UILabel如何自定義文字位置（左上？右上？左下？右下？）

我們有時候需要在一個Label上顯示文字，而該文字的位置位於Label的左上角，我寫個一個小Demo，研究了一下。
.h文件
#import <UIKit/UIKit.h>

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

@interface xxxLabel : UILabel
@property (nonatomic) VerticalAlignment verticalAlignment;
@end




.m文件
#import "xxxLabel.h"

@implementation xxxLabel
@synthesize verticalAlignment = verticalAlignment_;
- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        self.verticalAlignment = VerticalAlignmentMiddle;
    }
    returnself;
}

- (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:
        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