Component Controllers Edit on GitHub
Remember the analogy made in Philosophy: components are like a stencil. They are an immutable snapshot of how a view should be configured at a given moment in time.
Every time something changes, an entirely new component is created and the old one is thrown away. This means components are short-lived, and their lifecycle is not under your control.
But sometimes, you do need an object with a longer lifecycle. Component controllers fill that role:
- Components can’t be delegates because they are short-lived, but component controllers can be delegates.
- Network downloads take time to complete; the component may have been recreated by the time the download completes. The controller can handle the callback.
- You may need an object to own some other object that should have a long lifetime.
- Controllers are instantiated automatically by ComponentKit. Don’t try to create them manually.
- Define a controller by simply creating a subclass of
CKComponentControllerthat has the same name as your component plus “Controller”.
- Your component must have a
CKComponentScopeto have a controller. (If you forget, you will get an assertion failure.)
CKComponentActionmethods handled by your component can also be handled by the controller.
- The component controller is created with the first component.
- When the component is updated, a new instance is generated…
- But the component controller stays the same.
Communication between Component and Component Controller
There is a only a one-way communication channel between the component and its component controller - you can only pass data off of a component to a component controller. A component has no reference its corresponding component controller. This is by design.
To pass data from a component to its controller, expose a
@property on the component in a class extension. The controller can initialize itself with the properties in
initWithComponent:. If these properties will be changing in subsequent state changes (i.e. a new component is being created with different values for these properties), keep them up to date in