Use case
RenderBox.localToGlobal uses getTransformTo which is called during the layout phase. Calling getTransformTo at build phase to build an overlay child causes a frame delay because changes are scheduled for the next build. This can lead to bugs like #167359 and #168545.
Proposal
The new OverlayPortal.overlayChildLayoutBuilder was added to solve this problem:
|
/// Creates an [OverlayPortal] that renders the widget `overlayChildBuilder` |
|
/// builds on the closest [Overlay] when [OverlayPortalController.show] is |
|
/// called. |
|
/// |
|
/// Developers can use `overlayChildBuilder` to configure the overlay child |
|
/// based on the the size and the location of [OverlayPortal.child] within the |
|
/// target [Overlay], as well as the size of the [Overlay] itself. This allows |
|
/// the overlay child to, for example, always follow [OverlayPortal.child] and |
|
/// at the same time resize itself base on how close it is to the edges of |
|
/// the [Overlay]. |
|
/// |
|
/// The `overlayChildBuilder` callback is called during layout. To ensure the |
|
/// paint transform of [OverlayPortal.child] in relation to the target |
|
/// [Overlay] is up-to-date by then, all [RenderObject]s between the |
|
/// [OverlayPortal] to the target [Overlay] must establish their paint |
|
/// transform during the layout phase, which most [RenderObject]s do. One |
|
/// exception is the [CompositedTransformFollower] widget, whose [RenderObject] |
|
/// only establishes the paint transform when composited. Putting a |
|
/// [CompositedTransformFollower] between the [OverlayPortal] and the [Overlay] |
|
/// may resulting in an incorrect child paint transform being provided to the |
|
/// `overlayChildBuilder` and will cause an assertion in debug mode. |
|
OverlayPortal.overlayChildLayoutBuilder({ |
Migrate usage of OverlayPortal with RenderBox.localToGlobal to OverlayPortal.overlayChildLayoutBuilder, for example, in RawMenuAnchor.