EXC_BAD_ACCESS when accessing parameters in andDo

问题:

I am trying to write an block of code using OCMock's stub andDo method.

In this case UIImageView extension class is being tested. I want to check that the extension calls [self setImage:] with parameter that is non-nil (later other image comparison will be used).

When using OCMock's andDo method, the test crashes with EXC_BAD_ACCESS after the block completes.

id mockView = [OCMockObject mockForClass:[UIImageView class]];
[[[mockView stub] andDo:^(NSInvocation *invocation)
  {
      UIImage *img;
      [invocation getArgument:&img atIndex:2]; <---- line causing the exception
      somebodySetImage |= (img != nil);

  }] setImage:OCMOCK_ANY];

  [mockView do_something_that_calls_setImage];

The only solution that I've found for now is using andCall instead of andDo, but this complicates the test.

Can I avoid the crash with andDo?

UPDATE Well, I will try to give a better example here: Here is the new piece of the test code:

- (void)testDownloadingThumbnail
{
    PInfo *_sut = [[PInfo alloc] init];

    __block id target = nil;

    id mock = [OCMockObject mockForClass:[NSOperationQueue class]];

    [[[mock expect] andDo:^(NSInvocation *inv)
    {
        NSInvocationOperation *op;
        [inv getArgument:&op atIndex:2];
        target = [[op invocation] target]; /* replacing this line with STAssert does not help either */
    }] addOperation:OCMOCK_ANY];

    [_sut setDownloadQueue:mock];
    [_sut startDownloadingImagesAsync:YES];

    [mock verify];

    STAssertEqualObjects(target, _sut, @"invalid op target");
}

Here is the tested code (single method from PInfo):

- (void)startDownloadingImagesAsync:(bool)isThumbnailImg
{
    NSInvocationOperation *inv;

    inv = [[NSInvocationOperation alloc] initWithTarget:self
                                     selector:@selector(loadThumbnailWorker:)
                                       object:nil];
    [[self downloadQueue] addOperation:inv];
}

The code still crashes upon exit from startDownloadingImagesAsync with EXC_BAD_ACCESS. If I add a breakpoint inside the andDo block, I see that the control reaches this point and retrieves correct objects via getArgument.

Yet, if I use getArgument inside the block, it crashes whatever I try to do.

P.S. Thanks for help.

回答1:

I ran into a similar problem when using NSProxy's forwardInvocation: method.

Can you try the below?

NSInvocationOperation *op; // Change this line
__unsafe_unretained NSInvocationOperation *op; // to this line

Or another approach could be to retain NSInvocation's arguments:

[invocation retainArguments];

http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSInvocation_Class/Reference/Reference.html#//apple_ref/occ/instm/NSInvocation/retainArguments

I'll try to add a more detailed explanation later.

回答2:

I think the problem is that you're trying to invoke a mock object directly. For what you're trying to do, you shouldn't need a mock object. Just call the method and verify that the image was set:

expect(myObject.imageView.image).to.beNil();
[myObject do_something_that_calls_setImage];
expect(myObject.imageView.image).not.to.beNil();

If you really want to use a mock for some reason, you could do it with a real UIImageView and a partial mock:

UIImageView *imageView = myObject.imageView;
id mockView = [OCMockObject partialMockForObject:imageView];
__block BOOL imageSet = NO;
[[[mockView stub] andDo:^(NSInvocation *invocation) {
      UIImage *img;
      [invocation getArgument:&img atIndex:2];
      imageSet = (img != nil);
  }] setImage:OCMOCK_ANY];

[myObject do_something_that_calls_setImage];
expect(imageSet).to.beTruthy();

回答3:

In my case this was happening because I introduced another parameter to this method, so the block parameter got shifted by one.

I fixed it by changing [inv getArgument:&op atIndex:2] to [inv getArgument:&op atIndex:3]