blocks|key|1236416|text|这两种方法都是正确的，但有时您应该使用init()方法中的初始化。例如，这里不会设置barButton的target，因为self还不存在。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1236417|class+Foo+{
++++var+barButton+=+UIBarButtonItem(title:+"add",+style:+.Plain,+target:+self,+action:+#selector(self.someMethod))

++++init(){
++++++++//init+here
++++}
}|code-block|syntax|javascript|1236418|对于这种情况，正确的方法是：|1236419|class+Foo+{
++++var+barButton+:+UIBarButton?+

++++init(){
++++++++barButton+=+UIBarButtonItem(title:+"add",+style:+.Plain,+target:+self,+action:+#selector(self.someMethod))
++++}
}|1236420|总而言之，这两种方法都是正确的，但你必须考虑何时使用每种方法。有关它的更多信息，请访问Apple+documentation|1236421|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html^0|J|6|1G|6|1P|4|0|0|0|0|17|J|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|18|8|@]|D|@$9|19|A|1A|1|1B]]|E|$]]|$1|Q|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]]]

Both ways are correct, but sometimes you should use the initialization in <code>init()</code> method. For example, here the <code>target</code> for barButton will be not set, cause the <code>self</code> does not exist yet.

<pre><code>class Foo {
 var barButton = UIBarButtonItem(title: "add", style: .Plain, target: self, action: #selector(self.someMethod))

 init(){
 //init here
 }
}
</code></pre>

The correct way for this case is : 

<pre><code>class Foo {
 var barButton : UIBarButton? 

 init(){
 barButton = UIBarButtonItem(title: "add", style: .Plain, target: self, action: #selector(self.someMethod))
 }
}
</code></pre>

To sum up, both ways are correct, but you have to consider when to use each one.
More information about it on <a href="https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html" rel="nofollow noreferrer">Apple documentation</a>

blocks|key|2344708|text|实际上，你有5种初始化属性的方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2344709|没有正确的方法，方法取决于需要。|2344710|基本上声明像UILabel这样的对象总是-如果可能的话-作为常量(let)。|offset|length|style|CODE|2344711|这5种方式是：|2344712|声明行中的|2344713|Initialization|unordered-list-item|2344714|2344715|让label+=+UILabel(frame:...|2344716|Initialization在init方法中，您不必将该属性声明为隐式取消包装可选。|2344717|2344718|让标签:+UILabel+init()+{+...label+=+UILabel(frame:+...+)+...+}|2344719|前两种方法实际上是相同的。|2344720|2344721|Initialization在像viewDidLoad这样的方法中，在这种情况下，您必须将属性声明为(隐式取消包装)+optional，也声明为var|2344722|2344723|var标签:+UILabel！在viewDidLoad()上...}|2344724|Initialization+=+UILabel(frame:...)使用闭包分配默认(计算)值。当类被初始化时，闭包被调用一次，并且不可能在闭包中使用类的其他属性。|2344725|2344726|let标签:+UILabel+={+lbl+=+UILabel(frame:...)lbl.text+=+"Foo“return+lbl+}()使用闭包进行|2344727|延迟初始化。当第一次访问该属性时，闭包被调用(一次)，您可以使用该类的其他属性。|2344728|2344729|该属性必须声明为var|2344730|让labelText+=+"Bar“惰性变量标签:+UILabel+={+lbl+=+UILabel(frame:...)lbl.text+=+"Foo“%2B+self.labelText+return+lbl+}()|2344731|entityMap^0|0|0|6|7|X|3|0|0|0|0|0|0|F|4|0|0|0|0|0|G|B|20|3|0|0|0|0|0|0|0|0|8|3|0|0^^$0|@$1|2|3|4|5|6|7|1K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1L|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1M|8|@$F|1N|G|1O|H|I]|$F|1P|G|1Q|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|1R|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|1S|8|@]|9|@]|A|$]]|$1|N|3|O|5|P|7|1T|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1U|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|1V|8|@]|9|@]|A|$]]|$1|T|3|U|5|P|7|1W|8|@$F|1X|G|1Y|H|I]]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1Z|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|20|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|21|8|@]|9|@]|A|$]]|$1|10|3|-4|5|6|7|22|8|@]|9|@]|A|$]]|$1|11|3|12|5|P|7|23|8|@$F|24|G|25|H|I]|$F|26|G|27|H|I]]|9|@]|A|$]]|$1|13|3|-4|5|6|7|28|8|@]|9|@]|A|$]]|$1|14|3|15|5|6|7|29|8|@]|9|@]|A|$]]|$1|16|3|17|5|P|7|2A|8|@]|9|@]|A|$]]|$1|18|3|-4|5|6|7|2B|8|@]|9|@]|A|$]]|$1|19|3|1A|5|6|7|2C|8|@]|9|@]|A|$]]|$1|1B|3|1C|5|P|7|2D|8|@]|9|@]|A|$]]|$1|1D|3|-4|5|6|7|2E|8|@]|9|@]|A|$]]|$1|1E|3|1F|5|6|7|2F|8|@$F|2G|G|2H|H|I]]|9|@]|A|$]]|$1|1G|3|1H|5|6|7|2I|8|@]|9|@]|A|$]]|$1|1I|3|-4|5|6|7|2J|8|@]|9|@]|A|$]]]|1J|$]]

Actually you have 5 ways to initialize properties.

There is no correct way, the way depends on the needs. 
Basically declare objects like <code>UILabel</code> always – if possible – as constant (<code>let</code>).

The 5 ways are:

<ul>
<li>Initialization in the declaration line

<pre><code>let label = UILabel(frame:...
</code></pre></li>
<li>Initialization in the <code>init</code> method, you don't have to declare the property as implicit unwrapped optional.

<pre><code>let label: UILabel
init() { ... label = UILabel(frame:...) ... }
</code></pre></li>
</ul>

The first two ways are practically identical.

<ul>
<li>Initialization in a method like <code>viewDidLoad</code>, in this case you have to declare the property as (implicit unwrapped) optional and also as <code>var</code>

<pre><code>var label: UILabel!

on viewDidLoad()
 ...
 label = UILabel(frame:...)
}
</code></pre></li>
<li>Initialization using a closure to assign a default (computed) value. The closure is called once when the class is initialized and it is not possible to use other properties of the class in the closure.

<pre><code>let label: UILabel = {
 let lbl = UILabel(frame:...)
 lbl.text = "Foo"
 return lbl
}()
</code></pre></li>
<li>Lazy initialization using a closure. The closure is called (once) when the property is accessed the first time and you can use other properties of the class. 
The property must be declared as <code>var</code> 

<pre><code>let labelText = "Bar"

lazy var label: UILabel = {
 let lbl = UILabel(frame:...)
 lbl.text = "Foo" + self.labelText
 return lbl
}()
</code></pre></li>
</ul>

blocks|key|5815162|text|+var+label:+UILabel!+|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|5815163|上面的语句意味着，变量标签可以为空|unstyled|5815164|var+label+=+UILabel()|5815165|但在这里，它将保存一个标签值。因为内存是为该变量分配的。因此，它不会为零。|5815166|请在此处找到更多详细信息|5815167|What's+the+difference+between+var+label:+UILabel!+and+var+label+=+UILabel(+)?|offset|length|5815168|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/28734235/whats-the-difference-between-var-label-uilabel-and-var-label-uilabel^0|0|0|0|0|0|0|25|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|13|8|@]|9|@$O|14|P|15|1|16]]|A|$]]|$1|Q|3|-4|5|F|7|17|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

<pre><code> var label: UILabel! 
</code></pre>

The above statements means, the variable label may be nil

<pre><code>var label = UILabel()
</code></pre>

But here it will hold a label value. Because the memory is allocated for that variable. So it will not be nil.

Please find more details here

<a href="https://stackoverflow.com/questions/28734235/whats-the-difference-between-var-label-uilabel-and-var-label-uilabel">What&#39;s the difference between var label: UILabel! and var label = UILabel( )?</a>

I have a question about variables initialization in swift. 

I have two ways to initialize a variable (as "property" of a class in Objective-C).

Which of them is the most correct?

<pre><code>class Class {

 var label: UILabel!

 init() { ... label = UILabel() ... }

}
</code></pre>

or

<pre><code>class Class {

 var label = UILabel()

 init() { … }

}
</code></pre>

Swift Variables Initialization

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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我有一个关于swift中变量初始化的问题。我有两种方法来初始化一个变量(在Objective-C中作为类的“属性”)。他们中哪一个是最正确的？class Class {  var label: UILabel!  init() { ... label = UILabel() ... }}或class Class {  ...

问Swift变量初始化
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