如何强制NSTextField仅允许数字？

Question

In Interface Builder I've created a textfield and stuck an NSNumberFormatter into the cell. However, the user can still type text into the textfield. Is there any way to restrict the input to numbers only using interface builder? I thought that was the point of the NSNumberFormatter.

Answer 1

Every formatter has this method:

- (BOOL) getObjectValue: (id*) object forString: (NSString*) string 
    errorDescription: (NSError**) error;

This is valid for every formatter.
If the string is not valid it returns false and the object passed as argument (dereferenced) will be nil.
So instead of dropping a number formatter to the text field, use your own formatter as instance variable.Observe the text field implementing the delegate protocol so that at every change of the text you can be notified.
Then invoke this method:

NSNumber* number;
BOOL success=[formatter getObjectValue: &number forString: [myTextField stringValue] errorDescription:nil];

At this point if success is false (or check if number is nil), there is an invalid string in the text field, so do the action that is more appropriate for you (maybe delete the entire string, or display 0.0 as value).

There is also another method:

- (BOOL) isPartialStringValid : (NSString*) partialString: (NSString*) partialString
    errorDescription: (NSString*) error;

This way you can know if a partial string is valid.For example with the scientific notation "1e" is not valid, but is partially valid because the user may add 1 and it will become "1e1".

Answer 2

Create an NSNumberFormatter subclass and put this in the implementation. In your code, set the YKKNumberFormatter as the formatter for the NSTextField/UITextField.

@implementation YKKNumberFormatter

- (BOOL)isPartialStringValid:(NSString *)partialString newEditingString:(NSString **)newString errorDescription:(NSString **)error {
    // Make sure we clear newString and error to ensure old values aren't being used
    if (newString) { *newString = nil;}
    if (error) {*error = nil;}

    static NSCharacterSet *nonDecimalCharacters = nil;
    if (nonDecimalCharacters == nil) {
        nonDecimalCharacters = [[[NSCharacterSet decimalDigitCharacterSet] invertedSet] retain];
    }

    if ([partialString length] == 0) {
        return YES; // The empty string is okay (the user might just be deleting everything and starting over)
    } else if ([partialString rangeOfCharacterFromSet:nonDecimalCharacters].location != NSNotFound) {
        return NO; // Non-decimal characters aren't cool!
    }

    return YES;
}

@end