> For the complete documentation index, see [llms.txt](https://3440217568.gitbook.io/rxswift/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://3440217568.gitbook.io/rxswift/decision_tree/flatmap.md).

# flatMap

**将 `Observable` 的元素转换成其他的 `Observable`，然后将这些 `Observables` 合并**

![](/files/-MWlwP8UTqIpHTuMoyee)

**flatMap** 操作符将源 `Observable` 的每一个元素应用一个转换方法，将他们转换成 `Observables`。 然后将这些 `Observables` 的元素合并之后再发送出来。

这个操作符是非常有用的，例如，当 `Observable` 的元素本身拥有其他的 `Observable` 时，你可以将所有**子** `Observables` 的元素发送出来。

## 演示

```swift
let disposeBag = DisposeBag()
let first = BehaviorSubject(value: "👦🏻")
let second = BehaviorSubject(value: "🅰️")
let subject = BehaviorSubject(value: first)

subject.asObservable()
        .flatMap { $0 }
        .subscribe(onNext: { print($0) })
        .disposed(by: disposeBag)

first.onNext("🐱")
subject.onNext(second)
second.onNext("🅱️")
first.onNext("🐶")
```

**输出结果：**

```swift
👦🏻
🐱
🅰️
🅱️
🐶
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://3440217568.gitbook.io/rxswift/decision_tree/flatmap.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.