// 在绑定数据前处理空值
dataGridView1.DataSource = yourDataSource.Select(x => new {
    Column1 = x.Column1 ?? "默认值",
    Column2 = x.Column2 ?? 0
}).ToList();

dataGridView1.CellFormatting += (sender, e) => {
    if (e.Value == null || e.Value == DBNull.Value) {
        e.Value = "空值"; // 或你想要的默认值
        e.FormattingApplied = true;
    }
};

dataGridView1.CellValidating += (sender, e) => {
    if (e.ColumnIndex == yourColumnIndex && string.IsNullOrEmpty(e.FormattedValue?.ToString())) {
        // 处理空值输入
        dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value = DBNull.Value;
    }
};

dataGridView1.DefaultCellStyle.NullValue = "N/A";

// 虚拟模式示例
dataGridView1.VirtualMode = true;
dataGridView1.CellValueNeeded += (sender, e) => {
    if (yourDataArray[e.RowIndex, e.ColumnIndex] == null) {
        e.Value = "空值";
    } else {
        e.Value = yourDataArray[e.RowIndex, e.ColumnIndex];
    }
};