如果未選擇組合框，則在Access數據庫中輸入空字符串

Question

當我在Access數據庫中輸入數據時，如果未在組合框中選擇任何項目，則會收到null異常錯誤。 那么，如何確保如果我沒有選擇任何項目，則將空數據插入到數據庫中？

OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + Application.StartupPath + "\\db\\it.accdb");

if (comboBox10.SelectedItem == null)
{
    comboBox10.Text = " ";
}

OleDbCommand cmd = new OleDbCommand();
cmd.CommandType = CommandType.Text;

cmd.CommandText = "insert into data ([Auto Date],AKA,[Phone Number],[R ID],[Related Phone],[Profession]) values ('" + textBox1.Text + "','" + textBox12.Text + "','" + textBox3.Text + "','" + textBox4.Text + "','" + textBox5.Text + "','" + comboBox10.SelectedItem.ToString() + "')";
cmd.Connection = con;

con.Open();
cmd.ExecuteNonQuery();
System.Windows.Forms.MessageBox.Show("Data Inserted Successfully");
con.Close();

Answer 1

您可以檢查SelectedItem屬性是否為null，然后設置一個臨時變量以在查詢字符串中使用。

string comboBox10Text = comboBox10.SelectedItem == null ? String.Empty : comboBox10.Text;

然后在查詢字符串中使用comboBox10Text。

編輯：

// Check if comboBox10.SelectedItem is null, set temp variable
string comboBox10Text = comboBox10.SelectedItem == null ? String.Empty : comboBox10.Text;

OleDbCommand cmd = new OleDbCommand();
cmd.CommandType = CommandType.Text;

// Update query string to use comboBox10Text instead of accessing SelectedItem
cmd.CommandText = "insert into data ([Auto Date],AKA,[Phone Number],[R ID],[Related Phone],[Profession]) values ('" + textBox1.Text + "','" + textBox12.Text + "','" + textBox3.Text + "','" + textBox4.Text + "','" + textBox5.Text + "','" + comboBox10Text + "')";
cmd.Connection = con;
con.Open();
cmd.ExecuteNonQuery();
System.Windows.Forms.MessageBox.Show("Data Inserted Successfully");
con.Close();

Answer 2

您可以進行空檢查並更改條件

If(comboBox10.SelectedItem != null)
{
  cmd.CommandText = "insert into data ([Auto Date],AKA,[Phone Number],[R ID],[Related Phone],[Profession]) values ('" + textBox1.Text + "','" + textBox12.Text + "','" + textBox3.Text + "','" + textBox4.Text + "','" + textBox5.Text + "','" + comboBox10.SelectedItem.ToString() + "')";
}
else
{
  cmd.CommandText = "insert into data ([Auto Date],AKA,[Phone Number],[R ID],[Related Phone],[Profession]) values ('" + textBox1.Text + "','" + textBox12.Text + "','" + textBox3.Text + "','" + textBox4.Text + "','" + textBox5.Text + "','" + "" + "')";
}