Q: C# - How To Enable / Disable Button According To If ListboxItem Selected

Question

I have a listbox and I want to do it. If my listbox is empty or not empty but no item selected, I want to disable button. But if listbox is not empty and it has a selected item, I want to enable button. I tried this but it doesn't work;

        if (lb.SelectedIndex == -1)
        {
            button1.Enabled = false;
        }
        else if(lb.SelectedIndex > -1)
        {
            button1.Enabled = true;
        }

Thank you for answers.

Answer 1

No need to use else if , just use else:

if (lb.SelectedIndex == -1)
{
   button1.Enabled = false;
}
else 
{
  button1.Enabled = true;
}

Answer 2

您首先将按钮设置为禁用，然后在您的列表框<your listboxid>_OnSelecIndexChanged事件上检查所选值并启用该按钮。

Answer 3

You need to add to listbox the SelectedIndexChanged event

In the properties of your listbox search for SelectedIndexChanged, then double click on it

Winforms selected index changed

private void listBox1_SelectedIndexChanged(object sender, System.EventArgs e)
{
   if (lb.SelectedIndex == -1)
   {
     button1.Enabled = false;
   }
   else 
   {
     button1.Enabled = true;
   }
}