# AnyObserver

**AnyObserver** 可以用来描叙任意一种观察者。

## 例如：

**打印网络请求结果：**

```swift
URLSession.shared.rx.data(request: URLRequest(url: url))
    .subscribe(onNext: { data in
        print("Data Task Success with count: \(data.count)")
    }, onError: { error in
        print("Data Task Error: \(error)")
    })
    .disposed(by: disposeBag)
```

可以看作是：

```swift
let observer: AnyObserver<Data> = AnyObserver { (event) in
    switch event {
    case .next(let data):
        print("Data Task Success with count: \(data.count)")
    case .error(let error):
        print("Data Task Error: \(error)")
    default:
        break
    }
}

URLSession.shared.rx.data(request: URLRequest(url: url))
    .subscribe(observer)
    .disposed(by: disposeBag)
```

**用户名提示语是否隐藏：**

```swift
usernameValid
    .bind(to: usernameValidOutlet.rx.isHidden)
    .disposed(by: disposeBag)
```

可以看作是：

```swift
let observer: AnyObserver<Bool> = AnyObserver { [weak self] (event) in
    switch event {
    case .next(let isHidden):
        self?.usernameValidOutlet.isHidden = isHidden
    default:
        break
    }
}

usernameValid
    .bind(to: observer)
    .disposed(by: disposeBag)
```

下一节将介绍 [Binder](/rxswift/rxswift_core/observer/binder.md) 以及 `usernameValidOutlet.rx.isHidden` 的由来。


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