Unity uses ExternalCall to implement webplayer read and write.

Application.ExternalCall

 

 

 

public static void  ExternalCall (string  functionName , params object[]  args );

Parameters

Description

Calls a function in the containing web page (Web Player only).

This will call JavaScript function functionName in the web page that contains the web player, passing given arguments to it. Supported argument types are the primitive types (string, int, float, char) and arrays of them. Any other objects are converted to string (using ToString method) and passed as strings.

The function is called non-blocking, i.e. ExternalCall immediately returns without waiting for the function that was called to complete.

The number of passed arguments can be varying:

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Example() {
        Application.ExternalCall("MyFunction1");
        Application.ExternalCall("MyFunction2", "Hello from Unity!");
        Application.ExternalCall("MyFunction3", "one", 2, 3.0F);
    }
}

The functions to be called are just declared in the HTML page using standard syntax, for example:

 

	// This should be contained in the host page in the appropriate <script> element.
	// Using the above call from Unity, this will receive
	// "Hello from Unity!" as the argument.
	function MyFunction2( arg )
	{
		alert (arg);
	}

If it is some xml files, only a large number of parameters can be sent to javascript in the form of string data, and then the activex control can be called in javascript to save the data.