Shape.OnRegionChanged Method (EventArgs)

Article
09/30/2015

Namespace: Microsoft.VisualBasic.PowerPacks
Assembly: Microsoft.VisualBasic.PowerPacks.Vs (in Microsoft.VisualBasic.PowerPacks.Vs.dll)

Syntax

protected virtual void OnRegionChanged(
    EventArgs e
)

protected:
virtual void OnRegionChanged(
    EventArgs^ e
)

abstract OnRegionChanged : 
        e:EventArgs -> unit
override OnRegionChanged : 
        e:EventArgs -> unit

Protected Overridable Sub OnRegionChanged (
    e As EventArgs
)

Parameters

e
Type: System.EventArgs

An EventArgs that contains the event data.

Remarks

Raising an event invokes the event handler through a delegate. For more information, see Handling and Raising Events.

The OnRegionChanged method also enables derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.

Notes to Inheritors:

When you override OnRegionChanged in a derived class, be sure to call the OnRegionChanged method of the base class so that registered delegates receive the event.

Examples

The following example is an event-raising method that is executed when the Enabled property value changes. The Shape class has several methods with the name pattern OnPropertyNameChanged that raise the corresponding PropertyNameChanged event when the PropertyName value changes (PropertyName represents the name of the corresponding property.)

The following example changes the color of a line when the Enabled property of a class derived from LineShape is changed to false.

public class DisabledLine :
    LineShape
{
    protected override void OnEnabledChanged(EventArgs e)
    {
        // Change the color of the line when selected.
        if (this.BorderColor == SystemColors.InactiveBorder)
        {
            this.BorderColor = Color.Black;
        }
        else
        {
            this.BorderColor = SystemColors.InactiveBorder;
        }
        base.OnEnabledChanged(e);
    }
}

Public Class DisabledLine
    Inherits LineShape
    Protected Overrides Sub OnEnabledChanged(ByVal e As EventArgs)
        ' Change the color of the line when selected.
        If Me.BorderColor = SystemColors.InactiveBorder Then
            Me.BorderColor = Color.Black
        Else
            Me.BorderColor = SystemColors.InactiveBorder
        End If
        MyBase.OnEnabledChanged(e)
    End Sub
End Class

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