how to set combobox value to null

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hi , here i am trying to insert values to the database but the combobox values are not adding when they are null . How to insert the combobox value when it is null. I am getting the error as "Object reference not set to an instance of an object."

VB

  ocon = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\Customer.mdb")
        ocon.Open()
        Dim s1 As String
        If TextBox1.Text = "" Or TextBox2.Text = "" Or TextBox3.Text = "" Or TextBox4.Text = "" Or TextBox5.Text = "" Or TextBox6.Text = "" Then
            MsgBox("Please enter all the fields")
        Else
            s1 = "insert into Customertable(cusid,cusname,cusdivision,cuslocation,cuscountry,custypeofproj,stage1,stage2,stage3,stage4,stage5,stage6,stage7,stage8,stage9,stage10,stage11,stage12,stage13,stage14)values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "','" + TextBox4.Text + "','" + TextBox5.Text + "','" + TextBox6.Text + "','" + ComboBox1.SelectedItem.ToString() + "','" + ComboBox2.SelectedItem.ToString() + "','" + ComboBox3.SelectedItem.ToString() + "','" + ComboBox4.SelectedItem.ToString() + "','" + ComboBox5.SelectedItem.ToString() + "','" + ComboBox6.SelectedItem.ToString() + "','" + ComboBox7.SelectedItem.ToString() + "','" + ComboBox8.SelectedItem.ToString() + "','" + ComboBox9.SelectedItem.ToString() + "','" + ComboBox10.SelectedItem.ToString() + "','" + ComboBox11.SelectedItem.ToString() + "','" + ComboBox12.SelectedItem.ToString() + "','" + ComboBox13.SelectedItem.ToString() + "','" + ComboBox14.SelectedItem.ToString() + "')"
ocmd.ExecuteNonQuery()
            TextBox1.Text = ""
            TextBox2.Text = ""
            TextBox3.Text = ""
            TextBox4.Text = ""
            TextBox5.Text = ""
            TextBox6.Text = ""
            ComboBox1.SelectedIndex = -1
            ComboBox2.SelectedIndex = -1
            ComboBox3.SelectedIndex = -1
            ComboBox4.SelectedIndex = -1
            ComboBox5.SelectedIndex = -1
            ComboBox6.SelectedIndex = -1
            ComboBox7.SelectedIndex = -1
            ComboBox8.SelectedIndex = -1
            ComboBox9.SelectedIndex = -1
            ComboBox10.SelectedIndex = -1
            ComboBox11.SelectedIndex = -1
            ComboBox12.SelectedIndex = -1
            ComboBox13.SelectedIndex = -1
            ComboBox14.SelectedIndex = -1
            TextBox1.Focus()
            MsgBox("Successfully inserted")
        End If

Posted 30-Nov-11 22:29pm

ANANTH P

Updated 1-Dec-11 2:05am

Scubapro

v3

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**Manoj K Bhoir** · Answer 1 · 2011-12-01T02:31:00

If combobox value is null then try to add empty string into the DataBase.

VB

Dim S As String 
If ComboBox1.Text = "" Then
   S = ComboBox1.Text
Else
   S = ""
End If
ComboBox1.Text

And try to set Default Text Value of ComboBox is "" then Wether it is visible or invisible it returns "" value, if comboBox value is not selected.I hope it will help you.:)

D K N T H · Answer 2 · 2011-11-30T23:04:00

Solution 1

try to check first if the combobox is null, try this,

VB

string itemSelected = combobox1.SelectedItem.ToString()

if(itemSelected ==null)
then
   itemSelected=string.empty

else

'do the adding

hope it helps,

don't forget to vote..

Posted 30-Nov-11 23:04pm

D K N T H

Comments

ANANTH P 1-Dec-11 5:33am

hi, i got the output,but if the combobox visible property is set to false then the above solution is not working