I found a solution using the information posted in this question... Listen to a value change of my text field
First of all I have to declare the NSTextFieldDelegate in the AppDelegate.h file
@interface AppDelegate : NSObject <NSApplicationDelegate, NSTextFieldDelegate>
After that, I have to instantiate the delegate for the NSTextField object I want to modify while the user update it in the AppDelegate.m file.
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
[self.textField setDelegate:self];
}
Finally, I implement the methods to detect field editing with the changes I want to set.
- (void)controlTextDidChange:(NSNotification *)notification {
NSTextField *textField = [notification object];
if ([textField doubleValue] < 0 | [textField doubleValue] > 255) {
textField.textColor = [NSColor redColor];
}
}
- (void)controlTextDidEndEditing:(NSNotification *)notification {
NSTextField *textField = [notification object];
if ([textField resignFirstResponder]) {
textField.textColor = [NSColor blackColor];
}
}