objective-c - 在 UICollectionViewCell 上创建视差焦点效果

Question

如何使用自定义 View 在 Collection View 单元格上创建视差焦点效果？如果我使用 ImageView ，要设置的属性将是 adjustsImageWhenAncestorFocused，但我的 Collection View 单元格包含一个子类 UIView，其中包含使用核心图形绘制的自定义内容。

Answer 1

@raulriera 的回答很好，但只是在 2D 中移动单元格。此外，OP 要求提供一个 Objective-C 示例。

出于完全相同的原因，我也希望实现这种效果 - 我有 UICollectionView，其单元格包含图像和标签。

我创建了一个 UIMotionEffectGroup 子类，因为接近 Apple TV 效果似乎需要四种不同的运动效果。前两个是@raulriera 中的平面运动，另外两个是 3D 旋转。

现在只是 Shiny 的环境层。有接盘者吗？ :-)

这是我的运动效果组代码:

(shiftDistance 和 tiltAngle 常量设置效果的幅度。给定的值看起来与 Apple TV 效果非常相似。)

#import <UIKit/UIKit.h>
#import "UIAppleTvMotionEffectGroup.h"

@implementation UIAppleTvMotionEffectGroup

- (id)init
{
    if ((self = [super init]) != nil)
    {
        // Size of shift movements
        CGFloat const shiftDistance = 10.0f;

        // Make horizontal movements shift the centre left and right
        UIInterpolatingMotionEffect *xShift = [[UIInterpolatingMotionEffect alloc]
                                              initWithKeyPath:@"center.x"
                                              type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];
        xShift.minimumRelativeValue = [NSNumber numberWithFloat: shiftDistance * -1.0f];
        xShift.maximumRelativeValue = [NSNumber numberWithFloat: shiftDistance];

        // Make vertical movements shift the centre up and down
        UIInterpolatingMotionEffect *yShift = [[UIInterpolatingMotionEffect alloc]
                                              initWithKeyPath:@"center.y"
                                              type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];
        yShift.minimumRelativeValue = [NSNumber numberWithFloat: shiftDistance * -1.0f];
        yShift.maximumRelativeValue = [NSNumber numberWithFloat: shiftDistance];

        // Size of tilt movements
        CGFloat const tiltAngle = M_PI_4 * 0.125;

        // Now make horizontal movements effect a rotation about the Y axis for side-to-side rotation.
        UIInterpolatingMotionEffect *xTilt = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"layer.transform" type:UIInterpolatingMotionEffectTypeTiltAlongHorizontalAxis];

        // CATransform3D value for minimumRelativeValue
        CATransform3D transMinimumTiltAboutY = CATransform3DIdentity;
        transMinimumTiltAboutY.m34 = 1.0 / 500;
        transMinimumTiltAboutY = CATransform3DRotate(transMinimumTiltAboutY, tiltAngle * -1.0, 0, 1, 0);

        // CATransform3D value for maximumRelativeValue
        CATransform3D transMaximumTiltAboutY = CATransform3DIdentity;
        transMaximumTiltAboutY.m34 = 1.0 / 500;
        transMaximumTiltAboutY = CATransform3DRotate(transMaximumTiltAboutY, tiltAngle, 0, 1, 0);

        // Set the transform property boundaries for the interpolation
        xTilt.minimumRelativeValue = [NSValue valueWithCATransform3D: transMinimumTiltAboutY];
        xTilt.maximumRelativeValue = [NSValue valueWithCATransform3D: transMaximumTiltAboutY];

        // Now make vertical movements effect a rotation about the X axis for up and down rotation.
        UIInterpolatingMotionEffect *yTilt = [[UIInterpolatingMotionEffect alloc] initWithKeyPath:@"layer.transform" type:UIInterpolatingMotionEffectTypeTiltAlongVerticalAxis];

        // CATransform3D value for minimumRelativeValue
        CATransform3D transMinimumTiltAboutX = CATransform3DIdentity;
        transMinimumTiltAboutX.m34 = 1.0 / 500;
        transMinimumTiltAboutX = CATransform3DRotate(transMinimumTiltAboutX, tiltAngle * -1.0, 1, 0, 0);

        // CATransform3D value for maximumRelativeValue
        CATransform3D transMaximumTiltAboutX = CATransform3DIdentity;
        transMaximumTiltAboutX.m34 = 1.0 / 500;
        transMaximumTiltAboutX = CATransform3DRotate(transMaximumTiltAboutX, tiltAngle, 1, 0, 0);

        // Set the transform property boundaries for the interpolation
        yTilt.minimumRelativeValue = [NSValue valueWithCATransform3D: transMinimumTiltAboutX];
        yTilt.maximumRelativeValue = [NSValue valueWithCATransform3D: transMaximumTiltAboutX];

        // Add all of the motion effects to this group
        self.motionEffects = @[xShift, yShift, xTilt, yTilt];

        [xShift release];
        [yShift release];
        [xTilt release];
        [yTilt release];
    }
    return self;
}

@end

我在我的自定义 UICollectionViewCell 子类中这样使用它:

@implementation MyCollectionViewCell

- (void)didUpdateFocusInContext:(UIFocusUpdateContext *)context withAnimationCoordinator:(UIFocusAnimationCoordinator *)coordinator
{
    // Create a static instance of the motion effect group (could do this anywhere, really, maybe init would be better - we only need one of them.)
    static UIAppleTVMotionEffectGroup *s_atvMotionEffect = nil;
    if (s_atvMotionEffect == nil)
    {
        s_atvMotionEffect = [[UIAppleTVMotionEffectGroup alloc] init];
    }

    [coordinator addCoordinatedAnimations: ^{
        if (self.focused)
        {
            [self addMotionEffect: s_atvMotionEffect];
        }
        else
        {
            [self removeMotionEffect: s_atvMotionEffect];
        }

                               completion: ^{

            }];
}

@end