I'm no expert on the layout machenism of android, but you dont really need
a reference to the LayoutParams to do these calculations since onMeasure
gets the "processed" values of these params. the width and height
MeasureSpecs contain the size and mode as recommended by the layout params.
What you're doing might be working in the instance you're testing on, but
might fail on others.
P.S - Maybe its because of there's missing code here, but it seems like
you're just having the parent layout having the same size as the child
layout (basically both have wrap_content on width and height)... why do you
need a custom class for that?
On Saturday, March 2, 2013 8:10:17 AM UTC+2, momo wrote:
>
> I have a custom ViewGroup that's only ever managing the size and position
> of one child. I've override onMeasure and onLayout so that LayoutParams
> are never examined, yet it fails unless I do provide LayoutParams. Here
> are abbreviated summaries of the relevant portions of the class:
>
>
> public class SomeSpecialLayoutManager extends ViewGroup {
>
> @Override
> protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
> measureChildren(widthMeasureSpec, heightMeasureSpec);
> int w = mChild.getMeasuredWidth();
> int h = mChild.getMeasuredHeight();
> w = Math.max(w, getSuggestedMinimumWidth());
> h = Math.max(h, getSuggestedMinimumHeight());
> w = resolveSize(w, widthMeasureSpec);
> h = resolveSize(h, heightMeasureSpec);
> setMeasuredDimension(w, h);
> }
>
> @Override
> protected void onLayout(boolean changed, int l, int t, int r, int b) {
> mChild.layout( 0, 0, mWidth, mHeight );
> }
> }
>
>
> Using the above, the following *does* work:
>
> LayoutParams lp = mChild.getLayoutParams();
> lp.width = mWidth;
> lp.height = mHeight;
> mChild.setLayoutParams( lp );
>
> But since neither `onMeasure` nor `onLayout` even makes reference to
> `LayoutParams`, I wonder why it's required, or even how it's referenced at
> all. I would assume that since the layout pass grabs `mWidth` and
> `mHeight` directly, there'd be no need for the `LayoutParams` at all - and
> that a call to requestLayout would update it appropriately.
>
> However, when I isolate the above in a small program outside of a
> complicated View tree with scrolling layers that exceed "normal" container
> sizes, it *does* work as expected, so I have to assume the issue is in the
> measure pass.
>
> I've read as much documentation as I can find about what's going on during
> the measure and layout passes, and examined the source, but I believe I
> must be missing something.
>
> TYIA.
>
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