Reputation: 1225
Apparently, I've been working with bindings too long, because I can't figure out how to do this. I have a table with several columns. When a row is selected, you can edit its priority, which modifies a core data attribute. I've also set this as an IBAction. Basically, I want to access the value of the Core Data attribute from my code. Then, I want to set the first column of whatever row is selected (and had its priority changed) to a number of exclamation marks corresponding to the priority level.
Sorry this is worded confusingly; here's an example:
Row 7 is selected. I change its priority to 2. Now, the Core Data attribute myPriority is set to 2. A code block is now triggered. It gets the priority of the selected row (row 7) form Core Data and wants to set column 1 of the selected row (row 7) to 2 exclamation marks (priority 2).
Thanks!
Upvotes: 0
Views: 405
Reputation: 11156
If you're used to bindings, then I'd recommend looking at NSValueTransformer; specifically, creating a subclass of that which converts a priority value to a string of exclamation marks. You'd then simply provide the name (the same one used in +setValueTransformer:forName:
) as the 'value transformer' attribute in your bindings.
For instance, the code would look like so:
@interface PriorityTransformer : NSValueTransformer
@end
@implementation PriorityTransformer
+ (Class) transformedValueClass { return ( [NSString class] ); }
+ (BOOL) allowsReverseTransformation { return ( NO ); }
- (id) transformedValue: (id) value
{
// this makes the string creation a bit simpler
static unichar chars[MAX_PRIORITY_VALUE] = { 0 };
if ( chars[0] == 0 )
{
// ideally you'd use a spinlock or such to ensure it's setup before
// another thread uses it
int i;
for ( i = 0; i < MAX_PRIORITY_VALUE; i++ )
chars[i] = (unichar) '!';
}
return ( [NSString stringWithCharacters: chars
length: [value unsignedIntegerValue]] );
}
@end
You would then put this code into the same file as a central class (such as the application delegate) and register it through that class's +initialize
method to ensure it's registered in time for any nibs to find it:
+ (void) initialize
{
// +initialize is called for each class in a hierarchy, so always
// make sure you're being called for your *own* class, not some sub- or
// super-class which doesn't have its own implementation of this method
if ( self != [MyClass class] )
return;
PriorityTransformer * obj = [[PriorityTransformer alloc] init];
[NSValueTransformer setValueTransformer: obj forName: @"PriorityTransformer"];
[obj release]; // obj is retained by the transformer lookup table
}
Upvotes: 1