added switchToTab on iOS (#1862)

e2e/ScreenStack.test.js

     await elementByLabel('Pop To Root').tap();
     await expect(elementByLabel('React Native Navigation!')).toBeVisible();
   });
+
+  it('switch to tab', async () => {
+    await elementByLabel('Switch to tab based app').tap();
+    await expect(elementByLabel('This is tab 1')).toBeVisible();
+    await elementByLabel('Switch To Tab 2').tap();
+    await expect(elementByLabel('This is tab 1')).toBeNotVisible();
+    await expect(elementByLabel('This is tab 2')).toBeVisible();
+  });
 });

lib/ios/RNNBridgeModule.m

 	[_commandsHandler dismissAllModals];
 }
 
+RCT_EXPORT_METHOD(switchToTab:(NSString*)containerId tabIndex:(nonnull NSNumber*)tabIndex) {
+	[_commandsHandler switchToTab:containerId tabIndex:tabIndex];
+}
+
 @end
 

lib/ios/RNNCommandsHandler.h

 
 -(void) dismissAllModals;
 
+-(void) switchToTab:(NSString*)containerId tabIndex:(NSNumber*)tabIndex;
+
 @end

lib/ios/RNNCommandsHandler.m

 	[_modalManager dismissAllModals];
 }
 
+-(void) switchToTab:(NSString *)containerId tabIndex:(NSNumber *)tabIndex {
+	[self assertReady];
+	
+	UIViewController* vc = [_store findContainerForId:containerId];
+	[vc.tabBarController setSelectedIndex:[tabIndex unsignedIntegerValue]];
+}
+
 #pragma mark - private
 
 -(void) assertReady {

lib/src/Navigation.js

     return this.commands.popToRoot(containerId);
   }
 
+  switchToTab(onContainerId, tabIndex) {
+    return this.commands.switchToTab(onContainerId, tabIndex);
+  }
+
   events() {
     return this.publicEventsRegistry;
   }

lib/src/adapters/NativeCommandsSender.js

     this.nativeCommandsModule.dismissAllModals();
     return Promise.resolve(true);
   }
+
+  switchToTab(containerId, tabIndex) {
+    this.nativeCommandsModule.switchToTab(containerId, tabIndex);
+    return Promise.resolve(containerId);
+  }
 }
 
 module.exports = NativeCommandsSender;

lib/src/commands/Commands.js

   popToRoot(containerId) {
     return this.nativeCommandsSender.popToRoot(containerId);
   }
+
+  switchToTab(containerId, tabIndex) {
+    return this.nativeCommandsSender.switchToTab(containerId, tabIndex);
+  }
 }
 
 module.exports = Commands;

lib/src/commands/Commands.test.js

       expect(result).toEqual('theContainerId');
     });
   });
+
+  describe('switchToTab', () => {
+    it('switch tab in tabs controller', () => {
+      const tabIndex = 1;
+      uut.switchToTab('theContainerId', tabIndex);
+      expect(mockCommandsSender.switchToTab).toHaveBeenCalledTimes(1);
+      expect(mockCommandsSender.switchToTab).toHaveBeenCalledWith('theContainerId', tabIndex);
+    });
+
+    it('returns a promise that resolves to targetId', async () => {
+      mockCommandsSender.switchToTab.mockReturnValue(Promise.resolve('theContainerId', 1));
+      const result = await uut.switchToTab('theContainerId');
+      expect(result).toEqual('theContainerId');
+    });
+  });
 });

playground/src/containers/TextScreen.js

         {this.renderTextFromFunctionInProps()}
         <Text style={styles.footer}>{`this.props.containerId = ${this.props.containerId}`}</Text>
         <Button title={'Set Tab Badge'} onPress={() => this.onButtonPress()} />
+        <Button title="Switch To Tab 2" onPress={() => this.onClickSwitchToTab()} />
       </View>
     );
   }
       tabBadge: `EnCyClOpEdIa`
     });
   }
+
+  onClickSwitchToTab() {
+    Navigation.switchToTab(this.props.containerId, 1);
+  }
 }
 module.exports = TextScreen;