# ImageCache large images

> Stop increasing the ImageCache maxByteSize to accommodate large images.




:::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

The `maxByteSize` of the `ImageCache` is no longer
automatically made larger to accommodate large images.

## Context

Previously, when loading images into the `ImageCache`
that had larger byte sizes than the `ImageCache`'s `maxByteSize`,
Flutter permanently increased the `maxByteSize` value
to accommodate those images.
This logic sometimes led to bloated `maxByteSize` values that
made working in memory-limited systems more difficult.

## Description of change

The following "before" and "after" pseudocode demonstrates
the changes made to the `ImageCache` algorithm:

```dart
// Old logic pseudocode
void onLoadImage(Image image) {
  if (image.byteSize > _cache.maxByteSize) {
    _cache.maxByteSize = image.byteSize + 1000;
  }
  _cache.add(image);
  while (_cache.count > _cache.maxCount
      || _cache.byteSize > _cache.maxByteSize) {
    _cache.discardOldestImage();
  }
}
```

```dart
// New logic pseudocode
void onLoadImage(Image image) {
  if (image.byteSize < _cache.maxByteSize) {
    _cache.add(image);
    while (_cache.count > _cache.maxCount
        || _cache.byteSize > cache.maxByteSize) {
      cache.discardOldestImage();
    }
  }
}
```

## Migration guide

There might be situations where the `ImageCache`
is thrashing with the new logic where it wasn't previously,
specifically if you load images that are larger than your
`cache.maxByteSize` value.
This can be remedied by one of the following approaches:

1. Increase the `ImageCache.maxByteSize` value
   to accommodate larger images.
1. Adjust your image loading logic to guarantee that
   the images fit nicely into the `ImageCache.maxByteSize`
   value of your choosing.
1. Subclass `ImageCache`, implement your desired logic,
   and create a new binding that serves up your subclass
   of `ImageCache` (see the [`image_cache.dart`][] source).

## Timeline

The old algorithm is no longer supported.

Landed in version: 1.16.3<br>
In stable release: 1.17

## References

API documentation:

* [`ImageCache`][]

Relevant issue:

* [Issue 45643][]

Relevant PR:

* [Stopped increasing the cache size to accommodate large images][]

Other:

* [`ImageCache` source][]


[Stopped increasing the cache size to accommodate large images]: https://github.com/flutter/flutter/pull/47387
[`ImageCache`]: https://api.flutter-io.cn/flutter/painting/ImageCache-class.html
[`image_cache.dart`]: https://github.com/flutter/flutter/blob/72a3d914ee5db0033332711224e728b8a5281d89/packages/flutter/lib/src/painting/image_cache.dart#L34
[`ImageCache` source]: https://github.com/flutter/flutter/blob/main/packages/flutter/lib/src/painting/image_cache.dart
[Issue 45643]: https://github.com/flutter/flutter/issues/45643