components/ButtonBar/src/private/MDCAppBarButtonBarBuilder.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 "MDCAppBarButtonBarBuilder.h"

#import <MDFInternationalization/MDFInternationalization.h>
#import <objc/runtime.h>

#import "MDCButtonBar+Private.h"
#import "MDCButtonBarButton.h"
#import "MaterialButtons.h"

// Additional insets for the left-most or right-most items.
static const CGFloat kEdgeButtonAdditionalMarginPhone = 4;
static const CGFloat kEdgeButtonAdditionalMarginPad = 12;

// The default MDCButton's alpha for display state is 0.1 which in the context of bar buttons makes
// it practically invisible. Setting button to a higher opacity is closer to what the button should
// look like when it is disabled.
static const CGFloat kDisabledButtonAlpha = (CGFloat)0.38;

// Default content inset for buttons.
static const UIEdgeInsets kButtonInset = {0, 12, 0, 12};

// Indiana Jones style placeholder view for UINavigationBar. Ownership of UIBarButtonItem.customView
// and UINavigationItem.titleView are normally transferred to UINavigationController but we plan to
// steal them away. In order to avoid crashing during KVO updates, we steal the view away and
// replace it with a sandbag view.
@interface MDCButtonBarSandbagView : UIView
@end

@interface UIBarButtonItem (MDCHeaderInternal)

// Internal version of the standard -customView property. When an item is pushed onto a
// UINavigationController stack, any -customView object is moved over to this property. This
// prevents UINavigationController from adding the customView to its own view hierarchy.
@property(nonatomic, strong, setter=mdc_setCustomView:) UIView *mdc_customView;

@end

@implementation MDCAppBarButtonBarBuilder {
  NSMutableDictionary<NSNumber *, UIFont *> *_fonts;
  NSMutableDictionary<NSNumber *, UIColor *> *_titleColors;
}

- (instancetype)init {
  self = [super init];
  if (self) {
    _fonts = [NSMutableDictionary dictionary];
    _titleColors = [NSMutableDictionary dictionary];
  }
  return self;
}

- (nullable UIFont *)titleFontForState:(UIControlState)state {
  UIFont *font = _fonts[@(state)];
  if (!font && state != UIControlStateNormal) {
    font = _fonts[@(UIControlStateNormal)];
  }
  return font;
}

- (void)setTitleFont:(UIFont *)font forState:(UIControlState)state {
  _fonts[@(state)] = font;
}

- (UIColor *)titleColorForState:(UIControlState)state {
  UIColor *color = _titleColors[@(state)];
  if (!color && state != UIControlStateNormal) {
    color = _titleColors[@(UIControlStateNormal)];
  }
  return color;
}

- (void)setTitleColor:(UIColor *)color forState:(UIControlState)state {
  _titleColors[@(state)] = color;
}

- (void)updateTitleColorForButton:(UIButton *)button withItem:(UIBarButtonItem *)item {
  // Apply title colors to the button in order of descending priority (last one wins).

  // General buttonTitleColor (proxy for contextual tint color)
  [button setTitleColor:self.buttonTitleColor forState:UIControlStateNormal];

  // Explicit -setTitleColor:forState:
  for (NSNumber *state in _titleColors) {
    UIColor *color = _titleColors[state];
    [button setTitleColor:color forState:(UIControlState)state.intValue];
  }

  // The item's explicit tintColor
  if (item.tintColor) {
    [button setTitleColor:item.tintColor forState:UIControlStateNormal];
  }
}

#pragma mark - MDCBarButtonItemBuilding

- (UIView *)buttonBar:(MDCButtonBar *)buttonBar
          viewForItem:(UIBarButtonItem *)buttonItem
          layoutHints:(MDCBarButtonItemLayoutHints)layoutHints {
  if (buttonItem == nil) {
    return nil;
  }

  // Transfer custom view ownership if necessary.
  [self transferCustomViewOwnershipForBarButtonItem:buttonItem];

  // Take the real custom view if it exists instead of sandbag view.
  UIView *customView =
      buttonItem.mdc_customView ? buttonItem.mdc_customView : buttonItem.customView;
  if (customView) {
    return customView;
  }

// NOTE: This assertion does not occur in release builds because it is accessing a private api.
#if DEBUG
  NSAssert(![[buttonItem valueForKey:@"isSystemItem"] boolValue],
           @"Instances of %@ must not be initialized with %@ when working with %@."
           @" This is because we cannot extract the system item type from the item.",
           NSStringFromClass([buttonItem class]),
           NSStringFromSelector(@selector(initWithBarButtonSystemItem:target:action:)),
           NSStringFromClass([MDCButtonBar class]));
#endif

  MDCButtonBarButton *button = [[MDCButtonBarButton alloc] init];
  [button setBackgroundColor:[UIColor clearColor] forState:UIControlStateNormal];
  button.disabledAlpha = kDisabledButtonAlpha;
  button.enableRippleBehavior = buttonBar.enableRippleBehavior;
  if (buttonBar.inkColor) {
    button.inkColor = buttonBar.inkColor;
  }

  button.exclusiveTouch = YES;

  [MDCAppBarButtonBarBuilder configureButton:button fromButtonItem:buttonItem];

  button.uppercaseTitle = buttonBar.uppercasesButtonTitles;
  [button setUnderlyingColorHint:self.buttonUnderlyingColor];
  for (NSNumber *state in _fonts) {
    UIFont *font = _fonts[state];
    [button setTitleFont:font forState:(UIControlState)state.intValue];
  }
  [self updateTitleColorForButton:button withItem:buttonItem];

  [self updateButton:button withItem:buttonItem barMetrics:UIBarMetricsDefault];

  // Contrary to intuition, UIKit provides the UIBarButtonItem as the action's first argument when
  // bar buttons are tapped, NOT the button itself. Simply adding the item's target/action to the
  // button does not allow us to pass the expected argument to the target.
  //
  // MDCButtonBar provides didTapButton:event: to which we can pass button events
  // so that the correct argument is ultimately passed along.
  [button addTarget:buttonBar
                action:@selector(didTapButton:event:)
      forControlEvents:UIControlEventTouchUpInside];

  UIEdgeInsets contentInsets = [MDCAppBarButtonBarBuilder
      contentInsetsForButton:button
              layoutPosition:buttonBar.layoutPosition
                 layoutHints:layoutHints
             layoutDirection:[buttonBar mdf_effectiveUserInterfaceLayoutDirection]
          userInterfaceIdiom:[self usePadInsetsForButtonBar:buttonBar] ? UIUserInterfaceIdiomPad
                                                                       : UIUserInterfaceIdiomPhone];

  button.contentEdgeInsets = contentInsets;
  button.enabled = buttonItem.enabled;
  button.accessibilityLabel = buttonItem.accessibilityLabel;
  button.accessibilityHint = buttonItem.accessibilityHint;
  button.accessibilityValue = buttonItem.accessibilityValue;
  button.accessibilityIdentifier = buttonItem.accessibilityIdentifier;

  return button;
}

#pragma mark - Private

// Used to determine whether or not to apply insets relevant for iPad or use smaller iPhone size
// Because only widths are affected, we use horizontal size class
- (BOOL)usePadInsetsForButtonBar:(MDCButtonBar *)buttonBar {
  const BOOL isPad = [[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPad;
  if (isPad && buttonBar.traitCollection.horizontalSizeClass == UIUserInterfaceSizeClassRegular) {
    return YES;
  }
  return NO;
}

+ (UIEdgeInsets)contentInsetsForButton:(MDCButton *)button
                        layoutPosition:(MDCButtonBarLayoutPosition)layoutPosition
                           layoutHints:(MDCBarButtonItemLayoutHints)layoutHints
                       layoutDirection:(UIUserInterfaceLayoutDirection)layoutDirection
                    userInterfaceIdiom:(UIUserInterfaceIdiom)userInterfaceIdiom {
  UIEdgeInsets contentInsets = kButtonInset;
  if ([button currentImage] || [button currentTitle].length) {
    BOOL isPad = userInterfaceIdiom == UIUserInterfaceIdiomPad;
    CGFloat additionalInset =
        (isPad ? kEdgeButtonAdditionalMarginPad : kEdgeButtonAdditionalMarginPhone);
    BOOL isFirstButton = (layoutHints & MDCBarButtonItemLayoutHintsIsFirstButton) ==
                         MDCBarButtonItemLayoutHintsIsFirstButton;
    BOOL isLastButton = (layoutHints & MDCBarButtonItemLayoutHintsIsLastButton) ==
                        MDCBarButtonItemLayoutHintsIsLastButton;
    if (isFirstButton && layoutPosition == MDCButtonBarLayoutPositionLeading) {
      // Left-most button in LTR, and right-most button in RTL.
      if (layoutDirection == UIUserInterfaceLayoutDirectionLeftToRight) {
        contentInsets.left += additionalInset;
      } else {
        contentInsets.right += additionalInset;
      }
    } else if (isFirstButton && layoutPosition == MDCButtonBarLayoutPositionTrailing) {
      // Right-most button in LTR, and left-most button in RTL.
      if (layoutDirection == UIUserInterfaceLayoutDirectionLeftToRight) {
        contentInsets.right += additionalInset;
      } else {
        contentInsets.left += additionalInset;
      }
    }
    if (isLastButton && layoutPosition == MDCButtonBarLayoutPositionTrailing) {
      // Left-most button in LTR, and right-most button in RTL.
      if (layoutDirection == UIUserInterfaceLayoutDirectionLeftToRight) {
        contentInsets.left += additionalInset;
      } else {
        contentInsets.right += additionalInset;
      }
    } else if (isLastButton && layoutPosition == MDCButtonBarLayoutPositionLeading) {
      // Right-most button in LTR, and left-most button in RTL.
      if (layoutDirection == UIUserInterfaceLayoutDirectionLeftToRight) {
        contentInsets.right += additionalInset;
      } else {
        contentInsets.left += additionalInset;
      }
    }
  } else {
    NSAssert(0, @"No button title or image");
  }

  return contentInsets;
}

+ (void)configureButton:(MDCButton *)destinationButton
         fromButtonItem:(UIBarButtonItem *)sourceButtonItem {
  if (sourceButtonItem == nil || destinationButton == nil) {
    return;
  }

  if (sourceButtonItem.title != nil) {
    [destinationButton setTitle:sourceButtonItem.title forState:UIControlStateNormal];
  }
  if (sourceButtonItem.image != nil) {
    [destinationButton setImage:sourceButtonItem.image forState:UIControlStateNormal];
  }
  if (sourceButtonItem.tintColor != nil) {
    destinationButton.tintColor = sourceButtonItem.tintColor;
  }

  if (sourceButtonItem.title) {
    destinationButton.inkStyle = MDCInkStyleBounded;
  } else {
    destinationButton.inkStyle = MDCInkStyleUnbounded;
  }

  destinationButton.tag = sourceButtonItem.tag;
}

- (void)updateButton:(UIButton *)button
            withItem:(UIBarButtonItem *)item
          barMetrics:(UIBarMetrics)barMetrics {
  [self updateButton:button withItem:item forState:UIControlStateNormal barMetrics:barMetrics];
  [self updateButton:button withItem:item forState:UIControlStateHighlighted barMetrics:barMetrics];
  [self updateButton:button withItem:item forState:UIControlStateDisabled barMetrics:barMetrics];
}

- (void)updateButton:(UIButton *)button
            withItem:(UIBarButtonItem *)item
            forState:(UIControlState)state
          barMetrics:(UIBarMetrics)barMetrics {
  NSString *title = item.title ? item.title : @"";
  if ([UIButton instancesRespondToSelector:@selector(setAttributedTitle:forState:)]) {
    NSMutableDictionary<NSString *, id> *attributes = [NSMutableDictionary dictionary];

    // UIBarButtonItem's appearance proxy values don't appear to come "for free" like they do with
    // typical UIView instances, so we're attempting to recreate the behavior here.
    NSArray *appearanceProxies = @ [[item.class appearance]];
    for (UIBarButtonItem *appearance in appearanceProxies) {
      [attributes addEntriesFromDictionary:[appearance titleTextAttributesForState:state]];
    }
    [attributes addEntriesFromDictionary:[item titleTextAttributesForState:state]];
    if ([attributes count] > 0) {
      [button setAttributedTitle:[[NSAttributedString alloc] initWithString:title
                                                                 attributes:attributes]
                        forState:state];
    }
  } else {
    [button setTitle:title forState:state];
  }

  UIImage *backgroundImage = [item backgroundImageForState:state barMetrics:barMetrics];
  if (backgroundImage) {
    [button setBackgroundImage:backgroundImage forState:state];
  }
}

- (void)transferCustomViewOwnershipForBarButtonItem:(UIBarButtonItem *)barButtonItem {
  UIView *customView = barButtonItem.customView;
  if (customView && ![customView isKindOfClass:[MDCButtonBarSandbagView class]]) {
    // Transfer ownership of any UIBarButtonItem.customView to the internal property
    // so that UINavigationController won't steal the view from us.
    barButtonItem.mdc_customView = customView;
    barButtonItem.customView = [[MDCButtonBarSandbagView alloc] init];
  }
}

@end

@implementation MDCButtonBarSandbagView
@end

@implementation UIBarButtonItem (MDCHeaderInternal)

@dynamic mdc_customView;

- (UIView *)mdc_customView {
  return objc_getAssociatedObject(self, _cmd);
}

- (void)mdc_setCustomView:(UIView *)customView {
  objc_setAssociatedObject(self, @selector(mdc_customView), customView,
                           OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end