IncrementalHitTester Class

Definition

public ref class IncrementalHitTester abstract

public abstract class IncrementalHitTester

type IncrementalHitTester = class

Public MustInherit Class IncrementalHitTester

Inheritance

Object

IncrementalHitTester

Derived

System.Windows.Ink.IncrementalLassoHitTester

System.Windows.Ink.IncrementalStrokeHitTester

Examples

The following example demonstrates how to add points to the IncrementalHitTester when the user inputs data with the stylus. The example includes a StrokeHit event handler that erases the part of the Stroke that the user intersects. To create a control that enables a user to erase ink, see How to: Erase Ink on a Custom Control.

// Prepare to collect stylus packets. Get the 
// IncrementalHitTester from the InkPresenter's 
// StrokeCollection and subscribe to its StrokeHitChanged event.
protected override void OnStylusDown(StylusDownEventArgs e)
{
    base.OnStylusDown(e);

    EllipseStylusShape eraserTip = new EllipseStylusShape(3, 3, 0);
    eraseTester = 
        presenter.Strokes.GetIncrementalStrokeHitTester(eraserTip);
    eraseTester.StrokeHit += new StrokeHitEventHandler(eraseTester_StrokeHit);
    eraseTester.AddPoints(e.GetStylusPoints(this));
}

// Collect the StylusPackets as the stylus moves.
protected override void OnStylusMove(StylusEventArgs e)
{
    if (eraseTester.IsValid)
    {
        eraseTester.AddPoints(e.GetStylusPoints(this));
    }
}

// Unsubscribe from the StrokeHitChanged event when the
// user lifts the stylus.
protected override void OnStylusUp(StylusEventArgs e)
{

    eraseTester.AddPoints(e.GetStylusPoints(this));
    eraseTester.StrokeHit -= new
        StrokeHitEventHandler(eraseTester_StrokeHit);
    eraseTester.EndHitTesting();
}

// When the stylus intersects a stroke, erase that part of
// the stroke.  When the stylus dissects a stoke, the 
// Stroke.Erase method returns a StrokeCollection that contains
// the two new strokes.
void eraseTester_StrokeHit(object sender,
    StrokeHitEventArgs args)
{
    StrokeCollection eraseResult =
        args.GetPointEraseResults();
    StrokeCollection strokesToReplace = new StrokeCollection();
    strokesToReplace.Add(args.HitStroke);
   
    // Replace the old stroke with the new one.
    if (eraseResult.Count > 0)
    {
        presenter.Strokes.Replace(strokesToReplace, eraseResult);
    }
    else
    {
        presenter.Strokes.Remove(strokesToReplace);
    }
}

     ' Prepare to collect stylus packets. Get the 
     ' IncrementalHitTester from the InkPresenter's 
     ' StrokeCollection and subscribe to its StrokeHitChanged event.
     Protected Overrides Sub OnStylusDown(ByVal e As StylusDownEventArgs)

         MyBase.OnStylusDown(e)

         Dim eraserTip As New EllipseStylusShape(3, 3, 0)
         eraseTester = presenter.Strokes.GetIncrementalStrokeHitTester(eraserTip)
         AddHandler eraseTester.StrokeHit, _
             AddressOf eraseTester_StrokeHit
         eraseTester.AddPoints(e.GetStylusPoints(Me))

     End Sub

     ' Collect the StylusPackets as the stylus moves.
     Protected Overrides Sub OnStylusMove(ByVal e As StylusEventArgs)

         If eraseTester.IsValid Then
             eraseTester.AddPoints(e.GetStylusPoints(Me))
         End If

     End Sub

     ' Unsubscribe from the StrokeHitChanged event when the
     ' user lifts the stylus.
     Protected Overrides Sub OnStylusUp(ByVal e As StylusEventArgs)

         eraseTester.AddPoints(e.GetStylusPoints(Me))

         RemoveHandler eraseTester.StrokeHit, _
             AddressOf eraseTester_StrokeHit
         eraseTester.EndHitTesting()

     End Sub


     ' When the stylus intersects a stroke, erase that part of
     ' the stroke.  When the stylus dissects a stoke, the 
     ' Stroke.Erase method returns a StrokeCollection that contains
     ' the two new strokes.
     Private Sub eraseTester_StrokeHit(ByVal sender As Object, _
             ByVal args As StrokeHitEventArgs)

         Dim eraseResult As StrokeCollection = _
             args.GetPointEraseResults()
         Dim strokesToReplace As New StrokeCollection()
         strokesToReplace.Add(args.HitStroke)

         ' Replace the old stroke with the new one.
         If eraseResult.Count > 0 Then
             presenter.Strokes.Replace(strokesToReplace, eraseResult)
         Else
             presenter.Strokes.Remove(strokesToReplace)
         End If

     End Sub

Remarks

The IncrementalHitTester dynamically determines whether the user "hits" a Stroke. This class enables you to provide immediate feedback to the user in situations such as selecting and erasing ink.

There are two classes that inherit from IncrementalHitTester:

• The IncrementalLassoHitTester hit tests strokes by determining whether a lasso path surrounds it.

• The IncrementalStrokeHitTester hit tests strokes by determining where an eraser path intersects it.

The following table lists where to learn how to manage digital ink on a custom control.

XAML Text Usage

This class is not typically used in XAML.

Properties

Methods

Applies to