blocks|key|105955|text|简化示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|105956|class+Shape+{
++++var+sideLength:+Double+{
++++get+{
++++++++return+self.sideLength
++++}
++++set+{
++++++++//+Implement+the+setter+here.
++++++++self.sideLength+=+newValue
++++}
++++}
}|code-block|syntax|javascript|105957|完整示例|105958|查看本例中的perimeter。|offset|length|style|CODE|105959|摘自:苹果公司。“Swift编程语言。”iBooks。https://itun.es/us/jEUH0.l|105960|class+EquilateralTriangle:+NamedShape+{
++++var+sideLength:+Double+=+0.0

++++init(sideLength:+Double,+name:+String)+{
++++++++self.sideLength+=+sideLength
++++++++super.init(name:+name)
++++++++numberOfSides+=+3
++++}

++++var+perimeter:+Double+{
++++get+{
++++++++return+3.0+*+sideLength
++++}
++++set+{
++++++++sideLength+=+newValue+/+3.0
++++}
++++}

++++override+func+simpleDescription()+->+String+{
++++++++return+"An+equilateral+triagle+with+sides+of+length+\(sideLength)."
++++}
}
var+triangle+=+EquilateralTriangle(sideLength:+3.1,+name:+"a+triangle")
triangle.perimeter
triangle.perimeter+=+9.9
triangle.sideLength”|105961|entityMap|0|LINK|mutability|MUTABLE|url|https://itun.es/us/jEUH0.l^0|0|0|0|6|9|0|R|Q|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|13|8|@$K|14|L|15|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|16|8|@]|9|@$K|17|L|18|1|19]]|A|$]]|$1|Q|3|R|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

<h2>Simplified Example:</h2>

<pre><code>class Shape {
    var sideLength: Double {
    get {
        return self.sideLength
    }
    set {
        // Implement the setter here.
        self.sideLength = newValue
    }
    }
}
</code></pre>

<h2>Full example</h2>

<p>Check out <code>perimeter</code> in this example.</p>

<p>Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. <a href="https://itun.es/us/jEUH0.l" rel="nofollow">https://itun.es/us/jEUH0.l</a></p>

<pre><code>class EquilateralTriangle: NamedShape {
    var sideLength: Double = 0.0

    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSides = 3
    }

    var perimeter: Double {
    get {
        return 3.0 * sideLength
    }
    set {
        sideLength = newValue / 3.0
    }
    }

    override func simpleDescription() -&gt; String {
        return "An equilateral triagle with sides of length \(sideLength)."
    }
}
var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
triangle.perimeter
triangle.perimeter = 9.9
triangle.sideLength”
</code></pre>


blocks|key|105998|text|不能重写存储属性的get/set，但可以使用属性观察器willSet/didSet|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|105999|var+totalSteps:+Int+=+0+{
++++willSet(newTotalSteps)+{
++++++++println("About+to+set+totalSteps+to+\(newTotalSteps)")
++++}
++++didSet+{
++++++++if+totalSteps+>+oldValue++{
++++++++++++println("Added+\(totalSteps+-+oldValue)+steps")
++++++++}
++++}
}|code-block|syntax|javascript|106000|willSet的默认参数名称为newValue，didSet的默认参数名称为oldValue，您也可以像在willSet(newTotalSteps)中那样自己命名它们。|106001|entityMap^0|9|3|D|3|R|7|Z|6|0|0|0|7|F|8|O|6|12|8|1H|M|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|N|$]]

<p>You can't override <code>get</code>/<code>set</code> for a stored property but you can use property observers <code>willSet</code>/<code>didSet</code>:</p>

<pre><code>var totalSteps: Int = 0 {
    willSet(newTotalSteps) {
        println("About to set totalSteps to \(newTotalSteps)")
    }
    didSet {
        if totalSteps &gt; oldValue  {
            println("Added \(totalSteps - oldValue) steps")
        }
    }
}
</code></pre>

<p>The default parameter names are <code>newValue</code> for <code>willSet</code> and <code>oldValue</code> for <code>didSet</code>, or you can name them yourself as in <code>willSet(newTotalSteps)</code>.</p>


blocks|key|4612604|text|如果你不想使用didSet，它有一个属性的值暂时错误的问题，你应该用一个计算属性来包装它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4612605|private+var+_foo:Int+=+0
var+foo:Int+{
++++get+{
++++++++return+_foo
++++}
++++set+{
++++++++if(newValue+>+999)+{
++++++++++++_foo+=+999
++++++++}+else+{
++++++++++++_foo+=+newValue
++++++++}
++++}
}|code-block|syntax|javascript|4612606|或者：|4612607|private+var+_foo:Int+=+0
var+foo:Int+{
++++get+{
++++++++return+_foo
++++}
++++set+{
++++++++guard+newValue+<=+999+else+{
++++++++++++_foo+=+999
++++++++++++return
++++++++}
++++++++_foo+=+newValue
++++}
}|4612608|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<p>If you don't want to use didSet, which has the problem that the property's value is temporarily wrong, you should wrap a computed property around it.</p>

<pre><code>private var _foo:Int = 0
var foo:Int {
    get {
        return _foo
    }
    set {
        if(newValue &gt; 999) {
            _foo = 999
        } else {
            _foo = newValue
        }
    }
}
</code></pre>

<p>Or:</p>

<pre><code>private var _foo:Int = 0
var foo:Int {
    get {
        return _foo
    }
    set {
        guard newValue &lt;= 999 else {
            _foo = 999
            return
        }
        _foo = newValue
    }
}
</code></pre>


<p>How do I overwrite the setter of stored property in Swift?</p>

<p>In Obj-C, I can overwrite its setter, but Swift doesn't seem to be happy about getter/setters being used for stored property.</p>

<p>Say I have a <code>Card</code> class with a property called <code>rank</code>. I don't want the client to give it any invalid value, therefore, in objective-C, I can overwrite <code>setRank</code> so that it performs additional check. But <code>willSet</code> in Swift doesn't seem to help because <code>newValue</code> is constant and it makes no sense to assign <code>rank</code> because setter will be called in a loop.</p>


Swift Programming: getter/setter in stored property

如何覆盖Swift中存储属性的setter？在Obj-C中，我可以覆盖它的setter，但是Swift似乎不喜欢getter/setter用于存储属性。假设我有一个带有一个名为rank的属性的Card类。我不希望客户端给它任何无效值，因此，在objective-C中，我可以重写setRank，以便它执行额外的检查。但是...

问Swift编程:存储属性中的getter/setter
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