Checking for empty NSString on ViewDidLoad?

Question

My app checks if an NSString is empty when it launches, like this:

if ([checkfieldstring1 isEqualToString:@""]) {

    checkboxButton.hidden = YES;
}
else {

    checkboxbutton.hidden = NO;
}

However, when there is an empty string, the button is not being hidden. I know this method works when I hook it up as an IBAction to a button, but not on ViewDidLoad...

Put a break point on the if... line and inspect checkfieldstring1. Could it be nil? — tassinari, Apr 01 '12 at 01:23
Shift your code from `viewDidLoad` to `viewWillAppear:` and try again. I think this is a issue because some of the variables are `nil` until viewDidLoad is completely executed. Let me know if it helps you. — Parth Bhatt, Apr 01 '12 at 17:56
@user1205856 Welcome to Stack Overflow (SO)! Please accept the answer that helps you the most in order to reward the people that help you. — lnafziger, Apr 06 '12 at 17:15

score 5 · Accepted Answer · edited Apr 01 '12 at 02:46

5

Checking for an empty string when the view is about to load needs to check for a nil string or an empty string as the string may not have been set up yet.

if (checkfieldstring1 == nil || [checkfieldstring1 length] == 0) {
    checkboxButton.hidden = YES;
} else {
    checkboxButton.hidden = NO;
}

Or, if you do as I do and have this in a set of common macros that I add to a project:

static inline BOOL isEmpty(id thing)) {
    return thing == nil
        || ([thing respondsToSelector:@selector(length)]
        && [(NSData *)thing length] == 0)
        || ([thing respondsToSelector:@selector(count)]
        && [(NSArray *)thing count] == 0);
}

Courtesy of Wil Shipley http://www.wilshipley.com/blog/2005/10/pimp-my-code-interlude-free-code.html

you could just check with:

if(isEmpty(checkfieldstring1) {
    checkboxButton.hidden = YES;
} else {
    checkboxButton.hidden = NO;
}

edited Apr 01 '12 at 02:46

lnafziger

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answered Apr 01 '12 at 01:24

Abizern

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This still is not working... Now the button is hidden regardless if it is empty. – user1205856 Apr 01 '12 at 01:49
It's not working because the above code sets `checkfieldstring1` to `nil` before testing it. Change the "=" to "==". – Hot Licks Apr 01 '12 at 02:22
Also, you don't need to check for the string being nil -- if it is, its length method will return 0. – Jul 17 '12 at 20:24

score 3 · Answer 2 · answered Apr 01 '12 at 03:06

Since checkfieldstring1 can be nilor empty ("") you need to check for both cases.

The easiest way to check both, since Objective-C simply returns 0 when you send a message to a nil object is to use the length method, like this, instead:

if ([checkfieldstring1 length] == 0) {
    checkboxButton.hidden = YES;
}
else {
    checkboxbutton.hidden = NO;
}

You can also shorten this by just assigning the result of the comparison:

checkboxButton.hidden = [checkfieldstring1 length] == 0;

This might not be quite as clear when you are reading it later though, so I would tend towards the first example.

score 1 · Answer 3 · answered Apr 22 '12 at 03:53

I can't believe I was so stupid... For future reference, in my ViewDidLoad, I was setting the text of the textfield from UserDefaults. I was checking for an empty string BEFORE the text was set, so it appeared empty every time. Now, I placed the code after setting up the text field, and it works like a charm.

score -1 · Answer 4 · answered Apr 01 '12 at 08:42

-1

i think this may helps you try this -

if(checkfieldstring1 == [NSNull null] || [checkfieldstring1 length] == 0) {
// do something
}

answered Apr 01 '12 at 08:42

hchouhan02

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an NSString instance will never be equal to [NSNull null] -- the most it can be is a simple nil or NULL. -1. – Jul 17 '12 at 20:23

Checking for empty NSString on ViewDidLoad?

4 Answers4