c# - Validating if a combobox it's SelectedText property is empty always fails -

September 15, 2014

simple problem: checking see if combobox has had item selected string.isnullorempty(). problem is, if is selected, error message appears. doing wrong?

here code:

private void button1click(object sender, eventargs e) {     if (string.isnullorempty(combobox1.selectedtext))//here should skip else - doesn't     {         messagebox.show("you must select conversion type", "error");     }     else     {         if (combobox1.selectedtext == "currency")         {             double input = convert.todouble(textbox1.text);             if (!string.isnullorempty(combobox2.selectedtext))             {                 string type = combobox2.selectedtext;                 double result = convertcurrency(type, input);                 if (result != -1)                 {                     label1.text = convert.tostring(result);                 }              }              else              {                  messagebox.show("you must select conversion type", "error");              }          }          else          {              messagebox.show("curency");          }      }  }

note: second ever c# program - please don't yell @ me if i'm being stupid.

generally few observations/suggestions.

first you're using string values , basing logic on these values, might want using enum , binding it's values combo box. use selecteditem property , compare enum.

when nothing selected selecteditem return null, option using selectedindex return -1 when no item has been selected.

so selectedindex become like;

if (combobox1.selectedindex == -1)//nothing selected {     messagebox.show("you must select conversion type", "error"); } else {     //do magic    }

generally using string comparisons should done when "strong" int comparison or better enum comparison not possible. (maybe it's me though strings change , scary sort of stuff.)

for enum suggestion possibly @ 1 of these links;

binding enum winforms combo box, , setting it

load values of enum type combobox

is possible load items enum combobox in .net 3.5?

binding combobox enumeration

i'm not sure .net version , things you're using binding alot easier in wpf in old windows form (in opinion).