设置lable内容不上下居中

#import <UIKit/UIKit.h>
typedef enum
{
    VerticalAlignmentTop = 0, // default文字居上
    VerticalAlignmentMiddle,
    VerticalAlignmentBottom,
} VerticalAlignment;

@interface mylable : UILabel

{
@private
    VerticalAlignment _verticalAlignment;
}

@property (nonatomic) VerticalAlignment verticalAlignment;

@end

#import "mylable.h"

@implementation mylable

@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];
}

mylable *lable = [[mylable alloc] initWithFrame:CGRectMake(10, 400, 100, 200)];
    lable.text = @"dajdiojajdajdjajdadakdajdiaodaiojdioajdioajidjaijdajdadadna";
    lable.backgroundColor = [UIColor grayColor];
    lable.numberOfLines = 0;
    [lable setVerticalAlignment:VerticalAlignmentTop];
    [self.view addSubview:lable];