# Deprecated `cacheExtent` and `cacheExtentStyle`

> The `cacheExtent` and `cacheExtentStyle` properties are deprecated. They are replaced by `scrollCacheExtent` with a `ScrollCacheExtent` object.




:::important
These breaking change docs are accurate, as of the release
under which they are published. Over time, the
workarounds described here might become inaccurate.
We don't, in general, keep these breaking change docs up
to date as of each release.

这些破坏性改动文档的准确性仅限于其发布时对应的版本。
随着时间的推移，文档中描述的方案可能会逐渐失效。
通常情况下，我们不会在每次发布新版本时都对这些文档进行同步更新。

The [breaking change index file](/release/breaking-changes)
lists the docs created for each release.

[破坏性改动列表](/release/breaking-changes) 
列出了每个版本的文档。

:::


## Summary

Flutter 3.44 deprecates `cacheExtent` and `cacheExtentStyle`
in scrolling-related widgets, such as
`ListView`, `GridView`, `CustomScrollView`, and `Viewport`,
and their corresponding render objects, such as `RenderViewport`.
The new `scrollCacheExtent` property encapsulates
both the value and the caching strategy (pixels or viewport).

## Background

Previously, `cacheExtent` was a `double` and
`cacheExtentStyle` determined how that `double` was interpreted
(either as pixels or as a fraction of the viewport).
This split made the setting harder to understand.

The new `scrollCacheExtent` property uses a `ScrollCacheExtent` object that
explicitly encapsulates both the value and
the caching strategy (pixels or viewport),
which provides type safety and clearer intent.

## Migration guide

### Widget layer

#### `cacheExtent` (pixels)

If your code uses `cacheExtent`,
which defaults to pixels,
use `scrollCacheExtent` with `ScrollCacheExtent.pixels`.

**Before:**

```dart
ListView(
  cacheExtent: 500.0,
  children: // ...
)
```

**After:**

```dart
ListView(
  scrollCacheExtent: const ScrollCacheExtent.pixels(500.0),
  children: // ...
)
```

#### `cacheExtentStyle` (viewport)

If your code uses `cacheExtent` with `CacheExtentStyle.viewport`,
which is common in `Viewport`,
use `scrollCacheExtent` with `ScrollCacheExtent.viewport`.

**Before:**

```dart
Viewport(
  cacheExtent: 0.5,
  cacheExtentStyle: CacheExtentStyle.viewport,
  slivers: // ...
)
```

**After:**

```dart
Viewport(
  scrollCacheExtent: const ScrollCacheExtent.viewport(0.5),
  slivers: // ...
)
```

### Render object layer

If your code manually sets properties on
`RenderViewport` or a similar render object,
use `scrollCacheExtent`.

**Before:**

```dart
renderViewport.cacheExtent = 500.0;
renderViewport.cacheExtentStyle = CacheExtentStyle.pixel;
```

**After:**

```dart
renderViewport.scrollCacheExtent = const ScrollCacheExtent.pixels(500.0);
```

## Timeline

Landed in version: 3.41.0-0.0.pre<br>
In stable release: 3.44

## References

API documentation:

* [`ScrollCacheExtent`][]
* [`ScrollView.scrollCacheExtent`][]
* [`RenderViewportBase.scrollCacheExtent`][]

Relevant PRs:

* [Introduce ScrollCacheExtent][pr-181092]

[`ScrollCacheExtent`]: https://api.flutter-io.cn/flutter/rendering/ScrollCacheExtent-class.html
[`ScrollView.scrollCacheExtent`]: https://api.flutter-io.cn/flutter/widgets/ScrollView/scrollCacheExtent.html
[`RenderViewportBase.scrollCacheExtent`]: https://api.flutter-io.cn/flutter/rendering/RenderViewportBase/scrollCacheExtent.html

[pr-181092]: https://github.com/flutter/flutter/pull/181092