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copied!<p>I agree with @Inaziger analysis. The delegate of UITextField instance is a kind of weak reference. It does not hold the delegate assigned to it. According ARC, the delegate will be nil is no one hold a reference to it. Therefore, it will be up to assigner to keep it so the delegate will be called. You code prior workaround is something like this:</p> <pre><code>- (void) somemethod { ... id<UITextFieldDelegate> tempDelegate = [NumericTextFieldDelegate new]; textFieldName.delegate = tempDelegate; ... } </code></pre> <p>the instance of textFieldName got a reference to a delegate created locally in somethod. ARC will set temDelegate to nil after the method call. However, the text field's delegate still holds the a pointer to memory assigned to, which is released by ARC afterwards. That's why you got the bad memory access crash.</p> <p>By keeping the del as static var in your class, it will be kept during your app run cycle as long as you have not set it to nil. I think it is better to keep the static del as a class level member and to provide a setter so that you should remember to release it. Something like:</p> <pre><code>// in interface definition +(NumericTextFieldDelegate *) getDelegate; +(void) setDelegate:(id)newDel; // in implementation static NumericTextFieldDelegate* del; +(NumericTextFieldDelegate *) getDelegate { @synchronized(del) { if(del == nil) del = [NumericTextFieldDelegate new]; } return del; } +(void) setDelegate:(id)newDel { del = newDel; } </code></pre> <p>By the way, you can also keep your prior workaround codes as they are. You can keep the delegate in the class of text field as a class member variable or property.</p> <pre><code>@interface myTextFieldContainer () { @proerpty (strong) id<UITextFieldDelegate> delHolder; ... } @implementaion myTextFieldContainer { @sythysis delHolder = _delHodler; ... self.delHolder = [NumericTextFieldDelegate new]; textFieldName.delegate = self.delHolder; </code></pre> <p>The benefit of above strategy is that you would not worry about release the delegate when your view controller is gone.</p>

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