1.頭文件
#import <Foundation/Foundation.h>
typedef enum VerticalAlignment {
    VerticalAlignmentTop,
    VerticalAlignmentMiddle,
    VerticalAlignmentBottom,
} VerticalAlignment;

@interface VerticallyAlignedLabel : UILabel
{
@private
    VerticalAlignment verticalAlignment_;
}

@property (nonatomic, assign) VerticalAlignment verticalAlignment;
@end

.M文件
#import "VerticallyAlignedLabel.h"

@implementation VerticallyAlignedLabel

@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];
}

- (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

 

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