无法推断通用参数“A”（Swift 4、Bond 和 ReactiveKit 框架从 Swift 2 迁移）答案

【问题标题】：Generic parameter 'A' could not be inferred (Swift 4, Bond and ReactiveKit frameworks migrating from Swift 2)无法推断通用参数“A”（Swift 4、Bond 和 ReactiveKit 框架从 Swift 2 迁移）
【发布时间】：2018-03-13 20:48:55
【问题描述】：

伙计们！我正在尝试从 Swift 2 迁移到 Swift 4。项目正在使用 Bond 和 ReactiveKit 框架。我有 UISearchBar 的扩展名。所以我面临着从这个迁移的问题：

import UIKit
import Bond
import ReactiveKit

public extension UISearchBar {
    public var bnd_delegate: ProtocolProxy {
        return protocolProxy(for: UISearchBarDelegate.self, setter: NSSelectorFromString("setDelegate:"))
    }
}

public extension UISearchBar {

    public var bnd_text: DynamicSubject<UISearchBar, String?> {
        let dispatcher: (PublishSubject<Void, NoError>, UISearchBar, String) -> Void = { _ in }
        let selector = #selector(UISearchBarDelegate.searchBar(_:textDidChange:))

    return DynamicSubject(
        target: self,
        signal: bnd_delegate.signal(for: selector, dispatch: dispatcher),
        get: { $0.text },
        set: { $0.text = $1 }
        )
    }
}

我已经做了一些修改，变成了这段代码：

import UIKit
import Bond
import ReactiveKit

public extension UISearchBar {
    public var delegate: ProtocolProxy {
    return protocolProxy(for: UISearchBarDelegate.self, setter: NSSelectorFromString("setDelegate:"))
}

public var text: DynamicSubject<String?> {
    let dispatcher: (PublishSubject<Void, NoError>, UISearchBar, String) -> Void = { _,_,_   in }
    let selector = #selector(UISearchBarDelegate.searchBar(_:textDidChange:))

    return DynamicSubject<String?>(
        target: self,
        signal: delegate.signal(for: selector, dispatch: dispatcher),
        get: { $0.text },
        set: { $0.text = $1 }
        )
    }
}

目前我对 DynamicSubject 有错误： Generic parameter 'A' could not be inferred。这很奇怪，因为我检查了我的“调度”将什么作为值：(for: Selector, dispatch: (PublishSubject< S, NoError>, A, B) -> R)。

我尝试使用多个变量进行调度，但一无所获。在我看来，Xcode 无法识别在 PublishSubject 参数之后开始的任何变量。

我想知道我做错了什么。

【问题讨论】：

标签： swift migration swift4 reactivekit swiftbond

【解决方案1】：

如果您曾经从旧版本的 ReactiveKit/Bond 实现的语法迁移，这里是如何为您的 UIKit 响应式扩展执行此操作：

import UIKit
import Bond
import ReactiveKit

extension ReactiveExtensions where Base: UISearchBar {

    var delegate: ProtocolProxy {
        return base.protocolProxy(for: UISearchBarDelegate.self, setter: NSSelectorFromString("setDelegate:"))
    }

    var text: DynamicSubject<String?> {

        let selector = #selector(UISearchBarDelegate.searchBar(_:textDidChange:))
        let textChanged = delegate.signal(for: selector) { (subj: SafePublishSubject<Void>, _: UISearchBar, _: NSString) in
            subj.next(())
        }

        return dynamicSubject(
            signal: textChanged,
            get: { $0.text },
            set: { $0.text = $1 }
        )
    }
}

extension UISearchBar: BindableProtocol {

    public func bind(signal: SafeSignal<String?>) -> Disposable {
        return reactive.text.bind(signal: signal)
    }
}

【讨论】：