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46 lines
2.3 KiB
HTML
46 lines
2.3 KiB
HTML
When it comes time to present errors or other messages in iOS with
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[UIAlertView] it is immediately obvious that a more convenient interface
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would involve the use of blocks. A [search on GitHub][github-search]
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shows just about every iOS developer has had the same thought and had a crack at it.
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[UIAlertView]: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIAlertView_Class/UIAlertView/UIAlertView.html
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[github-search]: https://github.com/search?type=Repositories&language=&q=uialertview&repo=&langOverride=&x=14&y=17&start_value=1
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After reviewing the better options (I.e. those that actually had a
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README with more than a few lines of content) on GitHub it appeared
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that one of the challenges was how to handle memory. This stems from
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the wrapper becoming the delegate for the UIAlertView but not having a
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strong reference from the caller. I saw various solutions to this, most
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involving adding a extra retain call to keep everything around until the
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delegate methods were called.
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Since my project is using ARC I looked for a solution that
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didn't involve marking the wrapper file as non-ARC and
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invoking `retain`. The solution I came up with was to use
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[`objc_setAssociatedObject`][set-object]. This Objective-C runtime
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function allows one object to be associated with another using various
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memory management strategies. I used this to associate the UIAlertView
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blocks based wrapper with the UIAlertView.
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[set-object]: http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocAssociativeReferences.html
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In the `init` method the wrapper instance is associated with its UIAlertView:
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objc_setAssociatedObject(alertView, _cmd, self, OBJC_ASSOCIATION_RETAIN);
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Note that I'm using the implicit second argument to the method, its
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selector, `_cmd` as the key for the associated object. This was
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suggested in a [tweet by Bill Bumgarner][bbum].
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[bbum]: http://twitter.com/bbum/status/3609098005
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Then in `alertView:didDismissWithButtonIndex:`, the association
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is removed, `dealloc` of the wrapper called as a result and the
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`UIAlertView` also released.
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SEL key = @selector(initWithTitle:message:);
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objc_setAssociatedObject(self.alertView, key, nil, OBJC_ASSOCIATION_RETAIN);
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The full [MIT licensed code][gist] is available as a [gist on GitHub][gist].
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[gist]: https://gist.github.com/1392611
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