iOS中UILabel滚动字幕动画的实现

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：

• 字幕向左或者右滚动
• 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) {                            
                         }
         ];
    }
}