未将对象引用设置到对象的实例

查看tb_birthday是否错误
实例：
print?for (int i = 0; i < iRows - 1; i++){for (int j = 1, k = 0; j < iCols; j++){if (dgvStudent.Columns[j].Visible){dimArray[i + 1, k] = dgvStudent.Rows[i].Cells[j].Value.ToString();k++;}}}
for (int i = 0; i < iRows - 1; i++){for (int j = 1, k = 0; j < iCols; j++){if (dgvStudent.Columns[j].Visible){dimArray[i + 1, k] = dgvStudent.Rows[i].Cells[j].Value.ToString();k++;}}}[csharp] view plaincopyprint?//其中public System.Windows.Forms.DataGridView dgvStudent;，dimArray为Excel中的单元格，即
//其中public System.Windows.Forms.DataGridView dgvStudent;，dimArray为Excel中的单元格，即[csharp] view plaincopyprint?//ws.get_Range(ws.Cells[1, 1], ws.Cells[iRows, iCols]).Value2 = dimArray;
//ws.get_Range(ws.Cells[1, 1], ws.Cells[iRows, iCols]).Value2 = dimArray;[csharp] view plaincopyprint?//ws 为Microsoft.Office.Interop.Excel.Worksheet
//ws 为Microsoft.Office.Interop.Excel.Worksheet这是从Datagridview导入Excel时的代码，但是出现了“未将对象引用设置到对象的实例”这个错误，我以为是不是我手动添加列时添加的不正确，所以我把函数 dgvStudent.Columns.Add(列名字符串变量, 列头名称字符串变量);改为了
[csharp]DataGridViewTextBoxColumn column = new DataGridViewTextBoxColumn();column.HeaderText = sh;column.Name = quesId;column.ReadOnly = false;dgvStudent.Columns.Add(column);
DataGridViewTextBoxColumn column = new DataGridViewTextBoxColumn();column.HeaderText = sh;column.Name = quesId;column.ReadOnly = false;dgvStudent.Columns.Add(column);不用DataGridViewColumn column = new DataGridViewColumn();由于会出现CellType为空的错误。