Thumb.DragDelta Event

Definition

Namespace:

System.Windows.Controls.Primitives

Assembly:

PresentationFramework.dll

Occurs one or more times as the mouse changes position when a Thumb control has logical focus and mouse capture.

C#

public event System.Windows.Controls.Primitives.DragDeltaEventHandler DragDelta;

Event Type

DragDeltaEventHandler

Examples

The following example shows how to assign an event handler for the DragDelta event to a Thumb control, and how to define the event handler. For the complete sample, see Thumb Drag Functionality Sample.

XAML

<Thumb Name="myThumb" Canvas.Left="80" Canvas.Top="80" Background="Blue" 
      Width="20" Height="20" DragDelta="onDragDelta" 
      DragStarted="onDragStarted" DragCompleted="onDragCompleted"
      />

C#

void onDragDelta(object sender, DragDeltaEventArgs e)
{
    //Move the Thumb to the mouse position during the drag operation
    double yadjust = myCanvasStretch.Height + e.VerticalChange;
    double xadjust = myCanvasStretch.Width + e.HorizontalChange;
    if ((xadjust >= 0) && (yadjust >= 0))
    {
        myCanvasStretch.Width = xadjust;
        myCanvasStretch.Height = yadjust;
        Canvas.SetLeft(myThumb, Canvas.GetLeft(myThumb) +
                                e.HorizontalChange);
        Canvas.SetTop(myThumb, Canvas.GetTop(myThumb) +
                                e.VerticalChange);
        changes.Text = "Size: " +
                        myCanvasStretch.Width.ToString() +
                         ", " +
                        myCanvasStretch.Height.ToString();
    }
}

Remarks

The Thumb control receives focus and mouse capture when the user presses the left mouse button while pausing the mouse pointer over the Thumb control. The Thumb control loses mouse capture when the user releases the left mouse button, or when the CancelDrag method is called.

A new DragDelta event occurs each time the mouse position moves on the screen. Therefore, this event can be raised multiple times without a limit when a Thumb control has mouse capture.

Routed Event Information

Item	Value
Identifier field	DragDeltaEvent
Routing strategy	Bubbling
Delegate	DragDeltaEventHandler

Applies to

See also

• IsDragging
• DragDeltaEventArgs
• DragStarted
• DragCompleted
• CancelDrag()