Simple problem: I am checking to see if a combobox has had an item selected with string.IsNullOrEmpty(). Problem is, even if is is selected, the error message appears. What am I doing wrong?
Here is my code:
private void button1Click(object sender, EventArgs e)
{
if (string.IsNullOrEmpty(comboBox1.SelectedText))//here should skip to else - but doesn't
{
MessageBox.Show("You must select a 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 a conversion type", "Error");
}
}
else
{
MessageBox.Show("curency");
}
}
}
Note: This is my second ever C# program - so please don't yell at me if I'm being stupid.
Generally a few observations/suggestions.
First you're using string values and are basing logic on these values, you might want to look into using an Enum and binding all it's values to the combo box. Then use the SelectedItem property and compare it to the Enum.
When nothing is selected the SelectedItem will return NULL, another option is using SelectedIndex which will return -1 when no item has been selected.
So with the SelectedIndex it would become something like;
if (comboBox1.SelectedIndex == -1)//Nothing selected
{
MessageBox.Show("You must select a conversion type", "Error");
}
else
{
//Do Magic
}
Generally using string comparisons should only be done when anything "strong" like an int comparison or even better an enum comparison is not possible. (Maybe it's just me though but strings change to often and are just scary for this sort of stuff.)
For the enum suggestion possibly look at one of these links;
Binding an enum to a WinForms combo box, and then setting it
Load values of enum type into a combobox
Is it possible to load items from an Enum to a ComboBox in .NET 3.5?
Binding a ComboBox to an Enumeration
I'm not sure which .NET version and things you're using as binding is alot easier in WPF then in the old windows form (in my opinion).
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