ASP.NET Drawing Application using HTML5 Canvas. Save to Server. JavaScript Error
Question
I have pulled together a simple ASP.NET drawing application using HTML5 Canvas. I have also written some code that uploads a PNG image of the Canvas to the server. My code is as follows:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="CanvasToServer._Default" %>
<!DOCTYPE html>
<html>
<head id="Head1" runat="server">
<title>iScribble Canvas To Server</title>
<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.6.1.min.js"></script>
<!--Load Draw application code-->
<script type="text/javascript" src="JScript.js"></script>
<!--CSS-->
<style type="text/css">
html, body
{
font-family: "Helvetica Neue" , Helvetica, Arial, sans-serif;
}
#graph
{
border: 1px solid #000;
}
#controls
{
font-family: "Helvetica Neue" , Helvetica, Arial, sans-serif;
font-weight: bold;
font-size: smaller;
padding: 3px;
width: 594px;
height: 25px;
}
select
{
font-family: "Helvetica Neue" , Helvetica, Arial, sans-serif;
font-size: medium;
}
</style>
<script type="text/javascript">
// Send the canvas image to the server.
$(function () {
$("#btnSend").click(function () {
var image = graph[0].toDataURL("image/png");
image = image.replace('data:image/png;base64,', '');
$.ajax({
type: 'POST',
url: 'Default.aspx/UploadImage',
data: '{ "imageData" : "' + image + '" }',
contentType: 'application/json; charset=utf-8',
dataType: 'json',
success: function (msg) {
alert('Image sent!');
}
});
});
});
</script>
</head>
<body>
<form id="form1" runat="server">
<div id="controls">
Size:
<select id="thickness" class="fixed">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="10">10</option>
<option value="20">20</option>
</select>
Color:
<select id="color">
<option value="#FFFFFF">#FFFFFF</option>
<option value="#AAAAAA">#AAAAAA</option>
<option value="#666666">#666666</option>
<option value="#000000">#000000</option>
<option value="#9BA16C">#9BA16C</option>
<option value="#CC8F2B">#CC8F2B</option>
<option value="#63631D">#63631D</option>
</select>
</div>
<canvas id="graph" width="200" height="150"></canvas>
<input id="btnSend" type="button" value="Send To Server" />
</form>
</body>
</html>
The code behind is:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.Services;
using System.IO;
using System.Web.Script.Services;
namespace CanvasToServer
{
[ScriptService]
public partial class _Default : System.Web.UI.Page
{
[WebMethod()]
public static void UploadImage(string imageData)
{
FileStream fs = new FileStream("C:\\image.png", FileMode.Create);
BinaryWriter bw = new BinaryWriter(fs);
byte[] data = Convert.FromBase64String(imageData);
bw.Write(data);
bw.Close();
}
}
}
The drawing part of the application works fine.
The problem arises when I click on the button 'Send To Server' I get the JavaScript Error:
'graph is not defined'
on the line:
var image = graph[0].toDataURL("image/png");
Can anyone help me resolve this issue please.
Thanks in advance.
Walter
1 answers
solution1
3 ACCPTED 2011-11-03 16:30:06
Replacing the line:
var image = graph[0].toDataURL("image/png");
with:
var image = document.getElementById("graph").toDataURL("image/png");
worked.
Thanks to vytautas.ziurlis at http://www.zvytas.com/
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