Maintaining the aspect ratio of a control

Any custom Windows Forms control can ensure it's aspect ratio is maintained when sized by overriding the OnSizeChanged method and forcing a specific width-height ratio.

It is possible to create a base-class from which other controls can be derived that manages this ability by providing a property to turn this feature on or off. This is necessary of course if you want to be able to set the initial aspect ratio in the first place. A control that represents say, a 16:9 video screen might explicitly set the ratio in the OnSizeChanged method.

The following class defines a control that, when unlocked, keeps a record of it's aspect ratio and when locked maintains that ratio whenever it's resized.

C#

using System;

using System.ComponentModel;

using System.Drawing;

using System.Windows.Forms;

namespace WFTT

{

  /// <summary>

  /// Creates a control with a selectively lockable aspect ratio.

  /// </summary>

  public class AspectBase : ScrollableControl

  {

    public AspectBase()

    {

    }

    float _currentRatio;

    bool _lockRatio=false;

    [

    Description("When true the aspect ratio of the control is locked"),

    Category("Behavior")

    ]

    public bool LockRatio

    {

      get{return _lockRatio;}

      set{_lockRatio=value;}

    }

    protected override void OnSizeChanged(EventArgs e)

    {

      if(!_lockRatio)

        this._currentRatio=(float)this.Height/(float)this.Width;

      else

        this.Height=(int)(this.Width*this._currentRatio);

      base.OnSizeChanged (e);

    }

  }

}

VB

Imports System

Imports System.ComponentModel

Imports System.Drawing

Imports System.Windows.Forms

Namespace WFTT

   '/ <summary>

   '/ Creates a control with a selectively lockable aspect ratio.

   '/ </summary>

   Public Class AspectBase

    Inherits ScrollableControl

    Public Sub New()

    End Sub 'New

    Private _currentRatio As Single

    Private _lockRatio As Boolean = False

    <Description("When true the aspect ratio of the control is locked"), Category("Behavior")>  _

    Public Property LockRatio() As Boolean

     Get

      Return _lockRatio

     End Get

     Set

      _lockRatio = value

     End Set

    End Property

    Protected Overrides Sub OnSizeChanged(e As EventArgs)

     If Not _lockRatio Then

      Me._currentRatio = CSng(Me.Height) / CSng(Me.Width)

     Else

      Me.Height = CInt(Me.Width * Me._currentRatio)

     End If

     MyBase.OnSizeChanged(e)

    End Sub 'OnSizeChanged

   End Class 'AspectBase

End Namespace 'WFTT

Any custom control deriving from this class will inherit the ability to maintain it's aspect ratio.

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