iphone - 使用 CAAnimation 实现 CATransition 推送

Question

如何在 iOS 中使用 CAAnimation 子类实现 kCATransitionPush？

CAAnimation *animation;
// How do you create an animation that does the same than:
// CATransition *animation = [CATransition animation];
// [animation setType:kCATransitionPush];        
[self.view.layer addAnimation:animation forKey:nil];

[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:1];        
[self.view addSubview:change];
[UIView commitAnimations];

我知道 UIView 动画可以 also可以使用，但如果我可以从头开始实现 kCATransitionPush 转换，它会帮助我更好地理解 Core Animation。

Answer 1

为了在两个图层上同时执行动画，您必须向每个图层添加足够的 CAAnimationGroup。

[nextView.layer addAnimation:nextViewAnimation forKey:nil];
[currentView.layer addAnimation:currentViewAnimation forKey:nil];

nextViewAnimation 将是:

CAAnimationGroup *nextViewAnimation = [CAAnimationGroup animation];
NSMutableArray *nextAnimations = [NSMutableArray array];

[nextAnimations addObject:[self opacityAnimation:YES]];  // fade in

CGPoint fromPoint = CGPointMake(forward ? nextView.center.x + nextView.frame.size.width : nextView.center.x - nextView.frame.size.width, nextView.center.y);
[nextAnimations addObject:[self positionAnimationFromPoint:fromPoint toPoint:nextView.center]];  // traslation in

nextViewAnimation.animations = nextAnimations;

和当前 View 动画:

CAAnimationGroup *currentViewAnimation = [CAAnimationGroup animation];
NSMutableArray *currentAnimations = [NSMutableArray array];
[currentSceneAnimations addObject:[self opacityAnimation:NO]]; // fade out

CGPoint toPoint = CGPointMake(forward ? currentView.center.x - currentView.frame.size.width : currentView.center.x + currentView.frame.size.width, currentView.center.y);
    [currentAnimations addObject:[self positionAnimationFromPoint:currentView.center toPoint:toPoint]];  // traslation out

currentViewAnimation.animations = currentAnimations;

这些方法创建了基本的动画:

- (CABasicAnimation *)opacityAnimation:(BOOL)fadeIn {
CABasicAnimation *a = [CABasicAnimation animationWithKeyPath:@"opacity"];
a.fromValue = [NSNumber numberWithFloat:fadeIn ? 0.0 : 1.0];
a.toValue = [NSNumber numberWithFloat:fadeIn ? 1.0 : 0.0];
return a;
}

- (CABasicAnimation *)positionAnimationFromPoint:(CGPoint)fromPoint toPoint:(CGPoint)toPoint {
CABasicAnimation *a = [CABasicAnimation animationWithKeyPath:@"position"];
a.fromValue = [NSValue valueWithCGPoint:fromPoint];
a.toValue = [NSValue valueWithCGPoint:toPoint];
return a;
}

使用 bool 值forward，您可以模拟“从左”或“从右”的过渡。