objective c - How to make a boolean both static and __block? in iOS? -

bool _hintexist; - (void)shownotreachable {     if (_hintexist) {         return;     }      nslog(@"show hint");      dispatch_after(dispatch_time(dispatch_time_now, (int64_t)(3 * nsec_per_sec)), dispatch_get_main_queue(), ^{         _hintexist = no;     }); } 

the code above fine. there button trigger method. actually, don't need _hintexist global variable. want make bool _hintexist in method.however, when tried add both static , __block in front of bool _hintexist. there compile error. amazed change _hintexist in block if made global variable. explain why? , what's difference if add static before bool _notreachablehintexist, global variable in code?

__block scope modifier local variable allows block modify value of local variable declared in outer scope.

your _hintexist variable isn't local variable. it's global. there no need __block modifier. block has access global variable other piece of code in same file.

if add static _hintexist variable, still global scoped file. , block, other code in file, can still access , modify file global variable.

another option make _hintexist variable local static variable this:

- (void)shownotreachable {     static bool _hintexist = false;      if (_hintexist) {         return;     }      nslog(@"show hint");      dispatch_after(dispatch_time(dispatch_time_now, (int64_t)(3 * nsec_per_sec)), dispatch_get_main_queue(), ^{         _hintexist = no;     }); } 

this works assuming want. variable scoped method being static means value independent of specific instance of class. again, being static means don't need __block modifier. it's global inside method.

btw - minor note on common naming conventions. don't use leading underscore variables except instance variables.

update based on andy's second comment below answer:

it seems want use instance variable since want each instance of class start own false value _hintexist.

add ivar @implementation block:

@implementation whateverclassthisis {     bool _hintexist; } 

and updated shownotreachable method:

- (void)shownotreachable {     if (_hintexist) {         return;     }      nslog(@"show hint");      dispatch_after(dispatch_time(dispatch_time_now, (int64_t)(3 * nsec_per_sec)), dispatch_get_main_queue(), ^{         _hintexist = no;     }); } 

like globals , statics, instance variable doesn't need __block qualifier. and, default, _hintexist have initial value of false.