Question

我想以模态方式显示UIViewController，并能够看到呈现它的视图的模糊版本。

遵循了许多类似的问题：

我在控制器的视图中添加了一个背景，该视图基于呈现控制器的捕获视图。我面临的问题是我的应用程序支持多个方向，当呈现和旋转模态视图时，底层背景图像不再匹配。

我尝试在模态viewController的didRotateFromInterfaceOrientation:中抓取呈现viewController的新快照，但看起来呈现的viewController的UI没有被更新，结果图像仍然是错误的方向。有没有办法强制重绘一个被模态隐藏的视图？

Answer 1

经过长时间的考虑，我想出了一个可行的方法来处理它。它的效果如何取决于您在呈现viewController时所拥有的内容类型。

一般的想法是在呈现新的viewController之前不要使用一个，而是两个屏幕截图 - 一个用于肖像，一个用于横向。这是通过更改顶部viewController和导航栏（如果适用）的帧来模拟不同的方向，获取结果的屏幕截图并将其更改回来实现的。用户永远不会在设备上看到此更改，但屏幕抓取仍会显示新的方向。

具体代码取决于您调用它的位置，但主要逻辑是相同的。我的实现从AppDelegate运行，因为它被UIViewController的几个子类重用。

以下是获取相应屏幕截图的代码。

// get references to the views you need a screenshot of
// this may very depending on your app hierarchy
UIView *container = [self.window.subviews lastObject]; // UILayoutContainerView
UIView *subview = container.subviews[0]; //  UINavigationTransitionView
UIView *navbar = container.subviews[1]; // UINavigationBar

CGSize originalSubviewSize = subview.frame.size;
CGSize originalNavbarSize = navbar.frame.size;

// compose the current view of the navbar and subview
UIImage *currentComposed = [self composeForeground:navbar withBackground:subview];

// rotate the navbar and subview
subview.frame = CGRectMake(subview.frame.origin.x, subview.frame.origin.y, originalSubviewSize.height, originalSubviewSize.width);
// the navbar has to match the width of the subview, height remains the same
navbar.frame = CGRectMake(navbar.frame.origin.x, navbar.frame.origin.y, originalSubviewSize.height, originalNavbarSize.height);

// compose the rotated view
UIImage *rotatedComposed = [self composeForeground:navbar withBackground:subview];

// change the frames back to normal
subview.frame = CGRectMake(subview.frame.origin.x, subview.frame.origin.y, originalSubviewSize.width, originalSubviewSize.height);
navbar.frame = CGRectMake(navbar.frame.origin.x, navbar.frame.origin.y, originalNavbarSize.width, originalNavbarSize.height);


// assign the variables depending on actual orientations
UIImage *landscape; UIImage *portrait;
if (originalSubviewSize.height > originalSubviewSize.width) {
    // current orientation is portrait
    portrait = currentComposed;
    landscape = rotatedComposed;
} else {
    // current orientation is landscape
    portrait = rotatedComposed;
    landscape = currentComposed;
}
CustomTranslucentViewController *vc = [CustomTranslucentViewController new];
vc.backgroundSnap = portrait;
vc.backgroundSnapLandscape = landscape;
[rooVC presentViewController:vc animated:YES completion:nil];

方法composeForeground:withBackground:是一种便捷方法，可根据两个输入视图（导航栏+视图控制器）生成适当的背景图像。除了将两个视图组合在一起之外，在旋转呈现的viewController时，使结果看起来更自然有点神奇。具体来说，它将屏幕截图扩展到1024x1024平方，并使用合成图像的镜像副本填充额外空间。在许多情况下，一旦模糊，这看起来就足够了，因为视图重新绘制的方向更改动画不可用。

- (UIImage *)composeForeground:(UIView *)frontView withBackground:(UIView *)backView {

    UIGraphicsBeginImageContextWithOptions(backView.frame.size, 0, 0);
    [backView.layer renderInContext:UIGraphicsGetCurrentContext()];

    // translation is necessary to account for the extra 20 taken up by the status bar
    CGContextTranslateCTM(UIGraphicsGetCurrentContext(), frontView.frame.origin.x, frontView.frame.origin.y);
    [frontView.layer renderInContext:UIGraphicsGetCurrentContext()];
    CGContextTranslateCTM(UIGraphicsGetCurrentContext(), -frontView.frame.origin.x, -frontView.frame.origin.y);

    // this is the core image, would have left it at this if we did not need to use fancy mirrored tiling
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // add mirrored sections
    CGFloat addition = 256; // 1024 - 768
    if (newImage.size.height > newImage.size.width) {
        // portrait, add a mirrored image on the right
        UIImage *horizMirror = [[UIImage alloc] initWithCGImage:newImage.CGImage scale:newImage.scale orientation:UIImageOrientationUpMirrored];
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(newImage.size.width+addition, newImage.size.height), 0, 0);
        [horizMirror drawAtPoint:CGPointMake(newImage.size.width, 0)];
    } else {
        // landscape, add a mirrored image at the bottom
        UIImage *vertMirror = [[UIImage alloc] initWithCGImage:newImage.CGImage scale:newImage.scale orientation:UIImageOrientationDownMirrored];
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(newImage.size.width, newImage.size.height+addition), 0, 0);
        [vertMirror drawAtPoint:CGPointMake(0, newImage.size.height)];
    }

    // combine the mirrored extension with the original image
    [newImage drawAtPoint:CGPointZero];
    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // for ios 6, crop off the top 20px
    if (SYSTEM_VERSION_LESS_THAN(@"7")) {
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(newImage.size.width, newImage.size.height-20), NO, 0);
        [newImage drawAtPoint:CGPointMake(0, -20)];
        newImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }

    return newImage;
}

生成的横向和纵向图像可以根据需要进行模糊和着色，并设置为显示的viewController的背景。使用此willRotateToInterfaceOrientation:duration:的{{1}}方法选择合适的图片。

注意：我尝试尽可能减少在图像和图形上下文中完成的工作量，但在生成背景时仍然有一点延迟（大约每个30-90毫秒） viewController迭代，取决于内容，在老式慢速iPad 2上。如果您知道进一步优化或简化上述解决方案的方法，请分享！

半透明模态ViewController - 如何处理旋转

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