ReactProp.java

// Copyright 2004-present Facebook. All Rights Reserved.

package com.facebook.react.uimanager;

import javax.annotation.Nullable;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Use this annotation to annotate properties of native views that should be exposed to JS. This
 * annotation should only be used for setter methods of subclasses of {@link ViewManager}.
 *
 * Each annotated method should return {@code void} and take exactly two arguments: first being
 * a view instance to be updated and second a value that should be set.
 *
 * Allowed types of values are:
 *  - primitives (int, boolean, double, float)
 *  - {@link String}
 *  - {@link Boolean}
 *  - {@link ReadableArray}
 *  - {@link ReadableMap}
 *
 * When property gets removed from the corresponding component in React, annotated setter will be
 * called with {@code null} in case of non-primitive value type or with a default value in case when
 * the value type is a primitive (use appropriate default field of this annotation to customize
 * default value that is going to be used: {@link #defaultBoolean}, {@link #defaultDouble}, etc.)
 *
 * Since in case of property removal for non-primitive value type setter will be called with value
 * set to {@code null} it's required that value type is annotated with {@link Nullable}.
 *
 * Note: Since boolean property type can be represented both as primitive and wrapped default value
 * set through {@link #defaultBoolean} is only respected for primitive type and for the wrapped type
 * {@code null} will be used as a default.
 */
@Retention(RUNTIME)
@Target(ElementType.METHOD)
public @interface ReactProp {

  // Used as a default value for "customType" property as "null" is not allowed. Moreover, when this
  // const is used in annotation declaration compiler will actually create a copy of it, so
  // comparing it using "==" with this filed doesn't work either. We need to compare using "equals"
  // which means that this value needs to be unique.
  String USE_DEFAULT_TYPE = "__default_type__";

  /**
   * Name of the property exposed to JS that will be updated using setter method annotated with
   * the given instance of {@code ReactProp} annotation
   */
  String name();

  /**
   * Type of property that will be send to JS. In most of the cases {@code customType} should not be
   * set in which case default type will be send to JS based on the type of value argument from the
   * setter method (e.g. for {@code int}, {@code double} default is "number", for
   * {@code ReadableArray} it's "Array"). Custom type may be used when additional processing of the
   * value needs to be done in JS before sending it over the brige. A good example of that would be
   * backgroundColor property, which is expressed as a {@code String} in JS, but we use
   * {@code processColor} JS module to convert it to {@code int} before sending over the bridge.
   */
  @Nullable String customType() default USE_DEFAULT_TYPE;

  /**
   * Default value for property of type {@code double}. This value will be provided to property
   * setter method annotated with {@link ReactProp} if property with a given name gets removed
   * from the component description in JS
   */
  double defaultDouble() default 0.0;

  /**
   * Default value for property of type {@code float}. This value will be provided to property
   * setter method annotated with {@link ReactProp} if property with a given name gets removed
   * from the component description in JS
   */
  float defaultFloat() default 0.0f;

  /**
   * Default value for property of type {@code int}. This value will be provided to property
   * setter method annotated with {@link ReactProp} if property with a given name gets removed
   * from the component description in JS
   */
  int defaultInt() default 0;

  /**
   * Default value for property of type {@code boolean}. This value will be provided to property
   * setter method annotated with {@link ReactProp} if property with a given name gets removed
   * from the component description in JS
   */
  boolean defaultBoolean() default false;
}