ios - 半透明模态 ViewController - 如何处理旋转

Question

我想以模态方式显示 UIViewController 并且能够看到呈现它的 View 的模糊版本。

下面是一些类似的问题，例如:

iOS 7 Translucent Modal View Controller

我已将背景添加到我的 Controller View 中，该 View 基于呈现 Controller 的捕获 View 。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。

我尝试在模态视图 Controller 的 didRotateFromInterfaceOrientation: 中获取呈现 View Controller 的新快照，但呈现 View Controller 的 UI 似乎没有更新，生成的图像仍然是错误的方向。有什么方法可以强制重绘被模态视图隐藏的 View 吗？

Answer 1

经过长时间的考虑，我想出了一个可以接受的处理方式。它的工作效果在一定程度上取决于您在呈现 viewController 中的内容类型。

总体思路是在呈现新的 viewController 之前截取两张屏幕截图，一张用于纵向，一张用于横向。这是通过更改顶部 viewController 和导航栏(如果适用)的框架以模拟不同的方向，获取结果的屏幕截图并将其更改回来来实现的。用户永远不会在设备上看到这种变化，但屏幕抓取仍然显示新的方向。

确切的代码将取决于您从何处调用它，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];

composeForeground:withBackground: 方法是一种基于两个输入 View (导航栏 + View Controller )生成适当背景图像的便捷方法。除了将两个 View 组合在一起之外，在旋转呈现的 viewController 时，它还可以使结果看起来更自然。具体来说，它将屏幕截图扩展到 1024x1024 正方形，并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，因为针对方向更改重新绘制 View 的动画不可用。

- (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，并设置为呈现的 viewController 的背景。使用此 viewController 的 willRotateToInterfaceOrientation:duration: 方法选择适当的图像。

注意:我已尝试尽可能减少对图像和图形上下文所做的工作量，但在生成背景时仍然存在轻微延迟(大约 30-90 毫秒/composeForeground:withBackground: 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!