Composing `Wrap` and `Container` result in a 0 siz...

# compose

[kioba]

Composing Wrap and Container result in a 0 sized child. is this the expected behavior?

[kioba]

both of the following code paints the entire wide area with Cyan

Container {
    Draw { canvas: Canvas, parentSize: PxSize ->
        canvas.drawRect(parentSize.toRect(), Paint().apply { color = Color.Cyan })
}}

Wrap {
    Draw { canvas: Canvas, parentSize: PxSize ->
        canvas.drawRect(parentSize.toRect(), Paint().apply { color = Color.Cyan })
}}

[kioba]

but here the parentSize is (0, 0, 0, 0):

Wrap {
    Container {
        Draw { canvas: Canvas, parentSize: PxSize ->
            canvas.drawRect(parentSize.toRect(), Paint().apply { color = Color.Cyan })
}}}

[kioba]

expanded argument sets the layout back to normal 🤔

Wrap {
    Container(expanded = true) {
    // …
    }
}

couldn’t figure out yet the wrap behavior

[Fudge]

wrap means that the child will take the minimum amount of space possible. Container matches the minimum size of its child, and since it has none, that size is 0. Therefore, you will get a 0 sized child.

[kioba]

What you say makes sense, they take the minimum amount of size. Actually that is what expected. But the Comtainer has the draw child which takes the size of the parent thats why the drawing not visible.
But using them separately both of them expand, composed they take minimum? That feels inconsistent behaviour for me

[kioba]

this is how I can formulate it:

wrap + draw = expanded // shouldn't be compressed?
container + draw = expanded
wrap + container + draw = compressed

[Fudge]

Draw is not a child in the composition phase. It's merely a callback for when the drawing happens, which is after the composition phase.

[Fudge]

In other words, Draw is "nothing"

[Fudge]

If you want to draw something, you need to order space for it in the composition phase, by using something like Card

[kioba]

yeah, I feel we are misunderstanding each other. I see how Draw is “nothing” the problem I have is the two component behavior.
wrap + nothing should be collapsed to minimum (0 sized), basically nothing because of the minimum size of nothing is well nothing. but instead of collapsing the space wrap actually expands it.

Container(expanded = false) + Nothing also expands the entire free space which also questionable

[Fudge]

How do you know it expands the entire free space?

[Fudge]

I think I see what you mean

[Fudge]

Wrap {
    Draw { canvas: Canvas, parentSize: PxSize ->
        canvas.drawRect(parentSize.toRect(), Paint().apply { color = Color.Cyan })
}}

Here Draw should not be expanded, unless I'm missing something

[Fudge]

Someone from google can comment

[Mihai Popa]

In general, both Wrap and Container(expanded = false) will match the size of their layout child

[Mihai Popa]

If they have no child, they will be (0, 0) or actually the minimum size the constraints received from their parent allow

[Mihai Popa]

However, the root of the layout hierarchy will always need to fill the screen, due to the constraints it is measured with. So if Wrap or Container are the root of the hierarchy, they will have to fill the screen

[Mihai Popa]

Hence their Draw children can draw in the whole screen space

[Mihai Popa]

Indeed only Layout elements can occupy layout space - this space can be then be used for Drawing. But layouts do not care about draws