PluginableFlowLayout

Reusable layout with alignment. Could be extended with plugins.

How to use PluginableFlowLayout

1. When creating collection layout use PluginableFlowLayout
2. Setup base UICollectionViewFlowLayout with your needs
   • properly setup scrollDirection
   • other settings
3. If needed custom alignment, modify UICollectionView – turn off isPagingEnabled (default value is false) and set decelerationRate to .fast.

PluginableFlowLayout

Layout descendant of UICollectionViewFlowLayout.

Has feature for alignment:

• lineStart – left alignment
• lineCenter – center alignment
• lineEnd – right alignment

If pass nil – there will not be any modifications for targetContentOffset (you can use default isPagingEnabled = true property for items with equal sizes).

Supports items with different sizes.

FlowLayoutPlugin

Protocol for custom plugins

PercentageFlowLayoutPlugin

Realization of FlowLayoutPlugin protocol for adding visibility percentage of items.

Example of horizontal layout:

Example of vertical layout:

Different percentage values

Each percentage value contains number in range [-1; 1] where

• value -1 means that cell is in before position (left position respectfull to center cell)
• value 0 means that cell is in center position (in case of alignment not in center – PercentageFlowLayoutPlugin respect alignment from PluginableFlowLayout)
• value +1 means that cell is in after position (right position respectfull to center cell)

Percentage info contains 3 values:

• collectionVisibility – visibility factor respectfull to bound of collectionView – intersection frame of cell in collectionView
• idealFrameVisibility – visibility factor respectfull to “ideal frame” (respecfull to alignment PluginableFlowLayout) – intersection frame of cell and “ideal frame”
• idealFrameAndCollectionVisibility – mixed visibility factor

Note: if cell has width of collectionView and layout has horizontal scrollDirection (height/vertical) – all values will be equal.

How to use PercentageFlowLayoutPlugin

• pass PercentageFlowLayoutPlugin in constructor of PluginableFlowLayout

let collectionView = UICollectionView(
    frame: .zero,
    collectionViewLayout: PluginableFlowLayout(
        alignment: .lineStart,
        plugins: [PercentageFlowLayoutPlugin()]
    )
)

• override method apply(_ layoutAttributes: UICollectionViewLayoutAttributes) and use custom attribute values

override func apply(_ layoutAttributes: UICollectionViewLayoutAttributes) {

    // convert `UICollectionViewLayoutAttributes` to `PluginableFlowLayoutAttributes`
    guard let pluginableAttributes = layoutAttributes as? PluginableFlowLayoutAttributes else {
        return super.apply(layoutAttributes)
    }

    // get custom percentage attribute value
    let percentage = pluginableAttributes.percentageInfo.collectionVisibility ?? 0

    // set UIImageView translation
    let translationX = -percentage / 2 * imageView.bounds.width
    imageView.transform = .init(
        translationX: translationX,
        y: 0
    )

    // set alpha for dimm view
    dimmView.alpha = 1 - abs(percentage * 2)
}

Custom FlowLayoutPlugin

To add custom plugin, you need to realize protocol FlowLayoutPlugin and return modified PluginableFlowLayoutAttributes.

PluginableFlowLayoutAttributes

Kind of sttributes, that store values in dictionary. You can write extension to these class and realize setter/getter for values (like in file PercentageFlowLayoutPlugin.swift).

GitHub

View Github