Objective C : validity check for an enum variable

Question

I am having a delegate function which asks for UIActivityIndicatorViewStyle from delegate.

@protocol StatusViewCustomizationDelegate <NSObject>

@optional
-(UIActivityIndicatorViewStyle)activityIndicatorStyle;

@end

Inside a private function I check if delegate responds to this selector and if it responds I call the method. Below is the code:

-(void)configureView
{
   UIActivityIndicatorViewStyle activityIndicatorStyleFromDelegate;
    if ([self.delegate respondsToSelector:@selector(activityIndicatorViewStyle)])
    {
        activityIndicatorStyleFromDelegate = [self.delegate activityIndicatorStyle];
    }
}

What is the correct way to check the enum value I received in activityIndicatorStyleFromDelegate variable is a valid UIActivityIndicatorViewStyle enum value?

Edit: UIActivityIndicatorViewStyle is an iOS defined enum.

typedef NS_ENUM(NSInteger, UIActivityIndicatorViewStyle) {
    UIActivityIndicatorViewStyleWhiteLarge,
    UIActivityIndicatorViewStyleWhite,
    UIActivityIndicatorViewStyleGray,
};

check this: http://stackoverflow.com/questions/7154304/objective-c-check-if-using-enum-option — x4h1d, May 07 '15 at 10:31

Ashley Mills · Accepted Answer · 2015-05-07T10:51:50.840

Generally, when checking enum values you're limited to one of two methods.

If the enum values are in a contiguous sequence, you can check the value is within its range:

if (activityIndicatorStyle >= UIActivityIndicatorViewStyleWhiteLarge && 
    activityIndicatorStyle <= UIActivityIndicatorViewStyleGray) {
    NSLog(@"Good");
} else {
    NSLog(@"Bad");
}

Otherwise you'll just have to test check against each value in turn:

switch (activityIndicatorStyle) {
    case UIActivityIndicatorViewStyleGray:
    case UIActivityIndicatorViewStyleWhite:
    case UIActivityIndicatorViewStyleWhiteLarge:
        NSLog(@"Good");
        break;
    default:
        NSLog(@"Bad");
}

Second one looks more descriptive and clear. Thanks. – dev gr May 08 '15 at 11:54 — dev gr, May 08 '15 at 11:54

trojanfoe · Answer 2 · 2015-05-07T10:47:19.453

1

Use this code:

if (style >= UIActivityIndicatorViewStyleWhiteLarge &&
    style <= UIActivityIndicatorViewStyleGray) {
    // valid
} else {
    // invalid
}

edited May 07 '15 at 10:47

answered May 07 '15 at 10:43

trojanfoe

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`UIActivityIndicatorViewStyle` is not user defined. – Schemetrical May 07 '15 at 10:46
You mean Apple :p, but yeah they use NSUIntegers for more recent enums. – Schemetrical May 07 '15 at 10:47
@Schemetrical Yeah. You think they are infallible? – trojanfoe May 07 '15 at 10:48
Of course, this relies on the enum values being contiguous. – Ashley Mills May 07 '15 at 10:48
@AshleyMills Which they are. – trojanfoe May 07 '15 at 10:49
Which they are! (Didn't read the question properly - was thinking generally). Of course, this could change… – Ashley Mills May 07 '15 at 10:49
@trojanfoe I never said they were infallible, and I'm assuming its that they are reluctant to change old APIs to prevent problems (god knows what people are doing to compare enums). – Schemetrical May 07 '15 at 10:50

score 0 · Answer 3 · edited May 23 '17 at 10:27

You can take the last value of the enum and compare if the supplied enum is less or equal than the last value of the enum, so:

- (void)configureView
{
   UIActivityIndicatorViewStyle activityIndicatorStyleFromDelegate;
    if ([self.delegate respondsToSelector:@selector(activityIndicatorViewStyle)])
    {
        if ([self.delegate activityIndicatorStyle] >= UIActivityIndicatorViewStyleWhiteLarge &&
    [self.delegate activityIndicatorStyle] <= UIActivityIndicatorViewStyleGray) {
            activityIndicatorStyleFromDelegate = [self.delegate activityIndicatorStyle];
        }
    }
}

Also, a common convention is to add one more enumeration that is called num_types and you can check if the enums are less than num_types, but this is not possible in your context.

Objective C : validity check for an enum variable

3 Answers3