CODEWITHSUNDEEP
c#winformsdrag-and-dropcharts
Eric H
Eric H

Reputation: 597

WinForms Chart: How can I identify a DataPoint within the DragDrop event?

In my C# WinForms application, I'm using drag-and-drop to move items from a TreeView control to a Chart control. (It's a scheduling app with a list of jobs, and the user drops them onto the schedule). When the user drops an item onto an existing DataPoint on the chart, I want the new item to become a DataPoint and displace the old one (moving it down in the queue).

Here's what I have for the DragDrop event handler that's not quite (but almost) working:

 private void chart1_DragDrop(object sender, DragEventArgs e)
 {
     if (draggedJob != null) // This is set when user starts dragging
     {
         HitTestResult testResult = chart1.HitTest(e.X, e.Y, ChartElementType.DataPoint);
         switch (testResult.ChartElementType)
         {
              case ChartElementType.DataPoint:
                  // This should happen if I dropped an item onto an existing DataPoint
                  // ...but testResult.ChartElementType is always "Nothing"
                  DataPoint existingPoint = (DataPoint)testResult.Object;
                  JobOrder jobToDisplace = (JobOrder)existingPoint.Tag;

                  ScheduleJob(draggedJob, jobToDisplace);
                  break;
              default:
                  //This happens every time (it adds the item to the end of the schedule)
                  ScheduleJob(draggedJob);
                  break;
         }                                        

         RefreshTreeView();
         RefreshChart();     

         draggedJob = null;
     }
 }

Can anyone save my sanity and help me figure out how I can tell which DataPoint the user is dropping the job onto?

Upvotes: 3

Views: 1730

Answers (1)

Hans Passant
Hans Passant

Reputation: 941317

The mouse position you get (e.X, e.Y) is in screen coordinates. You have to map it to the chart control. Fix:

var pos = chart1.PointToClient(new Point(e.X, e.Y));
HitTestResult testResult = chart1.HitTest(pos.X, pos.Y, ChartElementType.DataPoint);

Upvotes: 2

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