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This section helps you to understand the core concepts of Kohii.

Renderer and Container

When we play a Video to a destination surface, we call that surface a Renderer. Some examples of a Renderer are VideoView in Android framework, PlayerView in ExoPlayer.

A component that can contain a Renderer is called Container. If a PlayerView renderer is added directly to a FrameLayout, that FrameLayout is a container. In Kohii, by calling bind(someView), you are placing your Video to a Container. The renderer can also be the container when it contains itself.


Currently in Kohii, we only support ViewGroup containers, but theoretically it can be anything. In the future, we will try to expand the concept of container to other types.

The idea of Renderer and Container allows Kohii to build the abstractions around them where a renderer can be attached to a container, detached from a container and passed around, and therefore renderers can be reused for unlimited number of Videos. This behavior is supported out of the box by kohii-exoplayer and kohii-androidx packages.

Playback and Playable

Playback is a component in Kohii, designed to manage the container. Like Fragment in the Android framework which (optionally) has a View and lifecycle, Playback manages a view which is the container, and it has a lifecycle controlled by another component called Manager. A Playback's lifecycle is scoped to the container's lifecycle and the Manager's lifecycle, which is as large as an Activity or a Fragment's lifecycle.

When you place a Video in a container by calling bind(container), Kohii allows you to have some configurations such as tag, delay, visible threshold by which the Video should start or pause, etc. These configurations are passed to the Playback, processed and passed down to lower layer to construct resources for an actual playback. So you can have a Video playing with one configuration in a container, but another configuration in another container. It is helpful when you want to switch a Video playback from list to full-screen and vice-versa.

Playable is a component in Kohii, designed to manage the renderer. A Playable is created when the client calls bind(container), and there is no Playable created previously for the same Video information. In other words, a Playable will be available when there is a Playback requests it.

Kohii manages Playable globally, which means that its lifecycle is scoped to the Application lifetime. But once a Playable is no longer needed, it will be destroyed. In Kohii, when a Playable is not used by any Playback, it will be released and scheduled to be destroyed. Though, during transient states like configuration change, current Playback will be destroyed (because its container is destroyed) and new Playback is still under construction, Kohii will give the Playable a few more time to wait for a Playback to request it. After this duration, if a Playable is not requested, Kohii will destroy it to reclaim its memory.

The idea of Playable and Playback allows client to use the same Video and player resource for different renderers, which help to reduce the memory usage and enable developers to build complicated scenarios much easier.

Bucket, Manager and Group

Considering an Application where you have an Activity contains 3 Fragments: A, B and C. A has a RecyclerView (named RA) contains a lot of Videos. B has a ScrollView (named SB) contains many Videos and another RecyclerView (named RB) contains many Videos too. You only want RB to start playing the Videos automatically, and later you want to disable the Video playback of RB and enable it for RA. Kohii makes this possible by using a number of management components: Bucket, Manager and Group.

Bucket is a component designed to manage a big View component like RecyclerView, NestedScrollView or ViewPager. Bucket is built by the Manager from the View it manages. And it has the responsibility to tell Manager about UI updates, as well as to select which Video to play from all Videos it knows about. The View is called the root of a Bucket. You can setup any View to be the root of a Bucket. A simple FrameLayout can be the root for a Bucket of all the Renderers it contains.

Most of the time you want to use the most suitable root for your use case. For example, in your screen you have a RecyclerView whose each child is a FrameLayout with a PlayerView in it. Either the RecyclerView or each of its FrameLayout children can be the root of a Bucket, but if you want to manage all the Videos at once, you need to use build the Bucket from the RecyclerView. Kohii has built-in factory methods to build Bucket for RecyclerView, NestedScrollView, ViewPager, ViewPager2 and the general ViewGroup. You can have many Bucket in a single screen to enable complicated behavior. For example: when a RecyclerView with many Videos is nested in another RecyclerView, you can build the Bucket for both the RecyclerViews to control the Videos of the nested one.

Manager is a component designed to manage a Fragment or an Activity which contains big View*s using Buckets. Manager creates and manages Buckets for Views on demand. You only need to create Bucket for the View whose Video need to be controlled. So in our scenario above, Fragment B only need to register the RecyclerView to **Kohii*, the Manager will then acknowledge this RecyclerView and create a Bucket for it. Manager also manages all Playbacks in all Buckets, and closely communicates with the Group about any UI change.

Group is as important as an Activity in Android framework. It contains many Managers just like an Activity can contain many Fragments, and it listens to Managers request to refresh the overall state. Because we will only allow a small number of videos from one Bucket of one Manager at a time to be playing, Group exists to take care of playback state of all Managers, and will carefully update the whole screen (i.e the Activity) accordingly.

Master, Engine

Master is the component that controls everything used by the library. In short term, it is the brain of Kohii. There will be only one Master instance exists at one time. It controls the Playable's lifecycle, including destroying them when they are not needed anymore. It manages all the Groups of an Application, dispatch the playback events and so on. The client should never need to access the Master directly.

Engine is a component that connects the client with the Master. An Engine has 3 important responsibilities: to initialize other important components like Managers, Groups, to help the client to bind the Video resource to a Container, and to build Playable for the Video. Most of the time, developer only needs to work with the Engine. You can also build custom Engine for your need.