英文:
Make a sequence of 2 requests with Combine in Swift?
问题
我有以下的代码：
import Combine
func login() -> Future<Token, Error> { ... }
func updateImage() -> Future<Status, Never> { ... }
login()
.flatMap { response -> Future<Status, Error> in
// 处理响应并在本地保存令牌
return updateImage()
}
.sink(receiveCompletion: { error in
... // 处理错误
}, receiveValue: { response in
... // 处理响应和不同的错误
})
.store(in: ...)
我想要将 login() 和 updateImage() 连接成一个序列。但是，我发现 zip 只适用于并行请求。我需要一种方法来按顺序链接它们，我不确定 map、tryMap 或 mapError 方法是否能帮助我实现这一点。我不仅需要转换，还需要处理每个函数的响应数据和错误。
如何解决这个问题？
英文:
I have the following code:
import Combine
func login() -> Future<Token, Error> { ... }
func updateImage() -> Future<Status, Never> { ... }
login()
.flatMap { response -> Future<Status, Error> in
// handle response and save token locally
return updateImage()
}
.sink(receiveCompletion: { error in
... //handleError
}, receiveValue: { response in
... // handle response and a different error
})
.store(in: ...)
I want to join login() and updateImage() into a sequence. However, I found that zip is only for parallel requests. I need a way to chain them sequentially, and I am not sure if map, tryMap, or mapError methods can help me achieve that. I need to not only transform but also handle the response data and errors from each function.
How to solve this issue?
答案1
得分: 1
在iOS 14+中，有一个新的flatMap重载，允许您将其平坦映射到一个永不失败的发布者，因此您只需更改闭包的显式返回类型以匹配updateImage返回的类型：
.flatMap { response -> Future<Status, Never> in // 将 "Error" 更改为 "Never"
在iOS 14之前，您需要使用setFailureType(to:)：
.flatMap { response -> Publishers.SetFailureType<Future<Status, Never>, Error> in
// ...
return updateImage().setFailureType(to: Error.self)
}
如果您不喜欢这样的长类型名称，请使用AnyPublisher：
.flatMap { response -> AnyPublisher<Status, Error> in
// ...
return updateImage().setFailureType(to: Error.self).eraseToAnyPublisher()
}
英文:
In iOS 14+, there is a new overload of flatMap that allows you flat map to a publisher that Never fails, so you just need to change the explicit return type of your closure to match the type that updateImage returns:
.flatMap { response -> Future<Status, Never> in // change "Error" to "Never"
Prior to iOS 14, you would need to use setFailureType(to:):
.flatMap { response -> Publishers.SetFailureType<Future<Status, Never>, Error> in
// ...
return updateImage().setFailureType(to: Error.self)
}
If you don't like such a long type name, use AnyPublisher:
.flatMap { response -> AnyPublisher<Status, Error> in
// ...
return updateImage().setFailureType(to: Error.self).eraseToAnyPublisher()
}
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