My catch isn't working on url request - swift

Question

I am trying to do my first try catch in Swift.
Essentially the user can give a name to something. So say he/she types in Gmail and hits submit.
Since G is the first letter of the String (doesn't matter if its lower or upper case) the image will load a picture of a G.
If the user also adds in a URL so say gmail.com or www.gmail.com it will pull the favicon for gmail.
So far so good.
HOWEVER. If the person types gmailllllll.com
it loads a picture of a globe (which I think is the default)
What I am trying to do is only put the gmail favicon in the image view if it is actually the image. If it is nil then I want to put the image of the G which I provided.
I understand why my code isn't working. I just do not know how to add to it to do what I want.
DispatchQueue.main.async {
let myURLString: String = "http://www.google.com/s2/favicons?domain=\(self.serviceArray[row].serviceUrl)"
let myURL = URL(string: myURLString)
do {
let myData = try Data(contentsOf: myURL!)
cell.serviceLogoImage.image = UIImage(data: myData)
} catch {
cell.serviceLogoImage.image = UIImage.init(named: "\(self.getLetterOrNumberAndChooseImage(text: self.serviceArray[row].serviceName))")
}
}
Also, If the user were to type in www.go google.com
with the space it has an optional crashe!
I tried saying
if myData == nil {...}
But it says it always returns false...
Any help would be appreciated

Answer 1

Optional binding
This solution avoids force unwrapping (ie myURL!) with optional binding.
Note that try? returns an optional. It returns nil rather than throwing an error. It is appropriate when you want to handle all errors in the same way.
let myURLString: String = "http://www.google.com/s2/favicons?domain=\(self.serviceArray[row].serviceUrl)"
if let myURL = URL(string: myURLString), let myData = try? Data(contentsOf: myURL), let image = UIImage(data: myData) {
cell.serviceLogoImage.image = image
}
else {
cell.serviceLogoImage.image = UIImage.init(named: "\(self.getLetterOrNumberAndChooseImage(text: self.serviceArray[row].serviceName))")
}

Answer 2

This expression Data(contentsOf: myURL!) is unsafe. I think you expect it to raise an error, but it will just crash your code (by design) if the URL cannot be parsed. Here is a safe example:
if let url = URL(string:mystring) {
do {
let data = try Data(contentsOf:url)
} catch {
print ("network issue")
}
} else {
print("bad string")
}

Answer 3

First of all, never EVER use ! unless you are sure that there is a value and not nil because forced unwrapping will crash your entire app. Second of all, I don't really get what are you trying to do with that Dispatch. I mean, if the user hits submit, you should make a function for example and you would call that when the submit button is tapped.
I would write something like this:
func updateImage() {
var myData: Data?
let myURLString: String = "http://www.google.com/s2/favicons?domain=\(self.serviceArra‌​y[row].serviceUrl)"
let myURL = URL(string: myURLString)
if let url = myURL {
do {
myData = try Data(contentfOf: url)
} catch {
print("error")
}
}
if let data = myData {
cell.serviceLogo.image = UIImage(data: data)
} else {
cell.serviceLogo.image = UIImage.init(named: "\(self.getLetterOrNumberAndChooseImage(text: self.serviceArray[row].serviceName))")
}
I really can't figure out what you were trying with that Dispatch, but eventually I'm thinking that first you should use a Dispatch.global(qos: .background).async where you would first verify what the user has entered and eventually download the necessary photos and then, when you're trying to update the UI, you should come back to the main thread with Dispatch.main.async. I guess.