swift 跑马灯（50行代码完美实现，超简单）

Posted 2022-12-08 ihoudf

1、(10行)创建一个跑马灯背景

    let BG = UIView()
    BG.layer.cornerRadius = 6
    BG.backgroundColor = .black.withAlphaComponent(0.4)
    self.view.addSubview(BG)
    BG.snp.makeConstraints  make in
        make.left.equalTo(20)
        make.width.equalTo(300)
        make.top.equalTo(200)
        make.height.equalTo(50)
    

2、（8行）为第三步创建一个隐藏的父view，clipsToBounds = true是关键，可以让文字不超出去。

    let announceBG = UIView()
    announceBG.clipsToBounds = true
    BG.addSubview(announceBG)
    announceBG.snp.makeConstraints  make in
        make.left.equalTo(40)
        make.right.equalTo(-10)
        make.top.bottom.equalTo(0)
    

3、（8行）创建一个label，用来显示文字并滚动。布局的make.left.equalTo(announceBG.snp.right)是关键，让label在父视图的右侧开始。

    let announceL = UILabel()   
    announceL.textColor = .white
   announceL.font = .systemFont(ofSize: 18)
   announceBG.addSubview(announceL)
   announceL.snp.makeConstraints  make in
       make.top.bottom.equalToSuperview()
       make.left.equalTo(announceBG.snp.right)
   

4、（26行）动画

 func showScrollAnimation(content: String) 

        // 如果没有内容移除动画，并隐藏
        if content.removeAllSapce.count <= 0 
            announceL.layer.removeAllAnimations()
            self.isHidden = true
            return
        
        
        // 根据文字长度计算一个时间
        self.isHidden = false
        self.announceL.text = content
        var duration = CGFloat(content.count)/4.0
        
        let charW = sizeWithText(text: content, font: .systemFont(ofSize: 18), size: .zero)
        let announceBgW = kScreenWidth - 56 - 21
        
        if charW < announceBgW + 30 
            duration = 7
        
        
        // 动画
        let anim = CABasicAnimation()
        anim.toValue = -announceBgW-charW
        anim.duration = duration
        anim.repeatCount = MAXFLOAT
        anim.isRemovedOnCompletion = false
        announceL.layer.add(anim, forKey: "transform.translation.x")
    
    
    // 计算字符串长度
    func sizeWithText(text: String, font: UIFont, size: CGSize) -> CGFloat 
        let attributes = [NSAttributedString.Key.font: font]
        let option = NSStringDrawingOptions.usesLineFragmentOrigin
        let width = text.boundingRect(with: size, options: option, attributes: attributes, context: nil).size.width
        return width
    

5、大功告成。求打赏、点赞、关注、收藏。