List

Material Design Lists are a continuous group of text or images. The elements comprising Lists are referred to as List Items. The MDCBaseCell is a List Item at its simplest--a basic UICollectionViewCell subclass with Material Ink Ripple and Elevation.

Description

The Material guidelines for Lists are extensive, and there is no class at this time for implementing any one of them, let alone all of them. However, the MDCBaseCell provides a starting point to build anything the guidelines provide.

To build a List using the MDCBaseCell simply treat it like you would any other UICollectionViewCell.

The MDCBaseCell has two configurable properties--Ink Ripple color (currentInkColor) and Elevation (elevation).

Below is an example:

Example Walkthrough / How to implement your own List Cell

The example files can be found here

Our example consists of a custom UICollectionViewController: examples/CollectionListCellExampleTypicalUse.m and also of a custom UICollectionViewCell: examples/supplemental/CollectionViewListCell.m.

The main focus will be on the custom cell as that's where all the logic goes in, whereas the collection view and its controller are using mostly boilerplate code of setting up a simple example and collection view.

Layout

For our example we will have a layout consisting of a left aligned UIImageView, a title text UILabel and a details text UILabel. The title text will have a max of 1 line whereas the details text can be up to 3 lines. It is important to note that neither the image nor the labels need to be set. To see more of the spec guidelines for Lists please see here: https://material.io/go/design-lists

To create our layout we used auto layout constraints that are all set up in the (void)setupConstraints method in our custom cell. It is important to make sure we set translatesAutoresizingMaskIntoConstraints to NO for all the views we are applying constraints on.

Ink Ripple

Interactable Material components and specifically List Cells have an ink ripple when tapped on. To add ink to your cells there are a few steps you need to take:

1. Add an MDCInkView property to your custom cell.

2. Initialize MDCInkView on init and add it as a subview:

_inkView = [[MDCInkView alloc] initWithFrame:self.bounds];
_inkView.usesLegacyInkRipple = NO;
[self addSubview:_inkView];

3. Initialize a CGPoint property in your cell (CGPoint _lastTouch;) to indicate where the last tap was in the cell.

4. Override the UIResponder's touchesBegan method in your cell to identify and save where the touches were so we can then start the ripple animation from that point:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  UITouch *touch = [touches anyObject];
  CGPoint location = [touch locationInView:self];
  _lastTouch = location;

  [super touchesBegan:touches withEvent:event];
}

5. Override the setHighlighted method for your cell and apply the start and stop ripple animations:

- (void)setHighlighted:(BOOL)highlighted {
  [super setHighlighted:highlighted];
  if (highlighted) {
    [_inkView startTouchBeganAnimationAtPoint:_lastTouch completion:nil];
  } else {
    [_inkView startTouchEndedAnimationAtPoint:_lastTouch completion:nil];
  }
}

6. When the cell is reused we must make sure no outstanding ripple animations stay on the cell so we need to clear the ink before:

- (void)prepareForReuse {
  [_inkView cancelAllAnimationsAnimated:NO];
  [super prepareForReuse];
}

Now there is ink in our cells!

Self Sizing

In order to have cells self-size based on content and not rely on magic number constants to decide how big they should be, we need to follow these steps:

1. apply autoulayout constraints of our added subviews relative to each other and their superview (the cell‘s contentView). We need to make sure our constraints don’t define static heights or widths but rather constraints that are relative or our cell won't calculate itself based on the dynamically sized content.

You can see how it is achieved in the (void)setupConstraints method in our example. If you'll notice there are some constraints that are set up to be accessible throughout the file:

  NSLayoutConstraint *_imageLeftPaddingConstraint;
  NSLayoutConstraint *_imageRightPaddingConstraint;
  NSLayoutConstraint *_imageWidthConstraint;

This is in order to support the changing layout if an image is set or not.

2. Because our list cells need to fill the entire width of the collection view, we want to expose the cell's width to be settable by the view controller when the cell is set up. For that we expose a setCellWidth method that sets the width constraint of the contentView:

- (void)setCellWidth:(CGFloat)width {
  _cellWidthConstraint.constant = width;
  _cellWidthConstraint.active = YES;
}

and then in the collection view's cellForItemAtIndexPath delegate method we set the width:

CGFloat cellWidth = CGRectGetWidth(collectionView.bounds);
#if defined(__IPHONE_11_0) && (__IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_11_0)
  if (@available(iOS 11.0, *)) {
    cellWidth -=
        (collectionView.adjustedContentInset.left + collectionView.adjustedContentInset.right);
  }
#endif
  [cell setCellWidth:cellWidth];

3. In our collection view's flow layout we must set an estimatedItemSize so the collection view will defer the size calculations to its content.

Note: It is better to set the size smaller rather than larger or constraints might break in runtime.

_flowLayout.estimatedItemSize = CGSizeMake(kSmallArbitraryCellWidth, kSmallestCellHeight);

Typography

For our example we use a typography scheme to apply the fonts to our cell's UILabel's. Please see Typography Scheme for more info.

Dynamic Type

Dynamic Type allows users to indicate a system-wide preferred text size. To support it in our cells we need to follow these steps:

1. Set each of the label fonts to use the dynamically sized MDC fonts in their set/update methods:

- (void)updateTitleFont {
  if (!_titleFont) {
    _titleFont = defaultTitleFont();
  }
  _titleLabel.font =
      [_titleFont mdc_fontSizedForMaterialTextStyle:MDCFontTextStyleSubheadline
                               scaledForDynamicType:_mdc_adjustsFontForContentSizeCategory];
  [self setNeedsLayout];
}

2. Add an observer in the cell to check for the UIContentSizeCategoryDidChangeNotification which tells us the a system-wide text size has been changed.

[[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(contentSizeCategoryDidChange:)
                                                 name:UIContentSizeCategoryDidChangeNotification
                                               object:nil];

In the selector update the font sizes to reflect the change:

- (void)contentSizeCategoryDidChange:(__unused NSNotification *)notification {
  [self updateTitleFont];
  [self updateDetailsFont];
}

3. Add an observer also in the UIViewController so we can reload the collection view once there is a change:

- (void)contentSizeCategoryDidChange:(__unused NSNotification *)notification {
  [self.collectionView reloadData];
}

iPhone X Safe Area Support

Our collection view needs to be aware of the safe areas when being presented on iPhone X. To do so need to set its contentInsetAdjustmentBehavior to be aware of the safe area:

#if defined(__IPHONE_11_0) && (__IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_11_0)
  if (@available(iOS 11.0, *)) {
    self.collectionView.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentAlways;
  }
#endif

Lastly, as seen in the self-sizing section on step 2, when setting the width of the cell we need to set it to be the width of the collection view bounds minus the adjustedContentInset that now insets based on the safe area.

Landscape Support

In your view controller you need to invalidate the layout of your collection view when there is an orientation change. Please see below for the desired code changes to achieve that:

- (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {
  [super traitCollectionDidChange:previousTraitCollection];
  [self.collectionView.collectionViewLayout invalidateLayout];
  [self.collectionView reloadData];
}

- (void)viewWillTransitionToSize:(CGSize)size
       withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {
  [super viewWillTransitionToSize:size withTransitionCoordinator:coordinator];

  [self.collectionView.collectionViewLayout invalidateLayout];

  [coordinator animateAlongsideTransition:nil completion:^(__unused id context) {
    [self.collectionView.collectionViewLayout invalidateLayout];
  }];
}

Right to Left Text Support

To support right to left text we need to import MDFInternationalization:

#import <MDFInternationalization/MDFInternationalization.h>

and for each of our cell's subviews me need to update the autoResizingMask:

_titleLabel.autoresizingMask =
    MDFTrailingMarginAutoresizingMaskForLayoutDirection(self.mdf_effectiveUserInterfaceLayoutDirection);