将 UIVIew 转换为 UIImage 而不呈现/显示 UIView

Question

我正在使用方法将 UIView 转换为 UIImage，并且当 UIView（要转换为 UIImage）已经存在/显示时它做得很好。但我的要求是将 UIView 转换为 UIImage 而不显示 UIView。不幸的是，在这种情况下，这段代码失败了，我被卡住了。任何帮助将不胜感激。

我正在使用以下方法：

+ (UIImage *) imageWithView:(UIView *)view
{
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.opaque,     [[UIScreen mainScreen] scale]); 
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}

Answer 1

隐藏所有子视图，然后将 UIview 快照到 UIImage 应该可以工作，请参见下面的代码

+ (UIImage *)custom_snapshotScreenInView:(UIView *)contentView
{
    if (!contentView) {
        return nil;
    }
    CGSize size = contentView.bounds.size; 
    UIGraphicsBeginImageContextWithOptions(size, NO, [UIScreen mainScreen].scale); 
    CGRect rect = contentView.bounds; 
    [contentView drawViewHierarchyInRect:rect afterScreenUpdates:YES];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext(); 
    UIGraphicsEndImageContext(); 
    UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil); 
    return image;
}

+ (UIImage *)custom_snapshotScreenWithoutSubviews:(UIView *)contentView
{
    // save hidden view's hash
    NSMutableArray *hideViewsHashs = [[NSMutableArray alloc]initWithCapacity:contentView.subviews.count];
    for (UIView *subview in contentView.subviews) {
        if (subview.hidden == NO) {
            [hideViewsHashs addObject:@(subview.hash)];
            NSLog(@"Dikey:video:snap:hash = %@", @(subview.hash));
        }
        subview.hidden = YES;
    }
    // view to image
    UIImage *image = [UIImage custom_snapshotScreenInView:contentView];
    // restore
    for (UIView *subview in contentView.subviews) {
        if ([hideViewsHashs containsObject:@(subview.hash)]) {
            subview.hidden = NO;
            NSLog(@"Dikey:video:snap:restore:hash = %@", @(subview.hash));
        }
    }
    // finish
    return image;
}

Answer 2

假设您已经有了一个工作视图，这段代码应该可以将UIView 转换为UIImage（我正在使用它将渐变转换为图像并将图像显示到UIProgressView。

斯威夫特：

let renderer = UIGraphicsImageRenderer(size: gradientView.bounds.size)
let image = renderer.image { ctx in
            gradientView.drawHierarchy(in: gradientView.bounds, afterScreenUpdates: true)
}

目标 C：

UIGraphicsImageRenderer *renderer = [[UIGraphicsImageRenderer alloc] initWithSize:gradientView.bounds.size];
UIImage *gradientImage = [renderer imageWithActions:^(UIGraphicsImageRendererContext * _Nonnull rendererContext) {
        [gradientView drawViewHierarchyInRect:gradientView.bounds afterScreenUpdates:true];
    }];

_progressView.progressImage = gradientImage;

上面的代码应该允许您将任何UIView 转换为UIImage。理想情况下，您应该在 viewWillAppear 中运行它（因为此时视图控制器将具有正确的布局大小）。如果您在让它工作时遇到任何问题，您可以查看我为该主题的指南制作的这些示例项目！ Objective C, Swift.

Answer 3

您的代码可能会失败，因为您没有布置视图的子视图（当您将视图添加为子视图时会自动完成）。试试我下面写的方法：

+ (UIImage *)imageFromView:(UIView *)view sized:(CGSize)size
{
    // layout the view
    view.frame = CGRectMake(0, 0, size.width, size.height);
    [view setNeedsLayout];
    [view layoutIfNeeded];

    // render the image
    UIGraphicsBeginImageContextWithOptions(size, view.opaque, 0.0f);
    [view drawViewHierarchyInRect:view.bounds afterScreenUpdates:NO];
    UIImage *renderedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return renderedImage;
}