RN iOS: Support View Manager Commands that are strings

Summary:
Right now JS triggers a view manager command with the following code:

```
UIManager.dispatchViewManagerCommand(
  nullthrows(this.scrollResponderGetScrollableNode()),
  UIManager.getViewManagerConfig('RCTScrollView').Commands.scrollTo,
  [x || 0, y || 0, animated !== false],
);
```

As we want to get rid of calls to UIManager, we need to stop looking for the integer defined in native from JavaScript. We will be changing methods like this to be:

```
UIManager.dispatchViewManagerCommand(
  nullthrows(this.scrollResponderGetScrollableNode()),
  'scrollTo',
  [x || 0, y || 0, animated !== false],
);
```

We need to support ints and Strings to be backwards compatible, but ints will be deprecated.

This is the same change as made for Android here: 3cae6fa950

Reviewed By: PeteTheHeat

Differential Revision: D15983041

fbshipit-source-id: 6cb0f3001553d1f9d26e7e8fb5481e16fbca6847

React/Base/RCTModuleData.h

@@ -44,6 +44,12 @@ typedef id<RCTBridgeModule>(^RCTBridgeModuleProvider)(void);
  */
 @property (nonatomic, copy, readonly) NSArray<id<RCTBridgeMethod>> *methods;
 
+/**
+ * Returns a map of the module methods. Note that this will gather the methods the first
+ * time it is called and then memoize the results.
+ */
+@property (nonatomic, copy, readonly) NSDictionary<NSString *, id<RCTBridgeMethod>> *methodsByName;
+
 /**
  * Returns the module's constants, if it exports any
  */

React/Base/RCTModuleData.mm

@@ -28,6 +28,7 @@
 }
 
 @synthesize methods = _methods;
+@synthesize methodsByName = _methodsByName;
 @synthesize instance = _instance;
 @synthesize methodQueue = _methodQueue;
 
@@ -225,6 +226,47 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
   }
 }
 
+- (void) calculateMethods
+{
+    if (_methods && _methodsByName) {
+      return;
+    }
+
+    NSMutableArray<id<RCTBridgeMethod>> *moduleMethods = [NSMutableArray new];
+    NSMutableDictionary<NSString *, id<RCTBridgeMethod>> *moduleMethodsByName = [NSMutableDictionary new];
+
+    if ([_moduleClass instancesRespondToSelector:@selector(methodsToExport)]) {
+        [moduleMethods addObjectsFromArray:[self.instance methodsToExport]];
+    }
+
+    unsigned int methodCount;
+    Class cls = _moduleClass;
+    while (cls && cls != [NSObject class] && cls != [NSProxy class]) {
+        Method *methods = class_copyMethodList(object_getClass(cls), &methodCount);
+
+        for (unsigned int i = 0; i < methodCount; i++) {
+            Method method = methods[i];
+            SEL selector = method_getName(method);
+            if ([NSStringFromSelector(selector) hasPrefix:@"__rct_export__"]) {
+                IMP imp = method_getImplementation(method);
+                auto exportedMethod = ((const RCTMethodInfo *(*)(id, SEL))imp)(_moduleClass, selector);
+                id<RCTBridgeMethod> moduleMethod = [[RCTModuleMethod alloc] initWithExportedMethod:exportedMethod
+                                                                                       moduleClass:_moduleClass];
+
+                NSString *str = [NSString stringWithUTF8String:moduleMethod.JSMethodName];
+                [moduleMethodsByName setValue:moduleMethod forKey:str];
+                [moduleMethods addObject:moduleMethod];
+            }
+        }
+
+        free(methods);
+        cls = class_getSuperclass(cls);
+    }
+
+    _methods = [moduleMethods copy];
+    _methodsByName = [moduleMethodsByName copy];
+}
+
 #pragma mark - public getters
 
 - (BOOL)hasInstance
@@ -267,37 +309,14 @@ RCT_NOT_IMPLEMENTED(- (instancetype)init);
 
 - (NSArray<id<RCTBridgeMethod>> *)methods
 {
-  if (!_methods) {
-    NSMutableArray<id<RCTBridgeMethod>> *moduleMethods = [NSMutableArray new];
+    [self calculateMethods];
+    return _methods;
+}
 
-    if ([_moduleClass instancesRespondToSelector:@selector(methodsToExport)]) {
-      [moduleMethods addObjectsFromArray:[self.instance methodsToExport]];
-    }
-
-    unsigned int methodCount;
-    Class cls = _moduleClass;
-    while (cls && cls != [NSObject class] && cls != [NSProxy class]) {
-      Method *methods = class_copyMethodList(object_getClass(cls), &methodCount);
-
-      for (unsigned int i = 0; i < methodCount; i++) {
-        Method method = methods[i];
-        SEL selector = method_getName(method);
-        if ([NSStringFromSelector(selector) hasPrefix:@"__rct_export__"]) {
-          IMP imp = method_getImplementation(method);
-          auto exportedMethod = ((const RCTMethodInfo *(*)(id, SEL))imp)(_moduleClass, selector);
-          id<RCTBridgeMethod> moduleMethod = [[RCTModuleMethod alloc] initWithExportedMethod:exportedMethod
-                                                                                 moduleClass:_moduleClass];
-          [moduleMethods addObject:moduleMethod];
-        }
-      }
-
-      free(methods);
-      cls = class_getSuperclass(cls);
-    }
-
-    _methods = [moduleMethods copy];
-  }
-  return _methods;
+- (NSDictionary<NSString *, id<RCTBridgeMethod>> *)methodsByName
+{
+    [self calculateMethods];
+    return _methodsByName;
 }
 
 - (void)gatherConstants

React/Modules/RCTUIManager.m

@@ -1060,7 +1060,7 @@ RCT_EXPORT_METHOD(findSubviewIn:(nonnull NSNumber *)reactTag atPoint:(CGPoint)po
 }
 
 RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
-                  commandID:(NSInteger)commandID
+                  commandID:(id /*(NSString or NSNumber) */)commandID
                   commandArgs:(NSArray<id> *)commandArgs)
 {
   RCTShadowView *shadowView = _shadowViewRegistry[reactTag];
@@ -1086,7 +1086,19 @@ RCT_EXPORT_METHOD(dispatchViewManagerCommand:(nonnull NSNumber *)reactTag
 
   Class managerClass = componentData.managerClass;
   RCTModuleData *moduleData = [_bridge moduleDataForName:RCTBridgeModuleNameForClass(managerClass)];
-  id<RCTBridgeMethod> method = moduleData.methods[commandID];
+
+  id<RCTBridgeMethod> method;
+  if ([commandID isKindOfClass:[NSNumber class]]) {
+    method = moduleData.methods[[commandID intValue]];
+  } else if([commandID isKindOfClass:[NSString class]]) {
+    method = moduleData.methodsByName[commandID];
+    if (method == nil) {
+      RCTLogError(@"No command found with name \"%@\"", commandID);
+    }
+  } else {
+    RCTLogError(@"dispatchViewManagerCommand must be called with a string or integer command");
+    return;
+  }
 
   NSArray *args = [@[reactTag] arrayByAddingObjectsFromArray:commandArgs];
   [method invokeWithBridge:_bridge module:componentData.manager arguments:args];