如何在IOS中应用部分淡入淡出？

我有两张照片。一个在另一个的后面。我想从左角开始淡出顶部图像。我该怎么做

---

我应该使用渐变蒙版吗？

为关键帧

内容定义自己的
CALayer
子类，并使用自己的
actionForKey
动画

@interface CustomLayer: CALayer

@end

@implementation CustomLayer


+ (id<CAAction>)actionForKey:(NSString*)event {

if ([event isEqualToString:@"contents"]) {
    CATransition* basicAnimation = [CATransition animation];
    basicAnimation.type = kCATransitionMoveIn;
    basicAnimation.subtype = kCATransitionFromLeft;
    return basicAnimation;
} else {
    return nil;
}
}

@end

与往常一样，您可以在事务中包装属性分配：

[CATransaction begin];
    ....
[CATransaction end];

如果您希望对转换的持续时间进行更多控制，但无论如何都会应用转换

编辑：

对于您想要的过渡类型，您可以看一看。寻找转换。这并不完全是你想要的，但它可以引导你走上正确的道路。
这里有一种技术，它可以从左上到右下淡出CALayer中的任何内容，显示CALayer下面的任何内容

假设我们将淡出名为
self.fadeView
的
UIImageView
层

我们将创建一个并将其用作
self.fadeView.layer.mask
。渐变将使用四个停止点从alpha=0（透明）变为alpha=1（不透明）：0、0、1、1。是的，两个零，然后两个一。当我们希望fadeView

不透明时，我们将停止位置设置为-1、.5、0、1。这样，两个alpha=0停止点就完全超出了层边界。当我们希望fadeView透明时，我们会将停止位置设置为0、1、1.5、2。这样，两个alpha=1停止点就完全超出了层边界。

CAGradientLayer

将自动为其停止位置的更改设置动画，创建交叉淡入淡出效果

代码如下：

#import "ViewController.h"

@implementation ViewController

@synthesize fadeView = _fadeView;

static NSArray *locations(float a, float b, float c, float d)
{
    return [NSArray arrayWithObjects:
        [NSNumber numberWithFloat:a],
        [NSNumber numberWithFloat:b],
        [NSNumber numberWithFloat:c],
        [NSNumber numberWithFloat:d],
        nil];
}

// In my test project, I put a swipe gesture recognizer on fadeView in my XIB
// with direction = Up and connected it to this action.
- (IBAction)fadeIn
{
    [CATransaction begin];
    [CATransaction setValue:[NSNumber numberWithDouble:2.0] forKey:kCATransactionAnimationDuration];
    ((CAGradientLayer *)self.fadeView.layer.mask).locations = locations(-1, -.5, 0, 1);
    [CATransaction commit];
}

// In my test project, I put a swipe gesture recognizer on fadeView in my XIB
// with direction = Down and connected it to this action.
- (IBAction)fadeOut
{
    [CATransaction begin];
    [CATransaction setValue:[NSNumber numberWithDouble:2.0] forKey:kCATransactionAnimationDuration];
    ((CAGradientLayer *)self.fadeView.layer.mask).locations = locations(0, 1, 1.5, 2);
    [CATransaction commit];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    CAGradientLayer *mask = [CAGradientLayer layer];
    mask.frame = self.fadeView.bounds;
    mask.colors = [NSArray arrayWithObjects:
        (__bridge id)[UIColor clearColor].CGColor,
        (__bridge id)[UIColor clearColor].CGColor,
        (__bridge id)[UIColor whiteColor].CGColor,
        (__bridge id)[UIColor whiteColor].CGColor,
        nil];
    mask.startPoint = CGPointZero; // top left corner
    mask.endPoint = CGPointMake(1, 1); // bottom right corner
    self.fadeView.layer.mask = mask;
    [self fadeIn]; // initialize mask.locations
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end

---

是否使用两个UIImageView？两个加莱耶？对我来说没关系。我想你的建议是为了过渡。我需要的是类似“谢谢”的东西，但我无法让代码正常工作。你有一个样本项目吗？正是我需要的！非常感谢你！！先生，我还想将动画与iPad的滚动或俯仰运动联系起来。我正在从传感器获取角度。所以，当我滚动iPad时，交叉淡入应该像在中一样发生。有什么想法吗？你可以通过改变

mask.startPoint

和

mask.endPoint

来改变淡入淡出的方向。是的，但例如，如果我将iPad滚动1度，渐变应该改变1度。我能做这个吗？

#import "ViewController.h"

@implementation ViewController

@synthesize fadeView = _fadeView;

static NSArray *locations(float a, float b, float c, float d)
{
    return [NSArray arrayWithObjects:
        [NSNumber numberWithFloat:a],
        [NSNumber numberWithFloat:b],
        [NSNumber numberWithFloat:c],
        [NSNumber numberWithFloat:d],
        nil];
}

// In my test project, I put a swipe gesture recognizer on fadeView in my XIB
// with direction = Up and connected it to this action.
- (IBAction)fadeIn
{
    [CATransaction begin];
    [CATransaction setValue:[NSNumber numberWithDouble:2.0] forKey:kCATransactionAnimationDuration];
    ((CAGradientLayer *)self.fadeView.layer.mask).locations = locations(-1, -.5, 0, 1);
    [CATransaction commit];
}

// In my test project, I put a swipe gesture recognizer on fadeView in my XIB
// with direction = Down and connected it to this action.
- (IBAction)fadeOut
{
    [CATransaction begin];
    [CATransaction setValue:[NSNumber numberWithDouble:2.0] forKey:kCATransactionAnimationDuration];
    ((CAGradientLayer *)self.fadeView.layer.mask).locations = locations(0, 1, 1.5, 2);
    [CATransaction commit];
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    CAGradientLayer *mask = [CAGradientLayer layer];
    mask.frame = self.fadeView.bounds;
    mask.colors = [NSArray arrayWithObjects:
        (__bridge id)[UIColor clearColor].CGColor,
        (__bridge id)[UIColor clearColor].CGColor,
        (__bridge id)[UIColor whiteColor].CGColor,
        (__bridge id)[UIColor whiteColor].CGColor,
        nil];
    mask.startPoint = CGPointZero; // top left corner
    mask.endPoint = CGPointMake(1, 1); // bottom right corner
    self.fadeView.layer.mask = mask;
    [self fadeIn]; // initialize mask.locations
}

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}

@end