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Document reasoning for why CustomMultiChildLayout size can't depend on children and how to do it (#47797)

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creativecreatorormaybenot 2020-01-08 02:48:01 +00:00 committed by Flutter GitHub Bot
parent a1bf03f87a
commit de2514c0e2
2 changed files with 10 additions and 2 deletions
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10
packages/flutter/lib/src/rendering/custom_layout.dart
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@ -29,7 +29,15 @@ class MultiChildLayoutParentData extends ContainerBoxParentData<RenderBox> {
/// given the previous instance.
///
/// Override [getSize] to control the overall size of the layout. The size of
/// the layout cannot depend on layout properties of the children.
/// the layout cannot depend on layout properties of the children. This was
/// a design decision to simplify the delegate implementations: This way,
/// the delegate implementations do not have to also handle various intrinsic
/// sizing functions if the parent's size depended on the children.
/// If you want to build a custom layout where you define the size of that widget
/// based on its children, then you will have to create a custom render object.
/// See [MultiChildRenderObjectWidget] with [ContainerRenderObjectMixin] and
/// [RenderBoxContainerDefaultsMixin] to get started or [RenderStack] for an
/// example implementation.
///
/// Override [performLayout] to size and position the children. An
/// implementation of [performLayout] must call [layoutChild] exactly once for

2
packages/flutter/lib/src/widgets/basic.dart
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@ -1955,7 +1955,7 @@ class LayoutId extends ParentDataWidget<CustomMultiChildLayout> {
/// the children.
///
/// [CustomMultiChildLayout] is appropriate when there are complex relationships
/// between the size and positioning of a multiple widgets. To control the
/// between the size and positioning of multiple widgets. To control the
/// layout of a single child, [CustomSingleChildLayout] is more appropriate. For
/// simple cases, such as aligning a widget to one or another edge, the [Stack]
/// widget is more appropriate.