blocks|key|2198972|text|对于第一个问题，您应该只扩展UIView并检查它是标签、文本字段还是带有if+let的文本视图。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2198973|extension+UIView+{
++++func+getText()+->+String+{
++++++++if+let+label+=+self+as?+UILabel+{
++++++++++++return+label.text+??+""
++++++++}+else+if+let+textField+=+self+as?+UITextField+{
++++++++++++return+textField.text+??+""
++++++++}+else+if+let+textView+=+self+as?+UITextView+{
++++++++++++return+textView.text+??+""
++++++++}

++++++++return+""
++++}
}|code-block|syntax|javascript|2198974|与创建协议相比，这种方法的优点是您可以轻松地扩展它，即使文本/标题可以用另一种方法检索，例如，使用UIButton。|2198975|[...]
else+if+let+button+=+self+as?+UIButton+{
++++return+button.title(for:+.normal)+??+""
}|2198976|entityMap^0|E|6|10|6|0|0|1D|8|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|P|$]]

For the first problem, you should only extend <code>UIView</code> and check whether its a label, a text field or a text view with <code>if let</code>.

<pre><code>extension UIView {
 func getText() -&gt; String {
 if let label = self as? UILabel {
 return label.text ?? ""
 } else if let textField = self as? UITextField {
 return textField.text ?? ""
 } else if let textView = self as? UITextView {
 return textView.text ?? ""
 }

 return ""
 }
}
</code></pre>

The advantage of this method over creating a protocol is that you can easily extend it, even if the text/title is retrievable with another method, for example, with a <code>UIButton</code>.

<pre><code>[...]
else if let button = self as? UIButton {
 return button.title(for: .normal) ?? ""
}
</code></pre>

blocks|key|932529|text|创建带有扩展的协议，然后扩展每个类以采用该协议:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|932530|protocol+GetTextProtocol+{
++++var+text:+String?+{get}
++++func+getText()+->+String
}

extension+GetTextProtocol+{
++++func+getText()+->+String+{
++++++++return+self.text+??+""
++++}
}

extension+UILabel:+GetTextProtocol+{
++++var+text:+String?+{
+++++++++return+self.text
++++}
}
extension+UITextView:+GetTextProtocol+{
++++var+text:+String?+{
++++++++return+self.text
++++}++++
}|code-block|syntax|javascript|932531|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Create a protocol with an extension and then extend every class to adopt the protocol :)

<pre><code>protocol GetTextProtocol {
 var text: String? {get}
 func getText() -&gt; String
}

extension GetTextProtocol {
 func getText() -&gt; String {
 return self.text ?? ""
 }
}

extension UILabel: GetTextProtocol {
 var text: String? {
 return self.text
 }
}
extension UITextView: GetTextProtocol {
 var text: String? {
 return self.text
 } 
}
</code></pre>

blocks|key|1101620|text|这里有一些可疑的东西:我不希望任何toInt()函数在出错时只返回-1或0。Swift有一个很好的选择系统是有原因的，并且返回-1或0引入了几个明显的陷阱。我也不知道您计划如何在getText()上实现UIView。很多视图都没有文本。我不知道这个实现意味着什么，也不知道会做什么。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1101621|因此，我将忽略这两个细节，将重点放在主要问题上，这似乎是扩展的冗余。有一个更干净的方法，通过协议扩展，减少重复。|1101622|protocol+TextProviding+{
++++var+text:+String?+{+get+}
}

extension+TextProviding+{
++++//+Following+your+example+here.+I+would+prefer+calling
++++//+this+a+`var+textOrEmpty:+String`+but+same+idea.
++++func+getText()+->+String+{
++++++++return+text+??+""
++++}
}

//+To+conform+additional+types,+you+just+need+1+line
extension+UILabel:+TextProviding+{+}
extension+UITextField:+TextProviding+{+}|code-block|syntax|javascript|1101623|编辑：正如一些人指出的，在extension+UITextView:+TextProviding+{+}中使用上面的代码是行不通的，因为UITextView的text是一个String!，而不是String?。不幸的是，这意味着如果您希望这也适用于UITextView，您应该将var+text要求重命名为其他东西(这意味着您需要几行额外的代码来手动遵守UILabel和<+code+>D13)。|BOLD|1101624|protocol+TextProviding+{
++++var+string:+String?+{+get+}
}

extension+TextProviding+{
++++var+stringOrEmpty:+String+{
++++++++return+string+??+""
++++}
}

extension+UILabel:+TextProviding+{+
++++var+string:+String?+{+return+text+}
}
extension+UITextField:+TextProviding+{+
++++var+string:+String?+{+return+text+}
}
extension+UITextView:+TextProviding+{
++++var+string:+String?+{+return+text+}
}|1101625|entityMap^0|H|7|2H|9|2T|6|0|0|0|0|2|D|13|1W|A|27|4|2E|7|2P|7|3V|8|4X|7|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|12|8|@$9|13|A|14|B|O]|$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|J|7|1J|8|@]|D|@]|E|$K|L]]|$1|R|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|S|$]]

There are a couple of dubious things here: I wouldn't want any <code>toInt()</code> function to just return -1 or 0 when things went wrong. Swift has a good optionality system for a reason, and there are several obvious pitfalls introduced by returning -1 or 0. I also don't know what you plan to do for implementing <code>getText()</code> on a <code>UIView</code>. Lots of views don't have text. I don't know what this implementation would mean or do.

So I'll ignore those two details and focus on the primary question, which seems to be the redundancy of your extensions. There is a cleaner way, via protocol extensions, to cut down on duplication.

<pre><code>protocol TextProviding {
 var text: String? { get }
}

extension TextProviding {
 // Following your example here. I would prefer calling
 // this a `var textOrEmpty: String` but same idea.
 func getText() -&gt; String {
 return text ?? ""
 }
}

// To conform additional types, you just need 1 line
extension UILabel: TextProviding { }
extension UITextField: TextProviding { }
</code></pre>

EDIT: as some have pointed out, using the above code with <code>extension UITextView: TextProviding { }</code> will not work, because <code>UITextView</code>'s <code>text</code> is a <code>String!</code>, not a <code>String?</code>. Unfortunately, this means if you want this to work for UITextView as well, you should rename the <code>var text</code> requirement to something else (and this means you will need a couple extra lines to manually conform <code>UILabel</code> and <code>UITextField</code>).

<pre><code>protocol TextProviding {
 var string: String? { get }
}

extension TextProviding {
 var stringOrEmpty: String {
 return string ?? ""
 }
}

extension UILabel: TextProviding { 
 var string: String? { return text }
}
extension UITextField: TextProviding { 
 var string: String? { return text }
}
extension UITextView: TextProviding {
 var string: String? { return text }
}
</code></pre>

blocks|key|1102304|text|这个单行比这里发布的所有其他答案减少了冗余代码(您想要的)。不需要疯狂的状态-检查或多个扩展。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1102305|extension+UIView+{
++++func+getText()+->+String?+{
++++++++return+self.responds(to:+#selector(getter:+UILabel.text))+?
++++++++self.perform(#selector(getter:+UILabel.text))?.takeUnretainedValue()+as?+String+:+nil
++++}
}|code-block|syntax|javascript|1102306|entityMap^0|2|2|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

This one-liner reduces redundant code (what you wanted) than all other answers posted here. No need for crazy condition-checks or multiple extensions.
<pre class="lang-swift prettyprint-override"><code>extension UIView {
 func getText() -&gt; String? {
 return self.responds(to: #selector(getter: UILabel.text)) ?
 self.perform(#selector(getter: UILabel.text))?.takeUnretainedValue() as? String : nil
 }
}
</code></pre>

For a lot of actions, I need to check if the content of <code>label.text</code>, <code>textView.text</code>, <code>textField.text</code> etc. is nil.

So I created some extensions:

<pre><code>extension UILabel {
 func getText() -&gt; String {
 return self.text ?? ""
 }
}

extension UITextField {
 func getText() -&gt; String {
 return self.text ?? ""
 }
}

extension UITextView {
 func getText() -&gt; String {
 return self.text ?? ""
 }
}
</code></pre>

The extensions are very redundant. A similar case is when I need to cast an <code>Int</code>, <code>Double</code>, <code>Float</code> etc. to another number format. What I want is a simple <code>toInt()</code> with a return of <code>-1</code> or <code>0</code> when something went wrong. 

So how can I create a generic function for the <code>toString()</code> or <code>toInt()</code>? I read about <a href="https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Extensions.html" rel="nofollow noreferrer">extensions</a> and <a href="https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html" rel="nofollow noreferrer">generics</a> in the Apple documentation, but I didn't see a solution for my problem.

Finally, I tried to expand <code>UIView</code> with the same extension, because it's a superclass of <code>UILabel</code> etc., but I can't call <code>getText()</code>.

So what is a good method to create generic extensions?

Generic `getText()` function for UI elements in Swift

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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对于很多操作，我需要检查label.text、textView.text、textField.text等的内容是否为零。所以我创建了一些扩展：extension UILabel {    func getText() -> String {        return self.text ?? ""    }}exte...

问Swift中UI元素的泛型``getText()‘函数
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问Swift中UI元素的泛型``getText()‘函数EN