让 UILabel 垂直方向顶端对齐的代码

　　UILabel 里放入多行文字，会发现 label 默认居中对齐，很不符合左对齐的传统习惯，下面这段 CocoaChina 版主“angellixf”分享的代码可以让 UILabel 以垂直方向顶端对齐，也就是我们常说的左对齐或右对齐

　　//

　　// VerticallyAlignedLabel.h

　　//

　　#import <Foundation/Foundation.h>

　　typedef enum VerticalAlignment {

　　VerticalAlignmentTop,

　　VerticalAlignmentMiddle,

　　VerticalAlignmentBottom,

　　} VerticalAlignment;

　　@interface VerticallyAlignedLabel : UILabel {

　　@private

　　VerticalAlignment verticalAlignment_;

　　}

　　@property (nonatomic, assign) VerticalAlignment verticalAlignment;

@end


//
// VerticallyAlignedLabel.m
//

#import "VerticallyAlignedLabel.h"


@implementation VerticallyAlignedLabel

@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];
}