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16 lines
1.6 KiB
Markdown
Executable File
16 lines
1.6 KiB
Markdown
Executable File
---
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title: ASVisibility
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layout: docs
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permalink: /docs/asvisibility.html
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prevPage: debug-tool-ASRangeController.html
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nextPage: asenvironment.html
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---
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`ASNavigationController` and `ASTabBarController` both implement the `ASVisibility` protocol. These classes can be used even without `ASDisplayNodes`, making them suitable base classes for your inheritance hierarchy. For any child view controllers that are <a href="containers-asviewcontroller.html">`ASViewControllers`</a>, these classes know the exact number of user taps it would take to make the view controller visible (0 if currently visible).
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Knowing a view controller’s visibility depth allows view controllers to automatically take appropriate actions as a user approaches or leaves them. Non-default tabs in an app might preload some of their data; a controller 3 levels deep in a navigation stack might progressively free memory for images, text, and fetched data as it gets deeper.
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Any container view controller can implement a simple protocol to integrate with the system. For example, `ASNavigationController` will return a visibility depth of it's own `visibilityDepth` + 1 for a view controller that would be revealed by tapping the back button once.
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You can opt into some of this behavior automatically by enabling `automaticallyAdjustRangeModeBasedOnViewEvents` on `ASViewController`s. With this enabled, if either the view controller or its node conform to `ASRangeControllerUpdateRangeProtocol` (`ASCollectionNode` and `ASTableNode` do by default), the ranges will automatically be decreased as the visibility depth increases to save memory.
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