RxSwift官方執行個體七（UIPickerView）

代碼下載下傳

UIPickerView的Rx實作分析

RxPickerViewDelegateProxy分析

RxCocoa

已經實作了

RxPickerViewDelegateProxy

，該類繼承

DelegateProxy

基類，遵守

DelegateProxyType

、

UIPickerViewDelegate

協定：

extension UIPickerView: HasDelegate {
        public typealias Delegate = UIPickerViewDelegate
    }

    open class RxPickerViewDelegateProxy
        : DelegateProxy<UIPickerView, UIPickerViewDelegate>
        , DelegateProxyType 
        , UIPickerViewDelegate {

        /// Typed parent object.
        public weak private(set) var pickerView: UIPickerView?

        /// - parameter pickerView: Parent object for delegate proxy.
        public init(pickerView: ParentObject) {
            self.pickerView = pickerView
            super.init(parentObject: pickerView, delegateProxy: RxPickerViewDelegateProxy.self)
        }

        // Register known implementationss
        public static func registerKnownImplementations() {
            self.register { RxPickerViewDelegateProxy(pickerView: $0) }
        }
    }

UIPickerViewDelegate

協定的所有函數在這個類中都沒有實作，最終會進行消息轉發。

RxPickerViewDataSourceProxy分析

RxCocoa

已經實作了

RxPickerViewDataSourceProxy

，該類繼承

DelegateProxy

基類，遵守

DelegateProxyType

、

UIPickerViewDataSource

協定：

extension UIPickerView: HasDataSource {
    public typealias DataSource = UIPickerViewDataSource
}

private let pickerViewDataSourceNotSet = PickerViewDataSourceNotSet()

final private class PickerViewDataSourceNotSet: NSObject, UIPickerViewDataSource {
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 0
    }
    
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return 0
    }
}

/// For more information take a look at `DelegateProxyType`.
public class RxPickerViewDataSourceProxy
    : DelegateProxy<UIPickerView, UIPickerViewDataSource>
    , DelegateProxyType
    , UIPickerViewDataSource {

    /// Typed parent object.
    public weak private(set) var pickerView: UIPickerView?

    /// - parameter pickerView: Parent object for delegate proxy.
    public init(pickerView: ParentObject) {
        self.pickerView = pickerView
        super.init(parentObject: pickerView, delegateProxy: RxPickerViewDataSourceProxy.self)
    }

    // Register known implementations
    public static func registerKnownImplementations() {
        self.register { RxPickerViewDataSourceProxy(pickerView: $0) }
    }

    private weak var _requiredMethodsDataSource: UIPickerViewDataSource? = pickerViewDataSourceNotSet

    // MARK: UIPickerViewDataSource

    /// Required delegate method implementation.
    public func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return (_requiredMethodsDataSource ?? pickerViewDataSourceNotSet).numberOfComponents(in: pickerView)
    }

    /// Required delegate method implementation.
    public func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return (_requiredMethodsDataSource ?? pickerViewDataSourceNotSet).pickerView(pickerView, numberOfRowsInComponent: component)
    }
    
    /// For more information take a look at `DelegateProxyType`.
    public override func setForwardToDelegate(_ forwardToDelegate: UIPickerViewDataSource?, retainDelegate: Bool) {
        _requiredMethodsDataSource = forwardToDelegate ?? pickerViewDataSourceNotSet
        super.setForwardToDelegate(forwardToDelegate, retainDelegate: retainDelegate)
    }
}

擴充UIPickerView遵守HasDataSource協定，使

RxPickerViewDataSourceProxy

滿足條件進而實作了

DelegateProxyType

協定中定義的如下兩個函數：

extension DelegateProxyType where ParentObject: HasDataSource, Self.Delegate == ParentObject.DataSource {
    public static func currentDelegate(for object: ParentObject) -> Delegate? {
        return object.dataSource
    }

    public static func setCurrentDelegate(_ delegate: Delegate?, to object: ParentObject) {
        object.dataSource = delegate
    }
}

定義

PickerViewDataSourceNotSet

這個類為

UIPickerViewDataSource

協定提供預設資料

重寫

setForwardToDelegate

函數，将參數

forwardToDelegate

存儲在私有屬性

_requiredMethodsDataSource

中。

UIPickerViewDataSource

協定中的兩個函數在這個類中實作，調用屬性

_requiredMethodsDataSource

的方法傳回結果。

RxPickerViewAdapter分析

RxPickerViewAdapter

是用來處理

UIPickerViewDataSource

、

UIPickerViewDelegate

協定中定義的帶有傳回值的函數的。

RxCocoa

實作了3種

RxPickerViewAdapter

，分别是

RxStringPickerViewAdapter

、

RxAttributedStringPickerViewAdapter

、

RxPickerViewAdapter

。

RxPickerViewArrayDataSource分析

RxPickerViewArrayDataSource

是

RxStringPickerViewAdapter

、

RxAttributedStringPickerViewAdapter

、

RxPickerViewAdapter

的根類，遵守

UIPickerViewDataSource

、

SectionedViewDataSourceType

協定，還定義一個泛型

<T>

作為通用資料類型：

class RxPickerViewArrayDataSource<T>: NSObject, UIPickerViewDataSource, SectionedViewDataSourceType {
    fileprivate var items: [T] = []
    
    func model(at indexPath: IndexPath) throws -> Any {
        guard items.indices ~= indexPath.row else {
            throw RxCocoaError.itemsNotYetBound(object: self)
        }
        return items[indexPath.row]
    }

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return items.count
    }
}

items 數組屬性存儲所需資料，問題是他隻能存一組資料。
實作 UIPickerViewDataSource 協定。

RxPickerViewSequenceDataSource分析

RxPickerViewSequenceDataSource

這個類繼承自

RxPickerViewArrayDataSource

，是

RxStringPickerViewAdapter

、

RxAttributedStringPickerViewAdapter

、

RxPickerViewAdapter

的父類，遵守

RxPickerViewArrayDataSource<Sequence.Element>

RxPickerViewDataSourceType

協定，定義一個遵守

Swift.Sequence

協定的泛型

<Sequence>

：

class RxPickerViewSequenceDataSource<Sequence: Swift.Sequence>
    : RxPickerViewArrayDataSource<Sequence.Element>
    , RxPickerViewDataSourceType {
    typealias Element = Sequence

    func pickerView(_ pickerView: UIPickerView, observedEvent: Event<Sequence>) {
        Binder(self) { dataSource, items in
            dataSource.items = items
            pickerView.reloadAllComponents()
        }
        .on(observedEvent.map(Array.init))
    }
}

func pickerView(_ pickerView: UIPickerView, observedEvent: Event<Sequence>)

函數的實作：

建構一個 Binder 并執行 on 操作，實際相當于直接執行建構 Binder 的 binding 閉包。
将 Event<Sequence> 類型參數 observedEvent 轉化為 Event<Array> 作為 on 操作的參數。
在建構 Binder 的 binding 閉包中，将數組指派給 items 屬性并重新整理整個 UIPickerView 。

RxStringPickerViewAdapter、RxAttributedStringPickerViewAdapter、RxPickerViewAdapter分析

RxStringPickerViewAdapter

是不可被繼承的，自身繼承自

RxPickerViewSequenceDataSource

并且遵守

UIPickerViewDelegate

協定：

final class RxStringPickerViewAdapter<Sequence: Swift.Sequence>
    : RxPickerViewSequenceDataSource<Sequence>
    , UIPickerViewDelegate {
    
    typealias TitleForRow = (Int, Sequence.Element) -> String?
    private let titleForRow: TitleForRow
    
    init(titleForRow: @escaping TitleForRow) {
        self.titleForRow = titleForRow
        super.init()
    }
    
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return titleForRow(row, items[row])
    }
}

屬性

titleForRow

存儲将

items

數組中的元素轉化為

String

類型的閉包。

- (nullable NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component

函數中執行

titleForRow

閉包并傳回其結果。

RxAttributedStringPickerViewAdapter

、

RxPickerViewAdapter

的實作與

RxStringPickerViewAdapter

類似，不同的是分别存儲

attributedTitleForRow

（将數組中元素轉化為

NSAttributedString

富文本）、

viewForRow

（将數組中元素轉化為

UIView

視圖）的閉包，實作不同的

UIPickerViewDelegate

協定函數傳回執行閉包的傳回值：

final class RxAttributedStringPickerViewAdapter<Sequence: Swift.Sequence>: RxPickerViewSequenceDataSource<Sequence>, UIPickerViewDelegate {
    typealias AttributedTitleForRow = (Int, Sequence.Element) -> NSAttributedString?
    private let attributedTitleForRow: AttributedTitleForRow
    
    init(attributedTitleForRow: @escaping AttributedTitleForRow) {
        self.attributedTitleForRow = attributedTitleForRow
        super.init()
    }
    
    func pickerView(_ pickerView: UIPickerView, attributedTitleForRow row: Int, forComponent component: Int) -> NSAttributedString? {
        return attributedTitleForRow(row, items[row])
    }
}

final class RxPickerViewAdapter<Sequence: Swift.Sequence>: RxPickerViewSequenceDataSource<Sequence>, UIPickerViewDelegate {
    typealias ViewForRow = (Int, Sequence.Element, UIView?) -> UIView
    private let viewForRow: ViewForRow
    
    init(viewForRow: @escaping ViewForRow) {
        self.viewForRow = viewForRow
        super.init()
    }
    
    func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
        return viewForRow(row, items[row], view)
    }
}

基于UIPickerView的Reactive擴充分析

定義delegate、dataSource兩個函數用于擷取Rx代理對象，友善使用：

public var delegate: DelegateProxy<UIPickerView, UIPickerViewDelegate> {
            return RxPickerViewDelegateProxy.proxy(for: base)
        }
        public var dataSource: DelegateProxy<UIPickerView, UIPickerViewDataSource> {
            return RxPickerViewDataSourceProxy.proxy(for: base)
        }

定義setDelegate函數通過

installForwardDelegate

函數為Rx代理對象設定

forwardDelegate

并傳回一個置空

forwardDelegate

的

Disposables

：

public func setDelegate(_ delegate: UIPickerViewDelegate)
            -> Disposable {
                return RxPickerViewDelegateProxy.installForwardDelegate(delegate, retainDelegate: false, onProxyForObject: self.base)
        }

public func items<Source: ObservableType, Adapter: RxPickerViewDataSourceType & UIPickerViewDataSource & UIPickerViewDelegate>(adapter: Adapter) -> (_ source: Source) -> Disposable where Source.Element == Adapter.Element

函數，這個函數很重要，資料的綁定最終都會走到這個函數：

public func items<Source: ObservableType,
                          Adapter: RxPickerViewDataSourceType & UIPickerViewDataSource & UIPickerViewDelegate>(adapter: Adapter)
            -> (_ source: Source)
            -> Disposable where Source.Element == Adapter.Element {
                return { source in
                    let delegateSubscription = self.setDelegate(adapter)
                    let dataSourceSubscription = source.subscribeProxyDataSource(ofObject: self.base, dataSource: adapter, retainDataSource: true, binding: { [weak pickerView = self.base] (_: RxPickerViewDataSourceProxy, event) in
                        guard let pickerView = pickerView else { return }
                        adapter.pickerView(pickerView, observedEvent: event)
                    })
                    return Disposables.create(delegateSubscription, dataSourceSubscription)
                }
        }

此函數接收一個遵守 RxPickerViewDataSourceType 、 UIPickerViewDataSource 、 UIPickerViewDelegate 這三個協定的參數 adapter ，傳回一個 (_ source: Source) -> Disposable 綁定資料的閉包
建構傳回閉包，将原函數參數 adapter 通過 setDelegate 函數設定給 RxDelegate 代理對象的 forwardDelegate 。
将原函數參數 adapter 通過原函數參數 source 的 subscribeProxyDataSource （見下方分析）函數設定給 RxDataSource 代理對象的 forwardDelegate ，并在 binding 參數的閉包中執行 adapter 的 func pickerView(_ pickerView: UIPickerView, observedEvent: Event<Element>) 函數綁定資料。
最後将 setDelegate 和 subscribeProxyDataSource 函數傳回的 Disposables 組合成一個 Disposables 傳回。

itemTitles

，

itemAttributedTitles

，

items

這三個函數分别是将一個

Observable

中的資料綁定到

UIPickerView

的标題、富文本标題、以及view上：

public func itemTitles<Sequence: Swift.Sequence, Source: ObservableType>
            (_ source: Source)
            -> (_ titleForRow: @escaping (Int, Sequence.Element) -> String?)
            -> Disposable where Source.Element == Sequence {
                return { titleForRow in
                    let adapter = RxStringPickerViewAdapter<Sequence>(titleForRow: titleForRow)
                    return self.items(adapter: adapter)(source)
                }
        }
        public func itemAttributedTitles<Sequence: Swift.Sequence, Source: ObservableType>
            (_ source: Source)
            -> (_ attributedTitleForRow: @escaping (Int, Sequence.Element) -> NSAttributedString?)
            -> Disposable where Source.Element == Sequence {
                return { attributedTitleForRow in
                    let adapter = RxAttributedStringPickerViewAdapter<Sequence>(attributedTitleForRow: attributedTitleForRow)
                    return self.items(adapter: adapter)(source)
                }
        }
        public func items<Sequence: Swift.Sequence, Source: ObservableType>
            (_ source: Source)
            -> (_ viewForRow: @escaping (Int, Sequence.Element, UIView?) -> UIView)
            -> Disposable where Source.Element == Sequence {
                return { viewForRow in
                    let adapter = RxPickerViewAdapter<Sequence>(viewForRow: viewForRow)
                    return self.items(adapter: adapter)(source)
                }
        }

這三個函數的形式都是一樣的，接收一個 Observable 序列的資料參數，傳回一個閉包。
不同的是傳回的閉包的參數不一樣，分别是将原函數 Observable 序列的元素轉化為 String 、 NSAttributedString 、 UIView 的閉包。
原函數都是直接建構一個閉包傳回，在閉包中将轉換原函數 Observable 序列的元素的閉包參數分别建構為 RxStringPickerViewAdapter 、 RxAttributedStringPickerViewAdapter 、 RxPickerViewAdapter 對象，然後調用前面分析的 public func items<Source: ObservableType, Adapter: RxPickerViewDataSourceType & UIPickerViewDataSource & UIPickerViewDelegate>(adapter: Adapter) -> (_ source: Source) -> Disposable where Source.Element == Adapter.Element 函數通過各自的 adapter 将将原函數 Observable 序列的元素綁定到 UIPickerView 并傳回 Disposable 。

public func model<T>(at indexPath: IndexPath) throws -> T

函數用于擷取每個單元格中的資料對象：

public func model<T>(at indexPath: IndexPath) throws -> T {
            let dataSource: SectionedViewDataSourceType = castOrFatalError(self.dataSource.forwardToDelegate(), message: "This method only works in case one of the `rx.itemTitles, rx.itemAttributedTitles, items(_ source: O)` methods was used.")
            
            return castOrFatalError(try dataSource.model(at: indexPath))
        }

取出 self.dataSource.forwardToDelegate() 對象，實際上就是前面設定的 adapter 對象。
由于 adapter 對象的基類 RxPickerViewArrayDataSource 實作了 SectionedViewDataSourceType 協定中定義的 func model(at indexPath: IndexPath) throws -> Any 函數，是以傳回其調用結果。

使用消息轉發的方式實作

itemSelected

序列，并使用

map

操作符更改序列元素。

modelSelected

序列是通過

itemSelected

序列進行轉化而來：

public var itemSelected: ControlEvent<(row: Int, component: Int)> {
            let source = delegate
                .methodInvoked(#selector(UIPickerViewDelegate.pickerView(_:didSelectRow:inComponent:)))
                .map {
                    return (row: try castOrThrow(Int.self, $0[1]), component: try castOrThrow(Int.self, $0[2]))
                }
            return ControlEvent(events: source)
        }
        public func modelSelected<T>(_ modelType: T.Type) -> ControlEvent<[T]> {
            let source = itemSelected.flatMap { [weak view = self.base as UIPickerView] _, component -> Observable<[T]> in
                guard let view = view else {
                    return Observable.empty()
                }

                let model: [T] = try (0 ..< view.numberOfComponents).map { component in
                    let row = view.selectedRow(inComponent: component)
                    return try view.rx.model(at: IndexPath(row: row, section: component))
                }

                return Observable.just(model)
            }
            
            return ControlEvent(events: source)
        }

ObservableType擴充分析

func subscribeProxyDataSource<DelegateProxy: DelegateProxyType>(ofObject object: DelegateProxy.ParentObject, dataSource: DelegateProxy.Delegate, retainDataSource: Bool, binding: @escaping (DelegateProxy, Event<Element>) -> Void) -> Disposable

函數的作用是為

Rx

代理對象設定

forwardDelegate

對象和訂閱自身時執行

binding

參數中的閉包相關操作：

extension ObservableType {
            func subscribeProxyDataSource<DelegateProxy: DelegateProxyType>(ofObject object: DelegateProxy.ParentObject, dataSource: DelegateProxy.Delegate, retainDataSource: Bool, binding: @escaping (DelegateProxy, Event<Element>) -> Void)
                -> Disposable
                where DelegateProxy.ParentObject: UIView
                , DelegateProxy.Delegate: AnyObject {
                let proxy = DelegateProxy.proxy(for: object)
                let unregisterDelegate = DelegateProxy.installForwardDelegate(dataSource, retainDelegate: retainDataSource, onProxyForObject: object)
                // this is needed to flush any delayed old state (https://github.com/RxSwiftCommunity/RxDataSources/pull/75)
                object.layoutIfNeeded()

                let subscription = self.asObservable()
                    .observeOn(MainScheduler())
                    .catchError { error in
                        bindingError(error)
                        return Observable.empty()
                    }
                    // source can never end, otherwise it would release the subscriber, and deallocate the data source
                    .concat(Observable.never())
                    .takeUntil(object.rx.deallocated)
                    .subscribe { [weak object] (event: Event<Element>) in

                        if let object = object {
                            assert(proxy === DelegateProxy.currentDelegate(for: object), "Proxy changed from the time it was first set.\nOriginal: \(proxy)\nExisting: \(String(describing: DelegateProxy.currentDelegate(for: object)))")
                        }
                        
                        binding(proxy, event)
                        
                        switch event {
                        case .error(let error):
                            bindingError(error)
                            unregisterDelegate.dispose()
                        case .completed:
                            unregisterDelegate.dispose()
                        default:
                            break
                        }
                    }
                    
                return Disposables.create { [weak object] in
                    subscription.dispose()
                    object?.layoutIfNeeded()
                    unregisterDelegate.dispose()
                }
            }
        }

這個函數接收三個參數分别是Rx代理對象的持有者 object 、Rx代理類關聯類型 Delegate 的 dataSource 、是否持有 dataSource 的 retainDataSource 、資料綁定閉包 binding 。
首先調用Rx代理類的 proxy 函數獲得Rx代理對象，接着調用 installForwardDelegate 函數設定Rx代理對象的 forwardDelegate 。
然後本 Observable 序列執行 subscribe 操作進行訂閱并在其參數 on 閉包中執行 binding 閉包。
最後将自身訂閱和 installForwardDelegate 函數放回的 Disposable 組合成一個傳回。

UIPickerView示例

簡單的綁定

建構3個UIPickerView分别為pickerView1、pickerView2、pickerView3……

然後建構資料并分别綁定到上面的3個UIPickerView：

// 綁定pickerView1
        Observable.just([1, 2, 3, 4, 5, 6, 7, 8, 9])
            .bind(to: pickerView1.rx.itemTitles, curriedArgument: { "\($1)" })
            .disposed(by: bag)
        pickerView1.rx.itemSelected
            .subscribe(onNext: { print("選中了第\($1)列第\($0)行") })
            .disposed(by: bag)
        pickerView1.rx.modelSelected(Int.self)
            .subscribe(onNext: { print("選中了元素\($0.first ?? 0)") })
            .disposed(by: bag)
        
        // 綁定pickerView2
        Observable.just([1, 2, 3, 4, 5, 6, 7, 8, 9])
            .bind(to: pickerView2.rx.itemAttributedTitles, curriedArgument: { NSAttributedString(string: "\($1)", attributes: [NSAttributedString.Key.foregroundColor: UIColor.random]) })
            .disposed(by: bag)
        
        pickerView2.rx.itemSelected
            .subscribe(onNext: { print("選中了第\($1)列第\($0)行") })
            .disposed(by: bag)
        
        pickerView2.rx.modelSelected(Int.self)
            .subscribe(onNext: { print("選中了元素\($0.first ?? 0)") })
            .disposed(by: bag)
        
        // 綁定pickerView3
        Observable.just(Array(0..<10).map({ (_) -> UIColor in UIColor.random }))
            .bind(to: pickerView3.rx.items, curriedArgument: { _, color, _ in
                let view = UIView()
                view.backgroundColor = color
                return view
            }).disposed(by: bag)
        pickerView3.rx.itemSelected
            .subscribe(onNext: { print("選中了第\($1)列第\($0)行") })
            .disposed(by: bag)
        pickerView3.rx.modelSelected(UIColor.self)
            .subscribe(onNext: { print("選中了元素\($0.first ?? UIColor.white)") })
            .disposed(by: bag)

資料綁定過程分析

Observable.just([1, 2, 3, 4, 5, 6, 7, 8, 9])
            .bind(to: pickerView1.rx.itemTitles, curriedArgument: { "\($1)" })
            .disposed(by: bag)

RxCocoa對

func bind<R1, R2>(to binder: (Self) -> (R1) -> R2, curriedArgument: R1) -> R2

函數的實作：

public func bind<R1, R2>(to binder: (Self) -> (R1) -> R2, curriedArgument: R1) -> R2 {
         return binder(self)(curriedArgument)
    }

泛型

R1

為

(Int, Sequence.Element) -> String?

類型閉包，泛型

R2

為

Disposable

類型。于是上面資料綁定的代碼等價于：

pickerView1.rx
            .itemTitles(Observable.just([1, 2, 3, 4, 5, 6, 7, 8, 9]))({ "\($1)" })
            .disposed(by: bag)

資料綁定的完整過程：

建構元素是一個 [int] 類型的原資料 Observable 序列。
把原資料 Observable 序列作為參數執行 pickerView1.rx.itemTitles 函數，傳回一個 (titleForRow: (Int, Sequence.Element) -> String?) -> Disposable 類型的閉包。
将類型為 (Int, Sequence.Element) -> String? 的參數 curriedArgument 這個閉包再作為 titleForRow 參數執行上面的 (titleForRow: (Int, Sequence.Element) -> String?) -> Disposable 閉包。
(titleForRow: (Int, Sequence.Element) -> String?) -> Disposable 閉包内部使用 titleForRow 閉包建構 RxStringPickerViewAdapter 類型對象 adapter 。
然後用 adapter 作為參數執行 func items(adapter: Adapter) -> (source: Source) -> Disposable 函數傳回類型為 (source: Source) -> Disposable 的閉包。
将原資料 Observable 序列作為參數執行 (source: Source) -> Disposable 閉包。
閉包 (source: Source) -> Disposable 内部執行 setDelegate 函數設定 RxPickerViewDelegateProxy 類型的 forwardDelegate 屬性。
閉包 (source: Source) -> Disposable 内部執行 subscribeProxyDataSource 函數設定 RxPickerViewDataSourceProxy 類型的 forwardDelegate 屬性。
subscribeProxyDataSource 函數内部訂閱原資料 Observable 序列将 [int] 類型的元素作為參數執行 adapter 對象的 func pickerView(pickerView: UIPickerView, observedEvent: Event<Element>) 函數。
最後 func pickerView(pickerView: UIPickerView, observedEvent: Event<Element>) 函數中将 [int] 類型的元素儲存到 adapter 對象的 items 屬性中并執行 reloadAllComponents 重新整理 UIPickerView 。
UIPickerView 在重新整理時會調用其代理對象（ RxPickerViewDelegateProxy 、 RxPickerViewDataSourceProxy ）的函數，然後在實作的協定函數中執行其 forwardDelegate 屬性相應的函數傳回資料或者通過消息轉發的方式執行 forwardDelegate 中的函數。

pickerView1.rx.itemSelected
            .subscribe(onNext: { print("選中了第\($1)列第\($0)行") })
            .disposed(by: bag)
        pickerView1.rx.modelSelected(Int.self)
            .subscribe(onNext: { print("選中了元素\($0.first ?? 0)") })
            .disposed(by: bag)

itemSelected 通過消息轉發實作。
modelSelected 将 itemSelected 通過 flatMap 操作符轉化 Observable 序列的行列号元素為實際資料。

pickerView1

、

pickerView2

、

pickerView3

的資料綁定過程是一樣的。差別無非是将資料分别綁定到單元格的

title

、

attributedTitle

、

view

。

自定義綁定

從對

RxPickerViewArrayDataSource

的分析可以看出

RxCocoa

隻實作了将單組資料綁定到

UIPickerView

單元格的

title

、

attributedTitle

、

view

。

這往往滿足不了日常的開發需要，是以自定義綁定顯得很重要。

實作多組資料綁定

參照

RxCocoa

實作的

RxStringPickerViewAdapter

、

RxAttributedStringPickerViewAdapter

、

RxPickerViewAdapter

實作一個支援多組資料的基類

BaseSectionedPickerViewAdapter

：

class BaseSectionedPickerViewAdapter: NSObject, UIPickerViewDataSource, UIPickerViewDelegate, RxPickerViewDataSourceType, SectionedViewDataSourceType {
    typealias Element = [[CustomStringConvertible]]
    fileprivate var items: Element = []
    
    func model(at indexPath: IndexPath) throws -> Any {
        items[indexPath.section][indexPath.row]
    }
    
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        items.count
    }
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        items[component].count
    }
    
    func pickerView(_ pickerView: UIPickerView, observedEvent: Event<[[CustomStringConvertible]]>) {
        Binder(self) { (adapter, items) in
            adapter.items = items
            pickerView.reloadAllComponents()
        }.on(observedEvent)
    }
}

實作一個簡單的

SimpleSectionedPickerViewAdapter

，實作

func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String?

函數将資料的

description

屬性簡單地綁定到

title

上：

class SimpleSectionedPickerViewAdapter: BaseSectionedPickerViewAdapter {
    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return items[component][row].description
    }
}

在頁面上搭建一個

UIPickerView

命名為

pickerView

，然後進行資料綁定：

Observable.just([Array(0..<10), Array(10..<20), Array(20..<30)])
            .bind(to: pickerView.rx.items(adapter: SimpleSectionedPickerViewAdapter()))
            .disposed(by: bag)

RxCocoa

對

func bind<Result>(to binder: (Self) -> Result) -> Result

函數的實作：

public func bind<Result>(to binder: (Self) -> Result) -> Result {
        return binder(self)
    }

泛型

Result

為

Disposable

類型。于是上面資料綁定的代碼等價于：

pickerView.rx
            .items(adapter: SimpleSectionedPickerViewAdapter())(Observable.just([Array(0..<10), Array(10..<20), Array(20..<30)]))
            .disposed(by: bag)

資料綁定的完整過程：

首先建構一個 Observable 序列的原資料 Observable.just([Array(0..<10), Array(10..<20), Array(20..<30)])
建構一個 PickerViewViewAdapter 類型對象作為參數執行 func items(adapter: Adapter) -> (_ source: Source) -> Disposable 函數傳回類型為 (source: Source) -> Disposable 的閉包。
将原資料 Observable 序列作為參數執行 (source: Source) -> Disposable 閉包。
接下來的過程與上面的簡單綁定過程完全一緻。

就這樣實作了多組資料的簡單綁定，但是實際開發中往往需要控制

UIPickerView

單元格的寬、高、标題、視圖等内容，接下來實作更全面的資料綁定。

實作完整的資料綁定

實作一個

SectionedPickerViewAdapter

，與Rxcocoa實作的

RxPickerViewAdapter

類似：

class 
<T: CustomStringConvertible>: BaseSectionedPickerViewAdapter<T>, UIPickerViewDelegate {
    private var viewForRow: ((UIPickerView, Int, Int, UIView?) -> UIView)?
    private var titleForRow: ((UIPickerView, Int, Int) -> String)?
    private var attributedTitleForRow: ((UIPickerView, Int, Int) -> NSAttributedString)?
    private var widthForComponent: ((UIPickerView, Int) -> CGFloat)?
    private var heightForComponent: ((UIPickerView, Int) -> CGFloat)?
    
    func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
        if let aView = viewForRow {
            return aView(pickerView, row, component, view)
        } else {
            let label = UILabel()
            label.textAlignment = .center
            label.font = UIFont.systemFont(ofSize: 21.0)
            if let aAttributedTitle = attributedTitleForRow {
                label.attributedText = aAttributedTitle(pickerView, row, component)
            }
            else if let aTitle = titleForRow {
                label.text = aTitle(pickerView, row, component)
            }
            else {
                label.text = items[component][row].description
            }
            
            return label
        }
    }
    
    func pickerView(_ pickerView: UIPickerView, widthForComponent component: Int) -> CGFloat {
        if let width = widthForComponent {
            return width(pickerView, component)
        }
        
        return floor(UIScreen.main.bounds.width/CGFloat(items.count))
    }
    
    func pickerView(_ pickerView: UIPickerView, rowHeightForComponent component: Int) -> CGFloat {
        if let aHeight = heightForComponent {
            return aHeight(pickerView, component)
        }
        
        return 34.0
    }
    
    init(viewForRow: ((UIPickerView, Int, Int, UIView?) -> UIView)?, widthForComponent: ((UIPickerView, Int) -> CGFloat)? = nil, heightForComponent: ((UIPickerView, Int) -> CGFloat)? = nil, titleForRow: ((UIPickerView, Int, Int) -> String)? = nil, attributedTitleForRow: ((UIPickerView, Int, Int) -> NSAttributedString)? = nil) {
        super.init()
        self.viewForRow = viewForRow
        self.widthForComponent = widthForComponent
        self.heightForComponent = heightForComponent
    }
}

擴充

Base

類型為

UIPickerView

的

Reactive

實作一個

sectionedItems

函數，與

RxCocoa

的

func items(_ source: Source) -> (_ viewForRow: @escaping (Int, Sequence.Element, UIView?) -> UIView) -> Disposable

函數類似：

extension Reactive where Base: UIPickerView {
    func sectionedItems<T: CustomStringConvertible>
        (_ source: Observable<[[T]]>)
    -> ((viewForRow: (UIPickerView, Int, Int, UIView?) -> UIView, widthForComponent: ((UIPickerView, Int) -> CGFloat)?, heightForComponent: ((UIPickerView, Int) -> CGFloat)?, titleForRow:((UIPickerView, Int, Int) -> String)?, attributedTitleForRow: ((UIPickerView, Int, Int) -> NSAttributedString)?))
    -> Disposable {
        return { arg in
            let adapter = SectionedPickerViewAdapter<T>(viewForRow: arg.0, widthForComponent: arg.1, heightForComponent: arg.2, titleForRow: arg.3, attributedTitleForRow: arg.4)
            return items(adapter: adapter)(source)
        }
    }
}

最後進行資料綁定，其綁定過程與前邊分析基本一緻：

Observable.just([Array(0..<10), Array(10..<100), Array(100..<1000)])
            .bind(to: centerPickerView.rx.sectionedItems, curriedArgument: ({ (_, row, component, _) in
                let label = UILabel()
                label.font = UIFont.systemFont(ofSize: 12.0)
                label.textAlignment = .center
                label.backgroundColor = UIColor.random
                label.text = data[component][row].description
                return label
            }, { _, component in
                switch component {
                case 0:
                    return 40.0
                case 1:
                    return 80.0
                default:
                    return 120.0
                }
            }, { (_, _) in 50.0 }, nil, nil))
            .disposed(by: bag)

通過前面對RxCocoa實作UIPickerView綁定的分析，也可以通過如下方式綁定資料：

let adapter = SectionedPickerViewAdapter<Int>(viewForRow: { (_, row, component, _) -> UIView in
    let label = UILabel()
    label.font = UIFont.systemFont(ofSize: 12.0)
    label.textAlignment = .center
    label.backgroundColor = UIColor.random
    label.text = data[component][row].description
    return label
}, widthForComponent: { _, component in
    switch component {
    case 0:
        return 120.0
    case 1:
        return 80.0
    default:
        return 40.0
    }
}, heightForComponent: { (_, _) in 40.0 })
Observable.just([Array(0..<10), Array(10..<100), Array(100..<1000)])
    .bind(to: bottomPickerView.rx.items(adapter: adapter))
    .disposed(by: bag)

RxSwift官方執行個體七（UIPickerView）

UIPickerView的Rx實作分析

RxPickerViewDelegateProxy分析

RxPickerViewDataSourceProxy分析

RxPickerViewAdapter分析

RxPickerViewArrayDataSource分析

RxPickerViewSequenceDataSource分析

RxStringPickerViewAdapter、RxAttributedStringPickerViewAdapter、RxPickerViewAdapter分析

基于UIPickerView的Reactive擴充分析

ObservableType擴充分析

UIPickerView示例

簡單的綁定

資料綁定過程分析

自定義綁定

實作多組資料綁定

實作完整的資料綁定

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