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POSelection Highlight in NSCollectionView
 

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    <p>I have a working <code>NSCollectionView</code> with one minor, but critical, exception. Getting and highlighting the selected item within the collection.</p> <p>I've had all this working prior to Snow Leopard, but something appears to have changed and I can't quite place my finger on it, so I took my <code>NSCollectionView</code> right back to a basic test and followed Apple's documentation for creating an NSCollectionView here:</p> <p><a href="http://developer.apple.com/mac/library/DOCUMENTATION/Cocoa/Conceptual/CollectionViews/Introduction/Introduction.html" rel="noreferrer">http://developer.apple.com/mac/library/DOCUMENTATION/Cocoa/Conceptual/CollectionViews/Introduction/Introduction.html</a></p> <p>The collection view works fine following the quick start guide. However, this guide doesn't discuss selection other than <code>"There are such features as incorporating image views, setting objects as selectable or not selectable and changing colors if they are selected"</code>. </p> <p>Using this as an example I went to the next step of binding the Array Controller to the <code>NSCollectionView</code> with the controller key <code>selectionIndexes</code>, thinking that this would bind any selection I make between the <code>NSCollectionView</code> and the array controller and thus firing off a KVO notification. I also set the <code>NSCollectionView</code> to be selectable in IB.</p> <p>There appears to be no selection delegate for <code>NSCollectionView</code> and unlike most Cocoa UI views, there appears to be no default selected highlight.</p> <p>So my problem really comes down to a related issue, but two distinct questions.</p> <ol> <li>How do I capture a selection of an item?</li> <li>How do I show a highlight of an item?</li> </ol> <p><code>NSCollectionView</code>'s programming guides seem to be few and far between and most searches via Google appear to pull up pre-Snow Leopard implementations, or use the view in a separate XIB file.</p> <p>For the latter (separate XIB file for the view), I don't see why this should be a pre-requisite otherwise I would have suspected that Apple would not have included the view in the same bundle as the collection view item.</p> <p>I know this is going to be a "can't see the wood for the trees" issue - so I'm prepared for the "doh!" moment.</p> <p>As usual, any and all help much appreciated.</p> <p><strong>Update 1</strong></p> <p>OK, so I figured finding the selected item(s), but have yet to figure the highlighting. For the interested on figuring the selected items (assuming you are following the Apple guide):</p> <p>In the controller (in my test case the App Delegate) I added the following:</p> <p><em>In awakeFromNib</em></p> <pre><code>[personArrayController addObserver:self forKeyPath:@"selectionIndexes" options:NSKeyValueObservingOptionNew context:nil]; </code></pre> <p><em>New Method</em></p> <pre><code>-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { if([keyPath isEqualTo:@"selectionIndexes"]) { if([[personArrayController selectedObjects] count] &gt; 0) { if ([[personArrayController selectedObjects] count] == 1) { personModel * pm = (PersonModel *) [[personArrayController selectedObjects] objectAtIndex:0]; NSLog(@"Only 1 selected: %@", [pm name]); } else { // More than one selected - iterate if need be } } } </code></pre> <p><em>Don't forget to dealloc for non-GC</em></p> <pre><code>-(void)dealloc { [personArrayController removeObserver:self forKeyPath:@"selectionIndexes"]; [super dealloc]; } </code></pre> <p>Still searching for the highlight resolution...</p> <p><strong>Update 2</strong></p> <p>Took Macatomy's advice but still had an issue. Posting the relevant class methods to see where I've gone wrong.</p> <p><em>MyView.h</em></p> <pre><code>#import &lt;Cocoa/Cocoa.h&gt; @interface MyView : NSView { BOOL selected; } @property (readwrite) BOOL selected; @end </code></pre> <p><em>MyView.m</em></p> <pre><code>#import "MyView.h" @implementation MyView @synthesize selected; -(id)initWithFrame:(NSRect)frame { self = [super initWithFrame:frame]; if (self) { // Initialization code here. } return self; } -(void)drawRect:(NSRect)dirtyRect { NSRect outerFrame = NSMakeRect(0, 0, 143, 104); NSRect selectedFrame = NSInsetRect(outerFrame, 2, 2); if (selected) [[NSColor yellowColor] set]; else [[NSColor redColor] set]; [NSBezierPath strokeRect:selectedFrame]; } @end </code></pre> <p><em>MyCollectionViewItem.h</em></p> <pre><code>#import &lt;Cocoa/Cocoa.h&gt; @class MyView; @interface MyCollectionViewItem : NSCollectionViewItem { } @end </code></pre> <p>"MyCollectionViewItem.m*</p> <pre><code>#import "MyCollectionViewItem.h" #import "MyView.h" @implementation MyCollectionViewItem -(void)setSelected:(BOOL)flag { [(MyView *)[self view] setSelected:flag]; [(MyView *)[self view] setNeedsDisplay:YES]; } @end </code></pre>
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