未将对象引用设置到对象的实例

Question

for (int j = 0; j < dataGridView2.Rows.Count; j++)
                    {
                      
                        string tempStr="";
                        for (int k = 0; k < dataGridView2.Columns.Count; k++)
                        {
                           
                            if (k > 0)
                            {
                                tempStr += "\t";
                            }
                           
                            tempStr += dataGridView2.Rows[j].Cells[k].Value.ToString();
                        }                        sw.WriteLine(tempStr);
                    }
                    sw.Close();
                    myStream.Close();每次到 tempStr += dataGridView2.Rows[j].Cells[k].Value.ToString(); 都会出错，说是未将对象引用设置到对象的实例
不懂怎么回事。

Answer 1

  tempStr += dataGridView2.Rows[j].Cells[k].Value==null?"": dataGridView2.Rows[j].Cells[k].Value.ToString();

Answer 2

dataGridView2.Rows[j].Cells[k].Value可能为null。
if(dataGridView2.Rows[j].Cells[k].Value!=null)
{
tempStr += dataGridView2.Rows[j].Cells[k].Value.ToString(); 
}