Question

I’m a newbie in objective-c.
I got a problem in saving a string from UITextField.

I declared a string in property and synthesize it which named “familyName” to store user’s family name.
Then I want to save the familyName when the user press a button.

-(IBAction)textFieldDidBeginEditing:(UITextField *)textField;
{}

-(BOOL)textFieldShouldReturn:(UITextField *)textField{
familyName = inputFamilyName.text;  
NSLog(@"the user's family name is %@", familyName); //it works here.

if (inputFamilyName == textField) {
    [inputFamilyName resignFirstResponder];
}
return YES;
}

-(IBAction)goToNameWheel:(id)sender{

NSUserDefaults *userDefault = [NSUserDefaults standardUserDefaults];
[userDefault setObject:familyName forKey:@"family"];
[userDefault synchronize];
}

It crashes when it runs the saving code, it said “Thread 1:EXC_BAD_ACCESS (code=1, address = 0x……”

After that, I try another test to see what happens to familyName, then I wrote:

-(IBAction)test:(id)sender{
NSLog(@"1.the family name is %@", inputFamilyName.text); // This works...
NSLog(@"2.the family name is %@", familyName);} // This crashes...

Finally… I try to retain familyName in textFieldDidBeginEditing:

-(BOOL)textFieldShouldReturn:(UITextField *)textField{
familyName = inputFamilyName.text;  
NSLog(@"the user's family name is %@", familyName); //it works here.

if (inputFamilyName == textField) {
    [inputFamilyName resignFirstResponder];
}
[familyName retain]; // just added randomly...
return YES;
}

Then everything works fine, I can save the familyName, print it..etc..
My question is…what exactly happens here, why do I have to retain it? Anything wrong with my original code?
Thx for your time!

Answer 1

When you do

familyName = inputFamilyName.text; 

You’re not actually using the property. You’re using an instance variable with the same name as your property, but without the memory management stuff.

What you should be doing is

self.familyName = inputFamilyName.text; 

Then the property’s retain will kick in, and you won’t have to manually retain.

To make it harder to make the mistake, you could change your @synthesize statement to be:

@synthesize familyName = _familyName;

If you do that, then it means that the property called familyName will have an instance variable called _familyName backing it — which means it’s a lot harder to accidentally type the wrong one accidentally, thus avoiding this mistake.