# Messaging System

By sending a message from web page to Unity, you could control or notify your game. The UniWebView messaging system takes responsibility to observe some schemes navigation (from link clicking or JavaScript location navigation), then parse and forward specified navigating to Unity.

UniWebView inspects all links starts from uniwebview:// by default. That means if you have a link with "uniwebview" as the URL scheme, the OnMessageReceived event will be raised with a received UniWebViewMessage object:

webView.OnMessageReceived += (view, message) => {
    print(message.RawMessage);
};
webView.Load("uniwebview://action?key=value&anotherKey=anotherValue");

// This will print "uniwebview://action?key=value&anotherKey=anotherValue" as the raw message.

UniWebView messaging system also helps you to parse the input. You could access the Scheme, Path and Args properties to get information from the URL. For example, in the code about, you could get:

• Scheme - "uniwebview"
• Path - "action"
• Args - {"key": value, "anotherKey": "anotherValue"}

# Adding your own scheme

Besides of the default "uniwebview", you could also add your own URL scheme. Call AddUrlScheme with the one you need:

webView.AddUrlScheme("myscheme");

And then, all URLs started from "myscheme" will be messages sent to you.

A tricky thing here is you could even set "http" and "https" as the scheme. It will prevent all loading of web resources and send them to you. This gives a chance to inspect all traffic. A use case for it is you do not want your user to leave the current page. So you could first load your page, then, in the OnPageFinished event, disable all navigating by adding the "http(s)" scheme to UniWebView message system:

webView.Load("https://yourpage.com");

webView.OnPageFinished += (view, statusCode, url) => {
    webView.AddUrlScheme("http");
    webView.AddUrlScheme("https");

    // Now your user will not be able to navigate to other pages.
};

# Limitation

The messaging system is built on URL and Unity's message sender. It means you cannot send the unlimited size of data at once. The allowed max length of a URL is different from devices and system versions. But a safe length is ~16KB for a URL. If you have something huge to send from web page to Unity and encountered some problems, it would be better to split them into smaller pieces.