# ChatLayout

## Table of contents

- About
- Features
  - What ChatLayout doesn’t provide (And why it is good)
- Requirements
- Example
- Installation
- Contributing
- Todo
  - About `UICollectionViewDiffableDataSource`
  - About Supplementary Views
  - About Texture
  - About animation
  - About sticky headers or footers
- License
- Articles
- Sponsor this project
- Author

## About

`ChatLayout` is an alternative solution to MessageKit. It uses custom `UICollectionViewLayout` to provide you full control over the presentation as well as all the tools available in `UICollectionView`.

## Features

- Supports dynamic cells and supplementary view sizes.
- Animated insertion/deletion/reloading/moving of the items.
- Keeps content of the last visible item at the top or bottom of the `UICollectionView` during updates.
- Provides tools for precise scrolling to the required item.
- Shipped with generic container views to simplify the custom items implementation.

### What ChatLayout doesn’t provide (And why it is good)

`ChatLayout` is the custom `UICollectionViewLayout`, so:

- You don’t have to extend or override any custom `UIViewController` or `UICollectionView`. You need to instantiate them yourself and use them the way you like.

- `ChatLayout` does not rely on modified `UICollectionViewFlowLayout` nor does it rotate your `UICollectionView` upside-down. This means you can use your views as if they would be regular cells within `UICollectionView`. You can benefit from using the default `UIKit` implementations of `adjustedContextInsets` (and others) because your view controller is a normal view controller without any hacks or tricks.

- `ChatLayout` doesn’t require you to calculate all the cell sizes before it renders them on the screen. You can fully use auto-layout constraints and rely on the fact that the correct size will be calculated in the runtime. However, `ChatLayout` as any other `UICollectionViewLayout` will benefit from you providing the estimated sizes of your cells as it will allow you to get better performance.

- `ChatLayout` doesn’t enforce you to use any specific data model. You can store your messages and update `UICollectionView` the way you like. The only thing you need is to respect the natural boundaries that `UICollectionView` have and correctly implement `UICollectionViewDataSource`. The Example app uses DifferenceKit to process changes in the data model.

- `ChatLayout` doesn’t enforce you to use any specific `UIView`s to create your collection cells. You can create them the way you like. It can be any `UICollectionViewCell` or `UICollectionReusableView`. There are some generic `UIView`s bundled with the library that may help you to build them faster. However, you do not have to use them.

- `ChatLayout` doesn’t handle the keyboard appearance behavior. You have to implement that yourself from scratch or use the library you are already using in your project. It gives you full control over the keyboard presentation. The only thing you have to do is to update the `contentInsets` of your `UICollectionView`.

- `ChatLayout` doesn’t provide you any input control. You can use any one you like and customise it the way you like. The Example app for instance uses InputBarAccessoryView.

## Example

To run the example project, clone the repo, and run `pod install` from the Example directory first.

## Installation

`ChatLayout` is available through CocoaPods, Carthage and SwiftPM. See the `Example` app for the usage details.

If you are using cocoapods you can install the whole package using `pod 'ChatLayout'`. If you do not need the additional components provided, you can install only the layout itself using `pod 'ChatLayout/Core'`

## Contributing

`ChatLayout` is in active development, and we welcome your contributions.

If you’d like to contribute to this repo, please read the contribution guidelines.

## Todo

- [ ] Improve the test coverage

### About `UICollectionViewDiffableDataSource`

`ChatLayout` can process any update commands that you send to your `UICollectionView`, so you can use `UICollectionViewDiffableDataSource` as well.

### About Supplementary Views

It can be tempting and it may look like it is the right way to go, but do not use supplementary views to decorate your messages or groups of them. `UICollectionView` processes them in a different order: `UICollectionViewCell`s first and only after switches to `UICollectionReusableView`s. You will most likely face some unexpected behaviour during the animation. I strongly advice you against using sections at all.

### About Texture

`ChatLayout` can be used together with Texture to improve the auto-layout performance. But keep in mind that it’s default wrapper is hardcoded to work exclusively with `UICollectionViewFlowLayout`. See issue. You will have to implement `ChatLayoutDelegate` yourself and propagate the node size manually.

### About animation

If you see a strange or unexpected animation during the updates, check your data model and the commands you send to the `UICollectionView`‘s `performBatchUpdates`. Especialy if you are using some diffing algorithms like DifferenceKit. It is very possible that you are sending delete/insert commands when you expect to see reload. The easiest way to check it is by adding `print("\(updateItems)")` into `ChatLayout.prepare(forCollectionViewUpdates:)` method. `ChatLayout` doesn’t know what you expected to see. It just processes your changes according to the commands it has received.

### About sticky headers or footers

Sticky headers or footers are not supported by `ChatLayout` but your contributions are welcome.

## License

`ChatLayout` is distributed under the MIT license.

`ChatLayout` is provided for your use, free-of-charge, on an as-is basis. We make no guarantees, promises or apologies. Caveat developer.

## Articles

English:

- My COVID-19 lockdown project or how I started to dig into a custom UICollectionViewLayout to get a ChatLayout

Russian:

- Мой Covid-19 lockdown проект, или, как я полез в кастомный UICollectionViewLayout и получил ChatLayout

## Sponsor this project

If you find this library useful, and especially if you are using it in production, please consider sponsoring this project here. I work on `ChatLayout` in my spare time, and your sponsorship would help me to continue developing and contributing to the Open Source community. Your support will enable me to dedicate more time and resources to this project, ensuring that it remains up-to-date and relevant for years to come.

Thank you for your consideration!

## Author

Evgeny Kazaev, eugene.kazaev@gmail.com. Twitter ekazaev

I am happy to answer any questions you may have. Just create a new issue.