blob: f037fcae78fe69ca92d4812a03d83e2dd2ba826a [file] [log] [blame]
// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'package:engine/ui.dart';
import 'box.dart';
/// Signature for a function that takes a [RenderBox] and returns the [Size]
/// that the [RenderBox] would have if it were laid out with the given
/// [BoxConstraints].
///
/// The methods of [ChildLayoutHelper] adhere to this signature.
typedef ChildLayouter = Size Function(RenderBox child, BoxConstraints constraints);
/// A collection of static functions to layout a [RenderBox] child with the
/// given set of [BoxConstraints].
///
/// All of the functions adhere to the [ChildLayouter] signature.
class ChildLayoutHelper {
// This class is not meant to be instantiated or extended; this constructor
// prevents instantiation and extension.
const ChildLayoutHelper._();
/// Returns the [Size] that the [RenderBox] would have if it were to
/// be laid out with the given [BoxConstraints].
///
/// This method calls [RenderBox.getDryLayout] on the given [RenderBox].
///
/// This method should only be called by the parent of the provided
/// [RenderBox] child as it binds parent and child together (if the child
/// is marked as dirty, the child will also be marked as dirty).
///
/// See also:
///
/// * [layoutChild], which actually lays out the child with the given
/// constraints.
static Size dryLayoutChild(RenderBox child, BoxConstraints constraints) {
return child.getDryLayout(constraints);
}
/// Lays out the [RenderBox] with the given constraints and returns its
/// [Size].
///
/// This method calls [RenderBox.layout] on the given [RenderBox] with
/// `parentUsesSize` set to true to receive its [Size].
///
/// This method should only be called by the parent of the provided
/// [RenderBox] child as it binds parent and child together (if the child
/// is marked as dirty, the child will also be marked as dirty).
///
/// See also:
///
/// * [dryLayoutChild], which does not perform a real layout of the child.
static Size layoutChild(RenderBox child, BoxConstraints constraints) {
child.layout(constraints, parentUsesSize: true);
return child.size;
}
}