React Navigation源代码阅读 ： addNavigationHelpers.js

/**
 *
 * 此模块导出一个函数，该函数用于增强一个 navigation 的功能，
 * 为其添加各种导航函数，所添加的各个导航函数的逻辑其实是
 * 构造相应的 action,然后使用 navigation 的 dispatch 方法
 * 派发出去
 */

import NavigationActions from './NavigationActions';
import invariant from './utils/invariant';

export default function(navigation) {
  return {
    // 使用展开运算符将带增强对象属性全部复制到目标对象
    ...navigation,
      /**
       * goBack 导航函数
       * @param key
       */
    goBack: key => {
      let actualizedKey = key;
      if (key === undefined && navigation.state.key) {
        invariant(
          typeof navigation.state.key === 'string',
          'key should be a string'
        );
        actualizedKey = navigation.state.key;
      }
      return navigation.dispatch(
        NavigationActions.back({ key: actualizedKey })
      );
    },

      /**
       * navigate 导航函数
       * @param navigateTo
       * @param params
       * @param action
       */
    navigate: (navigateTo, params, action) => {
      if (typeof navigateTo === 'string') {
        return navigation.dispatch(
          NavigationActions.navigate({ routeName: navigateTo, params, action })
        );
      }
      invariant(
        typeof navigateTo === 'object',
        'Must navigateTo an object or a string'
      );
      invariant(
        params == null,
        'Params must not be provided to .navigate() when specifying an object'
      );
      invariant(
        action == null,
        'Child action must not be provided to .navigate() when specifying an object'
      );
      return navigation.dispatch(NavigationActions.navigate(navigateTo));
    },

      /**
       *  pop 导航函数
       * @param n
       * @param params
       */
    pop: (n, params) =>
      navigation.dispatch(
        NavigationActions.pop({ n, immediate: params && params.immediate })
      ),

      /**
       * popToTop 导航函数
       * @param params
       */
    popToTop: params =>
      navigation.dispatch(
        NavigationActions.popToTop({ immediate: params && params.immediate })
      ),

    /**
     * For updating current route params. For example the nav bar title and
     * buttons are based on the route params.
     * This means `setParams` can be used to update nav bar for example.
     */
      /**
       * 设置路由参数
       * @param params
       */
    setParams: params => {
      invariant(
        navigation.state.key && typeof navigation.state.key === 'string',
        'setParams cannot be called by root navigator'
      );
      const key = navigation.state.key;
      return navigation.dispatch(NavigationActions.setParams({ params, key }));
    },

      /**
       * 获取路由参数
       * @param paramName
       * @param defaultValue
       * @returns {*}
       */
    getParam: (paramName, defaultValue) => {
      const params = navigation.state.params;

      if (params && paramName in params) {
        return params[paramName];
      }

      return defaultValue;
    },

      /**
       * push 导航函数
       * @param routeName
       * @param params
       * @param action
       */
    push: (routeName, params, action) =>
      navigation.dispatch(
        NavigationActions.push({ routeName, params, action })
      ),

      /**
       *  replace 导航函数
       * @param routeName
       * @param params
       * @param action
       */
    replace: (routeName, params, action) =>
      navigation.dispatch(
        NavigationActions.replace({
          routeName,
          params,
          action,
          key: navigation.state.key,
        })
      ),
  };
}