使用snapshotViewAfterScreenUpdates创建的UIView的UIImage： [英] UIImage from a UIView created with snapshotViewAfterScreenUpdates:

问题描述

是否可以从使用 snapshotViewAfterScreenUpdates 创建的UIView获取UIImage？

Is it possible to get a UIImage from a UIView created with snapshotViewAfterScreenUpdates?

从 snapshotViewAfterScreenUpdates 返回的UIView在作为子视图添加时看起来很好，但以下内容会产生黑色图像：

A UIView returned from snapshotViewAfterScreenUpdates looks fine when added as a subview, but the following produces a black image:

UIView *snapshotView = [someView snapshotViewAfterScreenUpdates:YES]; 
UIImage *snapshotImage = [self imageFromView:snapshotView]; 

- (UIImage *)imageFromView:(UIView *)view
{
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, YES, 0.0);
    // [view.layer renderInContext:UIGraphicsGetCurrentContext()]; // <- same result...
    [view drawViewHierarchyInRect:view.bounds afterScreenUpdates:NO];
    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return img;
}

当然可以在不依赖<$ c $的情况下获取图像c> snapshotViewAfterScreenUpdates ：

UIImage *snapshotImage = [self imageFromView:someView];

不幸的是，在捕获复杂视图时， drawViewHierarchyInRect 无法匹配 snapshotViewAfterScreenUpdates 的速度。我希望从 snapshotViewAfterScreenUpdates 创建的视图中获取 UIImage 会更快，这可能吗？

Unfortunately, when capturing a complex view, drawViewHierarchyInRect can't match the speed of snapshotViewAfterScreenUpdates. I was hoping that it would be faster to get the UIImage from a view created by snapshotViewAfterScreenUpdates, is this possible?

推荐答案

答案似乎是 NO 和Apple的 documentation 隐含地证实了这一点：

The answer seems to be NO and Apple's documentation implicitly confirms this:

如果要对快照应用图形效果（如模糊），请使用 drawViewHierarchyInRect： afterScreenUpdates：方法
而不是。

If you want to apply a graphical effect, such as blur, to a snapshot, use the drawViewHierarchyInRect:afterScreenUpdates: method instead.

值得注意的是实施参与用户界面在WWDC13上的iOS 会话中列出 snapshotViewAfterScreenUpdates 作为最快的方法，但在示例代码中使用 drawViewHierarchyInRect 。

It's worth noting that the Implementing Engaging UI on iOS session from WWDC13 lists snapshotViewAfterScreenUpdates as the fastest method, but uses drawViewHierarchyInRect in the example code.

这篇关于使用snapshotViewAfterScreenUpdates创建的UIView的UIImage：的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！