Persisting the position of jQuery Draggables in ASP.NET
For the purposes of this example, the markup for the page is extremely simple:
<form id="form1" runat="server">
<div>
<img src="images/alfie.jpg" alt="" id="d1" runat="server" />
</div>
</form>
This is a simple html image, that has been converted to an ASP.NET HtmlControl by adding runat="server". I need to do this, because later, I want to reference the image from Code-Behind. In the meantime, I'll get to the Javascript that makes the image draggable:
<script src="script/jquery-1.3.1.min.js" type="text/javascript"></script>
<script src="script/ui.core.min.js" type="text/javascript"></script>
<script src="script/ui.draggable.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function() {
$("#d1").draggable(
{
drag: function(event, ui) {
$("#d1").css("opacity", "0.6"); // Semi-transparent when dragging
},
stop: function(event, ui) {
saveCoords(ui.absolutePosition.left, ui.absolutePosition.top, ui.helper.attr('id'));
$("#d1").css("opacity", "1.0"); // Full opacity when stopped
},
cursor: "move"
});
});
</script>
Most of this is familiar if you read the previous article, so I won't dwell on it. The major difference, however is that a call to a new function, saveCoords() is made within the stop callback. 3 arguments are supplied: the x coordinate, y coordinate and the id of the current draggable - ui.helper.attr('id'). Let's look at what that function does:
function saveCoords(x, y, el, id) {
$.ajax({
type: "POST",
url: "Services/Coordinates.asmx/SaveCoords",
data: "{x: '" + x + "', y: '" + y + "', element: '" + el + "', userid: '1'}",
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function(response) {
if (response.d != '1') {
alert('Not Saved!');
}
},
error: function(response) {
alert(response.responseText);
}
});
}
If you have seen my previous articles on Web Services with jQuery, you will immediately spot that this function makes a call to a Web Service called Coordinates, invoking its method, SaveCoords(). It passes in the x and y coordinates, the id of the element and a user ID (hardcoded for thos example, bit could be provided by a session variable, for instance). Here's the Web Service:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Script.Services;
using System.Data.SqlClient;
using System.Data;
/// <summary>
/// Summary description for SaveCoords
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
[ScriptService]
public class Coordinates : WebService {
[WebMethod]
public int SaveCoords(int x, int y, string element, int userid)
{
string connect = "Server=MyServer;Database=Tests;Trusted_Connection=True;";
int result = 0;
using (SqlConnection conn = new SqlConnection(connect))
{
string query = "UPDATE Coords SET xPos = @xPos, yPos = @yPos WHERE Element = @Element AND UserID = @UserID";
using (SqlCommand cmd = new SqlCommand(query, conn))
{
cmd.Parameters.AddWithValue("xPos", x);
cmd.Parameters.AddWithValue("yPos", y);
cmd.Parameters.AddWithValue("Element", element);
cmd.Parameters.AddWithValue("UserID", userid);
conn.Open();
result = (int)cmd.ExecuteNonQuery();
}
}
return result;
}
}
The WebMethod simply takes the arguments passed to it and saves them to the database. It returns the number of rows affected for error checking. Great. So the position of the element is saved. How does that get translated to a draggable being positioned where it was left when the page is next requested by the user with the ID of 1? We need another Web Method:
[WebMethod]
public DataTable GetSavedCoords(int userid)
{
DataTable dt = new DataTable();
string connect = "Server=MyServer;Database=Tests;Trusted_Connection=True;";
using (SqlConnection conn = new SqlConnection(connect))
{
string query = "SELECT xPos, yPos, Element FROM Coords WHERE UserID = @UserID";
using (SqlCommand cmd = new SqlCommand(query, conn))
{
cmd.Parameters.AddWithValue("UserID", userid);
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(dt);
return dt;
}
}
}
Taking the User ID as an argument, this method returns a DataTable filled with the positions of all elements saved against the user, and it is invoked in the Page_Load() event in the Code Behind:
public partial class PersistDraggable : Page
{
protected void Page_Load(object sender, EventArgs e)
{
Coordinates coords = new Coordinates();
DataTable dt = coords.GetSavedCoords(1);
foreach (DataRow row in dt.Rows)
{
HtmlControl ctl = (HtmlControl)this.FindControl(row["element"].ToString());
if (ctl != null)
{
ctl.Style.Add("left", row["xPos"].ToString() + "px");
ctl.Style.Add("top", row["yPos"].ToString() + "px");
}
}
}
}
The Web Service class is instantiated and its GetSavedCoords() method is called. For each row in the returned DataTable, an element on the page is sought with the same id as one saved in the database. If it is found, it has a dash of CSS applied to it through Attributes.Add(). These set the CSS top and left values, and Voila! When the page is rendered again, the image is exactly where it was left last time.
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Date Posted:
04 February 2009 22:29
Last Updated:
26 April 2009 20:45
Posted by:
Mikesdotnetting
Total Views to date:
10217
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Comments
31 March 2009 21:01 from Bob
Thanks Mike. What was probably simple for you would have taken me days if not weeks!
24 April 2009 06:48 from Sharjeel
Is it necessary to have a WebService for this, or i can do something in me cs page itself also?
24 April 2009 20:01 from Mikesdotnetting
@Sharjeel
No - you can use a Page Method, or you can simply put the code in a codebehind of a blank aspx file.
24 April 2009 21:03 from Tim
Any chance you can post up a download for this? I like the work you did and you explained it well, but am still trying to figure out how all the webservice stuff works.
Thanks
26 April 2009 12:40 from Liammcmullen
Great bit of code. saved me a load of work many thanks.
Should this be given away free?
26 April 2009 21:00 from Mikesdotnetting
@Tim
I don't do downloads, I'm afraid. But you don't need a web service for this. You can use a Page Method instead. Have a look here for how to so that:
http://encosia.com/2008/05/29/using-jquery-to-directly-call-aspnet-ajax-page-methods/
26 April 2009 21:01 from Mikesdotnetting
@Liam,
I am occasionally in Belfast. You are permitted to buy me a beer when I am next there :-)
28 April 2009 07:45 from Sharjeel
thanks mike for the answer, i actually want to save the coords to a session variable or something for easy access.
28 April 2009 10:03 from Daren
Mike, that's fanstic.
I am hoping to create a restricted set of div containers (regions) on my page where the users can drag and drop stuff, but I don't them to lay stuff on top of each other, I just want the the widgets to sit nicely next to or on top of each other, and then to record their position as an index perhaps?
Any ideas on how this would best be accomplished?
21 May 2009 07:03 from janlie mcdovish
hey mike, great sample you have there. it helps in our project a lot :)
05 March 2010 16:53 from Harvey
Thanks for this great tutorial Mike.
Is there any chance you could explain the best way to approach adding multiple divs on a page all of which are draggable and updateable? I am going to use your web service Methods, but I need to have approx. 6 x divs on my page. many thanks
30 March 2009 20:08 from jamie
excellent! i done this a few years ago, i remember the pain i went through to get it working! no its all in one area!