Lesson 5 - Try catch

We want to change string “8” to number 8. We do like this

let a="8"

let number = NSNumberFormatter().numberFromString(a)

var num = number!.integerValue

let b=9+num

Change “8” to “8m”, error mark at line let b=9+num because can’t change “8m” to number.

We use Try catch like this.

do {

let number = try NSNumberFormatter().numberFromString(a)

var num = number!.integerValue

let b=9+num

}

catch let error as NSError{

print("Error cast string to number")

}

It still show error, because Swift doesn’t support try catch like this.

To catch exception in this case, we do this way.

if let number = NSNumberFormatter().numberFromString(a){

var num = number.integerValue

let b=9+num

}

else{

print("Error cast string to number ")

}

Run to see result, programme still run, not crash.

Remove character m in variable a, it run normally, result show 17.

Try catch useless here but sometime you must use it when make app, for example, to check when read txt file.

This lesson let you know about it, that ‘s all.