react4j.annotations

Annotation Type PreUpdate

@Documented
 @Target(value=METHOD)
public @interface PreUpdate

Identifies a method that is called before a component is updated or re-rendered. There must only be one method annotated with this annotation in a single component. This method is invoked in the "commit" phase using reacts getSnapshotBeforeUpdate() lifecycle method.

This method is used to get access to the DOM prior to it being updated. This is useful if there is state stored on the DOM that is not present in the VirtualDOM. The method annotated with PreUpdate can query the DOM and then apply the necessary changes in PostMountOrUpdate. Scroll position is an example of data stored on the DOM but not present in the VirtualDOM and implementing auto-scrolling to new content would require use of this lifecycle method to calculate the new offset.

The method must also conform to the following constraints:

• Must not be annotated with any other react4j annotation
• Must have 0 parameters
• Must not return a value
• Must not be private
• Must not be public
• Must not be static
• Must not be abstract
• Must not throw exceptions
• Must be accessible from the same package as the class annotated by ReactComponent
• Should not be public as not expected to be invoked outside the component. A warning will be generated but can be suppressed by the SuppressWarnings or SuppressReact4jWarnings annotations with a key "React4j:PublicMethod". This warning is also suppressed by the annotation processor if it is implementing an interface method.
• Should not be protected if in the class annotated with the ReactComponent annotation as the method is not expected to be invoked outside the component. A warning will be generated but can be suppressed by the SuppressWarnings or SuppressReact4jWarnings annotations with a key "React4j:ProtectedMethod".