“if” that doesn't work perfectly

Question

What wrong with this code? Either combobox is "Wholesale" or "Retail" the form show the second statement (true, true). If I untick the checkbox the else works ( true , false ). Any idea why?

private void checkBox3_CheckedChanged(object sender, EventArgs e)
    {
        if (checkBox3.Checked == true || comboBox1.SelectedText == "Standalone")
        {

            this.checkBox1.BackColor = Color.Gray;
            this.checkBox1.Enabled = false;
            this.checkBox2.BackColor = Color.Gray;
            this.checkBox2.Enabled = false;
        }

        if (checkBox3.Checked == true || comboBox1.SelectedText == "Retail")
        {
            this.checkBox1.BackColor = default(Color);
            this.checkBox1.Enabled = true;
            this.checkBox2.BackColor = default(Color);
            this.checkBox2.Enabled = true;
       }
       else
       {
            this.checkBox1.BackColor = default(Color);
            this.checkBox1.Enabled = true;
            this.checkBox2.BackColor = Color.Gray
            this.checkBox2.Enabled = false;
       }

Answer 1

A simple else if and the usage of && should do the trick:

if (checkBox3.Checked == true && comboBox1.SelectedText == "Standalone")
{
    ...
    //If this case is true, the following cases are not going to be checked
}
else if (checkBox3.Checked == true && comboBox1.SelectedText == "Retail")
{
    ...
    //If this case is true, the following cases are not going to be checked
}
else
{
    ...
    //No case before was true
}

Note that the usage of an simple if behind an if is NOT the same as the usage of an else if behind an if .

Also note that your method checkBox3_CheckedChanged only gets called after the state of your third CheckBox was changed (unless you took the method for other events)

Answer 2

I suggest eliminating all if here and operate with boolean formulas only. First, let's get rid of pesky (checkBox3.Checked == true || comboBox1.SelectedText == "Standalone") :

 bool isRetail = checkBox3.Checked && comboBox1.SelectedText == "Retail";
 bool isStandalone = checkBox3.Checked && comboBox1.SelectedText == "Standalone";

Then try to guess when CheckBox s should be Enabled :

 // checkBox2 is enabled if and only if isRetail 
 //TODO: can see, how checkBox2 is unreadable? Change the name into, say "boxIsRetail"
 this.checkBox2.Enabled = isRetail;
 // checkBox2 is enabled if and only if neither isRetail nor isStandalone
 //TODO: can see, how checkBox1 is unreadable? Change the name into, say "boxIsNeither"
 this.checkBox1.Enabled = !(isRetail || isStandalone);

Finally, we should update their Color s. CheckBox 's Color depends on Enabled only:

 this.checkBox1.BackColor = this.checkBox1.Enabled ? default(Color) : Color.Gray;
 this.checkBox2.BackColor = this.checkBox2.Enabled ? default(Color) : Color.Gray;

Putting all together we have

 private void checkBox3_CheckedChanged(object sender, EventArgs e) {
   bool isRetail = checkBox3.Checked && comboBox1.SelectedText == "Retail";
   bool isStandalone = checkBox3.Checked && comboBox1.SelectedText == "Standalone";

   checkBox2.Enabled = isRetail;
   checkBox1.Enabled = !(isRetail || isStandalone);

   //TODO: these lines are good candidate to be extracted into a method "UpdateColor"
   checkBox1.BackColor = checkBox1.Enabled ? default(Color) : Color.Gray;
   checkBox2.BackColor = checkBox2.Enabled ? default(Color) : Color.Gray;
 }

Please, notice, that you can easily add another bool variables like isWholesale , isReserved etc. and implement corresponding logic without roaming among trees of if , else and if else