代码之家 › 专栏 › 技术社区 › aunnnn

如何检查通用视图类是否实际实现了init(帧:)?

generics swift ios

aunnnn · 技术社区 · 6 年前

假设我有一个带有指定初始值设定项的自定义uiview子类:

class MyView: UIView {

    init(custom: String) {
        super.init(frame: .zero)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}

如我所料不能呼叫 MyView(frame: .zero) 因为它不是 automatically inherited 从 UIView .

那么假设我有一个视图生成器类:

class Builder<V: UIView> {
    func build() -> V? {
        // Check if can call init(frame:) or not
        if V.instancesRespond(to: #selector(V.init(frame:))) {
            return V.init(frame: .zero) // <-- Crash here, because the check doesn't work
        } else { 
            return nil 
        }
    }
}

这里我先检查了自定义视图 V 有 init(frame:) 或者不,如果是的话,那就叫它。

但是,它不起作用, Builder<MyView>().build() 将与以下对象碰撞:

致命错误:对类“ulldb_expr_14.myview”使用了未实现的初始值设定项“init(frame:)”

V.instancesRespond(to: #selector(V.init(frame:))) 总是返回 true ,使此支票无效。(或者我用错了吗?)

问题:如何检查通用视图类 V 实际响应 初始化(帧:) ?

更新1: V.responds(to: #selector(V.init(frame:))) false MyView

framework

enum ViewBuildMethod {
    case nib
    case nibName(String)
    case frame(CGRect)
    case custom(() -> UIView)
}

protocol SomeViewProtocol where Self: UIView {

    // ... other funcs

    static func buildMethod() -> ViewBuildMethod
}

override init(frame:) fatalError buildMethod .frame(.zero)

class MyView: UIView, SomeViewProtocol {

    init(custom: String) {
        super.init(frame: .zero)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    // ILLEGAL!!
    static func buildMethod() -> ViewBulidMethod {
        return .frame(.zero) // <-- Illegal, the framework will call V.init(frame: .zero) eventually
    }

    // LEGAL
    // static func buildMethod() -> ViewBuildMethod {
    //     return .custom({ () -> UIView in
    //         return MyView(custom: "hello")
    //     })
    // }
}

V.init(frame:) is called indirectly but V doesn't override this designated initializer. Please override init(frame:) to fix this issue

3 回复 | 直到 6 年前

Taras Chernyshenko 6 年前

UIView init(frame:)

instancesRespond(to:) true

protocol

Buildable init(frame: CGRect)

protocol Buildable {
    init(frame: CGRect)
}

class MyView: UIView, Buildable {...}

Builder

class Builder<V: Buildable>  {
    func build() -> V? {
        return V(frame: .zero)
    }
}

Builder<MyView>().build() compile-time

class SecondView: UIView {
    init(custom: String) {
        super.init(frame: .zero)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}

Builder<SecondView>().build()

error: type 'SecondView' does not conform to protocol 'Buildable'
Builder<SecondView>().build()

sang 6 年前

Cristik 6 年前

init(frame:)

var methodCount: UInt32 = 0
let methods = class_copyMethodList(MyView.self, &methodCount)!      
for i in 0..<methodCount {
    let method = method_getName(methods[Int(i)])
    print(method, method_getImplementation(methods[Int(i)]))
}
let method = class_getMethodImplementation(UIView.self,  #selector(UIView.init(frame:)))!
print("UIView's init(frame:)",method_getImplementation(method))

initWithCoder: 0x00000001054125b0
initWithFrame: 0x0000000105412790
UIView's init(frame:) 0xffee1be8ffffee20

UIView