NSInvocationOperation Question

I would like to know how to remove duplicate nsoperations, i.e is there a way to check the nsoperation queue and see if I am making a duplicate request?

Basically, I am requesting 开发者_如何转开发images depending on the iphone screen rotation. When the view is loaded the shouldautorate is called twice.

If(rotation==portrait){
  request portrait image.
}

The issue is that shoud autorotate will be checked twice. And on both ocassions, it will turn out to be portrait hence requesting the same image twice. Anyone with a good idea? I forgot to mention I am using a queue.

Thanks.

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NEW, better answer:

Don't use the shouldAutorotate... method. It only asks whether a rotation is allowed to happen. This may happen any time and may not necessarily lead to a rotation. Instead, use willRotate... or didRotate..., as these methods are only invoked exactly once and only if the rotation actually happens.

Your operation will then be added only once.

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OLD, but not false answer:

How about using a instance variable to remember the last seen rotation? Like so:

if (rotation != lastSeenRotation) {
    // REQUEST image here
}