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#compose
Title
# compose
f

Fudge

07/20/2020, 2:58 PM
Is there a way to constrain an element absolutely, without letting it relayout itself to fit within the available space? The use case is to create a component that can swipe between different screens. (I already have it implemented, but the children keep moving around as they're getting constrained) This image illustrates the idea:
a

Adam Powell

07/20/2020, 3:10 PM
Not quite sure I understand
f

Fudge

07/20/2020, 3:10 PM
More images, then
a

Adam Powell

07/20/2020, 3:12 PM
You can do anything you want in a layout modifier as long as the modifier itself obeys the constraints it was given; you can measure the child element with whatever constraints you like and place it however you like, the parent will only see the modifier's size and frame of reference
I think we're still missing a 
Modifier.layout {}
API for defining these quickly without explicitly declaring a LayoutModifier class but it should be coming soon
f

Fudge

07/20/2020, 3:14 PM
This code snippet produces the behavior I don't want:
Copy code
Box(Modifier.width(20.dp)) {
        Text("Foo Bar")
    }
Are you saying I can achieve this by using some custom layout with 
Layout()
?
a

Adam Powell

07/20/2020, 3:14 PM
You can if you want to arrange multiple children, if you only want to modify a single element, write a LayoutModifier instead
And you can choose to add a clip modifier before it or not, up to you
f

Fudge

07/20/2020, 3:17 PM
I'll try to figure out how LayoutModifier and co work, thanks
This is a big interface 😨
o

okarm

07/20/2020, 3:20 PM
I have never tried Compose, but couldn’t you just set maxLines=1 on the Text widget?But maybe I’m talking out of my butt here.
f

Fudge

07/20/2020, 3:20 PM
@okarm That might work, but the goal is for this to work for any arbitrary component and without modifying individual existing components
Text is just an example, this could also be applied to icons
o

okarm

07/20/2020, 3:21 PM
Ah, yes, I wasn’t sure.
a

Adam Powell

07/20/2020, 3:28 PM
You can ignore everything but the measure method from the interface, the rest has defaults
The signature is gnarly and that's why it could benefit from a builder
But it's identical to the signature of the Layout composable except it deals with one element instead of multiple
f

Fudge

07/20/2020, 3:31 PM
I think the 
measure
method decides the constraints that are given to the children? What decides what constraints are given to the parent?
I'm probably misunderstunding though
Maybe it's the other way around?..
Ok, I can't seem to figure it out. This is what I have
Copy code
private data class CutModifier(
    private val maxWidth: Dp
) : LayoutModifier {

    override fun MeasureScope.measure(
        measurable: Measurable,
        constraints: Constraints,
        layoutDirection: LayoutDirection
    ): MeasureScope.MeasureResult {
        val placeable = measurable.measure(constraints)
        return layout(maxWidth.toIntPx(), placeable.height) {
            placeable.place(0, 0)
        }
    }

}
Is this right? It seems like the modifier is not doing anything
ah, I simply needed to add a clip modifier before, it was so simple...
And also set the width constraint to infinity
a

Adam Powell

07/20/2020, 4:21 PM
Yep. The constraints param to the measure method is the constraints the parent is measuring you with. You can change those constraints before measuring the modified element and account for those changes in your own sizing and placement.
So for example, the preferred size modifiers set min/max constraints for the child to the target value, coerced within the parent supplied constraints.
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