How to use try catch in iOS?

Question

I wanna check the UITextField is String or number by using try catch. But it seems doesn't work. Here is my code:

- (IBAction)add {

    @try {
        double firstNumber = self.firstNumber.text.doubleValue;
        double secondNumber = self.secondNumber.text.doubleValue;

        Calculator *calcu = [[Calculator alloc] initWithFirstNumber:firstNumber andSecondNumber:secondNumber andOperation:@"+"];

        self.result.text = calcu.calculateTwoNumber;
    }
    @catch (NSException *exception) {
        self.result.text = @"Please enter right number!";
    }
    @finally {

    }
}

Well I think the problem is that there's nothing in your `@try` that's throwing an exception... — rebello95, Mar 10 '15 at 04:05
Do not use `try/catch` for such a task. It's not the right tool for the job. — rmaddy, Mar 10 '15 at 04:05
What do you think will throw an exception? Calling `doubleValue` on a string that doesn't actually have a number simply returns 0 as stated in the docs. — rmaddy, Mar 10 '15 at 04:06
Or sending a message to a `nil` value doesn't cause a crash. If `self.result` is nil, nothing happens. — Ozgur Vatansever, Mar 10 '15 at 04:37
try-catch should only be used for checking exception. If you want to validate the field, implement your own method to check if the text satisfies your requirements. — huong, Mar 10 '15 at 05:01
iOS is not Java. Exception are what they are named "Exceptions" and not error handlers — Thallius, Mar 10 '15 at 07:26
possible duplicate of [Objective-C Exceptions](http://stackoverflow.com/questions/4648952/objective-c-exceptions) — dandan78, Mar 10 '15 at 07:44

score 5 · Answer 1 · edited Sep 16 '16 at 09:21

5

Follow code:

    @try {
       self.labelName.text=[arrName ObjectAtIndex:indexPath.row];
    }
    @catch (NSException *exception) {
        NSLog(@"Something missing...");
    }
    @finally {

    }

edited Sep 16 '16 at 09:21

siburb

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answered Sep 07 '16 at 10:58

Mr.Javed Multani

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dandan78 · Answer 2 · 2015-03-10T07:53:18.723

What Claus Bönnhoff wrote in the comments cannot be overemphasized: Objective-C is not Java or C#.

The accepted way to use exceptions in Obj-C is for unrecoverable errors, not simple flow control.

The answer to your question, then, is that exceptions should be used very rarely. In several years of iOS development, I haven't used them a single time. I also have not come accross them in anyone else's code.

I have, however, encountered exceptions thrown by the Obj-C runtime, which I suppose gives some indication of what their role might be.

How to use try catch in iOS?

2 Answers2