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Created June 4, 2012 22:18
What would you like to do?
This was nice and fast... but it takes up WAY TOO MUCH space. And it's annoying to write.
(I like the way I can just step into the function that calls the delegate for debugging)
What's a better way to not make me call respondsToSelector in the middle of my code? Some proxy?
struct {
unsigned int delegateWillDisplayDocument:1;
unsigned int delegateDidDisplayDocument:1;
unsigned int delegateDidShowPageView:1;
unsigned int delegateDidRenderPageView:1;
unsigned int delegateDidChangeViewMode:1;
unsigned int delegateDidTapOnPageView:1;
unsigned int delegateDidTapOnAnnotation:1;
unsigned int delegateShouldDisplayAnnotation:1;
unsigned int delegateViewForAnnotation:1;
unsigned int delegateAnnotationViewForAnnotation:1;
unsigned int delegateWillShowAnnotationView:1;
unsigned int delegateDidShowAnnotationView:1;
unsigned int delegateDidLoadPageView:1;
unsigned int delegateWillUnloadPageView:1;
unsigned int delegateDidEndPageScrollingAnimation:1;
unsigned int delegateDidEndZoomingAtScale:1;
unsigned int delegateWillShowControllerAnimated:1;
unsigned int delegateDidShowControllerAnimated:1;
} delegateFlags_;
- (void)setDelegate:(id<PSPDFViewControllerDelegate>)delegate {
if (delegate != delegate_) {
delegate_ = delegate;
delegateFlags_.delegateWillDisplayDocument = [delegate respondsToSelector:@selector(pdfViewController:willDisplayDocument:)];
delegateFlags_.delegateDidDisplayDocument = [delegate respondsToSelector:@selector(pdfViewController:didDisplayDocument:)];
delegateFlags_.delegateDidShowPageView = [delegate respondsToSelector:@selector(pdfViewController:didShowPageView:)];
delegateFlags_.delegateDidRenderPageView = [delegate respondsToSelector:@selector(pdfViewController:didRenderPageView:)];
delegateFlags_.delegateDidChangeViewMode = [delegate respondsToSelector:@selector(pdfViewController:didChangeViewMode:)];
delegateFlags_.delegateDidTapOnPageView = [delegate respondsToSelector:@selector(pdfViewController:didTapOnPageView:info:coordinates:)];
delegateFlags_.delegateDidTapOnAnnotation = [delegate respondsToSelector:@selector(pdfViewController:didTapOnAnnotation:page:info:coordinates:)];
delegateFlags_.delegateShouldDisplayAnnotation = [delegate respondsToSelector:@selector(pdfViewController:shouldDisplayAnnotation:onPageView:)];
delegateFlags_.delegateViewForAnnotation = [delegate respondsToSelector:@selector(pdfViewController:viewForAnnotation:onPageView:)];
delegateFlags_.delegateAnnotationViewForAnnotation = [delegate respondsToSelector:@selector(pdfViewController:annotationView:forAnnotation:onPageView:)];
delegateFlags_.delegateWillShowAnnotationView = [delegate respondsToSelector:@selector(pdfViewController:willShowAnnotationView:onPageView:)];
delegateFlags_.delegateDidShowAnnotationView = [delegate respondsToSelector:@selector(pdfViewController:didShowAnnotationView:onPageView:)];
delegateFlags_.delegateDidLoadPageView = [delegate respondsToSelector:@selector(pdfViewController:didLoadPageView:)];
delegateFlags_.delegateWillUnloadPageView = [delegate respondsToSelector:@selector(pdfViewController:willUnloadPageView:)];
delegateFlags_.delegateDidEndPageScrollingAnimation = [delegate respondsToSelector:@selector(pdfViewController:didEndPageScrollingAnimation:)];
delegateFlags_.delegateDidEndZoomingAtScale = [delegate respondsToSelector:@selector(pdfViewController:didEndPageZooming:atScale:)];
delegateFlags_.delegateWillShowControllerAnimated = [delegate respondsToSelector:@selector(pdfViewController:willShowController:embeddedInController:animated:)];
delegateFlags_.delegateDidShowControllerAnimated = [delegate respondsToSelector:@selector(pdfViewController:didShowController:embeddedInController:animated:)];
- (void)delegateWillDisplayDocument {
if (delegateFlags_.delegateWillDisplayDocument) {
[self.delegate pdfViewController:self willDisplayDocument:self.document];
- (void)delegateDidDisplayDocument {
if(delegateFlags_.delegateDidDisplayDocument) {
[self.delegate pdfViewController:self didDisplayDocument:self.document];
(etc, etc)
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So, if you don't want to use these structs, you can use a proxy; you could probably even get the proxy to cache the information. But it will still be slightly slower than this.

If you don't want to go that route, you can at least clean this up by using a compound literal; also, don't prepend every single field with delegate. It's not necessary, and makes you type more.

// first, give your struct a real type, you'll see why in a second
struct _delegate_flags_t { ... } _delegateResponds;

// then, assign to it when needed
_delegateResponds = (_delegate_flags_t) { 
  .viewForAnnotation = [delegate respondsToSelector:@selector(pdfViewController:viewForAnnotation:onPageView)];
  // ...

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wrap in a C preprocessor macro
(can't write it off the top of my head but the call could be just like a function)


make it an inlined function (better to debug + cleaner) or a category on nsobject

e.g. id performSelectorIfAvailable(id target, SEL selector, id args, ...)

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jverkoey commented Jun 4, 2012

Out of genuine curiousity, how much of a performance improvement does respondsToSelector: caching provide?

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I'd be interested in hearing about that too. I tend to make these gigantic structs not because I care about caching, but rather because it's rather more elegant to check a flag than to litter my code with super-ugly -respondsToSelector: messages. And because I've learnt to be cautious with proxies.

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steipete commented Jun 4, 2012

I did a few tests back then, but it's not a big performance hit. My reasons were much more to have a consistent jump function (and partly because I've seen Apple doing it)

But writing this stuff manually is rather annoying. Is there an example somewhere how proxy forwarding would look?

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I'm sure there is, but it might be slightly different under ARC. You can't use -forwardingTargetForSelector:, because if you return nil from there, it will just try to use -forwardInvocation:. Basically:

  1. Implement -methodSignatureForSelector: or whatever, using your target as a base.
  2. Implement -forwardInvocation:. If your target responds to the selector, set the return value of the invocation to your target's address. If the target doesn't respond, set the return value to nil. You'll probably need to fiddle around with ownership qualifiers here (like __autoreleasing). Someone who has done this more recently than I have can probably help if you have trouble.

But remember! This is a whole new layer you have to debug. So, it's pretty cool to have, but make sure you're committed to making it perfect.

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steipete commented Jun 4, 2012

uhh... I really don't wanna mess around with NSInvocation, that would be orders of magnitude slower.
Isn't there a new way, what if we just do the respondsToSelector check in forwardingTargetForSelector and decide if we return the delegate target, and don't do anything in -forwardInvocation:? But still, I'm not sure if I wanna go there. Maybe a macro/inline function is the cleaner way.

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steipete commented Jun 4, 2012

Also I'm not sure if I fully grasp the compound literal trick - I can build the struct on the fly? struct _delegate_flags_t { ... }

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  1. Like I said, you can't use -forwardingTargetForSelector:, because if nothing happens there, the runtime will try -forwardInvocation:.
  2. The compound literal is so that you can build the struct in one pass, without having to set all of its values individually. So, the following are equivalent:
// this is retarded:
point.x = 1.f;
point.y = 3.f;

// this is awesome:
point = (CGPoint) { .x = 1.f, .y = 3.f };

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a macro or a simple function or method would look good and could even use the caching (don't know If Id want that though)...

anyways :) id be interested in hearing what you finally decide on

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macguru commented Jun 5, 2012

I prefer to check the respondsToSelector in place. Generally rather dislike such caches. I usually don't have that much delegate methods though...

However, you could build a proxy class that assembles method implementations automatically using runtime calls. That'd be extremely elegant, albeit a bit of work and probably shooting with canons on pigeons. You could open-source it afterwards though ;)

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hatfinch commented Aug 1, 2012

No proxy tricks, but FWIW I use ids directly:

    id willDisplayDocumentDelegate;
    id didDisplayDocumentDelegate;
    // etc.
} _delegates;

- (void)setDelegate:(id <PSPDFViewControllerDelegate>)delegate
    if (delegate)
        if ([delegate respondsToSelector:@selector(pdfViewController:willDisplayDocument:)])
            _delegates.willDisplayDocumentDelegate = delegate;

        if ([delegate respondsToSelector:@selector(pdfViewController:didDisplayDocument:)])
            _delegates.didDisplayDocumentDelegate = delegate;

        // etc.
        memset(_delegates, 0, sizeof(_delegates));

- (void)delegateWillDisplayDocument
    [_delegates.willDisplayDocumentDelegate pdfViewController:self willDisplayDocument:self.document];

- (void)delegateDidDisplayDocument
    [delegates_.didDisplayDocumentDelegate pdfViewController:self didDisplayDocument:self.document];

// etc.

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I like your approach, @hatfinch, but should the zeroing of the _delegates table not should happen first, and unconditionally, as the if statements only set the fields for methods that are present in the new delegate. If there was a previous setting for a field and the new delegate doesn't implement that method, the old value would still be present (causing the old delegate to be called for some methods).

Also, I believe that object refs in a struct are no longer allowed under ARC, but (__weak) ivars could work just as well.

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