com.facebook.litho.annotations

Annotation Type LayoutSpec

@Retention(value=RUNTIME)
public @interface LayoutSpec

A class that is annotated with this annotation will be used to create a composite component that is made up of other components. A layout spec is the logical equivalent of a composite view in Android.

The class annotated with LayoutSpec must implement a method with the OnCreateLayout or OnCreateLayoutWithSizeSpec annotation. It may also implement methods with the following annotations:

• OnCreateInitialState
• OnCreateTreeProp
• OnCreateTransition
• OnUpdateState
• OnEvent
• OnLoadStyle
• OnEnteredRange
• OnExitedRange
• OnRegisterRanges
• OnCalculateCachedValue
• ShouldUpdate

Example:

 @LayoutSpec
 public class CounterSpec {

   @OnCreateLayout
   static Component onCreateLayout(
     ComponentContext c,
     @Prop int id,
     @State int count) {

     return Row.create(c)
       .backgroundColor(Color.WHITE)
       .heightDip(64)
       .paddingDip(YogaEdge.ALL, 8)
       .child(
         Text.create(c)
           .text(" + ")
           .clickHandler(Counter.onClick(c))
       )
       .child(
         Text.create(c)
           .text(String.valueOf(count))
       )
       .build();
   }

   @OnCreateInitialState
   static void onCreateInitialState(
       ComponentContext c,
       StateValue<Integer> count) {
     count.set(0);
   }

   @OnEvent(ClickEvent.class)
   static void onClick(ComponentContext c, @Prop int id) {
     Counter.increment(c, id);
   }

   @OnUpdateState
   static void increment(StateValue<Integer> count, @Param int counterId) {
     count.set(count.get() + 1);
   }
 }

If you want to create a component that mounts its own content, then use MountSpec instead. See more docs at https://fblitho.com

See Also:

Prop, TreeProp, InjectProp, State, Param, FromPreviousCreateLayout

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
java.lang.Class<?>[]	events
boolean	isPublic
boolean	isPureRender
java.lang.String	simpleNameDelegate
java.lang.Class<?>[]	triggers
java.lang.String	value Class name of the generated component.

Element Detail

value

public abstract java.lang.String value

Class name of the generated component. When not provided defaults to name of the annotated class sans the "Spec" suffix. E.g. "MyComponentSpec" to "MyComponent".

In order to avoid confusion, this should only be used if you have a very good reason for it. For instance to avoid naming collisions.

Default:

""

isPublic

public abstract boolean isPublic

Returns:

Boolean indicating whether the generated class should be public. If not, it will be package-private.

Default:

true

isPureRender

public abstract boolean isPureRender

Returns:

Boolean indicating Whether the component implements a pure render function. If this is true and the Component didn't change during an update of the ComponentTree measurements and LayoutOutputs will be reused instead of being calculated again.

Default:

false

events

public abstract java.lang.Class<?>[] events

Returns:

List of event POJOs this component can dispatch. Used to generate event dispatch methods.

Default:

{}

triggers

public abstract java.lang.Class<?>[] triggers

Returns:

List of trigger POJOs this component can dispatch. Used to generate trigger creation methods.

Default:

{}

simpleNameDelegate

public abstract java.lang.String simpleNameDelegate

Returns:

the prop name of the Component this component will delegate getSimpleName calls to. This will cause getSimpleName to include the name of that component in its return. This is useful for seeing better debug information when using generic wrapping components (like error boundary wrappers).

Default:

""