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POHow to interact with layer-backed views on the Mac
 

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  1. POHow to interact with layer-backed views on the Mac
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    <p>I am designing a user interface containing several labels and text fields. I would like to style the UI like this:</p> <ol> <li>setting a background pattern for the content view of my <code>NSWindow</code></li> <li>adding a custom icon to the background in the upper left corner</li> </ol> <p>I solved the first problem by making the content view a <em>layer-backed view</em> as described in <a href="http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ApplicationKit/Classes/NSView_Class/Reference/NSView.html" rel="nofollow noreferrer">Apple's documentation of <code>NSView</code></a>:</p> <blockquote> <p>A layer-backed view is a view that is backed by a Core Animation layer. Any drawing done by the view is the cached in the backing layer. You configured a layer-backed view by simply invoking <code>setWantsLayer:</code> with a value of <code>YES</code>. The view class will automatically create the a backing layer for you, and you use the view class’s drawing mechanisms. <strong>When using layer-backed views you should never interact directly with the layer.</strong></p> <p>A layer-hosting view is a view that contains a Core Animation layer that you intend to manipulate directly. You create a layer-hosting view by instantiating an instance of a Core Animation layer class and setting that layer using the view’s <code>setLayer:</code> method. After doing so, you then invoke <code>setWantsLayer:</code> with a value of <code>YES</code>. <strong>When using a layer-hosting view you should not rely on the view for drawing, nor should you add subviews to the layer-hosting view.</strong></p> </blockquote> <p>and then generating a <code>CGColorRef</code> out of a <code>CGPattern</code> which draws my <code>CGImage</code>:</p> <pre><code>NSView *mainView = [[self window]contentView]; [mainView setWantsLayer:YES]; </code></pre> <p>To set the background image as a pattern I used the answer from <a href="https://stackoverflow.com/questions/2520978/how-to-tile-the-contents-of-a-calayer">How to tile the contents of a CALayer</a> here on SO to get the first task done.</p> <p>However for the second task, adding the icon I used the code below:</p> <pre><code>CGImageRef iconImage = NULL; NSString *path = [[NSBundle mainBundle] pathForResource:@"icon_128" ofType:@"png"]; if(path != nil) { NSURL *imageURL = [NSURL fileURLWithPath:path]; provider = CGDataProviderCreateWithURL((CFURLRef)imageURL); iconImage = CGImageCreateWithPNGDataProvider(provider,NULL,FALSE,kCGRenderingIntentDefault); CFRelease(provider); } CALayer *iconLayer = [[CALayer alloc] init]; // layer is the mainView's layer CGRect layerFrame = layer.frame; CGFloat iconWidth = 128.f; iconLayer.frame = CGRectMake(0.f, CGRectGetHeight(layerFrame)-iconWidth, 128.f, 128.f); iconLayer.contents = (id)iconImage; CGImageRelease(iconImage); [layer insertSublayer:iconLayer atIndex:0]; [iconLayer release]; </code></pre> <h2>The Questions</h2> <ol> <li>I am not sure if I am violating Apple's restrictions concerning <em>layer-backed</em> views that you should never interact directly with the layer. When setting the layer's background color <em>I am</em> interacting directly with the layer or am I mistaken here?</li> <li>I have a bad feeling about interacting with the layer hierarchy of a <em>layer-backed</em> view directly and inserting a new layer like I did for my second task. Is this possible or also violating Apple's guidelines? I want to point out that this content view of course has several subviews such as labels, a text view and buttons.</li> <li>It seems to me that just using one single <em>layer-hosting</em> <code>NSView</code> seems to be the cleanest solution. All the text labels could then be added as <code>CATextLayers</code> etc. However if I understand Apple's documentation correctly I cannot add any controls to the view anymore. Would I have to code all the controls myself in custom <code>CALayers</code> to get it working? Sounds like reinventing the wheel <em>de luxe</em>. I also have no idea how one would code a <code>NSTextField</code> solely in CoreAnimation.</li> </ol> <p>Any advice on how split designing user interfaces with CoreAnimation and standard controls is appreciated.</p> <p><strong>Please note that I am talking about the Mac here.</strong></p>
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