通过使用 renderInContext 在 UIImage 上绘制 UIView 来截取屏幕截图时，我的 UIImage 不显示

Question

我几乎一字不差地使用来自http://developer.apple.com/library/ios/#qa/qa1714/_index.html 的示例代码，我可以保存我的背景图像或我的叠加层，但我不能将两者结合起来。当我尝试使用以下代码组合它们时，叠加层会将背景呈现为白色，并且我假设它会覆盖背景。知道这是为什么吗？

这是我尝试将视图叠加层与图像结合起来的方法：

-(void) annotateStillImage
{
    UIImage *image = stillImage;

    // Create a graphics context with the target size
    CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);

    CGContextRef context = UIGraphicsGetCurrentContext();


    // Draw the image returned by the camera sample buffer into the context. 
    // Draw it into the same sized rectangle as the view that is displayed on the screen.
    UIGraphicsPushContext(context);

    [image drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
    UIGraphicsPopContext();

    // -renderInContext: renders in the coordinate space of the layer,
    // so we must first apply the layer's geometry to the graphics context
    CGContextSaveGState(context);
    // Center the context around the window's anchor point
    CGContextTranslateCTM(context, [[self view] center].x, [[self view] center].y);
    // Apply the window's transform about the anchor point
    CGContextConcatCTM(context, [[self view] transform]);
    // Offset by the portion of the bounds left of and above the anchor point
    CGContextTranslateCTM(context,
                          -[[self view] bounds].size.width * [[[self view] layer] anchorPoint].x,
                          -[[self view] bounds].size.height * [[[self view] layer] anchorPoint].y);

    // Render the layer hierarchy to the current context
    [[[self view] layer] renderInContext:context];

    // Restore the context
    CGContextRestoreGState(context);

    // Retrieve the screenshot image containing both the camera content and the overlay view
    stillImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
}

这是我的方法的一个 sn-p，它在相关的情况下创建视图：

CGRect layerRect = [[[self view] layer] bounds];
[[self previewLayer] setBounds:layerRect];
[[self previewLayer] setPosition:CGPointMake(CGRectGetMidX(layerRect),  CGRectGetMidY(layerRect))];
[[[self view] layer] addSublayer:[self previewLayer]];

UIButton *overlayButton = [UIButton buttonWithType:UIButtonTypeCustom];
[overlayButton setImage:[UIImage imageNamed:@"acceptButton.png"] forState:UIControlStateNormal];
[overlayButton setFrame:[self rectForAcceptButton] ];
[overlayButton setAutoresizesSubviews:TRUE];
[overlayButton setAutoresizingMask:UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleLeftMargin];
[overlayButton addTarget:self action:@selector(acceptButtonPressed) forControlEvents:UIControlEventTouchUpInside];
[[self view] addSubview:overlayButton];

我希望 annotate 方法中的图像是背景，视图绘图中的接受按钮将添加到顶部。我得到的只是接受按钮和白色背景，但如果我不运行 renderInContext 方法，我得到的只是图像背景，没有覆盖。

谢谢！

Answer 1

事实证明，我将叠加层添加到与预览层相同的视图中，而不是将其放在自己的视图中。我通过查看这个涵盖所有可能类型的屏幕截图的伟大项目来意识到这一点：https://github.com/cocoacoderorg/Screenshots

修复是在 IB 中创建一个具有透明背景的单独叠加视图，并将我的叠加元素添加到其中。