struct · iOS 16.0+ · SDK 27.1
@frozen struct ProposedViewSizeA proposal for the size of a view. During layout in SwiftUI, views choose their own size, but they do that in response to a size proposal from their parent view. When you create a custom layout using the ``Layout`` protocol, your layout container participates in this process using `ProposedViewSize` instances. The layout protocol's methods take a proposed size input that you can take into account when arranging views and calculating the size of the composite container. Similarly, your layout proposes a size to each of its own subviews when it measures and places them. Layout containers typically measure their subviews by proposing several sizes and looking at the responses. The container can use this information to decide how to allocate space among its subviews. A layout might try the following special proposals: * The ``zero`` proposal; the view responds with its minimum size. * The ``infinity`` proposal; the view responds with its maximum size. * The ``unspecified`` proposal; the view responds with its ideal size. A layout might also try special cases for one dimension at a time. For example, an ``HStack`` might measure the flexibility of its subviews' widths, while using a fixed value for the height.
static get unspecified(): ProposedViewSizestatic let unspecified: ProposedViewSizeThe proposed size with both dimensions left unspecified. Both dimensions contain `nil` in this size proposal. Subviews of a custom layout return their ideal size when you propose this value using the ``LayoutSubview/dimensions(in:)`` method. A custom layout should also return its ideal size from the ``Layout/sizeThatFits(proposal:subviews:cache:)`` method for this value.
replacingUnspecifiedDimensions(size?: { width: number; height: number }): { width: number; height: number }func replacingUnspecifiedDimensions(by size: CGSize = CGSize(width: 10, height: 10)) -> CGSizeCreates a new proposal that replaces unspecified dimensions in this proposal with the corresponding dimension of the specified size. Use the default value to prevent a flexible view from disappearing into a zero-sized frame, and ensure the unspecified value remains visible during debugging. - Parameter size: A set of concrete values to use for the size proposal in place of any unspecified dimensions. The default value is `10` for both dimensions. - Returns: A new, fully specified size proposal.
static get zero(): ProposedViewSizestatic let zero: ProposedViewSizeA size proposal that contains zero in both dimensions. Subviews of a custom layout return their minimum size when you propose this value using the ``LayoutSubview/dimensions(in:)`` method. A custom layout should also return its minimum size from the ``Layout/sizeThatFits(proposal:subviews:cache:)`` method for this value.
get width(): (number) | nullvar width: CGFloat?The proposed horizontal size measured in points. A value of `nil` represents an unspecified width proposal, which a view interprets to mean that it should use its ideal width.
set width(value: (number) | null)var width: CGFloat?The proposed horizontal size measured in points. A value of `nil` represents an unspecified width proposal, which a view interprets to mean that it should use its ideal width.
static initWidthHeight(width?: (number) | null, height?: (number) | null): ProposedViewSizeinit(width: CGFloat?, height: CGFloat?)Creates a new proposed size using the specified width and height. - Parameters: - width: A proposed width in points. Use a value of `nil` to indicate that the width is unspecified for this proposal. - height: A proposed height in points. Use a value of `nil` to indicate that the height is unspecified for this proposal.
get height(): (number) | nullvar height: CGFloat?The proposed vertical size measured in points. A value of `nil` represents an unspecified height proposal, which a view interprets to mean that it should use its ideal height.
set height(value: (number) | null)var height: CGFloat?The proposed vertical size measured in points. A value of `nil` represents an unspecified height proposal, which a view interprets to mean that it should use its ideal height.
static get infinity(): ProposedViewSizestatic let infinity: ProposedViewSizeA size proposal that contains infinity in both dimensions. Both dimensions contain <doc://com.apple.documentation/documentation/CoreFoundation/swift/floatingpoint/infinity> in this size proposal. Subviews of a custom layout return their maximum size when you propose this value using the ``LayoutSubview/dimensions(in:)`` method. A custom layout should also return its maximum size from the ``Layout/sizeThatFits(proposal:subviews:cache:)`` method for this value.
static init(size: { width: number; height: number }): ProposedViewSizeinit(_ size: CGSize)Creates a new proposed size from a specified size. - Parameter size: A proposed size with dimensions measured in points.
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