How to Merge Duplicate Cells in a WinForms DataGridView's First Column?

WinForms DataGridView Cell Merge

Question:

In DataGridView, data is arranged in a grid format, containing rows and columns. Each row and column intersection is represented by a cell. In this example, the data is displayed in a format such that duplicate values ​​in the first column (Hd1) are not merged, resulting in multiple rows for the same value.

Requirements:

The goal is to merge cells with duplicate values ​​in the first column (Hd1) to improve visuals and consolidate data efficiently.

Solution:

To merge cells in DataGridView, you can follow these steps:

1. Find duplicate values:

   • Create a method named IsTheSameCellValue that compares the values ​​of two adjacent cells in the first column. If the values ​​are the same, true is returned, otherwise false is returned.

bool IsTheSameCellValue(int column, int row)
{
    DataGridViewCell cell1 = dataGridView1[column, row];
    DataGridViewCell cell2 = dataGridView1[column, row - 1];
    if (cell1.Value == null || cell2.Value == null)
    {
       return false;
    }
    return cell1.Value.ToString() == cell2.Value.ToString();
}

2. Cell drawing:

   • Override the CellPainting event handler and modify the cell's AdvancedBorderStyle property:

private void dataGridView1_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
{
    e.AdvancedBorderStyle.Bottom = DataGridViewAdvancedCellBorderStyle.None;
    if (e.RowIndex < 1 || e.ColumnIndex < 0)
        return;
    if (IsTheSameCellValue(e.ColumnIndex, e.RowIndex))
    {
        e.AdvancedBorderStyle.Top = DataGridViewAdvancedCellBorderStyle.None;
    }
    else
    {
        e.AdvancedBorderStyle.Top = dataGridView1.AdvancedCellBorderStyle.Top;
    }  
}

3. Cell formatting:

   • Override the CellFormatting event handler to set the value to an empty string if the cell is a duplicate:

if (e.RowIndex == 0)
    return;
if (IsTheSameCellValue(e.ColumnIndex, e.RowIndex))
{
    e.Value = "";
    e.FormattingApplied = true;
}

4. Other settings:

   • Set dataGridView1.AutoGenerateColumns to false in the form load event to prevent columns from being automatically generated.

dataGridView1.AutoGenerateColumns = false;

Result:

Performing these steps will merge cells with duplicate values ​​in the first column of the DataGridView, making the data display more compact and organized.

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