JLStringToBoolValueTranformer

If you use Cocoa Bindings and have an array of NSStrings where one entry controls a check box in your user interface, you need to provide a Value Transformer in Interface Builder.

I couldn’t find one, so I wrote one. The core are two methods:

- (id)transformedValue:(id)value
{
  if(value 
  && [[NSString stringWithString:value] 
  isEqualToString:@"1"]) {
    return [NSNumber numberWithBool:YES];
  } else {
    return [NSNumber numberWithBool:NO];
  }
}



(id)reverseTransformedValue:(id)value
{
if([value boolValue] == YES) {
return [NSString stringWithString:@"1"];
} else {
return [NSString stringWithString:@"0"];
}
}

They convert an NSString to a BOOL and vice versa. This is not exactly true, as these functions work on objects and not with the native BOOL type. To create an object that represents a boolean value, you do [NSNumber numberWithBool:YES];.

Finally, you must register your new value transformer with your controller. I use -(id) init for that:

[NSValueTransformer setValueTransformer: 
    [[JLStringToBoolValueTranformer new] autorelease]
  forName: @"JLStringToBoolValueTranformer"];

You can now select the JLStringToBoolValueTranformer in the Value Transformer drop down list on the bindings pane of your checkbox.

If there is a more-preferred way to do this, please let me know.