iOS migration guides

Removed background parameter in UIKitView and UIKitViewController

Deprecated UIKitView and UIKitViewController APIs have the background parameter, while the new ones don't. The parameter was deemed redundant and removed:

• If you need to set the interop view background for new instances, you can do it using the factory parameter.

• If you need the background to be updatable, put the corresponding code in the update lambda.

Touches or gestures may stop working as expected

The new default touch behavior uses delays to determine if the touch is meant for the interop view or for the Compose container of that view: the user has to hold still for at least 150 ms before the interop view will receive it.

If you need Compose Multiplatform to process touches like it used to, consider the new experimental UIKitInteropProperties constructor. It has the interactionMode parameter, which you can set to UIKitInteropInteractionMode.NonCooperative to make Compose transfer touches directly to interop views.

The constructor is marked experimental because we ultimately intend to keep the interactability of interop views described by a single bool flag. The behavior described explicitly in the interactionMode parameter will most likely be derived automatically in the future.

accessibilityEnabled replaced by isNativeAccessibilityEnabled, and turned off by default

The accessibilityEnabled parameter of the old UIKitView and UIKitViewController constructors was moved and renamed to be available as the UIKitInteropProperties.isNativeAccessibilityEnabled property. It is also set to false by default.

The isNativeAccessibilityEnabled property taints the merged Compose subtree with native accessibility resolution. So it is not recommended to set to true unless you need rich accessibility capabilities of the interop view (such as web views).

For the rationale behind this property and its default value, see the in-code documentation for the UIKitInteropProperties class.

onResize parameter removed

The onResize parameter of the old UIKitView and UIKitViewController constructors set a custom frame based on the rect argument but didn't affect the Compose layout itself, so it was not intuitive to use. On top of that, the default implementation of the onResize parameter needed to properly set the frame of interop view and contained some implementation details about properly clipping the view.

How to make do without onResize:

• If you need to react to the interop view frame change, you can:

  • override layoutSubviews of the interop UIView,

  • override viewDidLayoutSubviews of the interop UIViewController,

  • or add onGloballyPositioned to the Modifier chain.

• If you need to set the frame of your interop view, use the corresponding Compose modifiers: size, fillMaxSize, and so on.

Some onReset usage patterns were invalidated

It is incorrect to use a non-null onReset lambda along with remember { UIView() }.

Consider the following code:

When a UIKitView enters the composition, either factory or onReset is called, never both. So, if onReset is not null, the remembered view can be different from the one that is shown onscreen: A composable can leave the composition and leave behind an instance of the view that will be reused after resetting it in onReset instead of allocating a new one using factory.

To avoid such mistakes, don't specify an onReset value in the constructor. You may need to perform callbacks from within the interop view based on the context in which the function emitting it entered the composition: In this case, consider storing the callback inside the view using update on onReset.