iOS Blocks - use of undeclared identifier self

Question

I am new to blocks. I am inside a singleton and I do this

void (^ myBlock)() = ^(){ [self doStuff]; };

I receive this error use of undeclared identifier self.

doStuff is a method inside the singleton.

but if this block is declared inside another method, Xcode is OK.

Why is that? thanks.

where are you writing this line?? – g.revolution Nov 25 '12 at 16:47 — g.revolution, Nov 25 '12 at 16:47

g.revolution · Accepted Answer · 2012-11-25T17:09:17.813

2

you can define the block in your interface and initialize in any of your methods (including initializers ) in your @implementation file like below:

@interface YourClass {
   void (^ myBlock)();
}

@implementation YourClass

  - (void)yourMethod {
    myBlock = ^(){ [self doStuff]; };
  }


@end

edited Nov 25 '12 at 17:09

answered Nov 25 '12 at 16:48

g.revolution

it should work then .. if you are defining the block as i have mentioned above .. it should work . – g.revolution Nov 25 '12 at 16:52
ah, you probably mean void (^ myBlock)(); inside the interface and myBlock = ^(){ [self doStuff]; }; inside a method.... – Duck Nov 25 '12 at 17:06
unless you're using ARC, you need to copy the block – newacct Nov 25 '12 at 20:30

score 2 · Answer 2 · edited May 23 '17 at 12:33

2

You shouldn't call self directly in a block.
Rather you should make a safe block-pointer from self and access it inside your block.

__block id safeBlockSelf = self;
void (^ myBlock)() = ^(){ [safeBlockSelf doSomething]; };

edited May 23 '17 at 12:33

Community

answered Nov 25 '12 at 22:48

yinkou

score 0 · Answer 3 · answered Nov 25 '12 at 22:32

0

because every method gets passed self as a hidden param. self is a variable like any other and the block can 'see it/capture it' if in the method

if it is not in a method, self is not a variable set anywhere and the block cant 'see it'

answered Nov 25 '12 at 22:32

Daij-Djan

3 Answers3