我是苹果开发的新手，对Core Animation有疑问，根据我的理解，你可以用对象/图像创建动画。
有很多教程，但它们都只显示代码，而不是真正解释它是如何工作的。因此，在我的应用程序中尝试使用Core Animation时，我遇到了一些困难。
我的目标是使用可填充图像创建一个永无止境的图像的幻觉。我对基本概念有所了解，我有2个UIImageViews设置，最初我尝试使用NSTimer每0.01秒调用2个方法来设置它们。一个人通过简单地在每次调用Y值时添加1来移动对象，另一个在每次调用时检查每个UIImageView的位置，然后当它到达允许它完全离开屏幕底部的像素时重置它到顶部，不幸的是它非常滞后，重置永远不会正常工作。
现在我转向Core Animation，因为我得到的印象是这是创建移动对象的预期方式。我用它对它的最小知识来创建一些动画，但我尝试过的任何东西都没有。
希望有人可以用两个UIImageViews帮我创建无限图像的错觉。我不介意你是否解释如何使用Core Animation制作一个，或者如果你想解决我写的原始代码的想法。
非常感谢任何帮助。
答案 0 :(得分：0)
这是我掀起的样本UIViewController。它使用基本UIView实例而不是UIImageView，但这些实例应该是直接交换项。
在我的测试中，效果是一个永无止境的红色和蓝色横幅的外观（即视图控制器的白色背景从未见过）。
NOT 使用CAAnimation，而是使用为UIView提供的基于块的动画，我认为这更容易管理。
这会给你你想要的吗？
注意：这忽略了包含头文件ViewController.h，但它完全没有任何代码。
// ViewController.m
#import "ViewController.h"
// Private Interface
@interface ViewController ()
#pragma mark -
#pragma mark - UI Controls
@property (strong, nonatomic) UIView *view1;
@property (strong, nonatomic) UIView *view2;
#pragma mark -
#pragma mark - Private Properties
@property (assign, nonatomic) BOOL isVisible;
@property (strong, nonatomic) NSLayoutConstraint *view1HeightConstraint;
@property (strong, nonatomic) NSLayoutConstraint *view2HeightConstraint;
@property (strong, nonatomic) NSLayoutConstraint *view1TopConstraint;
@property (strong, nonatomic) NSLayoutConstraint *view2TopConstraint;
@end
@implementation ViewController
#pragma mark -
#pragma mark - View Lifecycle
- (void)viewDidLoad {
[super viewDidLoad];
[self setupUserInterface];
}
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
// At this point, self.view has its correct size,
// so use it to set the height of the sub views
self.view1HeightConstraint.constant = self.view.frame.size.height;
self.view2HeightConstraint.constant = self.view.frame.size.height;
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
// The screen has been shown, so store this value and begin the animations
self.isVisible = YES;
[self slideDown1];
}
- (void)viewDidDisappear:(BOOL)animated {
[super viewDidDisappear:animated];
// So that the animations will stop and this view controller can be released
self.isVisible = NO;
}
#pragma mark -
#pragma mark - Animations
- (void)slideDown1 {
// This sets the top of view1's frame equal to the bottom of self.view.frame
self.view1TopConstraint.constant = self.view.frame.size.height;
// This sets the top of view2's frame equal to the top of self.view.frame
self.view2TopConstraint.constant = 0.0f;
// If we didn't call this block, the changes set above would take effect "immediately"
[UIView animateWithDuration:1.0f
animations:^{
// Calling this inside of an animation causes the changes above to be animated
[self.view layoutIfNeeded];
}
completion:^(BOOL finished) {
// This block will execute when the animations finish
// This moves self.view1 so that its bottom is aligned with the top of self.view
self.view1TopConstraint.constant = -1.0f * self.view.frame.size.height;
// This causes the line above to take place immediately
[self.view layoutIfNeeded];
if (self.isVisible == YES) {
// If the screen is still visible, start the next animation
[self slideDown2];
}
}
];
}
- (void)slideDown2 {
self.view1TopConstraint.constant = 0.0f;
self.view2TopConstraint.constant = self.view.frame.size.height;
[UIView animateWithDuration:1.0f
animations:^{
[self.view layoutIfNeeded];
}
completion:^(BOOL finished) {
self.view2TopConstraint.constant = -1.0f * self.view.frame.size.height;
[self.view layoutIfNeeded];
if (self.isVisible == YES) {
[self slideDown1];
}
}
];
}
#pragma mark -
#pragma mark - UI Setup
- (void)setupUserInterface {
[self createControls];
[self setupControls];
[self layoutControls];
}
- (void)createControls {
self.view1 = [[UIView alloc] init];
self.view2 = [[UIView alloc] init];
}
- (void)setupControls {
self.view1.backgroundColor = [UIColor redColor];
// This line is required for our "full auto layout",
// which just means (in this case) that we're doing it all in code
[self.view1 setTranslatesAutoresizingMaskIntoConstraints:NO];
self.view2.backgroundColor = [UIColor blueColor];
[self.view2 setTranslatesAutoresizingMaskIntoConstraints:NO];
}
- (void)layoutControls {
// The subviews have to be added to self.view before we can constrain them
[self.view addSubview:self.view1];
[self.view addSubview:self.view2];
// This sets up the subviews to make their width equal to self.view's width
// You could have also used this method for the views' heights
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view1
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeWidth
multiplier:1.0f
constant:0.0f]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:self.view2
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeWidth
multiplier:1.0f
constant:0.0f]];
// This gives us properties we can use later to animate the views' movements
self.view1TopConstraint = [NSLayoutConstraint constraintWithItem:self.view1
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeTop
multiplier:1.0f
constant:0.0f];
// You created the constraint, but it has to be installed/added
[self.view addConstraint:self.view1TopConstraint];
// A different and probably less effective way to set the heights of the subviews
self.view1HeightConstraint = [NSLayoutConstraint constraintWithItem:self.view1
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0f
constant:0.0f];
[self.view addConstraint:self.view1HeightConstraint];
self.view2TopConstraint = [NSLayoutConstraint constraintWithItem:self.view2
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.view
attribute:NSLayoutAttributeTop
multiplier:1.0f
constant:0.0f];
[self.view addConstraint:self.view2TopConstraint];
self.view2HeightConstraint = [NSLayoutConstraint constraintWithItem:self.view2
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:nil
attribute:NSLayoutAttributeNotAnAttribute
multiplier:1.0f
constant:0.0f];
[self.view addConstraint:self.view2HeightConstraint];
}
@end