iOS-设置UILabel文本靠最顶部展示

╰+哭是因爲堅強的太久メ 2023-10-05 15:46 9阅读 0赞

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