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自定义UILabel设置垂直方向的居上，居中，居下

IOS系统框架中UILabel的属性textAlignment只调整水平方向的居中，居左，居右，而没有垂直方向的调整。所以要自定义一个继承自UILabel的类，在类的实现文件中进行文字的重绘，达到垂直方向的位置调整。

新建一个类文件，继承自UILabel，头文件如下:

#import <UIKit/UIKit.h>
 
typedef NS_ENUM(NSInteger,VerticalAlignment){
    VerticalAlignmentTop,
    VerticalAlignmentMiddle,
    VerticalAlignmentBottom
};
 
@interface FSVerticallyAlignedLabel : UILabel
 
@property (nonatomic,assign) VerticalAlignment verticalAlignment;
 
@end

在.m文件中，实现verticalAlignment的设置方法

@implementation FSVerticallyAlignedLabel
 
- (id)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        self.verticalAlignment = VerticalAlignmentMiddle;
    }
     
    return self;
}
 
/**
 *  设置属性方法
 *
 *  @param verticalAlignment 垂直调整位置
 */
- (void)setVerticalAlignment:(VerticalAlignment)verticalAlignment
{
    _verticalAlignment = verticalAlignment;
     
    [self setNeedsDisplay];
}
 
/**
 *  计算文字的矩形区域
 *
 *  @param bounds        label矩形区域
 *  @param numberOfLines 行数
 *
 *  @return 返回文字所占的矩形区域
 */
- (CGRect)textRectForBounds:(CGRect)bounds limitedToNumberOfLines:(NSInteger)numberOfLines
{
    CGRect textRect = [super textRectForBounds:bounds limitedToNumberOfLines:numberOfLines];
     
    //通过设定字体区域的y值来调整垂直位置
    switch (self.verticalAlignment) {
        case VerticalAlignmentTop:
            textRect.origin.y = bounds.origin.y;
            break;
        case VerticalAlignmentMiddle:
            textRect.origin.y = bounds.origin.y + (bounds.size.height - textRect.size.height) / 2.0;
            break;
        case VerticalAlignmentBottom:
            textRect.origin.y = bounds.origin.y + bounds.size.height - textRect.size.height;
            break;
    }
     
    return textRect;
}
 
//重写父类方法
- (void)drawTextInRect:(CGRect)rect
{
    CGRect actualRect = [self textRectForBounds:rect limitedToNumberOfLines:self.numberOfLines];
    [super drawTextInRect:actualRect];
}
 
@end