Why must I push IBAction Button twice for action to occur? - xcode

Question

I'm making an app that does a calculation when the IBAction button is pressed. It works fine, but I have to press it twice for the Action to occur. Anyone have experience with this? Below is some code from the #IBAction button in question:
#IBAction func CalculateGPA(sender: AnyObject) {
gpa = (gp + gp2 + gp3
+ gp4 + gp5 + gp6
+ gp7) / (ch + ch2
+ ch3 + ch4 + ch5
+ ch6 + ch7)
gpaLabel.text = NSString(format: " Your GPA is %.2f", gpa) as String
//added if textField == ">9" after first submission
if textField1.text == "10"{
gpaLabel.text = "Enter 1-9 Credit Hours"
}
if textField2.text == "10"{
gpaLabel.text = "Enter 1-9 Credit Hours"
}
And for your info, this Button makes a calculation and changes the input of a label. My guess why I have to press it twice is that the first press does the calculation, the second press changes the label to show the result.

Answer 1

First of all, the formula that you are using to calculate GPA is incorrect. You should not add up total grades and divide by total credit hours as it appears that you are doing. You have to multiply each grade by the the number of credit hours, add that up, then divide by total credit hours:
gpa = (gp * ch + gp2 * ch2 + gp3 * ch3 + gp4 * ch4 +
gp5 * ch5 + gp6 * ch6 + gp7 * ch7) /
(ch + ch2 + ch3 + ch4 + ch5 + ch6 + ch7)
Also, you might want to use an array in a for loop so that if the number of classes changes you can process any number of classes. Imagine if you had 100 classes, putting all this in a giant statement would be silly and time-consuming:
gpa = (gp * ch + gp2 * ch2 + gp3 * ch3 + gp4 * ch4 +
gp5 * ch5 + gp6 * ch6 + gp7 * ch7 ... gp100 * ch100) /
(ch + ch2 + ch3 + ch4 + ch5 + ch6 + ch7 + ... ch100)
Instead say:
var numerator: Int = 0
var totalCh : Int = 0
var gpa : Double = 0.0
// gp and ch should be arrays that are instance variables;
// they should already be filled in either in this function or
// from another location
for (var i: Int = 0; i < gp.count; i++) {
numerator += gp [i] * ch [i]
totalCh += ch [i]
}
if (totalCh > 0) {
gpa = Double (numerator) / Double (totalCh)
} else {
gpa = 0.0 // can't divide by 0. Might want an error message to user here
}
// ...
Also, you should do your validation of user input at the top of your function instead of after you have done the calculation. If the user made an error, you should give some feedback to the user on what he did wrong and how to fix it (as you have done), but do not do the calculation at all until all validations are good.
To answer your original question, we need to see all the code for that function. If textfield1 and textfield2 are filled elsewhere, it would help to see where they fit in.
It is possible that you don't have the IBAction hooked up correctly to your button. Go into the Connections Inspector and click on the button in your StoryBoard, and make a screenprint of what you see and post it here so that we can check to see if you did the connections correctly.
However, since you have to press the button twice to see any results, there is a higher probability that you failed to initialize something, so it had a value of zero or null the first time you pressed the button, but then it got initialized by the end of the function, so when you pressed the button again, it did the calculation and entered an answer into the label.
To see exactly what is going on, you should try stepping through the debugger. If you don't have any experience with that, you could put a bunch of print statements at key locations in your IBAction function to see what is being calculated and to see what statements are executing and to make sure that the function got started at all; at least enter one at the beginning of the function that says "entering IBAction calculateGPA".