ReoGrid provides the ICellBody interface and CellBody base class for creating custom cell types. A cell body is embedded within a cell, conforming to the cell’s dimensions and handling rendering, mouse, and keyboard events.

Namespace

using unvell.ReoGrid.CellTypes;
using unvell.ReoGrid.Events;
using unvell.ReoGrid.Rendering;

Quick Start

Create a class that inherits from CellBody, override the methods you need, and attach it to a cell:

class MyCellBody : CellBody
{
    public override void OnPaint(CellDrawingContext dc)
    {
        dc.DrawCellBackground();
        // Custom drawing here
        dc.DrawCellText();
    }
}

// Attach to a cell
sheet["C3"] = new MyCellBody();
// Or:
sheet.Cells["C3"].Body = new MyCellBody();

Remove a cell body:

sheet.Cells["C3"].Body = null;

CellBody Base Class

The CellBody class provides default implementations for all ICellBody members. Override only the methods you need.

Properties

Lifecycle Methods

Rendering Methods

Mouse Methods

All return bool — return true to consume the event, false for default behavior.

Keyboard Methods

Behavior Properties

CellDrawingContext

The CellDrawingContext provides the drawing surface for OnPaint:

ContentCellBody Base Class

For cell bodies with a content region (like checkboxes and radio buttons), inherit from ContentCellBody:

Owner Drawing

Drawing an Ellipse

class EllipseCell : CellBody
{
    public override void OnPaint(CellDrawingContext dc)
    {
        var bounds = GetBodyBounds();
        dc.Graphics.DrawEllipse(Pens.Blue,
            new Rectangle(0, 0, bounds.Width, bounds.Height));
    }
}

Drawing Default Background and Text

Call DrawCellBackground() and DrawCellText() to include the default rendering:

public override void OnPaint(CellDrawingContext dc)
{
    dc.DrawCellBackground();
    // Custom drawing between background and text
    dc.DrawCellText();
    // Additional drawing on top
}

Drawing a Diagonal Line

class DiagonalLineCell : CellBody
{
    public bool FromTopLeft { get; set; } = true;

    public override void OnPaint(CellDrawingContext dc)
    {
        var bounds = GetBodyBounds();
        if (FromTopLeft)
            dc.Graphics.DrawLine(Pens.Black, new Point(0, 0),
                new Point(bounds.Right, bounds.Bottom));
        else
            dc.Graphics.DrawLine(Pens.Black, new Point(0, bounds.Bottom),
                new Point(bounds.Right, 0));
    }
}

sheet["B2"] = new DiagonalLineCell();
sheet["D2"] = new DiagonalLineCell { FromTopLeft = false };

Disable Cell Edit

Return false from OnStartEdit to prevent editing:

class ReadOnlyBody : CellBody
{
    public override bool OnStartEdit() => false;
}

Modify Edit Results

Return modified data from OnEndEdit:

class UpperCaseBody : CellBody
{
    public override object OnEndEdit(object data, EndEditReason reason)
    {
        if (data is string s)
            return s.ToUpperInvariant();
        return data;
    }
}

Handle Mouse Events

class ClickableProgressCell : CellBody
{
    public override bool OnMouseDown(CellMouseEventArgs e)
    {
        var bounds = GetBodyBounds();
        int value = (int)Math.Round(e.RelativePosition.X * 100f / bounds.Width);
        Cell.Worksheet.SetCellData(e.CellPosition, value);
        return true; // consume the event
    }

    public override void OnPaint(CellDrawingContext dc)
    {
        dc.DrawCellBackground();
        var bounds = GetBodyBounds();
        int value = Cell?.Data is int v ? v : 0;
        float width = bounds.Width * value / 100f;
        dc.Graphics.FillRectangle(new Rectangle(0, 0, width, bounds.Height),
            SolidColor.LightGreen);
        dc.DrawCellText();
    }
}

Handle Keyboard Events

class KeyHandlerCell : CellBody
{
    public override bool OnKeyDown(KeyCode e)
    {
        if (e == KeyCode.Space)
        {
            // Toggle value
            Cell.Data = !(Cell.Data is true);
            return true;
        }
        return false;
    }
}

Data Binding with Formulas

Bind two cells’ data using a formula so the cell body reacts to another cell:

sheet["C3"] = new ClickableProgressCell();
sheet["C7"] = "=C3";  // C7 mirrors C3's value

Intercept Data Changes

Override OnSetData to validate or transform data before it’s stored:

class ClampedCell : CellBody
{
    public override object OnSetData(object data)
    {
        if (data is double d)
            return Math.Clamp(d, 0.0, 1.0);
        return data;
    }
}

Cell Body Bounds

The body bounds are calculated from the cell size minus padding. The GetBodyBounds() method returns a Rectangle relative to the cell’s top-left corner:

public override void OnPaint(CellDrawingContext dc)
{
    var bounds = GetBodyBounds();
    // bounds.X, bounds.Y = padding offset
    // bounds.Width, bounds.Height = available area
}

To change the available area, adjust the cell’s padding style:

sheet.Cells["C3"].Style.Padding = new PaddingValue(5, 5, 5, 5);

Class Hierarchy

Built-in cell types extend CellBody at various levels:

ICellBody (interface)
  └─ CellBody (base class)
       ├─ ContentCellBody (content region with alignment)
       │    ├─ CheckBoxCell
       │    └─ RadioButtonCell
       ├─ ButtonCell
       │    └─ ImageButtonCell
       ├─ DropdownCell (abstract — panel infrastructure)
       │    ├─ DropdownListBaseCell
       │    │    ├─ DropdownListCell
       │    │    └─ ComboListCell
       │    ├─ ColumnDropdownListCell
       │    └─ DatePickerCell
       ├─ ProgressCell
       │    └─ NegativeProgressCell
       ├─ HyperlinkCell
       └─ ImageCell

Related Topics

• Built-in Cell Types — All built-in cell body types
• Dropdown List Cell — Dropdown selection
• Combo List Cell — Editable combo box
• How to Create Custom Drop-down Cell — Custom dropdown tutorial