Why can't I use signals that return constant numbers in my layout chain? about reactivecocoalayout

[jspahrsummers]

The reason you're running into a crash is because setting rcl_frame generates a value on rcl_frameSignal, leading to an infinite loop.

What is that code actually intended to do? It's generally a bad idea to create a feedback signal like this.

[zakdances]

I just want to horizontally center self.playButton and set its y coordinate to 0. (so it's top is aligned to its superview top)

[jspahrsummers]

In that case, I would observe rcl_boundsSignal or rcl_intrinsicContentSizeSignal. You don't actually care about the frame, since the origin is completely discarded, and only the size remains.

[zakdances]

Ok, I think I understand better. Does this also create an infinite loop?

RAC(myButton,rcl_bounds) = [myButton.rcl_boundsSignal 
replaceWidth:myButton.superview.rcl_boundsSignal.width];

If so, what's the best way to set the bounds or frame relative to its current value? That's what I'm trying to do here. Do I need to create a whole new rect signal when use RAC/RCL to set bounds/frame?

[jspahrsummers]

If so, what's the best way to set the bounds or frame relative to its current value? That's what I'm trying to do here.

Since signals operate over time, it doesn't really make sense to do that. What's your end goal?

[zakdances]

I just want to position and size my UIView's. Nothing abnormal. The reason I've used the above code is to avoid doing something more verbose like this everytime:

RAC(myButton,rcl_bounds) = [RACSignal rectsWithX:[RACSignal return:@20] 
Y:myButton.superview.rcl_boundsSignal.y width:[RACSignal return:@40] 
height:myButton.superview.rcl_boundsSignal.height];

Is this the recommended approach?

See how constructing a new rect signal is more verbose than just getting the current bounds rect and adjusting one property (like width using replaceWidth)? I guess my what I've been doing is wrong so I'm gonna go back and look at the demos some more.

I know you're busy so I'm gonna close this (I won't keep responding). Your answers are VERY HELPFUL so thank you. If you get a chance, just let me know if the rectsWithX: approach is a bit more on the right trail. Or point me to the relevant line in one of the demos.

[jspahrsummers]

Constructing a new rect is indeed the recommended way to do it. RCL favors creating layouts from scratch, rather than trying to modify the existing properties of a view, because signal feedback is very tricky to handle correctly.

If you really want to base your layout on the current bounds rectangle, that's possible. You just don't want it to update when it changes in the future. Create a signal from the current value – don't observe the property:

RAC(myButton,rcl_bounds) = [[RACSignal
    return:MEDBox(myButton.bounds)]
    replaceWidth:myButton.superview.rcl_boundsSignal.width];

[zakdances]

Perfect, thank you again.

[jspahrsummers]

No problem!