Swift语言精要 - 属性

短命女 2021-12-24 13:27 283阅读 0赞

**1. Stored Property**

eg:

var number: Int = 0

**2. Computed Property**

eg:

var area : Double \{  
　　get \{  
　　　　return width \* height  
　　\}

...

完整代码如下:

class Rectangle {
        var width: Double = 0.0
        var height: Double = 0.0
        var area : Double {
            // computed getter
            get {
                return width * height
            }
            // computed setter
            set {
                // Assume equal dimensions (i.e., a square)
                width = sqrt(newValue)
                height = sqrt(newValue)
            }
        }
    }

测试代码:

var rect = Rectangle()
    rect.width = 3.0
    rect.height = 4.5
    rect.area // = 13.5
    rect.area = 9 // width & height now both 3.0

**3. Property Observer(属性观察者)**

class PropertyObserverExample {
        var number : Int = 0 {
            willSet(newNumber) {
                println("About to change to \(newNumber)")
            }
            didSet(oldNumber) {
                println("Just changed from \(oldNumber) to \(self.number)!")
            }
        }
    }

测试代码如下：

var observer = PropertyObserverExample()
    observer.number = 4
    // prints "About to change to 4", then "Just changed from 0 to 4!"

**4. Lazy Property(属性迟绑定)**

class SomeExpensiveClass {
        init(id : Int) {
            println("Expensive class \(id) created!")
        }
    }
    
    class LazyPropertyExample {
        var expensiveClass1 = SomeExpensiveClass(id: 1)
        lazy var expensiveClass2 = SomeExpensiveClass(id: 2)    
        init() {
            println("First class created!")
        }
    }

测试代码如下:

var lazyExample = LazyPropertyExample()
    // prints "Expensive class 1 created", then "First class created!"
    lazyExample.expensiveClass1 // prints nothing, it's already created
    lazyExample.expensiveClass2 // prints "Expensive class 2 created!"

转载于:https://www.cnblogs.com/davidgu/p/5346042.html