Invoke block iOS

Question

I try to invoke some block, but I run into a EXC_BAD_ACCESS.

-(void) methodA {
   self.block = ^ {
       [self methodB];
   };
}

-(void) webViewDidFinishLoad:(UIWebView *)webView {
       [block invoke]; // error here (block is not valid id type).
}

-(void)methodB {
    //do something
}

Any thoughts on why this is happening?

How is the `block` property defined on the class? – Art Gillespie Feb 28 '12 at 15:17 — Art Gillespie, Feb 28 '12 at 15:17

score 15 · Answer 1 · answered Feb 28 '12 at 15:00

15

if you want to invoke the block you can simply do this block(); instead of [block invoke];

for more details, see the Block Programming Topics

answered Feb 28 '12 at 15:00

Julien

963
5
8

I try to call block(); and get error Called object '*(struct objc_object **)((char *)self + OBJC_IVAR_$_SettingsHelp.block)' is not a function – Matrosov Oleksandr Feb 28 '12 at 15:18
that is because you are declaring it as id. Take a look at [this question](http://stackoverflow.com/questions/3935574/can-i-use-objective-c-blocks-as-properties) to see how you can declare it properly. – murat Feb 28 '12 at 15:28
How to do same stuff with swift? i mean if i have a closure and i want just call func doneAction() { self.onActionSheetDone() } – Zaporozhchenko Oleksandr Feb 09 '17 at 02:07

score 9 · Accepted Answer · answered Feb 28 '12 at 15:22

9

You should use copy attribute when you are declaring block property. Like:

@property (nonatomic, copy)   id block;

answered Feb 28 '12 at 15:22

murat

4,893
4
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29

Art Gillespie · Answer 3 · 2012-02-28T15:29:49.207

1

You have to put the block on the heap:

self.block = Block_copy(^{
    [self someMethod];
});

EDIT: @murat's answer is correct, too (and probably better). One way or the other, you have to copy the block, since blocks are actually created on the stack and not on the heap.

For more on blocks you want to keep around, see "Copying Blocks" and "Patterns to Avoid" in the documentation.

edited Feb 28 '12 at 15:29

answered Feb 28 '12 at 15:21

Art Gillespie

8,747
1
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score 0 · Answer 4 · answered Mar 26 '12 at 11:00

you can declare a property for block in .h file like this and it will not give bad-excess -

    typedef int (^devideEquallyBlock)(int);
    @property (nonatomic, copy) devideEquallyBlock callbackBlock;

Make sure that you declare copy not retain for more details how to declare properties blocks programming in ios/objective-c

Invoke block iOS

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