NSUserDefaults problem - iphone

Question

I have two views.In One view when i click on custom button it goes into second view,In that i have text view and that data must store in temperary memory so i used following code:
NSString *myString=txtvNote.text;
[txtvNote setText:#""];
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
if (standardUserDefaults) {
[standardUserDefaults setObject:myString forKey:#"note"];
[standardUserDefaults synchronize];
}
and when i go back on 1st view by clicking on the add button it will save into database for that i used following code:
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSString *val = nil;
if (standardUserDefaults)
val = [standardUserDefaults objectForKey:#"note"];
NSLog(#"Note::%#",val);
and then pass this value in insert query.
Now my problem is when i left that value blank,it takes the value which is inserted before.

Answer 1

sequence must be like this
//first set text to something
[txtvNote setText:#""];
//then use that text
NSString *myString=txtvNote.text;

Answer 2

myString is a pointer to the text in txtvNote. So if you set that text to #"" then myString will be empty as well. To preserve the value of txtvNote at the time of assignment use copy or reset the text after saving it:
NSString *myString=[[txtvNote.text copy] autorelease];
[txtvNote setText:#""];
....

Answer 3

That's the way NSUserDefaults works - every value is stored in your app's preferences, and like any other collection in Obj-C, it doesn't take nil values. Use instance of NSNull class or empty string. Or even better - use intermediate controller to store values and use key-value observing in your first view.