获取UIView对象的快照
参考
API方法
UIScreen
- (UIView *)snapshotViewAfterScreenUpdates:(BOOL)afterUpdates;
UIView
// 获取当前文本的快照视图
- (UIView *)snapshotViewAfterScreenUpdates:(BOOL)afterUpdates;
// 给定一个可伸缩插值，返回基于当前视图的指定内容的快照视图，
- (UIView *)resizableSnapshotViewFromRect:(CGRect)rect afterScreenUpdates:(BOOL)afterUpdates withCapInsets:(UIEdgeInsets)capInsets;
// 将完整视图层次结构的快照呈现在当前上下文中。
- (BOOL)drawViewHierarchyInRect:(CGRect)rect afterScreenUpdates:(BOOL)afterUpdates;
Demo 示例
Snapshotting for Animation - 动画快照
自定义视图绘制方法：
// 生成旋转视图
- (void)generateRotations {
for (CGFloat angle = 0; angle < 2 * M_PI; angle += M_PI / 20.0) {
UIView *newView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 200, 250)];
newView.center = CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
newView.layer.borderColor = [UIColor grayColor].CGColor;
newView.layer.borderWidth = 1;
newView.backgroundColor = [UIColor colorWithWhite:0.8 alpha:0.4];
newView.transform = CGAffineTransformMakeRotation(angle);
newView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
[self addSubview:newView];
}
}
重新设置所有子视图的背景色:
- (void)recolorSubviews:(UIColor *)newColor {
for (UIView *subview in self.subviews) {
subview.backgroundColor = newColor;
}
}
在动画中使用UIView快照以简化复杂的视图
#import "ViewController.h"
#import "HQLRotatingViews.h"
@interface ViewController ()
@property (weak, nonatomic) IBOutlet UIView *containerView;
@end
@implementation ViewController {
HQLRotatingViews *_complexView;
}
#pragma mark - Lifecycle
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
[self createComplexView];
}
#pragma mark - Utility methods
// 向容器视图中添加旋转视图
- (void)createComplexView {
_complexView = [[HQLRotatingViews alloc] initWithFrame:self.view.bounds];
[self.containerView addSubview:_complexView];
}
- (void)animateViewAwayAndReset:(UIView *)view {
[UIView animateWithDuration:2.0
animations:^{
view.bounds = CGRectZero;
}
completion:^(BOOL finished) {
// 动画完成后删除视图并创建新视图
[view removeFromSuperview];
[self performSelector:@selector(createComplexView)
withObject:nil
afterDelay:1];
}];
}
#pragma mark - IBActions
/**
这两个方法演示了如何在动画中使用UIView快照以简化复杂的视图
*/
// ❇️ Animate 按钮——直接对 UIView 进行旋转
- (IBAction)handleAnimate:(id)sender {
[self animateViewAwayAndReset:_complexView];
}
// ❇️ 生成当前 UIView 的快照之后，对快照进行旋转
- (IBAction)handleSnapshot:(id)sender {
// 创建复合视图的快照
UIView *snapshotView = [_complexView snapshotViewAfterScreenUpdates:NO];
[self.containerView addSubview:snapshotView];
[_complexView removeFromSuperview];
[self animateViewAwayAndReset:snapshotView];
}
示例一：Animate 按钮——直接对 UIView 进行旋转
示例二：生成当前 UIView 的快照之后，对快照进行旋转
快照方法：
- (nullable UIView *)snapshotViewAfterScreenUpdates:(BOOL)afterUpdates;
测试快照方法中的 BOOL 参数
/**
这两种方法比较了是否允许屏幕更新的区别
- (nullable UIView *)snapshotViewAfterScreenUpdates:(BOOL)afterUpdates;
*/
- (IBAction)handlePreUpdateSnapshot:(id)sender {
// 更新视图
[_complexView recolorSubviews:[[UIColor redColor] colorWithAlphaComponent:0.3]];
// 创建快照，不等待更改被应用。
UIView *snapshotView = [_complexView snapshotViewAfterScreenUpdates:NO];
[self.containerView addSubview:snapshotView];
[_complexView removeFromSuperview];
[self animateViewAwayAndReset:snapshotView];
}
- (IBAction)handlePostUpdateSnapshot:(id)sender {
// 更新视图
[_complexView recolorSubviews:[[UIColor redColor] colorWithAlphaComponent:0.3]];
// 创建快照，等待渲染完成。
UIView *snapshotView = [_complexView snapshotViewAfterScreenUpdates:YES];
[self.containerView addSubview:snapshotView];
[_complexView removeFromSuperview];
[self animateViewAwayAndReset:snapshotView];
}
Pre 按钮——设置为 NO
Post 按钮——设置为 YES
生成快照图片
/**
此方法演示了如何向UIView快照添加图像效果
*/
- (IBAction)handleImageSnapshot:(id)sender {
// 创建一个图像上下文 - 复合视图的大小和缩放比例
UIGraphicsBeginImageContextWithOptions(_complexView.bounds.size, NO, 0.0);
// 将快照渲染到图像上下文中
[_complexView drawViewHierarchyInRect:_complexView.bounds afterScreenUpdates:NO];
// 从图像上下文中抓取图像
UIImage *complexViewImage = UIGraphicsGetImageFromCurrentImageContext();
// 结束使用图像上下文
UIGraphicsEndImageContext();
// 在生成快照之前让当前的视图模糊化
UIImageView *iv = [[UIImageView alloc] initWithImage:[self applyBlurToImage:complexViewImage]];
iv.center = _complexView.center;
[self.containerView addSubview:iv];
[_complexView removeFromSuperview];
[self performSelector:@selector(animateViewAwayAndReset:)
withObject:iv
afterDelay:1.0];
}
// 模糊化UIImage
- (UIImage *)applyBlurToImage:(UIImage *)image {
CIContext *context = [CIContext contextWithOptions:nil];
CIImage *ci_image = [CIImage imageWithCGImage:image.CGImage];
CIFilter *filter = [CIFilter filterWithName:@"CIGaussianBlur"];
[filter setValue:ci_image forKey:kCIInputImageKey];
[filter setValue:@5 forKey:kCIInputRadiusKey];
CIImage *result = [filter valueForKey:kCIOutputImageKey];
CGImageRef cgImage = [context createCGImage:result fromRect:[result extent]];
return [UIImage imageWithCGImage:cgImage
scale:image.scale
orientation:image.imageOrientation];
}
Limitaions - 局限性
创建的快照必须在屏幕范围之内
