Dear DataGridView lovers,

I want a DataGridViewColumn that acts like a button but that shows an
image. Furthermore, when the user mouse-overs the image or clicks on it,
I want the image to change.

I've written some code the works, KINDA. Actually it works well, except
it generates error messages in the designer. I can't figure out why.

So, I'm going to post my code for 2 reasons:

1- To solicit help on perfecting the code. If you are a master at C#
custom controls, I need thee. Most importantly, there is an error that
happens not at run-time but in the designer, and I can't figure it out.

2- To share the code with others who are trying to write similar controls.

Problems with my code:

1- If you use the control in a DataGridView, close the form, then
re-open the form, you get an "Object reference not set to an instance of
an object" error message. You get 3 instances of that error, one for
each of the Images associated with the control. I'll paste a sample call
stack at the bottom of this message. (If you ignore the error and
continue then everything works properly. This error only appears in the
designer, not at run-time.)

2- I wanted a traditional Click event for the button. (The normal way of
testing for clicks within a DataGridView is a pain.) The way I got this
to work may is somewhat inelegant. It works though.

3- In order to get the mouseovers to work properly, I made
MouseEnterUnsharesRow always return true. This is probably bad design,
because it could lead to lots of memory being used by the DataGridView.

Without further ado, I give you the DataGridViewImageButtonColumn!
<cue applause>

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

namespace CustomControls
{
    public class DataGridViewImageButtonCell : DataGridViewTextBoxCell
    {
        public DataGridViewImageButtonCell()
            : base()
        {
        }
        enum MultiStateImageStates
        {
            StateNormal,
            StateMouseOver,
            StateClicked
        }
        Image imageToDraw = null;
        void SetImageFromState(MultiStateImageStates state, int rowIndex)
        {
            DataGridViewImageButtonColumn parent =
(DataGridViewImageButtonColumn)this.OwningColumn;
            if (parent != null) {
                switch (state) {
                    case MultiStateImageStates.StateNormal:
                        imageToDraw = parent.ImageNormal;
                        break;
                    case MultiStateImageStates.StateMouseOver:
                        imageToDraw = parent.ImageMouseOver;
                        break;
                    case MultiStateImageStates.StateClicked:
                        imageToDraw = parent.ImageClicked;
                        break;
                }
            }
            if (imageToDraw != null) {
                parent.DataGridView.InvalidateCell(parent.Index, rowIndex);
            }
        }
        protected override void Paint(System.Drawing.Graphics graphics,
System.Drawing.Rectangle clipBounds, System.Drawing.Rectangle
cellBounds, int rowIndex, DataGridViewElementStates elementState, object
value, object formattedValue, string errorText, DataGridViewCellStyle
cellStyle, DataGridViewAdvancedBorderStyle advancedBorderStyle,
DataGridViewPaintParts paintParts)
        {
            const int padding = 5;
            base.Paint(graphics, clipBounds, cellBounds, rowIndex,
elementState, value, String.Empty, errorText, cellStyle,
advancedBorderStyle, paintParts);
            if (imageToDraw == null) {
                DataGridViewImageButtonColumn parent =
(DataGridViewImageButtonColumn)this.OwningColumn;
                if (parent != null) {
                    imageToDraw = parent.ImageNormal;
                }
            }
            if (imageToDraw != null) {
                graphics.DrawImage(imageToDraw, cellBounds.Left +
padding, cellBounds.Top + padding);
            }
        }
        protected override void OnMouseEnter(int rowIndex)
        {
            SetImageFromState(MultiStateImageStates.StateMouseOver,
rowIndex);
            base.OnMouseEnter(rowIndex);
        }
        protected override void OnMouseLeave(int rowIndex)
        {
            SetImageFromState(MultiStateImageStates.StateNormal, rowIndex);
            base.OnMouseLeave(rowIndex);
        }
        protected override void
OnMouseDown(DataGridViewCellMouseEventArgs e)
        {
            SetImageFromState(MultiStateImageStates.StateClicked,
e.RowIndex);
            base.OnMouseDown(e);
        }
        protected override void OnClick(DataGridViewCellEventArgs e)
        {
            DataGridViewImageButtonColumn parent =
(DataGridViewImageButtonColumn)this.OwningColumn;
            if (parent != null) {
                parent.CellWasClicked(this);
            }
            base.OnClick(e);
        }
        protected override bool MouseEnterUnsharesRow(int rowIndex)
        {
            return true;
        }
    }
    public class DataGridViewImageButtonColumn : DataGridViewTextBoxColumn
    {
        public DataGridViewImageButtonColumn()
            : base()
        {
            this.ReadOnly = true;
            DataGridViewImageButtonCell template = new
DataGridViewImageButtonCell();
            base.CellTemplate = template;
        }
        void SetRowHeightFromImage(Image image)
        {
            const int verticalPadding = 10;
            if (image != null) {
                int minimumHeight = image.Height + verticalPadding;
                if (this.DataGridView.RowTemplate.Height < minimumHeight) {
                    this.DataGridView.RowTemplate.Height = minimumHeight;
                }
            }
        }
        Image imageNormal = null;
        public Image ImageNormal
        {
            get { return imageNormal; }
            set
            {
                imageNormal = value;
                SetRowHeightFromImage(imageNormal);
            }
        }
        Image imageMouseOver = null;
        public Image ImageMouseOver
        {
            get { return imageMouseOver; }
            set
            {
                imageMouseOver = value;
                SetRowHeightFromImage(imageMouseOver);
            }
        }
        Image imageClicked = null;
        public Image ImageClicked
        {
            get { return imageClicked; }
            set
            {
                imageClicked = value;
                SetRowHeightFromImage(imageClicked);
            }
        }
        internal void CellWasClicked(DataGridViewImageButtonCell cell)
        {
            if (CellClick != null) {
                EventArgs eventArgs = new EventArgs();
                CellClick(cell, eventArgs);
            }
        }
        public event EventHandler CellClick;
    }
}

******************************************************************

Sample call stack for the error in the designer:

Object reference not set to an instance of an object
at System.ComponentModel.ReflectPropertyDescriptor.SetValue(Object
component, Object value)
at
System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializePropertyAssignStatement(IDesignerSerializationManager
manager, CodeAssignStatement statement, CodePropertyReferenceExpression
propertyReferenceEx, Boolean reportError)
at
System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeAssignStatement(IDesignerSerializationManager
manager, CodeAssignStatement statement)
at
System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeStatement(IDesignerSerializationManager
manager, CodeStatement statement)