Simple strip container that can reveal/hide tab strip.

ios/chrome/browser/ui/strip/strip_container_view_controller.mm

+// Copyright 2016 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.
+
+// ======                        New Architecture                         =====
+// =         This code is only used in the new iOS Chrome architecture.       =
+// ============================================================================
+
+#import "ios/chrome/browser/ui/strip/strip_container_view_controller.h"
+
+#import "ios/chrome/browser/ui/ui_types.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace {
+CGFloat kStripHeight = 200.0;
+}
+
+@interface StripContainerViewController ()
+
+// Whichever view controller is at the top of the screen. This view controller
+// controls the status bar.
+@property(nonatomic, weak) UIViewController* topmostViewController;

[marq (ping after 24h), 2016/12/21 17:26:15]

I don't think you need this if we aren't going to vary the strip position (which
we aren't).

[edchin, 2016/12/22 10:17:17]

This container implementation accounts for when there is no tab strip view. So
doesn't it need to change the status bar based on that? In fact, perhaps I need
to implement it so that the status bar changes whenever one toggles the tab
strip. 

[marq (ping after 24h), 2016/12/22 11:33:07]

You are of course correct.

+
+@property(nonatomic, strong) Constraints* contentConstraintsWithStrip;
+@property(nonatomic, strong) Constraints* contentConstraintsWithoutStrip;
+@property(nonatomic, strong) Constraints* stripConstraints;
+
+// Cache for forwarding methods to child view controllers.
+@property(nonatomic, assign) SEL actionToForward;
+@property(nonatomic, weak) UIResponder* forwardingTarget;
+
+@property(nonatomic, strong) NSLayoutConstraint* stripHeightConstraint;
+
+// Contained view controller utility methods.
+- (void)removeChildViewController:(UIViewController*)viewController;
+
+// Called after a new content view controller is set, but before
+// |-didMoveToParentViewController:| is called on that view controller.
+- (void)didAddContentViewController;
+
+// Called after a new strip view controller is set, but before
+// |-didMoveToParentViewController:| is called on that view controller.
+- (void)didAddContentViewController;

[marq (ping after 24h), 2016/12/21 17:26:15]

-didAddStripViewController, right? Or is this error in the tab container as
well?

[edchin, 2016/12/22 10:17:17]

Error in tab container as well. Will update that in a separate CL. 

+
+// Methods to populate the constraint properties.
+- (void)updateContentConstraintsWithStrip;
+- (void)updateContentConstraintsWithoutStrip;
+- (void)updateStripConstraints;
+
+@end
+
+@implementation StripContainerViewController
+
+@synthesize contentViewController = _contentViewController;
+@synthesize stripViewController = _stripViewController;
+@synthesize topmostViewController = _topmostViewController;
+@synthesize contentConstraintsWithStrip = _contentConstraintsWithStrip;
+@synthesize contentConstraintsWithoutStrip = _contentConstraintsWithoutStrip;
+@synthesize stripConstraints = _stripConstraints;
+@synthesize actionToForward = _actionToForward;
+@synthesize forwardingTarget = _forwardingTarget;
+@synthesize stripHeightConstraint = _stripHeightConstraint;
+
+#pragma mark - Public properties
+
+- (void)setContentViewController:(UIViewController*)contentViewController {
+  if (self.contentViewController == contentViewController)
+    return;
+
+  // Remove the current content view controller, if any.
+  [NSLayoutConstraint
+      deactivateConstraints:self.contentConstraintsWithoutStrip];
+  [NSLayoutConstraint deactivateConstraints:self.contentConstraintsWithStrip];
+  [self removeChildViewController:self.contentViewController];
+
+  // Add the new content view controller.
+  [self addChildViewController:contentViewController];
+  contentViewController.view.translatesAutoresizingMaskIntoConstraints = NO;
+  [self.view addSubview:contentViewController.view];
+  _contentViewController = contentViewController;
+  [self didAddContentViewController];
+  [self.view setNeedsUpdateConstraints];
+  [self.contentViewController didMoveToParentViewController:self];
+}
+
+- (void)setStripViewController:(UIViewController*)stripViewController {
+  if (self.stripViewController == stripViewController)
+    return;
+
+  // Remove the current strip view controller, if any.
+  [NSLayoutConstraint deactivateConstraints:self.stripConstraints];
+  [NSLayoutConstraint deactivateConstraints:self.contentConstraintsWithStrip];
+  [self removeChildViewController:self.stripViewController];
+
+  // Add the new strip view controller.
+  [self addChildViewController:stripViewController];
+  stripViewController.view.translatesAutoresizingMaskIntoConstraints = NO;
+  [self.view addSubview:stripViewController.view];
+  _stripViewController = stripViewController;
+  [self didAddStripViewController];
+  [self.view setNeedsUpdateConstraints];
+  [self.stripViewController didMoveToParentViewController:self];
+}
+
+#pragma mark - UIViewController
+
+- (void)updateViewConstraints {
+  if (self.stripViewController) {
+    [NSLayoutConstraint activateConstraints:self.stripConstraints];
+    [NSLayoutConstraint activateConstraints:self.contentConstraintsWithStrip];
+  } else {
+    [NSLayoutConstraint
+        activateConstraints:self.contentConstraintsWithoutStrip];
+  }
+  [super updateViewConstraints];
+}
+
+- (UIViewController*)childViewControllerForStatusBarHidden {
+  return self.topmostViewController;
+}
+
+- (UIViewController*)childViewControllerForStatusBarStyle {
+  return self.topmostViewController;
+}
+
+#pragma mark - UIResponder
+
+// Before forwarding actions up the responder chain, give both contained
+// view controllers a chance to handle them.
+- (BOOL)canPerformAction:(SEL)action withSender:(id)sender {
+  self.actionToForward = nullptr;
+  self.forwardingTarget = nil;
+  for (UIResponder* responder in
+       @[ self.contentViewController, self.stripViewController ]) {
+    if ([responder canPerformAction:action withSender:sender]) {
+      self.actionToForward = action;
+      self.forwardingTarget = responder;
+      return YES;
+    }
+  }
+  return [super canPerformAction:action withSender:sender];
+}
+
+#pragma mark - NSObject method forwarding
+
+- (id)forwardingTargetForSelector:(SEL)aSelector {
+  if (aSelector == self.actionToForward) {
+    return self.forwardingTarget;
+  }
+  return nil;
+}
+
+#pragma mark - Private methods
+
+- (void)removeChildViewController:(UIViewController*)viewController {
+  if (viewController.parentViewController != self)
+    return;
+  [viewController willMoveToParentViewController:nil];
+  [viewController.view removeFromSuperview];
+  [viewController removeFromParentViewController];
+}
+
+- (void)didAddContentViewController {
+  if (self.stripViewController) {
+    [self updateContentConstraintsWithStrip];
+  } else {
+    self.topmostViewController = self.contentViewController;
+    [self updateContentConstraintsWithoutStrip];
+  }
+  if (!self.stripViewController) {
+    self.topmostViewController = self.contentViewController;
+  }
+}
+
+- (void)didAddStripViewController {
+  [self updateStripConstraints];
+  // If there's already a content view controller, update the constraints for
+  // that, too.
+  if (self.contentViewController) {
+    [self updateContentConstraintsWithStrip];
+  }
+  self.topmostViewController = self.stripViewController;
+}
+
+- (void)updateContentConstraintsWithoutStrip {
+  UIView* contentView = self.contentViewController.view;
+  self.contentConstraintsWithoutStrip = @[
+    [contentView.topAnchor constraintEqualToAnchor:self.view.topAnchor],
+    [contentView.bottomAnchor constraintEqualToAnchor:self.view.bottomAnchor],
+    [contentView.leadingAnchor constraintEqualToAnchor:self.view.leadingAnchor],
+    [contentView.trailingAnchor
+        constraintEqualToAnchor:self.view.trailingAnchor],
+  ];
+}
+
+- (void)updateContentConstraintsWithStrip {
+  UIView* contentView = self.contentViewController.view;
+  self.contentConstraintsWithStrip = @[
+    [contentView.topAnchor
+        constraintEqualToAnchor:self.stripViewController.view.bottomAnchor],
+    [contentView.bottomAnchor constraintEqualToAnchor:self.view.bottomAnchor],
+    [contentView.leadingAnchor constraintEqualToAnchor:self.view.leadingAnchor],
+    [contentView.trailingAnchor
+        constraintEqualToAnchor:self.view.trailingAnchor],
+  ];
+}
+
+- (void)updateStripConstraints {
+  UIView* stripView = self.stripViewController.view;
+  self.stripHeightConstraint =
+      [stripView.heightAnchor constraintEqualToConstant:0.0];
+  self.stripConstraints = @[
+    [stripView.topAnchor constraintEqualToAnchor:self.view.topAnchor],
+    [stripView.leadingAnchor constraintEqualToAnchor:self.view.leadingAnchor],
+    [stripView.trailingAnchor constraintEqualToAnchor:self.view.trailingAnchor],
+    self.stripHeightConstraint,
+  ];
+}
+
+// Action for UIResponder chain that toggles visibility of tab strip.

[marq (ping after 24h), 2016/12/21 17:26:15]

Nit: all actions are by definition using the responder chain. "Action to toggle
visibility of the tab strip".

[edchin, 2016/12/22 10:17:17]

Done.

+- (void)toggleTabStrip:(id)sender {

[marq (ping after 24h), 2016/12/21 17:26:15]

Add a ui/actions/tab_strip_actions.h file with a TabStripActions protocol for
this.

[edchin, 2016/12/22 10:17:17]

Done.

+  self.stripHeightConstraint.constant =
+      self.stripHeightConstraint.constant > 0 ? 0.0 : kStripHeight;
+  [self.view setNeedsUpdateConstraints];

[marq (ping after 24h), 2016/12/21 17:26:15]

Is this needed? No constraints have been added or removed. Changing the constant
of an active constraint should mark the constrained views as dirty and trigger a
layout.

[edchin, 2016/12/22 10:17:17]

Done.

+  [self.view updateConstraintsIfNeeded];
+}
+
+@end