[android-developers] When and how are LayoutParams examined, aside from onLayout and onMeasure

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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