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Improve image entity documentation (#1822)

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Co-authored-by: Franck Nijhof <git@frenck.dev>
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Erik Montnemery 2023-06-28 13:24:23 +02:00 committed by GitHub
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docs/core/entity/image.md
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@ -9,8 +9,6 @@ The image entity is a simplified version of the [`camera`](/docs/core/entity/cam
An implementation can provide either a URL from where an image will automatically be fetched or image data as `bytes`. When providing a URL, the fetched image will be cached in `self._cached_image`, set `self._cached_image` to `None` to invalidate the cache. An implementation can provide either a URL from where an image will automatically be fetched or image data as `bytes`. When providing a URL, the fetched image will be cached in `self._cached_image`, set `self._cached_image` to `None` to invalidate the cache.
To make frontend refetch the image, bump the `image_last_updated` property.
## Properties ## Properties
:::tip :::tip
@ -20,14 +18,20 @@ Properties should always only return information from memory and not do I/O (lik
| Name | Type | Default | Description | | Name | Type | Default | Description |
| ------------------------ | --------- | ------------ | ---------------------------------------------------------------------------------------------------------------------------------- | | ------------------------ | --------- | ------------ | ---------------------------------------------------------------------------------------------------------------------------------- |
| content_type | str | `image/jpeg` | The content-type of the image, set automatically if the image entity provides a URL. | | content_type | str | `image/jpeg` | The content-type of the image, set automatically if the image entity provides a URL. |
| image_last_updated | datetime | `None` | Timestamp of when the image was last updated. Used to determine `state`. | | image_last_updated | datetime | `None` | Timestamp of when the image was last updated. Used to determine `state`. Frontend will refetch the image when this changes. |
| image_url | str or None | `UNDEFINED` | Optional URL from where the image should be fetched. | | image_url | str or None | `UNDEFINED` | Optional URL from where the image should be fetched. |
## Methods ## Methods
### Image ### Image
Implement if your entity returns bytes of the image instead of providing a URL. Implement `async_image` or `image` if your entity returns bytes of the image instead of providing a URL.
Note that:
- The image entity's `async_image` or `image` method is only called when frontend fetches the image.
- Frontend will only refetch the image when the image entity's state changes.
This means it's incorrect to bump the `image_last_updated` property inside `async def async_image`. It should instead be done as part of a state update to signal that an updated image is available.
```python ```python
class MyImage(ImageEntity): class MyImage(ImageEntity):