Pass in Actions

Follow this simple rule: Selectors should be implemented in the same file they are referenced.

The following counterexample establishes a hidden coupling between the parent and child component. If another component tries to use ChildComponent or if the method is renamed in ParentComponent, it will crash at runtime.

@implementation ParentComponent
+ (instancetype)new
{
  return [super newWithComponent:[ChildComponent new]];
}
- (void)someAction:(CKComponent *)sender
{
  // Do something
}
@end
@implementation ChildComponent
+ (instancetype)new
{
  return [super newWithComponent:
          CK::ButtonComponentBuilder
          .action(@selector(someAction:))
          .build()];
}
@end

Instead, always pass selectors from parents to children. In the following example, it is explicit that the child component needs a CKTypedComponentAction<> selector. If the parent component renames the someAction: method, it's far easier to catch renaming the parameter.

@implementation ParentComponent
+ (instancetype)new
{
  CKComponentScope scope(self);
  return [super newWithComponent:
          [ChildComponent
           newWithAction:{scope, @selector(someAction:)}]];
}
- (void)someAction:(CKComponent *)sender
{
  // Do something
}
@end
@implementation ChildComponent
+ (instancetype)newWithAction:(CKTypedComponentAction<>)action
{
  return [super newWithComponent:
          CK::ButtonComponentBuilder()
          .action(action)
          .build()];
}
@end