Unexpected exception with NSInvocation

Question

Following code throws an exception.

vcClass is a Class object (inheritor from UIViewController). Self contains my implementation of viewWillAppear:

SEL viewWillAppearSEL = @selector(viewWillAppear:);
IMP viewWillAppearWithSuperIMP = [self methodForSelector:viewWillAppearSEL];
class_addMethod(vcClass, viewWillAppearSEL, viewWillAppearWithSuperIMP, @encode(BOOL));
NSMethodSignature *methodSignature = [vcClass instanceMethodSignatureForSelector:viewWillAppearSEL];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
[invocation setSelector:viewWillAppearSEL];

With message:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSInvocation setArgument:atIndex:]: index (1) out of bounds [-1, -1]

Additional info: iOS5, ARC. Can someone explain me what's wrong?

UPDATED:

This code code gives me responds message. So my class object is correct [vcClass instancesRespondToSelector:viewWillAppearSEL] ? NSLog(@"responds") : NSLog(@"not responds");

Alse Im getting crash right after [invocation setSelector:viewWillAppearSEL];. That's why I called topic title as Unexpected exception with NSInvocation.

UPDATED2:

Also my implementation of viewWillAppear:

- (void)viewWillAppear:(BOOL)animated {
    Class parentViewController = [self superclass];
    void (*superViewWillAppear)(id, SEL, BOOL) =(void(*)(id, SEL, BOOL))class_getMethodImplementation(parentViewController, _cmd);
    superViewWillAppear(self, _cmd, animated);
    NSLog(@"view will appear with super");
}

It means you have the wrong class in `vcClass`, and it didn't implement that selector. — Richard J. Ross III, May 10 '13 at 12:32
`[vcClass instancesRespondToSelector:viewWillAppearSEL] ? NSLog(@"responds") : NSLog(@"not responds");` Returns **"responds"** message — user1248568, May 10 '13 at 12:37
@lxt no, he wants to use the vc, not the view -- also I don't see a mistake in the 4 lines shown above. it crashes when you setArgument — Daij-Djan, May 10 '13 at 12:53
@newacct, yes. Also print description gives a lot of lines heading with "number of arguments = 3" — user1248568, May 16 '13 at 12:25

score 1 · Answer 1 · answered May 10 '13 at 12:43

1

BOOL *arg1;

NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
[invocation setSelector:viewWillAppearSEL];
[invocation setArgument:&arg1 atIndex:2];   // argument indexing is offset by 2 hidden args

answered May 10 '13 at 12:43

Thilina Chamath Hewagama

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Сan u please comment your answer? – user1248568 May 10 '13 at 12:57
that's the issue for sure. -viewWillAppear: accepts 1 argument, and invocation doesn't contain any – art-divin May 10 '13 at 12:57
1

@art-divin, And? Im getting exception right after `[invocation setSelector:viewWillAppearSEL];` – user1248568 May 10 '13 at 12:59
set the second argument as specified in this answer so your invocation will contain enough data to actually invoke the method – art-divin May 10 '13 at 13:00
1

@art-divin: you are completely misunderstanding what the OP is saying. He is not getting the exception on trying to run the invocation. He is unable to set a selector in the first place. – newacct May 10 '13 at 23:35

score 1 · Accepted Answer · answered May 18 '13 at 09:45

One problem with your code is the type encoding that you are passing to class_addMethod(). This type encoding must include: 1) the return type, 2) the types for self and _cmd (the first two hidden parameters), and then 3) the types of all the other parameters.

For a method like - (void)viewWillAppear:(BOOL)animated, the type encoding should be the string

v@:c

v -- for void, return type
@ -- for id, type for self
: -- for SEL, type for _cmd
c -- for char, this is what BOOL is. This is what you get when you did @encode(BOOL)

Unexpected exception with NSInvocation

2 Answers2