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// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "ui/views/layout/flex_layout.h"
#include <algorithm>
#include <functional>
#include <string>
#include <utility>
#include <vector>
#include "base/bind.h"
#include "base/callback.h"
#include "base/logging.h"
#include "base/numerics/safe_conversions.h"
#include "base/strings/stringprintf.h"
#include "ui/events/event_target.h"
#include "ui/events/event_target_iterator.h"
#include "ui/gfx/geometry/rect.h"
#include "ui/views/layout/flex_layout_types.h"
#include "ui/views/layout/flex_layout_types_internal.h"
#include "ui/views/view.h"
#include "ui/views/view_properties.h"
// Module-private declarations -------------------------------------------------
namespace views {
namespace internal {
namespace {
// Layout information for a specific child view in a proposed layout.
struct ChildLayout {
ChildLayout(View* view, const FlexSpecification& flex)
: view(view), flex(flex) {}
ChildLayout(ChildLayout&& other) = default;
View* view = nullptr;
bool excluded = false;
// Indicates whether external code has called SetVisible(false) on the view.
bool hidden_by_owner = false;
// Indicates whether the layout has chosen to display this child view.
bool visible = false;
// Start with zero size rather than unspecified size bounds because we start
// all layouts with controls at their minimum allowed sizes.
NormalizedSizeBounds available_size{0, 0};
NormalizedSize preferred_size;
NormalizedSize current_size;
NormalizedRect actual_bounds;
NormalizedInsets margins;
NormalizedInsets internal_padding;
FlexSpecification flex;
// Copying this struct would be expensive and they only ever live in a vector
// in Layout (see below) so we'll only allow move semantics.
// Represents a specific stored layout given a set of size bounds.
struct Layout {
explicit Layout(int64_t layout_counter) : layout_id(layout_counter) {}
// Indicates which layout pass this layout was created/last validated on. If
// this number disagrees with FlexLayoutInternal::layout_counter_, we need to
// re-validate the layout before using it.
mutable uint32_t layout_id;
std::vector<ChildLayout> child_layouts;
NormalizedInsets interior_margin;
NormalizedSizeBounds available_size;
NormalizedSize total_size;
// Preserves layouts for common layout requests, because we may be asked to
// recompute them many times but don't want to repeat the calculation.
// Specifically, we will be asked for:
// - The layout's minimum size (bounds = {0, 0})
// - The layout's preferred size (neither bound specified)
// - The final layout at the dimensions of the host view (both bounds nonzero)
// There is also the possibility of a view with a flex layout being embedded in
// a view with a flex layout, where the inner view has a nontrivial flex
// specification. In that case, in order to handle e.g. labels in the inner
// view, the outer layout manager will ask for the inner view's preferred height
// for its width, which potentially involves another layout calculation.
// However, these calculations are transient - they only happen when the layout
// is recalculated or validated, and in the latter case only one set of bounds
// is evaluated. So we will keep exactly one of these layouts around.
// As a first pass, we'll store all of these specifically. In the future we can
// switch to using something more sophisticated, like an MRU cache, if we find
// we're thrashing for some other reason.
class LayoutCache {
// Removes all saved layouts.
void Clear() {
// Gets a cached layout, or nullptr if no layout is cached for the specified
// bounds.
Layout* Get(const NormalizedSizeBounds& bounds) const {
if (bounds == NormalizedSizeBounds(0, 0))
return minimum_.get();
if (bounds == NormalizedSizeBounds())
return preferred_.get();
if (bounds == intermediate_.bounds)
return intermediate_.layout.get();
if (bounds == current_.bounds)
return current_.layout.get();
return nullptr;
// Caches a layout associated with the specified bounds.
void Put(const NormalizedSizeBounds& bounds, std::unique_ptr<Layout> layout) {
if (bounds == NormalizedSizeBounds(0, 0)) {
minimum_ = std::move(layout);
} else if (bounds == NormalizedSizeBounds()) {
preferred_ = std::move(layout);
} else if (!bounds.cross() || !bounds.main()) {
intermediate_.bounds = bounds;
intermediate_.layout = std::move(layout);
} else {
current_.bounds = bounds;
current_.layout = std::move(layout);
struct CacheEntry {
NormalizedSizeBounds bounds;
std::unique_ptr<Layout> layout;
std::unique_ptr<Layout> minimum_;
std::unique_ptr<Layout> preferred_;
// TODO(dfried): consider replacing these with an MRUCache if this ends up
// thrashing a lot (see note above).
CacheEntry intermediate_;
CacheEntry current_;
// Calculates and maintains 1D spacing between a sequence of child views.
class ChildViewSpacing {
// Given the indices of two child views, returns the amount of space that
// should be placed between them if they were adjacent. If the first index is
// absent, uses the left edge of the parent container. If the second index is
// absent, uses the right edge of the parent container.
using GetViewSpacingCallback =
base::RepeatingCallback<int(base::Optional<int>, base::Optional<int>)>;
explicit ChildViewSpacing(const GetViewSpacingCallback& get_view_spacing);
ChildViewSpacing(ChildViewSpacing&& other);
ChildViewSpacing& operator=(ChildViewSpacing&& other);
bool HasViewIndex(int view_index) const;
int GetLeadingInset() const;
int GetTrailingInset() const;
int GetLeadingSpace(int view_index) const;
int GetTrailingSpace(int view_index) const;
int GetTotalSpace() const;
// Returns the change in space required if the specified view index were
// added.
int GetAddDelta(int view_index) const;
// Add the view at the specified index.
// If |new_leading| or |new_trailing| is specified, it will be set to the new
// leading/trailing space for the view at the index that was added.
void AddViewIndex(int view_index,
int* new_leading = nullptr,
int* new_trailing = nullptr);
base::Optional<int> GetPreviousViewIndex(int view_index) const;
base::Optional<int> GetNextViewIndex(int view_index) const;
GetViewSpacingCallback get_view_spacing_;
// Maps from view index to the leading spacing for that index.
std::map<int, int> leading_spacings_;
// The trailing space (space preceding the trailing margin).
int trailing_space_;
const GetViewSpacingCallback& get_view_spacing)
: get_view_spacing_(get_view_spacing),
get_view_spacing.Run(base::Optional<int>(), base::Optional<int>())) {}
ChildViewSpacing::ChildViewSpacing(ChildViewSpacing&& other)
: get_view_spacing_(std::move(other.get_view_spacing_)),
trailing_space_(other.trailing_space_) {}
ChildViewSpacing& ChildViewSpacing::operator=(ChildViewSpacing&& other) {
if (this != &other) {
get_view_spacing_ = std::move(other.get_view_spacing_);
leading_spacings_ = std::move(other.leading_spacings_);
trailing_space_ = other.trailing_space_;
return *this;
bool ChildViewSpacing::HasViewIndex(int view_index) const {
return leading_spacings_.find(view_index) != leading_spacings_.end();
int ChildViewSpacing::GetLeadingInset() const {
if (leading_spacings_.empty())
return 0;
return leading_spacings_.begin()->second;
int ChildViewSpacing::GetTrailingInset() const {
return trailing_space_;
int ChildViewSpacing::GetLeadingSpace(int view_index) const {
auto it = leading_spacings_.find(view_index);
DCHECK(it != leading_spacings_.end());
return it->second;
int ChildViewSpacing::GetTrailingSpace(int view_index) const {
auto it = leading_spacings_.find(view_index);
DCHECK(it != leading_spacings_.end());
if (++it == leading_spacings_.end())
return trailing_space_;
return it->second;
int ChildViewSpacing::GetTotalSpace() const {
int space = trailing_space_;
for (auto& pr : leading_spacings_)
space += pr.second;
return space;
int ChildViewSpacing::GetAddDelta(int view_index) const {
base::Optional<int> prev = GetPreviousViewIndex(view_index);
base::Optional<int> next = GetNextViewIndex(view_index);
const int old_spacing = next ? GetLeadingSpace(*next) : GetTrailingInset();
const int new_spacing = get_view_spacing_.Run(prev, view_index) +
get_view_spacing_.Run(view_index, next);
return new_spacing - old_spacing;
void ChildViewSpacing::AddViewIndex(int view_index,
int* new_leading,
int* new_trailing) {
base::Optional<int> prev = GetPreviousViewIndex(view_index);
base::Optional<int> next = GetNextViewIndex(view_index);
const int leading_space = get_view_spacing_.Run(prev, view_index);
const int trailing_space = get_view_spacing_.Run(view_index, next);
leading_spacings_[view_index] = leading_space;
if (next)
leading_spacings_[*next] = trailing_space;
trailing_space_ = trailing_space;
if (new_leading)
*new_leading = leading_space;
if (new_trailing)
*new_trailing = trailing_space;
base::Optional<int> ChildViewSpacing::GetPreviousViewIndex(
int view_index) const {
auto it = leading_spacings_.lower_bound(view_index);
if (it == leading_spacings_.begin())
return base::Optional<int>();
return (--it)->first;
base::Optional<int> ChildViewSpacing::GetNextViewIndex(int view_index) const {
auto it = leading_spacings_.upper_bound(view_index);
if (it == leading_spacings_.end())
return base::Optional<int>();
return it->first;
// Utility functions -----------------------------------------------------------
gfx::Insets GetInternalPadding(const View* view) {
const gfx::Insets* const margins =
return margins ? *margins : gfx::Insets();
} // anonymous namespace
// Private implementation ------------------------------------------------------
// Holds child-view-specific layout parameters that are not stored in the
// properties system.
// We should consider storing some or all of these in the properites system.
struct ChildLayoutParams {
bool excluded = false;
bool hidden_by_owner = false;
base::Optional<FlexSpecification> flex_specification;
// Internal data structure and functionality for FlexLayout so we don't have to
// declare a bunch of classes and data in the .h file.
class FlexLayoutInternal {
explicit FlexLayoutInternal(FlexLayout* layout)
: layout_(*layout) {} //, cached_layouts_(kMaxCachedLayouts) {}
// Suggests that the current layout needs to be recalculated. Setting |force|
// to true indicates that we know all of the cached layouts are invalid and we
// should discard them; otherwise we will keep them and re-validate on the
// next layout pass.
void InvalidateLayout(bool force);
// Gets the proposed layout for a set of size bounds. Returns a cached layout
// if one is present and valid.
const Layout& CalculateLayout(const SizeBounds& bounds);
// Applies an existing layout to all child views, with the appropriate
// current alignment.
void DoLayout(const Layout& layout, const gfx::Rect& bounds);
LayoutOrientation orientation() const { return layout_.orientation(); }
// Determines whether a layout is still valid.
bool IsLayoutValid(const Layout& cached_layout) const;
// Creates a brand new layout from the available |bounds|.
// Call DoLayout() to actually apply the layout.
const Layout& CalculateNewLayout(const NormalizedSizeBounds& bounds);
// Calculates the position of each child view and the size of the overall
// layout based on tentative visibilities and sizes for each child.
void UpdateLayoutFromChildren(Layout* layout,
ChildViewSpacing* child_spacing,
const NormalizedSizeBounds& bounds) const;
// Calculates the cross-layout space available to a view based on the
// available space and margins.
base::Optional<int> GetAvailableCrossAxisSize(
const Layout& layout,
int child_index,
const NormalizedSizeBounds& bounds) const;
// Calculates a margin between two child views based on each's margin and any
// internal padding present in one or both elements. Uses properties of the
// layout, like whether adjacent margins should be collapsed.
int CalculateMargin(int margin1, int margin2, int internal_padding) const;
// Calculates the preferred spacing between two child views, or between a
// view edge and the first or last visible child views.
int CalculateChildSpacing(const Layout& layout,
base::Optional<int> child1_index,
base::Optional<int> child2_index) const;
const gfx::Insets& GetMargins(const View* view) const;
FlexLayout& layout_;
// Instead of marking each layout as dirty/needing validation, we instead keep
// a value that changes every time InvalidateLayout() is called. If the value
// stored in a cached layout doesn't match this value, we validate it and
// update the value. We use an int64_t because the odds of spurious collision
// (i.e. the counter wrapping back around to the *exact* same value before
// validating) are effectively zero.
uint32_t layout_counter_ = 0;
LayoutCache layout_cache_;
void FlexLayoutInternal::InvalidateLayout(bool force) {
if (force)
const Layout& FlexLayoutInternal::CalculateLayout(const SizeBounds& bounds) {
// If bounds are smaller than the minimum cross axis size, expand them.
NormalizedSizeBounds normalized_bounds = Normalize(orientation(), bounds);
if (normalized_bounds.cross() &&
*normalized_bounds.cross() < layout_.minimum_cross_axis_size()) {
normalized_bounds = NormalizedSizeBounds{normalized_bounds.main(),
// See if we have a cached layout already that is still valid.
Layout* const cached_layout = layout_cache_.Get(normalized_bounds);
if (cached_layout && IsLayoutValid(*cached_layout))
return *cached_layout;
// Calculate a new layout from scratch.
return CalculateNewLayout(normalized_bounds);
void FlexLayoutInternal::DoLayout(const Layout& layout,
const gfx::Rect& bounds) {
NormalizedPoint start = Normalize(orientation(), bounds.origin());
// Apply main axis alignment.
const int excess_main =
Normalize(orientation(), bounds.size()).main() - layout.total_size.main();
switch (layout_.main_axis_alignment()) {
case LayoutAlignment::kStart:
case LayoutAlignment::kCenter:
start.set_main(start.main() + excess_main / 2);
case LayoutAlignment::kEnd:
start.set_main(start.main() + excess_main);
case LayoutAlignment::kStretch:
NOTIMPLEMENTED() << "Main axis stretch/justify is not yet supported.";
// Position controls within the client area.
for (const ChildLayout& child_layout : layout.child_layouts) {
if (child_layout.excluded)
if (child_layout.visible != child_layout.view->visible())
layout_.SetViewVisibility(child_layout.view, child_layout.visible);
if (child_layout.visible) {
NormalizedRect actual = child_layout.actual_bounds;
actual.Offset(start.main(), start.cross());
gfx::Rect denormalized = Denormalize(orientation(), actual);
base::Optional<int> FlexLayoutInternal::GetAvailableCrossAxisSize(
const Layout& layout,
int child_index,
const NormalizedSizeBounds& bounds) const {
if (!bounds.cross())
return base::Optional<int>();
const ChildLayout& child_layout = layout.child_layouts[child_index];
const int leading_margin =
const int trailing_margin =
return std::max(0, *bounds.cross() - (leading_margin + trailing_margin));
int FlexLayoutInternal::CalculateMargin(int margin1,
int margin2,
int internal_padding) const {
const int result = layout_.collapse_margins() ? std::max(margin1, margin2)
: margin1 + margin2;
return std::max(0, result - internal_padding);
int FlexLayoutInternal::CalculateChildSpacing(
const Layout& layout,
base::Optional<int> child1_index,
base::Optional<int> child2_index) const {
const int left_margin =
child1_index ? layout.child_layouts[*child1_index].margins.main_trailing()
: layout.interior_margin.main_leading();
const int right_margin =
child2_index ? layout.child_layouts[*child2_index].margins.main_leading()
: layout.interior_margin.main_trailing();
const int left_padding =
? layout.child_layouts[*child1_index].internal_padding.main_trailing()
: 0;
const int right_padding =
? layout.child_layouts[*child2_index].internal_padding.main_leading()
: 0;
return CalculateMargin(left_margin, right_margin,
left_padding + right_padding);
const gfx::Insets& FlexLayoutInternal::GetMargins(const View* view) const {
const gfx::Insets* const margins = view->GetProperty(views::kMarginsKey);
return margins ? *margins : layout_.default_child_margins();
void FlexLayoutInternal::UpdateLayoutFromChildren(
Layout* layout,
ChildViewSpacing* child_spacing,
const NormalizedSizeBounds& bounds) const {
// Calculate starting minimum for cross-axis size.
int min_cross_size =
layout->interior_margin.cross_trailing(), 0));
layout->total_size = NormalizedSize(0, min_cross_size);
// For cases with a non-zero cross-axis bound, the objective is to fit the
// layout into that precise size, not to determine what size we need.
bool force_cross_size = false;
if (bounds.cross() && *bounds.cross() > 0) {
layout->total_size.SetToMax(0, *bounds.cross());
force_cross_size = true;
std::vector<Inset1D> cross_spacings(layout->child_layouts.size());
for (size_t i = 0; i < layout->child_layouts.size(); ++i) {
ChildLayout& child_layout = layout->child_layouts[i];
// We don't have to deal with excluded or invisible children.
if (child_layout.excluded || !child_layout.visible)
// Update the cross-axis margins and if necessary, the size.
Inset1D& cross_spacing = cross_spacings[i];
if (!force_cross_size) {
const int cross_size = std::min(child_layout.current_size.cross(),
layout->total_size.SetToMax(0, cross_spacing.size() + cross_size);
// Calculate main-axis size and upper-left main axis coordinate.
int leading_space;
if (child_spacing->HasViewIndex(i))
leading_space = child_spacing->GetLeadingSpace(i);
child_spacing->AddViewIndex(i, &leading_space);
layout->total_size.Enlarge(leading_space, 0);
const int size_main = child_layout.current_size.main();
layout->total_size.Enlarge(size_main, 0);
// Add the end margin.
layout->total_size.Enlarge(child_spacing->GetTrailingInset(), 0);
// Calculate cross-axis positioning based on the cross margins and size that
// were calculated above.
const Span cross_span(0, layout->total_size.cross());
for (size_t i = 0; i < layout->child_layouts.size(); ++i) {
ChildLayout& child_layout = layout->child_layouts[i];
// We don't have to deal with excluded or invisible children.
if (child_layout.excluded || !child_layout.visible)
// Start with a size appropriate for the child view. For child views which
// can become larger than the preferred size, start with the preferred size
// and let the alignment operation (specifically, if the alignment is set to
// kStretch) grow the child view.
const int starting_cross_size = std::min(
child_layout.current_size.cross(), child_layout.preferred_size.cross());
cross_span, layout_.cross_axis_alignment(), cross_spacings[i]);
const Layout& FlexLayoutInternal::CalculateNewLayout(
const NormalizedSizeBounds& bounds) {
DCHECK(!bounds.cross() ||
*bounds.cross() >= layout_.minimum_cross_axis_size());
std::unique_ptr<Layout> layout = std::make_unique<Layout>(layout_counter_);
layout->interior_margin = Normalize(orientation(), layout_.interior_margin());
std::map<int, std::vector<int>> order_to_view_index;
const bool main_axis_bounded = bounds.main().has_value();
// Step through the children, creating placeholder layout view elements
// and setting up initial minimal visibility.
View* const view =;
for (int i = 0; i < view->child_count(); ++i) {
View* child = view->child_at(i);
layout->child_layouts.emplace_back(child, layout_.GetFlexForView(child));
ChildLayout& child_layout = layout->child_layouts.back();
child_layout.excluded = layout_.IsViewExcluded(child);
if (child_layout.excluded)
child_layout.margins = Normalize(orientation(), GetMargins(child));
child_layout.internal_padding =
Normalize(orientation(), GetInternalPadding(child));
child_layout.preferred_size =
Normalize(orientation(), child->GetPreferredSize());
child_layout.hidden_by_owner = layout_.IsHiddenByOwner(child);
child_layout.visible = !child_layout.hidden_by_owner;
if (child_layout.hidden_by_owner)
// gfx::Size calculation depends on whether flex is allowed.
if (main_axis_bounded) {
child_layout.available_size = {
0, GetAvailableCrossAxisSize(*layout, i, bounds)};
child_layout.current_size = Normalize(
child, Denormalize(orientation(), child_layout.available_size)));
// We should revisit whether this is a valid assumption for text views
// in vertical layouts.
// Keep track of non-hidden flex controls.
const bool can_flex =
(child_layout.flex.weight() > 0 &&
child_layout.preferred_size.main() > 0) ||
child_layout.current_size.main() < child_layout.preferred_size.main();
if (can_flex)
} else {
// All non-flex or unbounded controls get preferred size.
child_layout.current_size = child_layout.preferred_size;
child_layout.visible = child_layout.current_size.main() > 0;
// Actual size and positioning will be set during the final layout
// calculation.
// Do the initial layout update, calculating spacing between children.
ChildViewSpacing child_spacing(
base::Unretained(this), base::ConstRef(*layout)));
UpdateLayoutFromChildren(layout.get(), &child_spacing, bounds);
if (main_axis_bounded && !order_to_view_index.empty()) {
// Step through each flex priority allocating as much remaining space as
// possible to each flex view.
for (auto flex_it = order_to_view_index.begin();
flex_it != order_to_view_index.end(); ++flex_it) {
// Check to see we haven't filled available space.
int remaining = *bounds.main() - layout->total_size.main();
if (remaining <= 0) {
// The flex algorithm we're using works as follows:
// * For each child view at a particular flex order:
// - Calculate the percentage of the remaining flex space to allocate
// based on the ratio of its weight to the total unallocated weight
// at that order.
// - If the child view is already visible (it will be at its minimum
// size, which may or may not be zero), add the space the child is
// already taking up.
// - If the child view is not visible and adding it would introduce
// additional margin space between child views, subtract that
// additional space from the amount available.
// - Ask the child view's flex rule how large it would like to be
// within the space available.
// - If the child view would like to be larger, make it so, and
// subtract the additional space consumed by the child and its
// margins from the total remaining flex space.
// Note that this algorithm isn't *perfect* for specific cases, which are
// noted below; namely when margins very asymmetrical the sizing of child
// views can be slightly different from what would otherwise be expected.
// We have a TODO to look at ways of making this algorithm more "fair" in
// the future (but in the meantime most issues can be resolved by setting
// reasonable margins and by using flex order).
// Build a list of the elements to flex.
int flex_total = 0;
std::for_each(flex_it->second.begin(), flex_it->second.end(),
[&](int index) {
auto weight = layout->child_layouts[index].flex.weight();
if (weight > 0)
flex_total += weight;
// Note: because the child views are evaluated in order, if preferred
// minimum sizes are not consistent across a single priority expanding
// the parent control could result in children swapping visibility.
// We currently consider this user error; if the behavior is not
// desired, prioritize the child views' flex.
for (auto index_it = flex_it->second.begin();
remaining >= 0 && index_it != flex_it->second.end(); ++index_it) {
const int view_index = *index_it;
ChildLayout& child_layout = layout->child_layouts[view_index];
// Offer a share of the remaining space to the view.
int flex_amount;
if (child_layout.flex.weight() > 0) {
const int flex_weight = child_layout.flex.weight();
// Round up so we give slightly greater weight to earlier views.
flex_amount =
int{std::ceil((float{remaining} * flex_weight) / flex_total)};
flex_total -= flex_weight;
} else {
flex_amount = remaining;
// If the layout was previously invisible, then making it visible
// may result in the addition of margin space, so we'll have to
// recalculate the margins on either side of this view. The change in
// margin space (if any) counts against the child view's flex space
// allocation.
// Note: In cases where the layout's internal margins and/or the child
// views' margins are wildly different sizes, subtracting the full delta
// out of the available space can cause the first view to be smaller
// than we would expect (see TODOs in unit tests for examples). We
// should look into ways to make this "feel" better (but in the
// meantime, please try to specify reasonable margins).
const int margin_delta = child_spacing.HasViewIndex(view_index)
? 0
: child_spacing.GetAddDelta(view_index);
// This is the space on the main axis that was already allocated to the
// child view; it will be added to the total flex space for the child
// view since it is considered a fixed overhead of the layout if it is
// nonzero.
const int old_size =
child_layout.visible ? child_layout.current_size.main() : 0;
// Offer the modified flex space to the child view and see how large it
// wants to be (or if it wants to be visible at that size at all).
const NormalizedSizeBounds available(
flex_amount + old_size - margin_delta,
const NormalizedSize new_size = Normalize(
child_layout.view, Denormalize(orientation(), available)));
if (new_size.main() <= 0)
// If the amount of space claimed increases (but is still within
// bounds set by our flex rule) we can make the control visible and
// claim the additional space.
const int to_deduct = (new_size.main() - old_size) + margin_delta;
DCHECK_GE(to_deduct, 0);
if (to_deduct > 0 && to_deduct <= remaining) {
child_layout.available_size = available;
child_layout.current_size = new_size;
child_layout.visible = true;
remaining -= to_deduct;
if (!child_spacing.HasViewIndex(view_index))
// Reposition the child controls (taking margins into account) and
// calculate remaining space.
UpdateLayoutFromChildren(layout.get(), &child_spacing, bounds);
const Layout& result = *layout;
layout_cache_.Put(bounds, std::move(layout));
return result;
bool FlexLayoutInternal::IsLayoutValid(const Layout& cached_layout) const {
// If we've already evaluated a layout for this size and not been
// invalidated since then, then this is a valid layout.
if (cached_layout.layout_id == layout_counter_)
return true;
// Need to compare preferred child sizes with what we're seeing.
View* const view =;
int child_index = 0;
for (const ChildLayout& proposed_view_layout : cached_layout.child_layouts) {
// Check that there is another child and that it's the view we expect.
DCHECK(child_index < view->child_count())
<< "Child views should not be removed without clearing the cache.";
const View* child = view->child_at(child_index++);
// Ensure child views have not been reordered.
if (child != proposed_view_layout.view)
return false;
// Ignore hidden and excluded views, unless their status has changed.
const bool excluded = layout_.IsViewExcluded(child);
if (proposed_view_layout.excluded != excluded)
return false;
if (excluded)
const bool hidden_by_owner = layout_.IsHiddenByOwner(child);
if (proposed_view_layout.hidden_by_owner != hidden_by_owner)
return false;
if (hidden_by_owner)
// Sanity check that a child's visibility hasn't been modified outside
// the layout manager.
if (proposed_view_layout.visible != child->visible())
return false;
if (proposed_view_layout.visible) {
// Check that view margins haven't changed for visible controls.
if (GetMargins(child) !=
Denormalize(orientation(), proposed_view_layout.margins))
return false;
// Same for internal padding.
if (GetInternalPadding(child) !=
Denormalize(orientation(), proposed_view_layout.internal_padding))
return false;
// Check that the control still has the same preferred size given its
// flex and visibility.
if (child->GetPreferredSize() !=
Denormalize(orientation(), proposed_view_layout.preferred_size))
return false;
const gfx::Size preferred = proposed_view_layout.flex.rule().Run(
child, Denormalize(orientation(), proposed_view_layout.available_size));
if (preferred !=
Denormalize(orientation(), proposed_view_layout.current_size))
return false;
DCHECK_EQ(child_index, view->child_count()) << "Child views added without "
"clearing the cache - this "
"should not happen.";
// This layout is still valid. Update the layout counter to show it's valid
// in the current layout context.
cached_layout.layout_id = layout_counter_;
return true;
} // namespace internal
// FlexLayout
// -------------------------------------------------------------------
: internal_(std::make_unique<internal::FlexLayoutInternal>(this)) {}
FlexLayout::~FlexLayout() {}
FlexLayout& FlexLayout::SetOrientation(LayoutOrientation orientation) {
if (orientation != orientation_) {
orientation_ = orientation;
return *this;
FlexLayout& FlexLayout::SetCollapseMargins(bool collapse_margins) {
if (collapse_margins != collapse_margins_) {
collapse_margins_ = collapse_margins;
return *this;
FlexLayout& FlexLayout::SetMainAxisAlignment(
LayoutAlignment main_axis_alignment) {
DCHECK_NE(main_axis_alignment, LayoutAlignment::kStretch)
<< "Main axis stretch/justify is not yet supported.";
if (main_axis_alignment_ != main_axis_alignment) {
main_axis_alignment_ = main_axis_alignment;
return *this;
FlexLayout& FlexLayout::SetCrossAxisAlignment(
LayoutAlignment cross_axis_alignment) {
if (cross_axis_alignment_ != cross_axis_alignment) {
cross_axis_alignment_ = cross_axis_alignment;
return *this;
FlexLayout& FlexLayout::SetInteriorMargin(const gfx::Insets& interior_margin) {
if (interior_margin_ != interior_margin) {
interior_margin_ = interior_margin;
return *this;
FlexLayout& FlexLayout::SetMinimumCrossAxisSize(int size) {
if (minimum_cross_axis_size_ != size) {
minimum_cross_axis_size_ = size;
return *this;
FlexLayout& FlexLayout::SetDefaultChildMargins(const gfx::Insets& margins) {
if (default_child_margins_ != margins) {
default_child_margins_ = margins;
return *this;
FlexLayout& FlexLayout::SetFlexForView(
const View* view,
const FlexSpecification& flex_specification) {
auto it = child_params_.find(view);
DCHECK(it != child_params_.end());
it->second.flex_specification = flex_specification;
return *this;
FlexLayout& FlexLayout::ClearFlexForView(const View* view) {
auto it = child_params_.find(view);
DCHECK(it != child_params_.end());
return *this;
FlexLayout& FlexLayout::SetViewExcluded(const View* view, bool excluded) {
auto it = child_params_.find(view);
DCHECK(it != child_params_.end());
if (excluded != it->second.excluded) {
it->second.excluded = excluded;
return *this;
FlexLayout& FlexLayout::SetDefaultFlex(
const FlexSpecification& flex_specification) {
default_flex_ = flex_specification;
return *this;
const FlexSpecification& FlexLayout::GetFlexForView(const View* view) const {
auto it = child_params_.find(view);
DCHECK(it != child_params_.end());
const base::Optional<FlexSpecification>& spec = it->second.flex_specification;
return spec ? *spec : default_flex_;
bool FlexLayout::IsViewExcluded(const View* view) const {
auto it = child_params_.find(view);
DCHECK(it != child_params_.end());
return it->second.excluded;
bool FlexLayout::IsHiddenByOwner(const View* view) const {
auto it = child_params_.find(view);
DCHECK(it != child_params_.end());
return it->second.hidden_by_owner;
gfx::Size FlexLayout::GetPreferredSize(const View* host) const {
DCHECK_EQ(host_, host);
return GetPreferredSize(SizeBounds());
int FlexLayout::GetPreferredHeightForWidth(const View* host, int width) const {
DCHECK_EQ(host_, host);
return GetPreferredSize(SizeBounds{width, base::Optional<int>()}).height();
gfx::Size FlexLayout::GetMinimumSize(const View* host) const {
DCHECK_EQ(host_, host);
return GetPreferredSize(SizeBounds{0, 0});
void FlexLayout::InvalidateLayout() {
void FlexLayout::Installed(View* host) {
host_ = host;
// Add all the existing children when the layout manager is installed.
// If new children are added, ViewAdded() will be called and we'll add data
// there.
for (int i = 0; i < host->child_count(); ++i) {
View* const child = host->child_at(i);
internal::ChildLayoutParams child_layout_params;
child_layout_params.hidden_by_owner = !child->visible();
child_params_.emplace(child, child_layout_params);
void FlexLayout::ViewAdded(View* host, View* view) {
DCHECK_EQ(host_, host);
internal::ChildLayoutParams child_layout_params;
child_layout_params.hidden_by_owner = !view->visible();
child_params_.emplace(view, child_layout_params);
void FlexLayout::ViewRemoved(View* host, View* view) {
void FlexLayout::ViewVisibilitySet(View* host, View* view, bool visible) {
DCHECK_EQ(host, host_);
DCHECK_EQ(view->parent(), host);
auto it = child_params_.find(view);
DCHECK(it != child_params_.end());
const bool hide = !visible;
if (it->second.hidden_by_owner != hide) {
it->second.hidden_by_owner = hide;
if (!it->second.excluded) {
// It's not always obvious to our host that an owner of a child view
// changing its visibility could change a layout. So we'll notify the host
// view that its layout is potentially invalid, and it will in turn call
// InvalidateLayout() on the layout manager (i.e. this object).
// Retrieve the preferred size for the control in the given bounds.
gfx::Size FlexLayout::GetPreferredSize(const SizeBounds& bounds) const {
if (!host_)
return gfx::Size();
const gfx::Insets insets = host_->GetInsets();
SizeBounds content_bounds = bounds;
content_bounds.Enlarge(-insets.width(), -insets.height());
const internal::Layout& proposed_layout =
gfx::Size result = Denormalize(orientation(), proposed_layout.total_size);
result.Enlarge(insets.width(), insets.height());
return result;
void FlexLayout::Layout(View* host) {
DCHECK_EQ(host, host_);
// TODO(dfried): for a handful of views which override GetInsets(), the way
// this method is implemented in View may be incorrect. Please revisit.
gfx::Rect bounds = host_->GetContentsBounds();
const internal::Layout& layout =
internal_->DoLayout(layout, bounds);
} // namespace views