So I’ve discovered the most horrible aspect of Xojo. It’s worse than anything I could imagine and I think my little dabbling with Objective-C doesn’t have anything this crazy bad. It’s the IOSLayoutConstraint. It’s something where you have to have an incredibly complex and non-understandable statement that to even make it readable you have to break it into 4 or 5 lines in the editor. Call that user friendly would ya! You know if this is the “new” Xojo, I’ll stick with the old that was easy to pick up and learn.
Anyhow, I digress but maybe not really.
So how do you set a width of a control with this “I need to be a rocket scientist to understand it” statement?
Constructor(firstItem As Object, firstAttribute As AttributeTypes, relation As RelationTypes, secondItem As Object, secondAttribute As AttributeTypes, multiplier As Double, addend As Double)
OK. So I have:
firstitem - so that’s the control I am wanting to set the width - right? OK Good.
firstattribute - OK so then this is iOSLayoutConstraint.AttributeTypes.Width
OK. So this makes sense. So far so good. Here’s where it breaks down.
Now for relation what do I put? I just want to set a width in pixels. So do I put: iOSLayoutConstraint.RelationTypes.Equal ???
OK so let’s assume I do. But now what do I use for the seconditem? The view? But equal to what in the view? I don’t want to use a formula. I just want to set a width for the control. I don’t want it equal to left left edge of the hypotenuse of the sine of the angle of the orbital path to Pluto. Yes, I know that didn’t make any sense but neither does this layout constraint bit when all I want to do is set a width.
And please don’t tell me to go look in the auto layout examples. Yeah, that’s a setting of a width there, but that is for a control that is already in the IDE not a dynamically created control.
So how do I just set a width or height of a control???
thats a layout constraint but broken into all the pieces
using this example
firstItem As Object = control_A
firstAttribute As AttributeTypes = edge_A
relation As RelationTypes = "="
secondItem As Object = control_B
secondAttribute As AttributeTypes = edge_B
multiplier As Double = factor
addend = offset
Typically you do NOT set the width or height - you set it relative to some other edge of the containing view or another control
You set a relation that says “keep this edge this far from some other edge” so that if you rotate the screen the control remains say 20 pixels from the edge of the view its in
Now IF you want to say “keep this to 10 pixels high” remember control_A.edge_A = control_B.edge_B * factor + offset
firstItem As Object = control_A = whatever control
firstAttribute As AttributeTypes = edge_A = HEIGHT
relation As RelationTypes = "="
secondItem As Object = control_B = NONE since there IS no other control involved (use NIL)
secondAttribute As AttributeTypes = edge_B = NONE (yes there is an edge called none)
multiplier As Double = factor = 1.0 (but in reality for this its ignored)
addend = offset = 10
and then you have
control.height = (nothing.no edge) * 1.0 + 10
and (nothing.no edge) * 1.0 evaluates to 0 so you have
Jon, I’m not sure if it will help you, but in the extensions module of iOSKit there are a few convenience extension methods to add a control dynamically to a view. Maybe you want to check them out to see if they can help you?
iOSLayoutConstraint is a bit painful but so is a lot of the code we have to write each day. I find that if I have a cup of coffee first, and concentrate for a couple of minutes, it all makes sense. Oh and Jason King’s aforementioned AddControlWithBounds/AtPoint extension methods are a sanity saver!
[quote=203621:@Jason King]Jon, I’m not sure if it will help you, but in the extensions module of iOSKit there are a few convenience extension methods to add a control dynamically to a view. Maybe you want to check them out to see if they can help you?
[quote=203618:@Norman Palardy]Constraints are mathemetical expressions but not written in mathematical form
Typically you do NOT set the width or height - you set it relative to some other edge of the containing view or another control
You set a relation that says “keep this edge this far from some other edge” so that if you rotate the screen the control remains say 20 pixels from the edge of the view its in
[/quote]
I get that. At this point, I’m just trying to walk slowly up the learning curve and get a few controls placed on the page. I don’t really care about dynamic resizing at this point.
[quote]
Now IF you want to say “keep this to 10 pixels high” remember control_A.edge_A = control_B.edge_B * factor + offset
firstItem As Object = control_A = whatever control
firstAttribute As AttributeTypes = edge_A = HEIGHT
relation As RelationTypes = "="
secondItem As Object = control_B = NONE since there IS no other control involved (use NIL)
secondAttribute As AttributeTypes = edge_B = NONE (yes there is an edge called none)
multiplier As Double = factor = 1.0 (but in reality for this its ignored)
addend = offset = 10
and then you have
control.height = (nothing.no edge) * 1.0 + 10
and (nothing.no edge) * 1.0 evaluates to 0 so you have
control.height = 10
Thank you! Now this is a good example/explanation. I had no idea you could set second item to Nil. And this is my point in the examples, if they were commented in a similar way to what you show here, then it would be a lot easier to figure out/understand.
Function withConstraint(extends o as iOSControl, width as double, relation as iOSLayoutConstraint.RelationTypes=iOSLayoutConstraint.RelationTypes.Equal) As iOSLayoutConstraint
Return new iOSLayoutConstraint(o,iOSLayoutConstraint.AttributeTypes.Width, Relation, nil, iOSLayoutConstraint.AttributeTypes.None, 1.0, width)
End Function
so instead of the long syntax just to set the width you can call:
