datasource-overview.md

title	layout	permalink
Overview	docs	/docs/datasource-overview.html

ComponentKit really shines when used with a UICollectionView.

Automatic reuse

Who hasn't had bugs with cell reuse? In ComponentKit, the declarative nature of a Component makes it so you don't have to worry about reuse anymore! This article in objc.io explains in great detail how we achieve automatic reuse and reconfiguration with ComponentKit.

Scroll performance

ComponentKit addresses common scroll performance issues holistically. Putting cells on screen is usually very performance sensitive. Cells are dequeued during scrolling, so any frame drop will be immediately visible.

Automatic and optimized reuse is already great for performance. But also, because generating a component and laying it out is just a succession of pure functions working with immutable data this operation can be very easily moved to the background.

As a result, the list view infrastructure provided by ComponentKit only spends a minimal amount of time in the main thread. No more stutters due to complex view hierarchies or expensive text layout!

The datasources

ComponentKit includes a standard datasource stack dedicated to render components directly in a UICollectionView and with a bit more effort, in a UITableView.

CKComponentDataSource

CKComponentDataSource is at the core of the list view infrastructure. Instances of this class are agnostic to the UICollectionView API. The role of a CKComponentDataSource is to:

1. Take as input changesets containing commands and models. *e.g: "Insert at index 0 in section 1 the item representing ModelA".
2. Generate and layout in the background the components associated to those changes.
3. Output a changeset along with handles to the generated components so that it can be used with a UITableView or a UICollectionView

CKComponentCollectionViewDataSource

CKComponentCollectionViewDataSource is a thin wrapper around CKComponentDataSource that implements the UICollectionViewDataSource API.

It can be used to easily bootstrap a UICollectionView using components. See how to display components in a collection view.

Philosophy

The UIKit way to add content to a collection view is:

1. Tell the UICollectionView to add/insert/update rows or sections.
2. Synchronously, the UICollectionView asks its datasource for number of rows, sections and layout info.
3. Depending on whether or not the updated index paths are visible the UICollectionView will synchronously call cellForItemAtIndexPath:.
4. Finally, the datasource returns a configured cell for this index path.

CKCollectionViewDataSource uses an idiom that is more "reactive":

1. Tell the CKCollectionViewDataSource to add/insert/update rows or sections.
2. Asynchronously, and in the background, computes the corresponding components.
3. When the computation is done, apply the changes to the UICollectionView.

Conceptually, we now have a one directional data flow. Obviously the back and forth between the UICollectionView and the CKCollectionViewDataSource still happens but it is now hidden.

What about UITableViews ?

To power a UITableView with components you can directly use CKComponentDataSource. See this code sample.