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ASP.NET - Drag and Drop on a Webpage

, 28 Dec 2004 284.3K 10.3K 121
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Drag and drop contained objects on a webpage.

Introduction

Many web applications are required to be complex yet intuitive to the user. One way to achieve this is to create objects or areas of the web page draggable and droppable. Unfortunately, ASP.NET server controls do not have the Drag events and DragEventArgs. Fortunately, there is a way to enable drag and drop functionalities within a web page. Now keep in mind, this is not like a Windows application where you can drag files from the user's PC to the application. The drag and drop is limited to the boundaries of the web page.

Using the code

  1. Create a web application within your solution.
  2. Create a web page.
  3. Add the provided JavaScript in the <HEAD> of your <HTML>.
  4. Add two textboxes and a button in the web form.
  5. Add the DrawContainers method to the code-behind of the web page.
  6. Ensure that the click event for the button calls the DrawContainers method.

or

  • Download the source code and run the sample application.

JavaScript

This is the JavaScript that enables the drag and drop to take place:

<!--<span class="code-comment">------- Drag and Drop JavaScript ------------></span>

var TimerID = 0;
var oEl     = null;
var oTarget = null;
var beginDrag = false;
var tmpHTML = "";
  
function killTimer()
{
    if (TimerID != 0 )
    {
        clearTimeout(TimerID);
        TimerID = 0;
    }
}
       
function fnShowDragWindow() 
{
    var obj = document.all("DW");
    
    killTimer();
    
    if (oEl == null)  
    {
        return;
    }
    
    obj.style.top        = oEl.offsetTop;
    obj.style.left        = oEl.offsetLeft;
    obj.style.height    = oEl.offsetHeight - 3;
    obj.style.width        = oEl.offsetWidth - 3;
    obj.innerText        = oEl.SpecimenId;
    obj.style.display    = "block";
    obj.style.zIndex    = 999;
    
    window.document.attachEvent( "onmousemove"  , fnMove );
    window.document.attachEvent( "onscroll"  , fnMove );
    window.document.attachEvent( "onmousemove" , fnCheckState );
    window.document.attachEvent( "onmouseup"    , fnRelease );
    window.document.attachEvent( "onselectstart", fnSelect );
    //window.document.attachEvent("onmouseover",setTarget);
    
    beginDrag = true;
}

function setTarget(id)
{
    var src = document.getElementById(id);
    
    if (src == null) 
    {
        return;
    }
    
    if (src.target == 'true')
    {
        oTarget = src;
    }
    else
    {
        oTarget = null;    
    }
}

function BeginDrag(id)
{
    // Get the item to be dragged.
    oEl = document.getElementById(id);
    
    // Is there an item?
    if(oEl == null)
    {
        return;
    }
    
    tmpHTML = oEl.innerHTML;
    // Set the window timeout.
    TimerID = setTimeout(fnShowDragWindow, 1);
}            


function fnCheckState()
{
    if(event.button != 1)
    {
        fnRelease();
    }
}

function fnSelect()
{
    return false;
}


function fnMove()
{
    if (event.button != 1)
    {
        fnRelease();
        return;
    }
    
    var obj = document.all("DW");
    
    obj.style.top = 
      event.clientY - (obj.offsetHeight/2) + window.document.body.scrollTop;  
    obj.style.left = event.clientX  + window.document.body.scrollLeft;
    window.status = 'Top=' + obj.style.top + ' Left=' + obj.style.left;
    
    if (event.clientY >

C# code behind - DrawContainers method

This is the code behind used to create the drag and drop objects:

private void DrawContainers()
{
    TableRowCollection trCol = this.Table1.Rows;
    TableRow tr = null;
    
    // Should we continue?
    if(this.txtContX.Text == null || this.txtContY.Text == null)
        return;
    
    // Size of the row.
    int rowSize = Int32.Parse(this.txtContX.Text); 
    // Number of rows.
    int rowNumber = Int32.Parse(this.txtContY.Text);
    // Total number of containers.
    int numberOfContainers = rowSize * rowNumber;
    // Boolean value for empty table cells.
    bool isEmpty = false;
    
    // Loop through all of the containers.
    for(int i=0; i< numberOfContainers; i++)
    {
        // new row mod.
        int newRow =  i % rowSize;
        
        // Should we create a new row?
        if(tr == null || newRow == 0)
        {
            tr = new TableRow();
            trCol.Add(tr);
        }

        // Empty cell generator.
        if((i+1)%17==0)
        {
            isEmpty = true;
        }
        else
        {
            isEmpty = false;
        }

        // Set the cell collection.
        TableCellCollection tdc = tr.Cells;

        // Create a new table cell.
        TableCell td = new TableCell();
        td.ID = "cell_" + i.ToString();
        
        // Set the cell backcolor.
        td.BackColor = Color.Turquoise;
        // Set the cell's class.
        td.CssClass = "SpecimenLoc";

        td.Attributes.Add("SpecimenId", "");

        // Is the cell empty?
        if(!isEmpty)
        {
            td.Attributes.Add("SpecimenId", i.ToString());
            td.BackColor = Color.Beige;
            td.Text = i.ToString();
        }
        
        // Add javascript attributes to the cell.
        td.Attributes.Add("target", "true");
        td.Attributes.Add("onmousedown", "BeginDrag(this.id);");
        td.Attributes.Add("onmouseup", "CancelDrag();"); 
        td.Attributes.Add("onmouseover", 
                "setTarget(this.id);this.style.cursor='hand';");
        td.Attributes.Add("onmouseout", 
                                "this.style.cursor='default';");
        td.Width = Unit.Pixel(35);
        td.Height = Unit.Pixel(35);

        // Add the cell to the cell collection.
        tdc.Add(td);
    }
}

C# code behind - button click event

The click event of the button:

private void btnDrawContainers_Click(object sender, System.EventArgs e)
{
    // Draw the containers.
    this.DrawContainers();
}

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Kenny Young
United States United States
Ken currently works as the Director of Software Engineering at the Pediatrics Epidemiology Center at the University of South Florida. He is involved in the architecture and design on numerous clinical trial projects. Some of the project include:

1. Rare Diseases Clinical Research Network
2. TrialNet - Diabetes
3. Teddy - Diabetes
4. CCOP - Cancer
5. AIDA - Diabetes

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Comments and Discussions

 
GeneralMy vote of 5 Pin
manoj kumar choubey9-Feb-12 21:13
membermanoj kumar choubey9-Feb-12 21:13 
QuestionExplaination Pin
sakshictr10-Jan-12 19:34
membersakshictr10-Jan-12 19:34 
QuestionNeed some Suggestions. Pin
supriya_rani2012-Sep-11 23:37
membersupriya_rani2012-Sep-11 23:37 
GeneralMy vote of 1 Pin
Member 449609922-Jun-09 20:55
memberMember 449609922-Jun-09 20:55 
GeneralGood Article Pin
khanjee7730-Dec-08 17:30
memberkhanjee7730-Dec-08 17:30 
GeneralMy vote of 2 Pin
Iyigun Cevik8-Dec-08 2:47
memberIyigun Cevik8-Dec-08 2:47 
Generalhii kenny Young Pin
ctcalyx6-Aug-07 21:06
memberctcalyx6-Aug-07 21:06 
GeneralRe: hii kenny Young Pin
Rockrebel7-Aug-08 1:42
memberRockrebel7-Aug-08 1:42 
GeneralRe: hii kenny Young Pin
Kenny Young7-Aug-08 2:26
memberKenny Young7-Aug-08 2:26 
QuestionHyperLinkBitmap Error Pin
diddy4332-Jul-07 6:39
memberdiddy4332-Jul-07 6:39 
GeneralDoens't work with firefox Pin
carlintveld31-May-07 7:50
membercarlintveld31-May-07 7:50 
GeneralRe: Doens't work with firefox Pin
vytas z.16-Aug-07 2:33
membervytas z.16-Aug-07 2:33 
GeneralRe: Doens't work with firefox Pin
bbol19-Nov-07 12:49
memberbbol19-Nov-07 12:49 
GeneralDoes n't Work with ASP.Net 2005 Pin
Hari Darshan26-Apr-07 1:17
memberHari Darshan26-Apr-07 1:17 
QuestionHow to get updated row after drag? Pin
davihigh12-Sep-06 3:29
memberdavihigh12-Sep-06 3:29 
AnswerRe: How to get updated row after drag? Pin
Kenny Young12-Sep-06 7:15
memberKenny Young12-Sep-06 7:15 
You will need to add client side attributes to the rows such as current index and previous index. In the javascript you will need to set these values accordingly. When a post-back occurs, you must re-order the rows based on the current and previous index values.

Thanks,

Kenny Young
QuestionCheckbox. Pin
py1rdj4-Sep-06 11:20
memberpy1rdj4-Sep-06 11:20 
AnswerRe: Checkbox. Pin
Kenny Young12-Sep-06 7:17
memberKenny Young12-Sep-06 7:17 
QuestionDrag n Drop from listbox to a datagrid Pin
kumarcs4-Sep-06 4:11
memberkumarcs4-Sep-06 4:11 
AnswerRe: Drag n Drop from listbox to a datagrid Pin
Kenny Young12-Sep-06 7:21
memberKenny Young12-Sep-06 7:21 
GeneralDatagrid to Datagrid drag drop Pin
sandeepautade31-Aug-06 2:31
membersandeepautade31-Aug-06 2:31 
GeneralRe: Datagrid to Datagrid drag drop Pin
Kenny Young31-Aug-06 2:39
memberKenny Young31-Aug-06 2:39 
GeneralDRAG DROP Pin
Mon217-Aug-06 20:45
memberMon217-Aug-06 20:45 
GeneralRe: DRAG DROP Pin
Kenny Young31-Aug-06 2:37
memberKenny Young31-Aug-06 2:37 
Generalmicrosoft treeview [modified] Pin
azidi13-Jul-06 14:37
memberazidi13-Jul-06 14:37 

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