Possible to render a UIView into a bitmap without attaching it to a window?

Question

Hi all,
I am trying to capture the visual output of a UIView into a bitmap which I can save to a file. However, it seems that all the information I have about rendering a UIView requires it to be attached to an UIWindow to give it a backing surface.
What I am trying to work out is a method (code!) to render the output of an arbitrary UIView into a bitmap. Once I have that bitmap I will use it in my app (e.g. save it).
The approaches I have tried include:
1) creating a CGBitmapContext, using UIGraphicsPushContext() and then calling the view's draw method:
// 'view' is the UIView instance.
CGRect bounds = [view bounds];
CGColorSpaceRef cgctxcs = CGColorSpaceCreateDeviceRGB();
unsigned char *bufDataPtr = malloc(bounds.size.width * bounds.size.height * 4); // 4 Bpp for RGBA
CGContextRef cgctx = CGBitmapContextCreate(bufDataPtr,
bounds.size.width,
bounds.size.height,
8,
bounds.size.width * 4,
cgctxcs,
kCGBitmapByteOrderDefault | kCGImageAlphaNoneSkipLast);
UIGraphicsPushContext(cgctx);
[view drawRect:bounds];
UIGraphicsPopContext();
but this does not appear to draw anything into the bitmap context.
2) Get the view's layer, and call -renderInContext on it.
[[view layer] renderInContext:cgctx]; // cgctx set up as above.
Again, this produces nothing.
At this stage I'm stuck. Anyone have any pointers?

Answer 1

That sample gives a nice example of method 2 I already tried.
There seems to be some reason why the layer backing the UIView I'm trying to capture can't be drawn. I'm wondering if this is because of something related to this note in the documentation for [CALayer renderInContext]:
"Important: The Mac OS X v10.5 implementation of this method does not support the entire Core Animation composition model. QCCompositionLayer, CAOpenGLLayer, and QTMovieLayer layers are not rendered. Additionally, layers that use 3D transforms are not rendered, nor are layers that specify backgroundFilters, filters, compositingFilter, or a mask values. Future versions of Mac OS X may add support for rendering these layers and properties."