what is object reference not set to an instance of an object

Sriram Ramki

In Windows Form , I Created ComboBox, when i try to Create a new name, it doesn't show any output. Instead of that it is showing " System.NullReferenceException : 'Object reference is not set to an instance of an object.

private void btnCountry_Click(object sender, EventArgs e)

{

MessageBox.Show(comboBox1.Text);

MessageBox.Show(comboBox1.SelectedItem.ToString());MessageBox.Show(comboBox1.SelectedIndex.ToString());

this.Close();

}

private void btnStates_Click(object sender, EventArgs e)

{

foreach(object obj in listBox1.SelectedItems)

{

MessageBox.Show(obj.ToString());

}

5 Replies

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Laxmidhar Sahoo7y ago
check in the button click
if(combobox.sectedIndex != -1)
Suraj Kumar7y ago
Change .ToString() to Convert.ToString() as shown below as it is null so converting null values to string gives error while Convert.ToString() handles exception and error while converting null value to string so it do not give any error.
if(comboBox1.SelectedIndex >= 1)
{
MessageBox.Show(Convert.ToString(comboBox1.SelectedItem));MessageBox.Show(Convert.ToString(comboBox1.SelectedIndex));
}
Hope this will help you.
Piyush Pansuriya7y ago
Hello,
When you click on button, combobox item must be selected.
This error shows object has null value.
In your case, when you converting selected item to string
comboBox1.SelectedItem.ToString()
SelectedItem must be there. if it is null you can not convert into string. so it throws an exception.
Laxmidhar Sahoo7y ago
I took two button and a textbox one button add the item and anoter display the select value
private void button1_Click(object sender, EventArgs e)
       {
           comboBox1.Items.Add(textBox1.Text);
           MessageBox.Show("Item added successfully");
       }

       private void button2_Click(object sender, EventArgs e)
       {
          var i = comboBox1.SelectedIndex;

           string text = comboBox1.Items[i].ToString();

           MessageBox.Show(text);
       }
Sreekanth Reddy7y ago
Hi Sriram Ramki,

Your code also should be based on your new name of combobox.

Let us think that you gave new name as "cmbcountry".

your following lines of code should get chnged as follows :

instead of comboBox1 change to "cmbCountry"

MessageBox.Show(cmbcountry.SelectedItem.ToString());MessageBox.Show(cmbcountry.SelectedIndex.ToString());

Mark it as answer if it helps else come up with your query.
Thank you.