Swift标准库协议--CustomStringConverti

在调试的时候总会发现在输出自定义的类与结构体时,会打印很多不想输出的变量,这就有了CustomStringConvertible,CustomDebugStringConvertible这两个协议的用处.

1 .Struct 中的应用

首先定义一个结构体,输出这个结构体,看 print 的结果:

struct Person {
    var age: Int
    var name: String
    var job: String
}

let meetings = Person(age: 24, name: "haha", job: "iOSDeveloper")

print(meetings)
/**
 *  "Person(age: 24, name: "haha", job: "iOSDeveloper")\n"
 */

如果让 Struct inheritance [CustomStringConvertible,CustomDebugStringConvertible],再看一下输出结果

struct Person:CustomStringConvertible,CustomDebugStringConvertible {
    var age: Int
    var name: String
    var job: String
    
    var description: String {
        return "\(age) \(name) \(job)"
    }
    
    var debugDescription: String {
        return "\(name) \(age) \(job)"
    }
}

let meetings = Person(age: 24, name: "haha", job: "iOSDeveloper")
print(meetings)
/**
 *  "24 haha iOSDeveloper\n"
 */
debugPrint(meetings)
/**
 *  "haha 24 iOSDeveloper\n"
 */

可以自定义输出的参数,这样在调试的时候就会方便很多,好处还有不少,就不一一列举.

2 .Class 中的应用

定义一个类的话, print 并不会输出类中的变量

class Wheel {
    var spokes: Int = 0
    var diameter: Double = 0.0
    
    init(spokes:Int = 32,diameter:Double = 26.0) {
        self.spokes = spokes
        self.diameter = diameter
    }
    
    func removeSpokes() {
        spokes = spokes > 0 ? spokes-- : spokes
    }
}

var wheel = Wheel(spokes: 36,diameter: 29)
print(wheel)
/**
 *  "Wheel\n"
 */

如果想要改变 print 的输出结果,最好用 Extension

class Wheel {
    var spokes: Int = 0
    var diameter: Double = 0.0
    
    init(spokes:Int = 32,diameter:Double = 26.0) {
        self.spokes = spokes
        self.diameter = diameter
    }
    
    func removeSpokes() {
        spokes = spokes > 0 ? spokes-- : spokes
    }
}

extension Wheel: CustomDebugStringConvertible,CustomStringConvertible {
    var description: String {
        return "wheel has \(spokes) spokes"
    }
    
    var debugDescription: String {
        return "wheel has \(spokes) spokes spokes "
    }
}

var wheel = Wheel(spokes: 36,diameter: 29)
print(wheel)
/**
 *  "wheel has 36 spokes\n"
 */
debugPrint(wheel)
/**
 *  "wheel has 36 spokes spokes \n"
 */

3 ViewController,NSObject 中的应用

如果想要改变一个 ViewController 中的 print 方法,
先看没有默认的输出结果

class WheelsViewController: UIViewController {
    var wheels = [Wheel]()
}

var wheels = WheelsViewController()
print(wheels)
/**
 *  "<__lldb_expr_124.WheelsViewController: 0x7fb91a634dc0>\n"
 */

这里只输出了className 一届内存地址,如果想要改变,并不能用 Extension 的方法,因为 UIViewController已经inheritance了这两个协议,那么就只能用 override 来实现 DIY 的 print

class WheelsViewController: UIViewController {
    var wheels = [Wheel]()
}

extension WheelsViewController {
    override var description: String {
        return "wheelsViewController has \(wheels)"
    }
    
    override var debugDescription: String {
        return "DEBUG__wheelsViewController has \(wheels)"
    }
}

var w = WheelsViewController()
w.wheels = [wheel]
print(w)
/**
 *  "wheelsViewController has [wheel has 36 spokes spokes ]\n"
 */
debugPrint(w)
/**
 * "DEBUG__wheelsViewController has [wheel has 36 spokes spokes ]\n"
 */

这样就得到了我们想要 print 出来的信息,方便了调试.