components/OverlayWindow/src/MDCOverlayWindow.m

// Copyright 2016-present the Material Components for iOS authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#import "MDCOverlayWindow.h"

#import <objc/runtime.h>

#import "MaterialApplication.h"
#import "MaterialAvailability.h"

/**
 A container view for overlay views.

 Used by MDCOverlayWindow, overlay views are added to the overlay window container when
 @c activateOverlay is called and removed from the overlay window when @c deactivateOverlay is
 called.
 */
@interface MDCOverlayWindowContainerView : UIView
@end

@interface MDCOverlayWindow ()

@property(nonatomic, strong) NSMutableArray *overlays;
@property(nonatomic, strong) MDCOverlayWindowContainerView *overlayView;

// Forward declaration so that MDCOverlayWindowContainerView can call this method.
- (void)noteOverlayRemoved:(UIView *)overlay;

@end

@implementation MDCOverlayWindowContainerView

- (void)willRemoveSubview:(UIView *)subview {
  [super willRemoveSubview:subview];

  MDCOverlayWindow *window = (MDCOverlayWindow *)self.window;
  [window noteOverlayRemoved:subview];
}

// Only allow a tap if it explicitly hit one of the overlays. Otherwise, behave as if this view
// doesn't exist at all.
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
  UIView *hitView = [super hitTest:point withEvent:event];
  return hitView == self ? nil : hitView;
}

@end

@implementation MDCOverlayWindow

- (instancetype)init {
  self = [super init];
  if (self) {
    [self commonInit];
  }
  return self;
}

- (instancetype)initWithFrame:(CGRect)frame {
  self = [super initWithFrame:frame];
  if (self) {
    [self commonInit];
  }
  return self;
}

- (instancetype)initWithCoder:(NSCoder *)aDecoder {
  self = [super initWithCoder:aDecoder];
  if (self) {
    [self commonInit];
  }
  return self;
}

#if MDC_AVAILABLE_SDK_IOS(13_0)
- (instancetype)initWithWindowScene:(UIWindowScene *)windowScene {
  self = [super initWithWindowScene:windowScene];
  if (self) {
    [self commonInit];
  }
  return self;
}
#endif  // MDC_AVAILABLE_SDK_IOS(13_0)

- (void)commonInit {
  self.backgroundColor = [UIColor clearColor];

  _overlays = [[NSMutableArray alloc] init];

  _overlayView = [[MDCOverlayWindowContainerView alloc] initWithFrame:self.bounds];
  _overlayView.autoresizingMask =
      (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);
  _overlayView.backgroundColor = [UIColor clearColor];
  [self addSubview:_overlayView];

  // Set a sane hidden state.
  [self updateOverlayHiddenState];
}

#pragma mark - Window positioning

// Regardless of what was added to this window, ensure that the overlay view is on top.
- (void)didAddSubview:(UIView *)subview {
  [super didAddSubview:subview];

  [self bringSubviewToFront:self.overlayView];
}

#pragma mark - Overlay Activation

- (void)updateOverlayHiddenState {
  BOOL hasOverlays = [self.overlays count] > 0;
  self.overlayView.hidden = !hasOverlays;
  [self updateAccessibilityIsModal];
}

- (void)updateAccessibilityIsModal {
  BOOL containsModal = NO;
  for (UIView *overlay in self.overlays) {
    if (overlay.accessibilityViewIsModal) {
      containsModal = YES;
      break;
    }
  }
  self.overlayView.accessibilityViewIsModal = containsModal;
}

- (void)noteOverlayRemoved:(UIView *)overlay {
  if (!overlay) {
    return;
  }

  // If the overlay argument wasn't managed by us, don't do anything when it goes away.
  if (![self.overlays containsObject:overlay]) {
    return;
  }

  // Clean up the level information stored on the view.
  [self removeLevelForOverlay:overlay];

  // Stop tracking the overlay view.
  [self.overlays removeObject:overlay];

  // Show or hide ourself as needed.
  [self updateOverlayHiddenState];
}

- (void)activateOverlay:(UIView *)overlay withLevel:(UIWindowLevel)level {
  if (!overlay) {
    return;
  }

  // Make sure the that the overlay is out of the view hierarchy, even our own (if this is a
  // re-activation with a new level). If @c overlay is already in the overlay view, then this call
  // will take care of cleaning up @c self.overlays, by way of @c noteOverlayRemoved:.
  [overlay removeFromSuperview];

  // Default to adding the overlay at the very end (on top) of all the other overlays. We'll check
  // the existing overlays to see if this one needs to go in before.
  __block NSUInteger insertionIndex = self.overlays.count;

  // Because @c self.overlays is already sorted by level, we can pick the first index which has a
  // level larger than @c level.
  [self.overlays enumerateObjectsUsingBlock:^(UIView *existing, NSUInteger idx, BOOL *stop) {
    UIWindowLevel existingLevel = [self windowLevelForOverlay:existing];
    if (level < existingLevel) {
      insertionIndex = idx;
      *stop = YES;
    }
  }];

  // Make sure that the overlay is as large as the overlay container view before adding it.
  overlay.bounds = self.overlayView.bounds;
  overlay.center = CGPointMake(CGRectGetMidX(overlay.bounds), CGRectGetMidY(overlay.bounds));
  overlay.translatesAutoresizingMaskIntoConstraints = YES;
  overlay.autoresizingMask = (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight);

  [self setLevel:level forOverlay:overlay];
  [self.overlayView insertSubview:overlay atIndex:insertionIndex];
  [self.overlays insertObject:overlay atIndex:insertionIndex];

  [self updateOverlayHiddenState];
}

- (void)deactivateOverlay:(UIView *)overlay {
  if (!overlay) {
    return;
  }

  // If the overlay wasn't managed by us, don't do anything to deactivate it.
  if (![self.overlays containsObject:overlay]) {
    return;
  }

  // If @c overlay is already in the overlay view, then this call will take care of cleaning up
  // @c self.overlays by way of @c noteOverlayRemoved:.
  [overlay removeFromSuperview];
}

#pragma mark - Level Storage

static char kLevelKey;

- (UIWindowLevel)windowLevelForOverlay:(__unused UIView *)overlay {
  NSNumber *levelObject = objc_getAssociatedObject(self, &kLevelKey);
  return [levelObject floatValue];
}

- (void)setLevel:(UIWindowLevel)level forOverlay:(UIView *)overlay {
  NSNumber *levelObject = @(level);
  objc_setAssociatedObject(overlay, &kLevelKey, levelObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void)removeLevelForOverlay:(UIView *)overlay {
  objc_setAssociatedObject(overlay, &kLevelKey, nil, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end