How to Set default combobox

问题:

So I've been looking to set a default value for my combobox. I found a few things but none of them seem to work.

Actually, it works if I create a simple combobox and use comboBox1.SelectedIndex = comboBox1.Items.IndexOf("something") but once I dynamically generate the contents of the comboboxes, I can't get it to work anymore.

This is how I fill my combo box (located in the class's constructor);

        string command = "SELECT category_id, name FROM CATEGORY ORDER BY name";
        List<string[]> list = database.Select(command, false);

        cbxCategory.Items.Clear();

        foreach (string[] result in list)
        {
            cbxCategory.Items.Add(new ComboBoxItem(result[1], result[0]));
        }

I can't seem to get it to work to set a default value, like if I place cbxCategory.SelectedIndex = cbxCategory.Items.IndexOf("New") below the above code, it won't work.

WinForms, by the way.

Thank you in advance.

回答1:

cbxCategory.SelectedIndex should be set to an integer from 0 to Items.Count-1 like

cbxCategory.SelectedIndex  = 2;

your

 cbxCategory.SelectedIndex = cbxCategory.Items.IndexOf("New") 

should return -1 as long as no ComboboxItem mutches the string ("New");

another solution though i don't like it much would be

foreach(object obj in cbxCategory.Items){ 
    String[2] objArray = (String[])obj ;
    if(objArray[1] == "New"){
       cbxCategory.SelectedItem = obj;
       break; 
    }
}

perhaps this also requires the following transformation to your code

    foreach (string[] result in list)
    {
      cbxCategory.Items.Add(result);
    }

I haven't tested the code and i am not sure about the casting to String[2] but something similar should work

回答2:

It looks like you're searching the cbxCategory.Items collection for a string, but it contains items of type ComboBoxItem. Therefore the search will return -1.

回答3:

You can use LINQ.

//string command = "SELECT category_id, name FROM CATEGORY ORDER BY name";
//List<string[]> list = database.Select(command, false);
// sample data...
List<string[]> list = new List<string[]> { new string[] { "aaa", "bbb" }, new string[] { "ccc", "ddd" } };

cbxCategory.Items.Clear();

foreach (string[] result in list)
{
    cbxCategory.Items.Add(new ComboBoxItem(result[1], result[0]));
}

ComboBoxItem tmp = cbxCategory.Items.OfType<ComboBoxItem>().Where(x => x.ResultFirst == "bbb").FirstOrDefault();
if (tmp != null)
    cbxCategory.SelectedIndex = cbxCategory.Items.IndexOf(tmp);

ComboBoxItem class:

class ComboBoxItem
{
    public string ResultFirst { get; set; }
    public string ResultSecond { get; set; }

    public ComboBoxItem(string first, string second)
    {
        ResultFirst = first;
        ResultSecond = second;
    }
}

回答4:

Here's my simple solution

        var list = comboBox1.Items.Cast<string>().ToList();
        cbxCategory.SelectedIndex = list.FindIndex(c => c.StartsWith("test"));

回答5:

My solution:

int? defaultID = null;
foreach (DataRow dr in dataSource.Tables["DataTableName"].Rows)
{
     if ((dr["Name"] != DBNull.Value) && ((string)dr["Name"] == "Default Name"))
     {
          defaultID = (int)dr["ID"];
     }
}
if (defaultID != null) comboBox.SelectedValue = defaultID;