iOS-设置UILabel文本靠最顶部展示

Posted 2021-12-10 MinggeQingchun

UILabel中只有设置文本横向靠左，居中，靠右显示，属性如下：

@property(nonatomic)        NSTextAlignment    textAlignment;   // default is NSTextAlignmentNatural (before ios 9, the default was NSTextAlignmentLeft)

但是想让文本垂直顶部，或者底部展示，是没有这个属性的，因此需要重写UILabel，首先创建一个BZAlertLabel继承UILabel，方法如下：

BZAlertLabel.h文件

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

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

@interface BZAlertLabel : UILabel

@property (nonatomic, assign) VerticalAlignment verticalAlignment;

@end

NS_ASSUME_NONNULL_END

BZAlertLabel.m文件

#import "BZAlertLabel.h"

@interface BZAlertLabel ()

@end

@implementation BZAlertLabel

- (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];
}


@end