UIViewAnimationOptionBeginFromCurrentState基本动画的意外行为 [英] UIViewAnimationOptionBeginFromCurrentState unexpected behaviour with basic animation
问题描述
我试图在收到按钮点击时执行这个基本的 UIView 动画：
I am trying to perform this basic UIView animation upon receiving a button click:
- (IBAction)buttonPress:(id)sender
{
self.sampleView.alpha = 0.0;
[UIView animateWithDuration:2.0
delay:0.0
options:UIViewAnimationOptionCurveEaseInOut | UIViewAnimationOptionBeginFromCurrentState
animations:^{self.sampleView.alpha = 1.0;}
completion:NULL];
}
在按钮之前单击视图是可见的，并且alpha值为1.0 。当我发送按钮动作时，我期望视图从alpha = 0.0到alpha = 1.0在2秒内淡入，但这不会发生。当我删除 UIViewAnimationOptionBeginFromCurrentState 的动画工作正常。
Prior to the button click the view is visible and has an alpha value of 1.0. When I send the button action I expect the view to fade in from alpha=0.0 to alpha=1.0 over 2 seconds but this does not happen. When I remove the UIViewAnimationOptionBeginFromCurrentState the animation works fine.
看起来像使用 UIViewAnimationOptionBeginFromCurrentState 选项集，alpha = 0.0未设置，因为它认为它已经在1.0。
It seems like with the UIViewAnimationOptionBeginFromCurrentState option set, the alpha=0.0 is not being set and the animation is skipped because it thinks it is already at 1.0.
我试图理解为什么会发生，因为苹果文档说明 UIViewAnimationOptionBeginFromCurrentState 无效：
I am trying to understand why this would be happening since Apple documentation states that the UIViewAnimationOptionBeginFromCurrentState has no effect if another animation is not in progress:
UIViewAnimationOptionBeginFromCurrentState
如果另一个动画不在飞行中，则此键不具有任何动画，如果另一个动画不在飞行中，则该键不具有效果。
"UIViewAnimationOptionBeginFromCurrentState
Start the animation from the current setting associated with an already in-flight animation. If this key is not present, any in-flight animations are allowed to finish before the new animation is started. If another animation is not in flight, this key has no effect."
推荐答案
事实证明，使用 UIViewAnimationOptionBeginFromCurrentState
查看此示例：
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
UIButton *theButton = [UIButton new];
[self.view addSubview:theButton];
theButton.frame = self.view.frame;
theButton.backgroundColor = [UIColor redColor];
theButton.alpha = 0.05;
[theButton addTarget:self action:@selector(actionPressed:) forControlEvents:UIControlEventTouchUpInside];
}
- (void)actionPressed:(UIButton *)theButton
{
theButton.alpha = 0.6;
[UIView animateWithDuration:5
delay:0
options:UIViewAnimationOptionBeginFromCurrentState
animations:^
{
// you expect to animate from 0.6 to 1. but it animates from 0.05 to 1
theButton.alpha = 1;
}
completion:nil];
}
在上面的例子中，你期望 .alpha 将动画从0.6到1.然而，动画从0.05到1.
In the example above you expect that .alpha would animate from 0.6 to 1. However, it animates from 0.05 to 1.
为了解决这个问题，你应该更改 actionPressed：：
In order to resolve the issue, you should change actionPressed: to the following:
- (void)actionPressed:(UIButton *)theButton
{
[UIView animateWithDuration:0
animations:^
{
// set new values INSIDE of this block, so that changes are
// captured in UIViewAnimationOptionBeginFromCurrentState.
theButton.alpha = 0.6;
}
completion:^(BOOL finished)
{
[UIView animateWithDuration:5
delay:0
options:UIViewAnimationOptionBeginFromCurrentState
animations:^
{
// now it really animates from 0.6 to 1
theButton.alpha = 1;
}
completion:nil];
}];
}
提供 animateWithDuration：0 !!!
规则很简单：只使用 UIViewAnimationOptionBeginFromCurrentState
The rule is easy: Only use an animation block with UIViewAnimationOptionBeginFromCurrentState AFTER some other animation block, so that all your previous changes are actually applied.
如果您不知道应该在<$ c $中包含什么内容c> animateWithDuration：0 阻止，那么你可以使用这个技巧：
In case you don't know what exactly should be included in animateWithDuration:0 block, then you can use this trick:
- (void)actionPressed:(UIButton *)theButton
{
// make all your changes outside of the animation block
theButton.alpha = 0.6;
// create a fake view and add some animation to it.
UIView *theFakeView = [UIView new];
theFakeView.alpha = 1;
[UIView animateWithDuration:0
animations:^
{
// we need this line so that all previous changes are ACTUALLY applied
theFakeView.alpha = 0;
}
completion:^(BOOL finished)
{
[UIView animateWithDuration:5
delay:0
options:UIViewAnimationOptionBeginFromCurrentState
animations:^
{
// now it really animates from 0.6 to 1
theButton.alpha = 1;
}
completion:nil];
}];
}
想要记住此错误的所有详细信息，然后只需将 Method Swizzling 应用于UIView类。
If you don't want to remember about all details of this bug, then just apply Method Swizzling to UIView class.
重要编辑：原因是下面的代码会在运行时导致崩溃，如果调用 performBatchUpdates：completion： c> UICollectionView 实例。所以，我不建议在这种情况下使用方法swizzling
IMPORTANT It turns out that the code below will cause a crash at runtime, if calling performBatchUpdates:completion: of UICollectionView instance. So, I do not recommend using method swizzling in this case!
您的代码可能如下所示：
Your code may look like this:
+ (void)load
{
static dispatch_once_t theOnceToken;
dispatch_once(&theOnceToken, ^
{
Class theClass = object_getClass(self);
SEL theOriginalSelector = @selector(animateWithDuration:delay:options:animations:completion:);
SEL theSwizzledSelector = @selector(swizzled_animateWithDuration:delay:options:animations:completion:);
Method theOriginalMethod = class_getClassMethod(theClass, theOriginalSelector);
Method theSwizzledMethod = class_getClassMethod(theClass, theSwizzledSelector);
if (!theClass ||!theOriginalSelector || !theSwizzledSelector || !theOriginalMethod || !theSwizzledMethod)
{
abort();
}
BOOL didAddMethod = class_addMethod(theClass,
theOriginalSelector,
method_getImplementation(theSwizzledMethod),
method_getTypeEncoding(theSwizzledMethod));
if (didAddMethod)
{
class_replaceMethod(theClass,
theSwizzledSelector,
method_getImplementation(theOriginalMethod),
method_getTypeEncoding(theOriginalMethod));
}
else
{
method_exchangeImplementations(theOriginalMethod, theSwizzledMethod);
}
});
}
+ (void)swizzled_animateWithDuration:(NSTimeInterval)duration
delay:(NSTimeInterval)delay
options:(UIViewAnimationOptions)options
animations:(void (^)(void))animations
completion:(void (^)(BOOL))completion
{
if (options & UIViewAnimationOptionBeginFromCurrentState)
{
UIView *theView = [UIView new];
theView.alpha = 1;
[UIView animateWithDuration:0
animations:^
{
theView.alpha = 0;
}
completion:^(BOOL finished)
{
[self swizzled_animateWithDuration:duration
delay:delay
options:options
animations:animations
completion:completion];
}];
}
else
{
[self swizzled_animateWithDuration:duration
delay:delay
options:options
animations:animations
completion:completion];
}
}
如果将此代码添加到自定义UIView类别，那么这段代码现在可以正常工作了：
If you add this code to your custom UIView category, then this code would work fine now:
- (void)actionPressed:(UIButton *)theButton
{
theButton.alpha = 0.6;
[UIView animateWithDuration:5
delay:0
options:UIViewAnimationOptionBeginFromCurrentState
animations:^
{
// you expect to animate from 0.6 to 1.
// it will do so ONLY if you add the above code sample to your project.
theButton.alpha = 1;
}
completion:nil];
}
在我的例子中，这个错误完全毁了我的动画。请参阅下文：
In my case, this bug has completely ruined my animations. See below:
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