iOS中UILabel滚动字幕动画的实现

By | 2012 年 8 月 29 日

有时候会遇到UILabel中的内容超出长度,显示不完全的问题。有一种解决方法是通过动画字幕来实现,比如:

  1. 字幕向左或者右滚动
  2. 字幕来回滚动

本文以后者为例来说明吧。这里先介绍UIView的通过Block实现的Animation以及其参数控制,最后是实现滚动字幕的代码。

  1. UIView有方便的动画实现方式,SDK4.0以上,提供了三个Block的动画方式:

    + (void)animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_4_0);
    
    + (void)animateWithDuration:(NSTimeInterval)duration animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_4_0); // delay = 0.0, options = 0
    
    + (void)animateWithDuration:(NSTimeInterval)duration animations:(void (^)(void))animations __OSX_AVAILABLE_STARTING(__MAC_NA,__IPHONE_4_0); // delay = 0.0, options = 0, completion = NULL
    

    其中第一个最全面,可以设置UIViewAnimationOptions来控制动画的参数,比如重复,自动reverse之类的。

  2. UIViewAnimationOptions具体定义如下:

    enum {
        UIViewAnimationOptionLayoutSubviews            = 1 <<  0,
        UIViewAnimationOptionAllowUserInteraction      = 1 <<  1, // turn on user interaction while animating
        UIViewAnimationOptionBeginFromCurrentState     = 1 <<  2, // start all views from current value, not initial value
        UIViewAnimationOptionRepeat                    = 1 <<  3, // repeat animation indefinitely
        UIViewAnimationOptionAutoreverse               = 1 <<  4, // if repeat, run animation back and forth
        UIViewAnimationOptionOverrideInheritedDuration = 1 <<  5, // ignore nested duration
        UIViewAnimationOptionOverrideInheritedCurve    = 1 <<  6, // ignore nested curve
        UIViewAnimationOptionAllowAnimatedContent      = 1 <<  7, // animate contents (applies to transitions only)
        UIViewAnimationOptionShowHideTransitionViews   = 1 <<  8, // flip to/from hidden state instead of adding/removing
        
        UIViewAnimationOptionCurveEaseInOut            = 0 << 16, // default
        UIViewAnimationOptionCurveEaseIn               = 1 << 16,
        UIViewAnimationOptionCurveEaseOut              = 2 << 16,
        UIViewAnimationOptionCurveLinear               = 3 << 16,
        
        UIViewAnimationOptionTransitionNone            = 0 << 20, // default
        UIViewAnimationOptionTransitionFlipFromLeft    = 1 << 20,
        UIViewAnimationOptionTransitionFlipFromRight   = 2 << 20,
        UIViewAnimationOptionTransitionCurlUp          = 3 << 20,
        UIViewAnimationOptionTransitionCurlDown        = 4 << 20,
        UIViewAnimationOptionTransitionCrossDissolve   = 5 << 20,
        UIViewAnimationOptionTransitionFlipFromTop     = 6 << 20,
        UIViewAnimationOptionTransitionFlipFromBottom  = 7 << 20,
    };
    typedef NSUInteger UIViewAnimationOptions;
    
  3. 本文实现方法就是使用Animation with Block的方式来实现UILabel来回滚动。代码如下:

    -(void)startAnimationIfNeeded{
        //取消、停止所有的动画
        [self.aUILabel.layer removeAllAnimations];
        CGSize textSize = [self.aUILabel.text sizeWithFont:self.aUILabel.font];
        CGRect lframe = self.aUILabel.frame;
        lframe.size.width = textSize.width;
        self.aUILabel.frame = lframe;
        const float oriWidth = 180;
        if (textSize.width > oriWidth) {
            float offset = textSize.width - oriWidth;
            [UIView animateWithDuration:3.0
                                  delay:0
                                options:UIViewAnimationOptionRepeat //动画重复的主开关
             |UIViewAnimationOptionAutoreverse //动画重复自动反向,需要和上面这个一起用
             |UIViewAnimationOptionCurveLinear //动画的时间曲线,滚动字幕线性比较合理
                             animations:^{
                                 self.aUILabel.transform = CGAffineTransformMakeTranslation(-offset, 0);
                             }
                             completion:^(BOOL finished) {
                                 
                             }
             ];
        }
    }
    

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