C# DataGridView: Long Text Truncated with "..." on the Left Side When the Column is Right-Aligned

Question

Hi,

I have a question about the cell truncation (replaced with "..."):

How to display the replacement "..." on the left side of a cell when the column is right-aligned?

I'm using non-equal-width font, so I cannot just count the characters to do some string manipulation as a workaround, I need a solution. I believe there should be.

To illustrate my question, I'm simulating my DataGridView here

Left Context (Right aligned column)        | Center Word | Right Context (Left aligned column)
                left context not truncated | CenterWord  | Right context not truncated
...Here is the long left context truncated | CenterWord  | Here is the long right context truncated...

I think I've made myself clear.

Thanks. Please help me out.

Peter

P.S.: the same question can be found at this link: http://objectmix.com/csharp/341736-datagridview-cell-format-question.html

Answer 1

It's definitely an unusual thing to do - but (like anything else) it can be done. It's a question of measuring the size of the string and comparing it with the size of the cell. (Note that I assume that the data is entered by a user. If you're databinding you basically have to consume other events.)

This works but might need some fine tuning:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        dataGridView1.Columns.Add("col1", "col1");
        dataGridView1.Columns[0].CellTemplate.Style.Alignment = DataGridViewContentAlignment.MiddleRight;
        dataGridView1.Columns.Add("col2", "col2");
        dataGridView1.Columns.Add("col3", "col3");

        dataGridView1.Rows.Add();
        dataGridView1.CellEndEdit += new DataGridViewCellEventHandler(dataGridView1_CellEndEdit);
        dataGridView1.ColumnWidthChanged += new DataGridViewColumnEventHandler(dataGridView1_ColumnWidthChanged);              
    }

    void dataGridView1_ColumnWidthChanged(object sender, DataGridViewColumnEventArgs e)
    {
        if (e.Column.Index == 0)
        {
            // We need to truncate everything again when the width changes
            foreach (DataGridViewRow row in dataGridView1.Rows)
            {
                RightTruncateText(row.Cells[0]);
            }
        }
    }

    void RightTruncateText(DataGridViewCell cell)
    {                        
        // check if the content is too long:
        using (Graphics g = Graphics.FromHwnd(this.Handle))
        {
            SizeF size = g.MeasureString((string)cell.Tag, dataGridView1.Font); // NOTE: using the tag

            if (size.Width > cell.Size.Width)
            {
                StringBuilder truncated = new StringBuilder((string)cell.Tag);

                truncated.Insert(0, "...");

                // Truncate the string until small enough (NOTE: not optimized in any way!)                        
                while (size.Width > cell.Size.Width)
                {
                    truncated.Remove(3, 1);
                    size = g.MeasureString(truncated.ToString(), dataGridView1.Font);
                }
                cell.Value = truncated.ToString();
            }
            else
            {
                cell.Value = cell.Tag;
            }
        }
    }

    void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
    {
        if (e.ColumnIndex == 0)
        {
            // Save the value in the tag but show the truncated value
            DataGridViewCell cell = dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex];
            cell.Tag = cell.Value; // Saving the actual state
            RightTruncateText(cell);
        }
    }
}

Answer 2

I have made an workaround, it's working except the "..." (truncation works well)

    protected override void OnCellPainting(DataGridViewCellPaintingEventArgs e)
    {
        base.OnCellPainting(e);

        if (e.RowIndex >= 0 && e.ColumnIndex >= 0 &&
            CustomRightToLeftColumnNames.Contains(this.Columns[e.ColumnIndex].Name))
        {
            // Method 2:
            e.PaintBackground(e.CellBounds, true);

            if (e.FormattedValue != null)
            {
                TextFormatFlags flags = TextFormatFlags.RightToLeft         |
                                        TextFormatFlags.VerticalCenter      |
                                        TextFormatFlags.Right               |
                                        TextFormatFlags.LeftAndRightPadding;// |
                                        //TextFormatFlags.EndEllipsis;
                TextRenderer.DrawText
                (
                    e.Graphics,
                    e.FormattedValue.ToString(),
                    e.CellStyle.Font,
                    e.CellBounds,
                    e.CellStyle.ForeColor,
                    flags
                );
            }

            e.Handled = true;
        }
    }

The only problem with this solution is I don't know how to Set the TextFormatFlags to get the right behavior I want, exactly same as when DataGridView.RightToLeft = Yes.

If I turn on TextFormatFlags.EndEllipsis, the three dots "..." will appear on the left side, but it truncates from the right end of the string.

I'm not sure which flag of TextFormatFlags enumeration to turn on.