c＃InvalidArgument =值'-1'对'索引'无效

Question

I have a cmbPlace(combobox) which it's item filled automatically with System.IO Drives(C:\\, D:\\, etc). while it's also have validating events. Code below:

using System.IO;
public FNamefile()
{
    InitializeComponent();
    DriveInfo[] allDrives = DriveInfo.GetDrives();
    foreach (DriveInfo d in allDrives)
    {
        cmbPlace.Items.Add(d.Name);
    }
}

private void FNamefile_Load(object sender, EventArgs e)
{
   errorProvider1.ContainerControl = this;
}

private bool ValidatePlace()
{
   bool bStatus = true;
   int m = cmbPlace.SelectedIndex;
   if ((cmbPlace.Items[m]).ToString() == cmbPlace.Text)
   {
       errorProvider1.SetError(cmbPlace, "");
   }
   else if (cmbPlace.Text == "" || (cmbPlace.Items[m]).ToString() != cmbPlace.Text)
   {
       errorProvider1.SetError(cmbPlace, "Please enter a valid location");
       bStatus = false;
   }
   return bStatus;
}
private void cmbPlace_Validating(object sender, CancelEventArgs e)
{
    ValidatePlace();
    int m = cmbPlace.SelectedIndex;

    if ((cmbPlace.Items[m]).ToString() == cmbPlace.Text)
    {  }
    else
    {
         cmbPlace.Focus();
    }
}

The problem is when I tried to test the validating errormessage1 and cmbPlace.Focus() like input 'null' or 'not in index' text, they won't trigger and show error

InvalidArgument=Value of '-1' is not valid for 'index'. Parameter name: index

here's the line/code that cause error, in ValidatePlace and cmbPlace_Validating

if ((cmbPlace.Items[m]).ToString() == cmbPlace.Text)

Answer 1

As I posted in the comments, when no item is selected the SelectedIndex Property returns -1 which is a invalid index for the accessing an array element by index (using cmbPlace.Items[m] ). Saying that, you need to check before accessing the selected element:

if(cmbPlace.SelectedIndex >= 0)
{
   // do something
}
else
{
  // No item selected, handle that or return
}