iOS中UILabel滚动字幕动画的实现

  By uniEagle | 2012 年 8 月 29 日 - 16:50 | Develop, iOS

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) {                                                      }         ];    }}