RxSwift 数据绑定

BindTo

官方摘录：Creates new subscription and sends elements to observer.

     func rxSwiftBindTo() {
        let mobile = Variable<String>(self.getExtra("phone") as! String)

        mobile.asObservable()
            .bind(to: rxViewModel.mobile)
            .disposed(by: dispose)

        bgView.msgVerifyCodeTextField.rx.text.orEmpty
            .bind(to: rxViewModel.mobileCode)
            .disposed(by: dispose)

        bgView.loginPwdTextField.rx.text.orEmpty
            .bind(to: rxViewModel.loginPwd)
            .disposed(by: dispose)

        bgView.regBtn.rx.tap
            .bind(to: rxViewModel.registerTaps)
            .disposed(by: dispose)
     }

Driver

官方摘录：Subscribes an element handler, a completion handler and disposed handler to an observable sequence.
This method can be only called from \`MainThread\`.

Error callback is not exposed because \`Driver\` can't error out.

    func driverTo() {
        let passwordViewModel = InputPasswordViewModel(passwordTextField.rx.text.orEmpty.asDriver())

        passwordViewModel.loginButtonEnabled.drive(onNext: { [unowned self] valid in
            self.loginBtn.isEnabled = valid
            self.loginBtn.isUserInteractionEnabled = valid
            self.loginBtn.backgroundColor =  valid ? UIColor(valueRGB: 0xc8a66b) :  UIColor(valueRGB: 0xc8a66b, alpha: 0.3)
        })
            .disposed(by: disposeBag)
    }

Driver是RxSwift精心制作的，专门提供给UI层的一个接口。Driver序列不允许发出error，监听只会在主线程中。

Practical usage example

let results = query.rx.text
    .throttle(0.3, scheduler: MainScheduler.instance)
    .flatMapLatest { query in
        fetchAutoCompleteItems(query)
    }

results
    .map { "\($0.count)" }
    .bind(to: resultCount.rx.text)
    .disposed(by: disposeBag)

results
    .bind(to: resultsTableView.rx.items(cellIdentifier: "Cell")) { (_, result, cell) in
        cell.textLabel?.text = "\(result)"
    }
    .disposed(by: disposeBag)

这段代码的主要目的是：

取出用户输入稳定后的内容
向服务器请求一组结果
将返回的结果绑定到两个 UI 元素上：tableView和显示结果数量的label

那么这里存在什么问题？

如果fetchAutoCompleteItems的序列产生了一个错误（网络请求失败），这个错误将取消所有绑定，当用户输入一个新的关键字时，是无法发起新的网络请求。
如果fetchAutoCompleteItems在后台返回序列，那么刷新页面也会在后台进行，这样就会出现异常崩溃。
返回的结果被绑定到两个 UI 元素上。那就意味着，每次用户输入一个新的关键字时，就会分别为两个 UI 元素发起 HTTP 请求，这并不是我们想要的结果。

一个更好的方案是这样的：

let results = query.rx.text
    .throttle(0.3, scheduler: MainScheduler.instance)
    .flatMapLatest { query in
        fetchAutoCompleteItems(query)
            .observeOn(MainScheduler.instance)  // 结果在主线程返回
            .catchErrorJustReturn([])           // 错误被处理了，这样至少不会终止整个序列
    }
    .share(replay: 1)                             // HTTP 请求是被共享的

results
    .map { "\($0.count)" }
    .bind(to: resultCount.rx.text)
    .disposed(by: disposeBag)

results
    .bind(to: resultsTableView.rx.items(cellIdentifier: "Cell")) {
      (_, result, cell) in
        cell.textLabel?.text = "\(result)"
    }
    .disposed(by: disposeBag)

以下是使用Driver优化后的代码：

let results = query.rx.text.asDriver()        // 将普通序列转换为 Driver
    .throttle(0.3, scheduler: MainScheduler.instance)
    .flatMapLatest { query in
        fetchAutoCompleteItems(query)
            .asDriver(onErrorJustReturn: [])  // 仅仅提供发生错误时的备选返回值
    }

results
    .map { "\($0.count)" }
    .drive(resultCount.rx.text)               // 这里改用 `drive` 而不是 `bindTo`
    .disposed(by: disposeBag)                 // 这样可以确保必备条件都已经满足了

results
    .drive(resultsTableView.rx.items(cellIdentifier: "Cell")) {
      (_, result, cell) in
        cell.textLabel?.text = "\(result)"
    }
    .disposed(by: disposeBag)

首先第一个asDriver方法将ControlProperty转换为Driver

然后第二个变化是：

.asDriver(onErrorJustReturn: [])

以下情况你可以使用Driver替换BindTo:

不能发出error
在主线程中监听
共享事件流（shareReplayLatestWhileConnected）

KVO

KVO是一个Objective-C机制。这意味着它没有考虑到安全类型。这个项目试图解决一些问题。

为什么说KVO是非类型安全的，参考《关于KVO的那些事之 KVO安全用法封装》

view
  .rx.observe(CGRect.self, "frame")
  .subscribe(onNext: { frame in
    ...
  })

view
  .rx.observeWeakly(CGRect.self, "frame")
  .subscribe(onNext: { frame in
    ...
  })

`rx.observe`

rx.observeis more performant because it's just a simple wrapper around KVO mechanism, but it has more limited usage scenarios

it can be used to observe paths starting fromselfor from ancestors in ownership graph (retainSelf = false)
it can be used to observe paths starting from descendants in ownership graph (retainSelf = true)
the paths have to consist only ofstrongproperties, otherwise you are risking crashing the system by not unregistering KVO observer before dealloc.

E.g.

self.rx.observe(CGRect.self, "view.frame", retainSelf: false)

`rx.observeWeakly`

rx.observeWeaklyhas somewhat slower thanrx.observebecause it has to handle object deallocation in case of weak references.

It can be used in all cases whererx.observecan be used and additionally

because it won't retain observed target, it can be used to observe arbitrary object graph whose ownership relation is unknown
it can be used to observeweakproperties

E.g.

someSuspiciousViewController.rx.observeWeakly(Bool.self, "behavingOk")

观察结构

RxCocoa has built in support for KVO observing ofCGRect,CGSizeandCGPointstructs.

翻译自：RxSwift官网

3.6 Data Binding