学步园

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) {
                                
                            }
            ];
       }
   }