Add "informative text" to Alert if TextFields are empty - objective-c

Question

I am trying to code a NSAlert, that appears when when some NSTextFields are empty.
I have 3 NSTextFields and I would like to have a NSAlert that shows which TextField ist empty in a list. It´s possible for me to do it for one text field, but how can I code it that the empty NSTextFields appear in the Alert ? If one Textfield is empty in the Altert should stand "TextField 1 is empty". If Field 1 and 2 are empty there should stand "TextField 1 is empty" and in the second row "TextField 2 is empty".
Here is my code:
if ([[TextField1 stringValue] length] == 0) {
NSAlert* alert = [[NSAlert alloc] init];
[alert addButtonWithTitle:#"OK"];
[alert setMessageText:#"Error"];
[alert setInformativeText:#"TextField 1 is empty"];
[alert beginSheetModalForWindow:[self.view window] completionHandler:^(NSInteger result) {
NSLog(#"Success");
}];
}

Answer 1

You can get the information automatically by a notification.
Assign the tags 1, 2, 3 to the text fields.
Set the delegate of all text fields in Interface Builder to the class you want to display the alert in.
implement this method
- (void)controlTextDidChange:(NSNotification *)aNotification
{
NSTextField *field = [aNotification object];
if ([[field stringValue] length] == 0) {
NSInteger tag = field.tag;
NSAlert* alert = [[NSAlert alloc] init];
[alert addButtonWithTitle:#"OK"];
[alert setMessageText:#"Error"];
[alert setInformativeText:[NSString stringWithFormat:#"TextField %ld is empty", tag]];
[alert beginSheetModalForWindow:[self.view window] completionHandler:^(NSInteger result) {NSLog(#"Success");}];
}
}

Answer 2

I would chain the if-statements to get the desired result.
Set up a empty string and check every textField one after another. Add the error line to the string if it is empty. Don't forget to add a line break after appending a string.
My words in code:
NSString* errorMessage = #"";
if ([[TextField1 stringValue] length] == 0) {
errorMessage = #"TextField 1 is empty.\n";
}
if ([[TextField2 stringValue] length] == 0) {
errorMessage = [errorMessage stringByAppendingString:#"TextField 2 is empty.\n"];
}
if ([[TextField3 stringValue] length] == 0) {
errorMessage = [errorMessage stringByAppendingString:#"TextField 3 is empty."];
}
if (![errorMessage isEqualToString:#""]) {
NSAlert* alert = [[NSAlert alloc] init];
[alert addButtonWithTitle:#"OK"];
[alert setMessageText:#"Error"];
[alert setInformativeText:errorMessage];
[alert beginSheetModalForWindow:[self.view window] completionHandler:^(NSInteger result) {
NSLog(#"Success");
}];
}
This way you get dynamic output depending on which NSTextField was empty.