UILabel显示不全时循环滚动显示，利用Runtime黑魔法全局修改

最近做项目的时候遇到一个需求，由于App兼容的语言类型太多，导致App内很多标签显示的文字不全，这时候需要滚动去显示。需求类似下面这个样子。

滚动效果展示

思考

1.整个App的label去做一个滚动显示，首先要考虑到性能问题，性能问题的话就不考虑使用UIView层去实现该效果，因此，文字滚动层考虑用Layer去处理。
2.能够影响到文本显示和是否能完全显示文本的属性有text、frame、font、textColor，因此我们需要对这几项属性进行处理。

在设置text的属性的时候，我们需要判断text的长度是否大于label的长度， 如果大于label的长度，我们需要将text文本处理到layer层，并且做滚动动画。在这是frame和font的时候我们需要重新做该判断，因为这两个属性影响了label的长度和文本的大小，设置textColor的时候我们需要把layer上的文本颜色也相应修改成该颜色。

实现

创建一个UILabel的子类，并且添加CATextLayer的属性

import UIKit

class LCAutoScrollLabel: UILabel {
        
    private var textLayer : CATextLayer = CATextLayer()
    
    private var shouldScroll : Bool = false
  
}

重写以上四个属性的set方法，加上判断是否需要滚动的逻辑

    override var text: String? {
        didSet {
            shouldScroll = false
            ///把String转化成NSString，根据文本和Font得到文本的Size
            let textString : NSString = NSString(string: self.text ?? "")
            let size = textString.size(withAttributes: [NSAttributedString.Key.font : self.font!])
            let stringWidth = size.width
            let labelWidth = frame.size.width
            if labelWidth < stringWidth {
                shouldScroll = true
            }
            if shouldScroll
            {
                /// 如果判断需要滚动，设置textLayer的属性
                let textString : NSString = self.text as NSString? ?? ""
                let size = textString.size(withAttributes: [NSAttributedString.Key.font : self.font!])
                let stringWidth = size.width
                let stringHeight = size.height
                textLayer.frame = CGRect(x: 0, y: (frame.height - stringHeight)/2, width: stringWidth, height: stringHeight)
                textLayer.string = text
                textLayer.alignmentMode = .center
                textLayer.font = font
                textLayer.fontSize = font.pointSize
                textLayer.foregroundColor = self.textColor.cgColor
                /// 动画
                let ani = CABasicAnimation(keyPath: "position.x")
                ani.toValue = -textLayer.frame.width
                ani.fromValue = textLayer.frame.width
                ani.duration = 4
                ani.fillMode = .backwards
                ani.repeatCount = 1000000000.0
                ani.isRemovedOnCompletion = false
                
                textLayer.add(ani, forKey: nil)
                layer.addSublayer(textLayer)
            }
            else
            {
                /// 如果不需要滚动，移除动画和layer
                textLayer.removeAllAnimations()
                textLayer.removeFromSuperlayer()
            }
        }
    }

因为四个重写的set方法里面逻辑基本一致，整理一下代码

    override var text: String? {
        didSet {
            shouldScroll = shouldAutoScroll()
            setTextLayerScroll()
        }
    }
    
    override var font: UIFont! {
        didSet {
            shouldScroll = shouldAutoScroll()
            setTextLayerScroll()
        }
    }
    
    override var frame: CGRect {
        didSet {
            shouldScroll = shouldAutoScroll()
            setTextLayerScroll()
        }
    }

    override var textColor: UIColor! {
        didSet {
            textLayer.foregroundColor = textColor.cgColor
        }
    }
    
    func setTextLayerScroll() {
        if shouldScroll
        {
            setTextLayer()
            textLayer.add(getLayerAnimation(), forKey: nil)
            layer.addSublayer(textLayer)
        }
        else
        {
            textLayer.removeAllAnimations()
            textLayer.removeFromSuperlayer()
        }
    }
    
    func shouldAutoScroll() -> Bool {
        var shouldScroll = false
        let textString : NSString = NSString(string: self.text ?? "")
        let size = textString.size(withAttributes: [NSAttributedString.Key.font : self.font!])
        let stringWidth = size.width
        let labelWidth = frame.size.width
        if labelWidth < stringWidth {
            shouldScroll = true
        }
        return shouldScroll
    }
    
    func setTextLayer() {
        let textString : NSString = self.text as NSString? ?? ""
        let size = textString.size(withAttributes: [NSAttributedString.Key.font : self.font!])
        let stringWidth = size.width
        let stringHeight = size.height
        textLayer.frame = CGRect(x: 0, y: (frame.height - stringHeight)/2, width: stringWidth, height: stringHeight)
        textLayer.string = text
        textLayer.alignmentMode = .center
        textLayer.font = font
        textLayer.fontSize = font.pointSize
        textLayer.foregroundColor = self.textColor.cgColor
    }
    
    func getLayerAnimation() -> CABasicAnimation {
        let ani = CABasicAnimation(keyPath: "position.x")
        ani.toValue = -textLayer.frame.width
        ani.fromValue = textLayer.frame.width
        ani.duration = 4
        ani.fillMode = .backwards
        ani.repeatCount = 1000000000.0
        ani.isRemovedOnCompletion = false
        return ani
    }

测试结果得到如下结果，因为忘记处理label自己本身显示的文本。

效果展示

我们可以出重写drawText的方法，根据是否需要滚动的判断去决定是否要显示text

    override func drawText(in rect: CGRect) {
        if !shouldScroll
        {
            super.drawText(in: rect)
        }
    }

经过简单测试，无论是改变font、frame、text都能够正常判断并且达到想要的效果。

但是有一个新的问题来了，由于项目是老项目，代码量已经十分庞大，如果要一个一个去把以前使用UILabel的地方全部替换成这个类，是一项非常耗时的工作，由于工期紧张，显然是给不了我这么多时间的。这时候我们就要用到我们的黑魔法Runtime了

黑魔法Runtime修改系统方法，快速达到目的

我们创建一个UILabel的分类，并且根据我们现有代码的逻辑，得到如下代码

#import "UILabel+AutoScroll.h"
#import 

static NSString * textLayer = @"textLayer";
static NSString * scrollAnimation = @"scrollAnimation";

@implementation UILabel (AutoScroll)

+ (void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        /// 替换系统方法，我们需要重写的方法我们都要替换
        Method setTextMethod = class_getInstanceMethod(self, @selector(setText:));
        Method setColorMethod = class_getInstanceMethod(self, @selector(setTextColor:));
        Method setFontMethod = class_getInstanceMethod(self, @selector(setFont:));
        Method setFrameMethod = class_getInstanceMethod(self, @selector(setFrame:));
        Method drawTextMethon = class_getInstanceMethod(self, @selector(drawTextInRect:));
        
        Method scrollSetTextMethod = class_getInstanceMethod(self, @selector(autoScrollSetText:));
        Method scrollSetColorMethod = class_getInstanceMethod(self, @selector(autoScrollSetTextColor:));
        Method scrollSetFontMethod = class_getInstanceMethod(self, @selector(autoScrollSetFont:));
        Method scrollSetFrameMethod = class_getInstanceMethod(self, @selector(autoScrollSetFrame:));
        Method scrollDrawText = class_getInstanceMethod(self, @selector(autoScrollDrawText:));

        method_exchangeImplementations(setTextMethod, scrollSetTextMethod);
        method_exchangeImplementations(setColorMethod, scrollSetColorMethod);
        method_exchangeImplementations(setFontMethod, scrollSetFontMethod);
        method_exchangeImplementations(setFrameMethod, scrollSetFrameMethod);
        method_exchangeImplementations(drawTextMethon, scrollDrawText);
    });
    
}

/// 用于替换系统setText方法
/// @param text 标签显示的文字
- (void)autoScrollSetText:(NSString *)text
{
    [self autoScrollSetText:text];
    // 这句是为了让textlayer超出label的部分不显示
    self.layer.masksToBounds = true;
    [self setTextLayerScroll];
}

/// 用于替换系统setTextColor方法
/// @param color 文字颜色
- (void)autoScrollSetTextColor:(UIColor *)color
{
    [self autoScrollSetTextColor:color];
    [self setTextLayerScroll];
}

/// 用于替换系统的setFont方法
/// @param font 字体
- (void)autoScrollSetFont:(UIFont *)font
{
    [self autoScrollSetFont:font];
    [self setTextLayerScroll];
}

/// 用于替换系统的setFrame方法
/// @param frame 坐标
- (void)autoScrollSetFrame:(CGRect)frame
{
    [self autoScrollSetFrame:frame];
    [self setTextLayerScroll];
}

/// 用于替换系统的drawText方法
/// @param rect frame
- (void)autoScrollDrawText:(CGRect)rect
{
    BOOL shouldScroll = [self shouldAutoScroll];
    if (!shouldScroll)
    {
        [self autoScrollDrawText:rect];
    }
}

/// 根据文字长短自动判断是否需要显示TextLayer，并且滚动
- (void)setTextLayerScroll
{
    BOOL shouldScroll = [self shouldAutoScroll];
    CATextLayer * textLayer = [self getTextLayer];
    if (shouldScroll)
    {
        CABasicAnimation * ani = [self getAnimation];
        [textLayer addAnimation:ani forKey:nil];
        [self.layer addSublayer:textLayer];
    }
    else
    {
        [textLayer removeAllAnimations];
        [textLayer removeFromSuperlayer];
    }
}

/// runtime存放textLayer，避免多次生成
- (CATextLayer *)getTextLayer
{
    CATextLayer * layer = objc_getAssociatedObject(self, &textLayer);
    if (!layer) {
        layer = [CATextLayer layer];
        objc_setAssociatedObject(self, &textLayer, layer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    CGSize size = [self.text sizeWithAttributes:@{NSFontAttributeName:self.font}];
    CGFloat stringWidth = size.width;
    CGFloat stringHeight = size.height;
    layer.frame = CGRectMake(0, (self.frame.size.height - stringHeight)/2, stringWidth, stringHeight);
    layer.alignmentMode = kCAAlignmentCenter;
    layer.font = (__bridge CFTypeRef _Nullable)(self.font.fontName);
    layer.fontSize = self.font.pointSize;
    layer.foregroundColor = self.textColor.CGColor;
    layer.string = self.text;
    return layer;
}

/// runtime存放动画对象，避免多次生成
- (CABasicAnimation *)getAnimation
{
    CABasicAnimation * ani = objc_getAssociatedObject(self, &scrollAnimation);
    if (!ani) {
        ani = [CABasicAnimation animationWithKeyPath:@"position.x"];
        objc_setAssociatedObject(self, &scrollAnimation, ani, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    CATextLayer * textLayer = [self getTextLayer];
    id toValue = @(-textLayer.frame.size.width);
    id fromValue = @(textLayer.frame.size.width);
    ani.toValue = toValue;
    ani.fromValue = fromValue;
    ani.duration = 4;
    ani.fillMode = @"backwards";
    ani.repeatCount = 1000000000.0;
    ani.removedOnCompletion = false;
    return ani;
}

/// 判断是否需要滚动
- (BOOL)shouldAutoScroll
{
    BOOL shouldScroll = false;
    CGSize size = [self.text sizeWithAttributes:@{NSFontAttributeName:self.font}];
    CGFloat stringWidth = size.width;
    CGFloat labelWidth = self.frame.size.width;
    if (labelWidth < stringWidth) {
        shouldScroll = true;
    }
    return shouldScroll;
}

@end

最后在pch文件中导入该分类，项目中所有的UILabel就能自动判断并且实现滚动显示的效果。
大家可以试一试，如果有问题可以相互交流一下。

手撸代码不易，如果对您有帮助的，可以帮忙点个赞！谢谢

代码地址：https://github.com/aYq524/AutoScrollLabel