> For the complete documentation index, see [llms.txt](https://ryukiedev.gitbook.io/wiki/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ryukiedev.gitbook.io/wiki/flutter/22.widget-shu-render-shu-element-shu.md).

# 22.Widget树\&Render树\&Element树

### Widget 的渲染原理

不是所有的 `Widget` 都会被独立渲染。只有继承 `RenderObjectWidget` 的才会创建 `RenderObject` 对象。

在 `Flutter` 中，有三个树非常重要， `Widget树` 、 `Render树` 、 `Element树`。`Flutter引擎`是针对 `Render树` 进行渲染。

### Widget树 、 Render树 、 Element树

* 每一个 `Widget` 都会创建一个 `Elememt` 对象
  * 隐式调用 `createElement` 方法。
    * `Element` 加入 `Element树` 中
    * 它会创建三种 `Element`
* `RenderElement` 主要是创建 `RenderObject` 对象
  * 继承 `RenderObjectWidget` 的 `Widget` 会创建 `RenderElement`
  * `Flutter` 会调用 `mount` 方法，调用 `createRanderObject` 方法
* `StatefulElement` 继承 `ComponentElement`
  * `StatefulWidget` 会创建 `StatefulElement`
  * 调用 `createState` 创建 `State`
  * 将 `Widget` 赋值给 `state`
  * 调用 `state` 的 `build` 方法，并将自己 `Element` 传出去
    * `build` 里面的 `context` 就是 `element`
* `StatelessElement` 继承 `ComponentElement`
  * `StatelessWidget` 会创建 `StatelessElement`
  * 主要就是调用 `build` 方法，并将自己 `Element` 传出去


---

# 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://ryukiedev.gitbook.io/wiki/flutter/22.widget-shu-render-shu-element-shu.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.