NSNumberformatter quasi Scientific notations - objective-c

Question

I need the NSNumberFormatter to conditionally display very huge or very small numbers as Scientific notation. But if the number can be presented without, i need it to be only decimal.
6.62e-34 is Ok, but 4,2E1 is not.
Elsewhere in the system, I have solved this using the following method:
- (NSString *) formatNumber: (double) d {
BOOL sci=NO;
double dd = d;
if (dd<0.0) dd=(-d);
if ((dd>0.0) && (dd<1e-3)) sci=YES;
if (dd>1e+8) sci=YES;
if (sci) [nf setNumberStyle:NSNumberFormatterScientificStyle];
else [nf setNumberStyle:NSNumberFormatterDecimalStyle];
return [nf stringFromNumber:[NSNumber numberWithDouble:d]];
}
But at this particular place, the whole thing is set up in the interface builder, with bindings to an managed object modell and using an array controller object. In the first text cell of the colum in the tableview, I have dragged in the numberformatter. I dont know if its possible to define some custom methods to be called to do the formatting, instead of using this NumberFormatter. If I take it away, I got errors when I run it.
anyone have some idea ?

Answer 1

What you want to do is write a subclass of NSValueTransformer. You can then provide the name of that transformer class in IB, in the bindings inspector. Here is an example:
#implementation RDTransformer
- (id)init {
if (self = [super init]) {
self.formatter = [[NSNumberFormatter alloc] init];
[self.formatter setNumberStyle:NSNumberFormatterScientificStyle];
[self.formatter setMaximumFractionDigits:3];
}
return self;
}
+(Class)transformedValueClass {
return [NSString class];
}
+(BOOL)allowsReverseTransformation {
return NO;
}
-(id)transformedValue:(NSNumber *)value {
if ([value compare:#1000] == NSOrderedAscending) {
return value.stringValue;
}else{
return [self.formatter stringFromNumber:value];
}
}
In IB, the column (in a single column table) has its value bound to Array Controller.arrangedObjects with a value transformer of RDTransformer. I don't have any formatters connected to the table cells.