UIControlStateSelected|UIControlStateDisabled, Objective C Explanation

Question

I am doing the stanford Course Assignments and he posted this code UIControlStateSelected|UIControlStateDisabled what exactly does this mean and what does the | operand do?

Also, I am trying to set the value on a button using this code but it wont work, any help?

if(!sender.isSelected){
        [sender setTitle:self.deck.drawRandomCard.contents forState:UIControlStateSelected];
    } else {
        [sender setTitle:@"" forState:UIControlStateDisabled];
    }

Objective-C is a superset of C. The `|` operator is the "bitwise or" operator from C. Do a quick search to see what that does. — rmaddy, Jun 09 '13 at 03:47

Mazyod · Answer 1 · 2013-06-10T04:21:03.003

Buttons have many states represented as enumeration values. What you have here are just two of them:

UIControlStateSelected|UIControlStateDisabled

The whole list in UIControl.h:

typedef NS_OPTIONS(NSUInteger, UIControlState) {
    UIControlStateNormal       = 0,
    UIControlStateHighlighted  = 1 << 0,      // used when UIControl isHighlighted is set
    UIControlStateDisabled     = 1 << 1,
    UIControlStateSelected     = 1 << 2,      // flag usable by app (see below)
    UIControlStateApplication  = 0x00FF0000,  // additional flags available for application use
    UIControlStateReserved     = 0xFF000000   // flags reserved for internal framework use
};

So, what does this mean? As you can see in the enumeration definition, the values set to the enumerations are single set bits for each value. So, here is the binary representation of the above:

1 << 0 = 0000 0001 b
1 << 1 = 0000 0010 b
.. and so on

As you can see, the << is a shift operator, and we are simply shifting the bits to the left, so that we can combine these enumerations together in a singe variable! what do I mean? Here:

0000 0011 b // This is essentially two flags set, on for the highlighted state one for the disabled

So, we usually use bit wise OR operator to combine these flags:

0000 0001 | 0000 0010 = 0000 0011

Finally, when combining these flags, and sending them to the method to set the title, you are telling the underlying implementation to change the title for those two options in a single method call.

...

As for your second question about the code that doesn't work, it would be useful to describe what "doesn't work" mean. Does it crash? What is the desired output your looking for?

Edit:

I just read the comments, and there seems a few more issues need to be covered by this answer:

In order to change the state of the button pragmatically, you should call something like:

[sender setEnabled:NO];

The code you have just tells the button to display that text AFTER it has changed to the disabled state.

Another issue regarding the || operator, that certainly is an OR operation, just not a bit-wise OR. This operator is used for boolean expressions instead of bit-wise operations.

score -1 · Answer 2 · edited May 23 '17 at 11:52

What does | mean (for the UIButton states case)?

It means applying the attribute when the button is selected and disabled at the same time.

The | operator means bitwise OR, as far as I understand. But somehow when you bitwise OR the UIControlState together, they must be met at the same time for the effect to take place. Yes, it is strange but that is how it behaves currently, based on my experience too.

Take a look at the other answer here, which shows that it also behaves like what I said: UIButton setTitle:forState: question

So for example, when a user is highlighting a button that is initially selected, you can apply a particular title for that UIControlStateHighlighted|UIControlStateSelected state.

Now about what your code does not work:

Your code is just setting the title of the button when the button is selected (or disabled for the else block), but it does not mean it will make the button selected (or disabled).

You need to make the button property to be selected (or disabled) to see the title change take place.

Those properties, such as enabled, selected, highlighted, can be triggered by the touch of the finger, or you can also set those properties programmatically. Take a look at the class reference of UIControl which include those properties listed.

For example:

myButton.enabled = NO;
myButton.highlighted = YES;
myButton.selected = YES;

The `|` operator is the "bitwise or" operator. It does not mean "at the same time". — rmaddy, Jun 09 '13 at 03:45
How would I make the button property be selected or disabled? I thought it would be selected if I click on it in the view when the app is running? Also wouldnt || be and OR operand or does that only exist for C? — user2076774, Jun 09 '13 at 04:08
@user2076774 the | is the bitwise OR, but seems to be a bug for the UIButton state. The answer found here also states so: http://stackoverflow.com/questions/4370466/uibutton-settitleforstate-question and also based on my own experience coding. You can try to run the code yourself. — Valent Richie, Jun 09 '13 at 14:52
@rmaddy **It is the "bitwise or" operator, but it does mean "at the same time".** At least for UIButton. — ooops, Jan 05 '18 at 11:38

UIControlStateSelected|UIControlStateDisabled, Objective C Explanation

2 Answers2

What does | mean (for the UIButton states case)?

Now about what your code does not work: