUILabel alloc] initWithFrame:CGRectMake(20, 50, 150, 600)];
UIColor *color = [UIColor colorWithPatternImage:[UIImage imageNamed:@"halfTransparent.png"]];//使用半透明图片作为label的背景色
lbl_mylabel.backgroundColor = color;
lbl_mylabel.textAlignment = UITextAlignmentLeft;
lbl_mylabel.textColor = UIColor.whiteColor;
lbl_mylabel.lineBreakMode = UILineBreakModeWordWrap;
lbl_mylabel.numberOfLines = 0;
[lbl_mylabel setVerticalAlignment:VerticalAlignmentTop];
[self addSubview:lbl_mylabel];