LayoutEngine Class

Definition

Namespace:

System.Windows.Forms.Layout

Assembly:

System.Windows.Forms.dll

Provides the base class for implementing layout engines.

public ref class LayoutEngine abstract

public abstract class LayoutEngine

type LayoutEngine = class

Public MustInherit Class LayoutEngine

Inheritance

Object

LayoutEngine

Examples

The following code example demonstrates the use of the LayoutEngine class to implement custom layout behavior.

#using <System.Drawing.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>

using namespace System;
using namespace System::Collections::Generic;
using namespace System::Drawing;
using namespace System::Text;
using namespace System::Windows::Forms;
using namespace System::Windows::Forms::Layout;

// This class demonstrates a simple custom layout engine.
public ref class DemoFlowLayout : public LayoutEngine
{
public:
    virtual bool Layout(Object^ container,
        LayoutEventArgs^ layoutEventArgs) override
    {
        Control^ parent = nullptr;
        try
        {
            parent = (Control ^) container;
        }
        catch (InvalidCastException^ ex)
        {
            throw gcnew ArgumentException(
                "The parameter 'container' must be a control", "container", ex);
        }
        // Use DisplayRectangle so that parent.Padding is honored.
        Rectangle parentDisplayRectangle = parent->DisplayRectangle;
        Point nextControlLocation = parentDisplayRectangle.Location;

        for each (Control^ currentControl in parent->Controls)
        {
            // Only apply layout to visible controls.
            if (!currentControl->Visible)
            {
                continue;
            }

            // Respect the margin of the control:
            // shift over the left and the top.
            nextControlLocation.Offset(currentControl->Margin.Left,
                currentControl->Margin.Top);

            // Set the location of the control.
            currentControl->Location = nextControlLocation;

            // Set the autosized controls to their
            // autosized heights.
            if (currentControl->AutoSize)
            {
                currentControl->Size = currentControl->GetPreferredSize(
                    parentDisplayRectangle.Size);
            }

            // Move X back to the display rectangle origin.
            nextControlLocation.X = parentDisplayRectangle.X;

            // Increment Y by the height of the control
            // and the bottom margin.
            nextControlLocation.Y += currentControl->Height +
                currentControl->Margin.Bottom;
        }

        // Optional: Return whether or not the container's
        // parent should perform layout as a result of this
        // layout. Some layout engines return the value of
        // the container's AutoSize property.

        return false;
    }
};

// This class demonstrates a simple custom layout panel.
// It overrides the LayoutEngine property of the Panel
// control to provide a custom layout engine.
public ref class DemoFlowPanel : public Panel
{
private:
    DemoFlowLayout^ layoutEngine;

public:
    DemoFlowPanel()
    {
        layoutEngine = gcnew DemoFlowLayout();
    }

public:
    virtual property System::Windows::Forms::Layout::LayoutEngine^ LayoutEngine
    {
        System::Windows::Forms::Layout::LayoutEngine^ get() override
        {
            if (layoutEngine == nullptr)
            {
                layoutEngine = gcnew DemoFlowLayout();
            }

            return layoutEngine;
        }
    }
};

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Windows.Forms.Layout;

// This class demonstrates a simple custom layout panel.
// It overrides the LayoutEngine property of the Panel
// control to provide a custom layout engine. 
public class DemoFlowPanel : Panel
{
    private DemoFlowLayout layoutEngine;

    public DemoFlowPanel()
    {
    }

    public override LayoutEngine LayoutEngine
    {
        get
        {
            layoutEngine ??= new DemoFlowLayout();

            return layoutEngine;
        }
    }
}

// This class demonstrates a simple custom layout engine.
public class DemoFlowLayout : LayoutEngine
{
    public override bool Layout(
        object container,
        LayoutEventArgs layoutEventArgs)
    {
        Control parent = container as Control;

        // Use DisplayRectangle so that parent.Padding is honored.
        Rectangle parentDisplayRectangle = parent.DisplayRectangle;
        Point nextControlLocation = parentDisplayRectangle.Location;

        foreach (Control c in parent.Controls)
        {
            // Only apply layout to visible controls.
            if (!c.Visible)
            {
                continue;
            }

            // Respect the margin of the control:
            // shift over the left and the top.
            nextControlLocation.Offset(c.Margin.Left, c.Margin.Top);

            // Set the location of the control.
            c.Location = nextControlLocation;

            // Set the autosized controls to their 
            // autosized heights.
            if (c.AutoSize)
            {
                c.Size = c.GetPreferredSize(parentDisplayRectangle.Size);
            }

            // Move X back to the display rectangle origin.
            nextControlLocation.X = parentDisplayRectangle.X;

            // Increment Y by the height of the control 
            // and the bottom margin.
            nextControlLocation.Y += c.Height + c.Margin.Bottom;
        }

        // Optional: Return whether or not the container's 
        // parent should perform layout as a result of this 
        // layout. Some layout engines return the value of 
        // the container's AutoSize property.

        return false;
    }
}

Imports System.Collections.Generic
Imports System.Drawing
Imports System.Text
Imports System.Windows.Forms
Imports System.Windows.Forms.Layout

' This class demonstrates a simple custom layout panel.
' It overrides the LayoutEngine property of the Panel
' control to provide a custom layout engine. 
Public Class DemoFlowPanel
    Inherits Panel

    Private layoutEng As DemoFlowLayout

    Public Sub New()
    End Sub

    Public Overrides ReadOnly Property LayoutEngine() As LayoutEngine
        Get
            If layoutEng Is Nothing Then
                layoutEng = New DemoFlowLayout()
            End If

            Return layoutEng
        End Get
    End Property
End Class

' This class demonstrates a simple custom layout engine.
Public Class DemoFlowLayout
   Inherits LayoutEngine

    Public Overrides Function Layout( _
    ByVal container As Object, _
    ByVal layoutEventArgs As LayoutEventArgs) As Boolean

        Dim parent As Control = container

        ' Use DisplayRectangle so that parent.Padding is honored.
        Dim parentDisplayRectangle As Rectangle = parent.DisplayRectangle
        Dim nextControlLocation As Point = parentDisplayRectangle.Location

        Dim c As Control
        For Each c In parent.Controls

            ' Only apply layout to visible controls.
            If c.Visible <> True Then
                Continue For
            End If

            ' Respect the margin of the control:
            ' shift over the left and the top.
            nextControlLocation.Offset(c.Margin.Left, c.Margin.Top)

            ' Set the location of the control.
            c.Location = nextControlLocation

            ' Set the autosized controls to their 
            ' autosized heights.
            If c.AutoSize Then
                c.Size = c.GetPreferredSize(parentDisplayRectangle.Size)
            End If

            ' Move X back to the display rectangle origin.
            nextControlLocation.X = parentDisplayRectangle.X

            ' Increment Y by the height of the control 
            ' and the bottom margin.
            nextControlLocation.Y += c.Height + c.Margin.Bottom
        Next c

        ' Optional: Return whether or not the container's 
        ' parent should perform layout as a result of this 
        ' layout. Some layout engines return the value of 
        ' the container's AutoSize property.
        Return False

    End Function
End Class

Remarks

Use the LayoutEngine class when you want to create custom layout behavior at run time. Derive your own class from the LayoutEngine class and override the Layout method to define your custom layout behavior.

Constructors

LayoutEngine()

Initializes a new instance of the LayoutEngine class.

Methods

Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
InitLayout(Object, BoundsSpecified)	Initializes the layout engine.
Layout(Object, LayoutEventArgs)	Requests that the layout engine perform a layout operation.
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• How to: Implement a Custom Layout Engine