previousRow.Cells[j].Visible是只读

如果C#的DataGridView控件中的Cells[j].Visible是只读的，您可以使用以下方法来合并第二行数据相同的列并且居中：

private void MergeRows()
{
    int rowCount = dataGridView1.Rows.Count;

    for (int i = rowCount - 2; i >= 0; i--)
    {
        DataGridViewRow currentRow = dataGridView1.Rows[i];
        DataGridViewRow previousRow = dataGridView1.Rows[i + 1];

        for (int j = 0; j < dataGridView1.Columns.Count; j++)
        {
            if (currentRow.Cells[j].Value == previousRow.Cells[j].Value)
            {
                // 设置当前单元格的高度为前一行单元格的高度
                currentRow.Cells[j].Style.Padding = new Padding(0, 0, 0, 0);
                currentRow.Cells[j].Style.Alignment = DataGridViewContentAlignment.MiddleCenter;
                currentRow.Cells[j].Style.BackColor = previousRow.Cells[j].Style.BackColor;
                currentRow.Cells[j].Style.ForeColor = previousRow.Cells[j].Style.ForeColor;

                DataGridViewTextBoxCell cell = new DataGridViewTextBoxCell();
                cell.Value = "";
                cell.Style.BackColor = dataGridView1.BackgroundColor;
                currentRow.Cells[j] = cell;

                // 隐藏前一行单元格
                previousRow.Cells.RemoveAt(j);
                previousRow.Cells.Insert(j, new DataGridViewTextBoxCell());
                previousRow.Cells[j].Style.BackColor = dataGridView1.BackgroundColor;
                previousRow.Cells[j].Style.ForeColor = dataGridView1.BackgroundColor;
            }
        }
    }

    // 居中显示
    DataGridViewCellStyle style = new DataGridViewCellStyle();
    style.Alignment = DataGridViewContentAlignment.MiddleCenter;
    foreach (DataGridViewColumn col in dataGridView1.Columns)
    {
        col.DefaultCellStyle = style;
    }
}

在这个方法中，我们使用RemoveAt和Insert方法来隐藏前一行单元格，以达到合并单元格的效果。我们还将前一行单元格的背景色和前景色设置为与DataGridView的背景色相同，以便它们在视觉上消失。最后，我们将所有列的单元格对齐方式设置为居中。