Use Analytics in a WebView on iOS

Calls to log events or set user properties fired from within a WebView must be forwarded to native code before they can be sent to Google Analytics for Firebase.

Implement Javascript handler

The first step in using Google Analytics for Firebase in a WebView is to create JavaScript functions to forward events and user properties to native code. The following example shows how to do this in a way that is compatible with both Android and iOS native code:
function logEvent(name, params) {
  if (!name) {
    return;
  }

  if (window.AnalyticsWebInterface) {
    // Call Android interface
    window.AnalyticsWebInterface.logEvent(name, JSON.stringify(params));
  } else if (window.webkit
      && window.webkit.messageHandlers
      && window.webkit.messageHandlers.firebase) {
    // Call iOS interface
    var message = {
      command: 'logEvent',
      name: name,
      parameters: params
    };
    window.webkit.messageHandlers.firebase.postMessage(message);
  } else {
    // No Android or iOS interface found
    console.log("No native APIs found.");
  }
}

function setUserProperty(name, value) {
  if (!name || !value) {
    return;
  }

  if (window.AnalyticsWebInterface) {
    // Call Android interface
    window.AnalyticsWebInterface.setUserProperty(name, value);
  } else if (window.webkit
      && window.webkit.messageHandlers
      && window.webkit.messageHandlers.firebase) {
    // Call iOS interface
    var message = {
      command: 'setUserProperty',
      name: name,
      value: value
   };
    window.webkit.messageHandlers.firebase.postMessage(message);
  } else {
    // No Android or iOS interface found
    console.log("No native APIs found.");
  }
}

Implement native interface

To invoke native iOS code from JavaScript, create a message handler class conforming to the WKScriptMessageHandler protocol. You can make Google Analytics for Firebase calls inside the userContentController:didReceiveScriptMessage: callback:

Swift

func userContentController(_ userContentController: WKUserContentController,
                           didReceive message: WKScriptMessage) {
  guard let body = message.body as? [String: Any] else { return }
  guard let command = body["command"] as? String else { return }
  guard let name = body["name"] as? String else { return }

  if command == "setUserProperty" {
    guard let value = body["value"] as? String else { return }
    FIRAnalytics.setUserPropertyString(value, forName: name)
  } else if command == "logEvent" {
    guard let params = body["parameters"] as? [String: NSObject] else { return }
    FIRAnalytics.logEvent(withName: name, parameters: params)
  }
}

Objective-C

- (void)userContentController:(WKUserContentController *)userContentController
      didReceiveScriptMessage:(WKScriptMessage *)message {
  if ([message.body[@"command"] isEqual:@"setUserProperty"]) {
    [FIRAnalytics setUserPropertyString:message.body[@"value"] forName:message.body[@"name"]];
  } else if ([message.body[@"command"] isEqual: @"logEvent"]) {
    [FIRAnalytics logEventWithName:message.body[@"name"] parameters:message.body[@"parameters"]];
  }
}

Finally, add the message handler to the webview's user content controller:

Swift

self.webView.configuration.userContentController.add(self, name: "firebase")

Objective-C

 [self.webView.configuration.userContentController addScriptMessageHandler:self
                                                                     name:@"firebase"];

Next Steps

For a fully functional implementation of Google Analytics for Firebase in a WebView, see the analytics-webview sample.

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