From b2444e6c618ee18f0a024d5320f6b773f8de0a95 Mon Sep 17 00:00:00 2001
From: Brent Vatne <brentvatne@gmail.com>
Date: Fri, 16 Feb 2018 17:06:16 -0800
Subject: [PATCH] Revert "Revert "Add getParam navigation helper (#3510)"
 (#3532)"

This reverts commit 5febb81a1cdf67a1e4a7f5a4a843087d6288fa1c.
---
 .../__tests__/addNavigationHelpers-test.js    | 39 +++++++++++++++++++
 .../src/addNavigationHelpers.js               | 10 +++++
 .../__snapshots__/StackNavigator-test.js.snap |  2 +
 3 files changed, 51 insertions(+)

diff --git a/packages/react-navigation/src/__tests__/addNavigationHelpers-test.js b/packages/react-navigation/src/__tests__/addNavigationHelpers-test.js
index d5ff1fba..b2877db7 100644
--- a/packages/react-navigation/src/__tests__/addNavigationHelpers-test.js
+++ b/packages/react-navigation/src/__tests__/addNavigationHelpers-test.js
@@ -76,4 +76,43 @@ describe('addNavigationHelpers', () => {
     });
     expect(mockedDispatch.mock.calls.length).toBe(1);
   });
+
+  it('handles GetParams action', () => {
+    const mockedDispatch = jest
+      .fn(() => false)
+      .mockImplementationOnce(() => true);
+    expect(
+      addNavigationHelpers({
+        state: { key: 'B', routeName: 'Settings', params: { name: 'Peter' } },
+        dispatch: mockedDispatch,
+        addListener: dummyEventSubscriber,
+      }).getParam('name', 'Brent')
+    ).toEqual('Peter');
+  });
+
+  it('handles GetParams action with default param', () => {
+    const mockedDispatch = jest
+      .fn(() => false)
+      .mockImplementationOnce(() => true);
+    expect(
+      addNavigationHelpers({
+        state: { key: 'B', routeName: 'Settings' },
+        dispatch: mockedDispatch,
+        addListener: dummyEventSubscriber,
+      }).getParam('name', 'Brent')
+    ).toEqual('Brent');
+  });
+
+  it('handles GetParams action with param value as null', () => {
+    const mockedDispatch = jest
+      .fn(() => false)
+      .mockImplementationOnce(() => true);
+    expect(
+      addNavigationHelpers({
+        state: { key: 'B', routeName: 'Settings', params: { name: null } },
+        dispatch: mockedDispatch,
+        addListener: dummyEventSubscriber,
+      }).getParam('name')
+    ).toEqual(null);
+  });
 });
diff --git a/packages/react-navigation/src/addNavigationHelpers.js b/packages/react-navigation/src/addNavigationHelpers.js
index a56721cf..559f8df9 100644
--- a/packages/react-navigation/src/addNavigationHelpers.js
+++ b/packages/react-navigation/src/addNavigationHelpers.js
@@ -61,6 +61,16 @@ export default function(navigation) {
       return navigation.dispatch(NavigationActions.setParams({ params, key }));
     },
 
+    getParam: (paramName, defaultValue) => {
+      const params = navigation.state.params;
+
+      if (params && paramName in params) {
+        return params[paramName];
+      }
+
+      return defaultValue;
+    },
+
     push: (routeName, params, action) =>
       navigation.dispatch(
         NavigationActions.push({ routeName, params, action })
diff --git a/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap b/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap
index 780892ed..59be7324 100644
--- a/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap
+++ b/packages/react-navigation/src/navigators/__tests__/__snapshots__/StackNavigator-test.js.snap
@@ -98,6 +98,7 @@ exports[`StackNavigator applies correct values when headerRight is present 1`] =
         Object {
           "addListener": [Function],
           "dispatch": [Function],
+          "getParam": [Function],
           "goBack": [Function],
           "navigate": [Function],
           "pop": [Function],
@@ -337,6 +338,7 @@ exports[`StackNavigator renders successfully 1`] = `
         Object {
           "addListener": [Function],
           "dispatch": [Function],
+          "getParam": [Function],
           "goBack": [Function],
           "navigate": [Function],
           "pop": [Function],