Getting selected value of a combobox

问题:

public class ComboboxItem { 
            public string Text { get; set; } 
            public string Value { get; set; }
            public override string ToString() { return Text; } 
        }

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            int selectedIndex = comboBox1.SelectedIndex;
            int selecteVal = (int)comboBox1.SelectedValue; 
            ComboboxItem selectedCar = (ComboboxItem)comboBox1.SelectedItem;
            MessageBox.Show(String.Format("Index: [{0}] CarName={1}; Value={2}", selectedIndex, selectedCar.Text, selecteVal));
        }

I'm adding them like:

ComboboxItem item = new ComboboxItem();
                    item.Text = cd.Name;
                    item.Value = cd.ID;
                    this.comboBox1.Items.Add(item);

I keep getting a NullReferenceExeption and not sure why. the text seems to show up just fine.

回答1:

Try this:

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    ComboBox cmb = (ComboBox)sender;
    int selectedIndex = cmb.SelectedIndex;
    int selectedValue = (int)cmb.SelectedValue;

    ComboboxItem selectedCar = (ComboboxItem)cmb.SelectedItem;
    MessageBox.Show(String.Format("Index: [{0}] CarName={1}; Value={2}", selectedIndex, selectedCar.Text, selecteVal));        
}

回答2:

You are getting NullReferenceExeption because of you are using the cmb.SelectedValue which is null. the comboBox doesn't know what is the value of your custom class ComboboxItem, so either do:

ComboboxItem selectedCar = (ComboboxItem)comboBox2.SelectedItem;
int selecteVal = Convert.ToInt32(selectedCar.Value);

Or better of is use data binding like:

ComboboxItem item1 = new ComboboxItem();
item1.Text = "test";
item1.Value = "123";

ComboboxItem item2 = new ComboboxItem();
item2.Text = "test2";
item2.Value = "456";

List<ComboboxItem> items = new List<ComboboxItem> { item1, item2 };

this.comboBox1.DisplayMember = "Text";
this.comboBox1.ValueMember = "Value";
this.comboBox1.DataSource = items;

回答3:

I had a similar error, My Class is

public class ServerInfo
{
    public string Text { get; set; }
    public string Value { get; set; }
    public string PortNo { get; set; }

    public override string ToString()
    {
        return Text;
    }
}

But what I did, I casted my class to the SelectedItem property of the ComboBox. So, i'll have all of the class properties of the selected item.

// Code above
ServerInfo emailServer = (ServerInfo)cbServerName.SelectedItem;

mailClient.ServerName = emailServer.Value;
mailClient.ServerPort = emailServer.PortNo;

I hope this helps someone! Cheers!

回答4:

The problem you have with the SelectedValue is not converting into integer. This is the main problem so usinge the following code snippet will help you:

int selectedValue;
bool parseOK = Int32.TryParse(cmb.SelectedValue.ToString(), out selectedValue);

回答5:

Try this:

int selectedIndex = comboBox1->SelectedIndex;
comboBox1->SelectedItem->ToString();
int selectedValue = (int)comboBox1->Items[selectedIndex];

回答6:

Try this:

private void cmbLineColor_SelectedIndexChanged(object sender, EventArgs e)
    {
        DataRowView drv = (DataRowView)cmbLineColor.SelectedItem;
        int selectedValue = (int)drv.Row.ItemArray[1];
    }