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RPAlertView blocks based wrapper around UIALertView that uses objc_setAssociatedObject to bind the lifetime of the wrapper to the alert view.

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LICENSE
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Copyright (C) 2011 by TrikeApps Pty Ltd
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
RPAlertView.h
Objective-C
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//
// RPAlertView.h
// Radiopaedia
//
// Created by Wesley Moore on 22/11/11.
// Copyright (c) 2011 TrikeApps. All rights reserved.
//
 
#import <Foundation/Foundation.h>
 
typedef void(^RPAlertViewButtonBlock)(void);
 
@interface RPAlertView : NSObject <UIAlertViewDelegate>
 
+ (void)presentError:(NSError *)error;
 
- (id)initWithTitle:(NSString *)title message:(NSString *)message;
- (void)addButtonWithTitle:(NSString *)title block:(RPAlertViewButtonBlock)buttonBlock;
- (void)show;
 
@end
RPAlertView.m
Objective-C
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//
// RPAlertView.m
// Radiopaedia
//
// Created by Wesley Moore on 22/11/11.
// Copyright (c) 2011 TrikeApps. All rights reserved.
//
 
#import <objc/runtime.h>
#import "RPAlertView.h"
 
@interface RPAlertView ()
 
@property(nonatomic, retain) UIAlertView *alertView;
@property(nonatomic, retain) NSMutableArray *buttons;
 
@end
 
@implementation RPAlertView
 
@synthesize alertView=_alertView;
@synthesize buttons=_buttons;
 
+ (void)presentError:(NSError *)error
{
NSString *message = [error localizedDescription];
if (message == nil) message = NSLocalizedString(@"Cause unknown, no reason given.", @"Unknown error cause message");
 
RPAlertView *alert = [[RPAlertView alloc] initWithTitle:NSLocalizedString(@"Error", nil)
message:message];
[alert addButtonWithTitle:NSLocalizedString(@"OK", nil) block:nil];
[alert show];
}
 
- (id)initWithTitle:(NSString *)title message:(NSString *)message
{
self = [super init];
if (self != nil) {
// Associate self with the alert view so that its lifetime is bound to the
// UIAlertView's.
// See http://twitter.com/bbum/status/3609098005 for the use of _cmd for the key
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:title message:message delegate:self cancelButtonTitle:nil otherButtonTitles:nil];
objc_setAssociatedObject(alertView, _cmd, self, OBJC_ASSOCIATION_RETAIN);
self.alertView = alertView;
self.buttons = [NSMutableArray array];
}
 
return self;
}
 
- (void)addButtonWithTitle:(NSString *)title block:(RPAlertViewButtonBlock)buttonBlock
{
[self.alertView addButtonWithTitle:title];
[self.buttons addObject:buttonBlock != nil ? [buttonBlock copy] : [NSNull null]];
}
 
- (void)show
{
[self.alertView show];
}
 
#pragma mark - UIAlertViewDelegate
 
//- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
 
- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex
{
// buttonIndex can be -1 if there are no button on the alert
if (buttonIndex >= 0 && [self.buttons objectAtIndex:buttonIndex] != [NSNull null]) {
RPAlertViewButtonBlock block = [self.buttons objectAtIndex:buttonIndex];
block();
}
 
// Need to clean up the retain cycle between RPAlertView and UIAlertView
// UIAlertView retains RPAlertView (via obj_setAssociatedObject)
// RPAlertView retains UIAlertView (via alertView property)
 
// This breaks the retain cycle and causes the RPAlertView to be released,
// which in turn releases this UIAlertView.
SEL key = @selector(initWithTitle:message:);
objc_setAssociatedObject(self.alertView, key, nil, OBJC_ASSOCIATION_RETAIN);
}
 
@end

Why not just inherit from uialertview and add an instance variable?

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