In swift for iOs,I have an if / else block of code, reacting to changes in a UISwitch. How to set the uiswitch back to off in some situations? - ios

Question

In my swift iOS application, I have a simple UISwitch control. I have connected the value changed outlet to my #IBAction. The code looks like this:
#IBAction func userDidSelectVisibiltySwitch(_ sender: Any) {
if self.visibilitySwitch.isOn {
if badCondition {
self.visibilitySwith.setOn(false, animated: false)
return
}
} else { // Strangely, it executes the else (I think because the compiler is evaluating the isOn condition again when it arrives to the else {}
// work to be done if the user has turned off the switch
}
}
I suspect that in this case, as I am turning the switch off before the else is evaluated, the compiler executes the else {} statement because it evaluates the above isOn expression again. But how is that possible, given that I placed a 'return' instruction ? that is really beyond me. A confirmation of my suspect comes from the fact that if I dispatch_async using GCD the 'self.visibilitySwith.setOn(false, animated: false)' statement, it works properly without executing the else {} statement, because the evaluation of the else takes place before the control is turned off by my statement. My code now looks like this, and it works:
#IBAction func userDidSelectVisibiltySwitch(_ sender: Any) {
if self.visibilitySwitch.isOn {
if badCondition {
DispatchQueue.main.async {
self.visibilitySwith.setOn(false, animated: false)
}
return
}
} else { // In this case it is normal, it does not execute the else {}
// work to be done if the user has turned off the switch
}
}
I think that I am missing something important of swift in this case. Any help is greatly appreciated. I have already provided a solution, but I want to understand the problem. Thanks a lot

Answer 1

Rather than accessing the UISwitch via your sender argument, you go directly to what I assume is the IBOutlet value. Instead of that approach, you can access the sender as outlined below:
#IBAction func userDidSelectVisibiltySwitch(_ sender: UISwitch) {
if sender.isOn && badCondition {
sender.setOn(false, animated: false)
} else { // In this case it is normal, it does not execute the else {}
// work to be done if the user has turned off the switch
}
}
The reason your fix is working is likely because of a slight delay introduced by the dispatch call which allows for the IBOutlet value to update its value.
I have also gone ahead and combined your if statement, as the sample you provide does not require a nested check.
UPDATED BASED ON RMADDY'S COMMENT
This being the solution struck me a bit of code smell, and upon further investigation, I was able to reproduce the scenarios described by OP. This was accomplished by setting the action in Storyboard as seen here:
With that setting, I saw the following:
Original code posted by OP would fail
Adding the DispatchQueue as demonstrated by OP would correct the switch after a brief delay
My posted solution would correctly work
Assuming that this is what the OP has done, then the first correction would be to change the event to Value Changed. Then, as stated by rmaddy in the comment, this would succeed regardless of whether you use the argument or the IBOutlet. Based on the original question, my interpretation was that there was an issue of the outlet value and the switch's state in the interface being out of sync.