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This is extremely minor but I couldn't help it.  Release Notes: - N/A
41 lines
2.3 KiB
Markdown
41 lines
2.3 KiB
Markdown
# Contexts
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GPUI makes extensive use of _context parameters_, typically named `cx` and positioned at the end of the parameter list, unless they're before a final function parameter. A context reference provides access to application state and services.
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There are multiple kinds of contexts, and contexts implement the `Deref` trait so that a function taking `&mut AppContext` could be passed a `&mut WindowContext` or `&mut ViewContext` instead.
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```
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AppContext
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/ \
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ModelContext WindowContext
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/
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ViewContext
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```
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- The `AppContext` forms the root of the hierarchy
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- `ModelContext` and `WindowContext` both dereference to `AppContext`
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- `ViewContext` dereferences to `WindowContext`
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## `AppContext`
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Provides access to the global application state. All other kinds of contexts ultimately deref to an `AppContext`. You can update a `Model<T>` by passing an `AppContext`, but you can't update a view. For that you need a `WindowContext`...
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## `WindowContext`
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Provides access to the state of an application window, and also derefs to an `AppContext`, so you can pass a window context reference to any method taking an app context. Obtain this context by calling `WindowHandle::update`.
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## `ModelContext<T>`
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Available when you create or update a `Model<T>`. It derefs to an `AppContext`, but also contains methods specific to the particular model, such as the ability to notify change observers or emit events.
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## `ViewContext<V>`
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Available when you create or update a `View<V>`. It derefs to a `WindowContext`, but also contains methods specific to the particular view, such as the ability to notify change observers or emit events.
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## `AsyncAppContext` and `AsyncWindowContext`
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Whereas the above contexts are always passed to your code as references, you can call `to_async` on the reference to create an async context, which has a static lifetime and can be held across `await` points in async code. When you interact with `Model`s or `View`s with an async context, the calls become fallible, because the context may outlive the window or even the app itself.
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## `TestAppContext` and `TestVisualContext`
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These are similar to the async contexts above, but they panic if you attempt to access a non-existent app or window, and they also contain other features specific to tests.
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