UITextFieldDelegate 与 UITextField 控件事件
如果我想处理 UITextField 的更改，例如用户在其中键入；看起来这可以通过将委托分配给该文本字段，然后让委托实现 shouldChangeCharactersInRange 来完成，或者通过将目标添加到文本字段并处理 UIControlEventEditingChanged 事件来完成。
除了使用委托方法，您可以返回 NO 并因此阻止用户进行编辑之外，这两件事之间有什么区别吗？
处理编辑开始或编辑结束的问题相同。可以使用适当的委托方法或适当的事件来完成。如果控制事件可以完成必要的工作，那么 textField 委托实际上有什么用？
If I want to handle changes to a UITextField, such as the user typing in it; it seems like this can be done either by assigning a delegate to that text field, and then having the delegate implement shouldChangeCharactersInRange, or by adding a target to the textField, and handling the UIControlEventEditingChanged event.
Aside from the fact that with the delegate method, you can return NO and therefor stop the user from making the edit, is there any difference between these 2 things?
Same question for handling the beginning of editing or the ending of editing. It could be done either with the appropriate delegate methods or with the appropriate events. What is the textField delegate actually for if the control events can do the necessary work?
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shouldChangeCharactersInRange在更改发生之前调用，让您有机会“取消”更改。UIControlEventEditingChanged在更改发生后调用。您可以在
shouldChangeCharactersInRange中确定 textField 的结果值，但您必须使用提供的范围手动将 replacementString 应用于现有文本。 （通过NSString stringByReplacingCharactersInRange）。如果您想知道生成的文本，使用UIControlEventEditingChanged会更简单、更高效。shouldChangeCharactersInRange通常用于实现输入的验证检查 - 也就是说，您可以在输入时过滤字符/粘贴的文本。例如，如果字段用于电话号码，则当用户键入非数字字符或尝试粘贴非数字文本时，您可以返回FALSE。如果您坚持使用 UIControlEvent 方法，您可能会发现可以为多个控件重用代码。
shouldChangeCharactersInRangeis called before a change occurs, and gives you opportunity to 'cancel' the change.UIControlEventEditingChangedis called after the change occurred.You can determine the resulting value of the textField in
shouldChangeCharactersInRange, but you have to manually apply the replacementString to the existing text, using the supplied range. (viaNSString stringByReplacingCharactersInRange). If you want to know the resulting text, it's easier and more efficient to useUIControlEventEditingChanged.shouldChangeCharactersInRangeis often used to implement validation checking of input - that is, you can filter characters/pasted text as it is entered. If a field is for phone numbers, for example, you can returnFALSEif the user types a non numeric character, or attempts to paste in text that isn't numeric.You might find a case where you can reuse code for multiple controls if you can stick with the
UIControlEvent-methods.你说得对;你基本上可以通过两者做同样的事情，但是 UIControl 级别较低，可以让你通过
[UIControl addTarget:action:forControlEvents:]将每个特定的 UIEvent 虹吸到不同的目标，因为只有一个代表。我还想说 UITextField 委托协议< /a> 只是 UIControl/UIEvent 的更方便、更高级别的替代方案，作为管理 UITextField 行为的方法。
最常见的委托模式是 UITableView DataSource 和 Delegate，我想说使用 UITextField 委托协议非常相似，因此看起来比直接从 UIControl 处理消息更直接，具有更明确的意图。
You're right; you can essentially do the same thing via both, but UIControl is lower level and lets you siphon off each particular UIEvent to different targets via
[UIControl addTarget:action:forControlEvents:]where as there is only a single delegate.I would also say that the UITextField delegate protocol is simply there as a more convenient, higher level alternative to UIControl/UIEvent as a way to manage the behaviour of a UITextField.
The most common delegate pattern is UITableView DataSource and Delegate and I would say that using the UITextField delegate protocol is quite similar and therefore looks far more straight forward with more defined intentions than handing the messages from UIControl directly.
我发现原始问题中提出的两种方法之间的一个关键区别是，委托
“shouldChangeCharactersInRange”在之前调用UITextField更改。UIControlEventEditingChanged的目标在UITextField中的值发生更改之后被调用。如果您使用这些事件来确保（例如）在启用“完成”按钮之前对话框中的所有字段都已完全填写，则目标方法可能更适合您。它对我有用。
One key difference I've found between the two approaches posed in the original question is that the delegate
"shouldChangeCharactersInRange"gets called BEFORE the value in theUITextFieldchanges. The target forUIControlEventEditingChangedgets called AFTER the value in theUITextFieldchanges.In the case that you're using these events to make sure (for example) that all fields in a dialog are completely filled in before enabling a "Done" button, the target approach may work better for you. It did for me.
委托方法是同质化
UITextField和UITextView行为的方法。UITextView没有控件事件。相反，UITextFieldDelegate和UITextviewDelegate提供并行方法。The delegation approach is the way to homogenize
UITextFieldandUITextViewbehavior.UITextViewdoes not have control events. In contrast,UITextFieldDelegateandUITextviewDelegateprovide parallel methods.我发现
shouldChangeCharactersInRange传递相同的NSRange来插入和删除文本。您附加一个空格，然后将其删除，并且来自shouldChangeCharactersInRange的参数与文本的重复部分没有区别。因此，shouldChangeCharactersInRange 实际上无法预测结果文本。
I have found out that
shouldChangeCharactersInRangepasses the sameNSRangefor insertion and deletion of text. You append a space and then delete it, and the parameters fromshouldChangeCharactersInRangeare indistinguishable from duplication of the text.So
shouldChangeCharactersInRangeactually cannot predict the resulting text.