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What are "arbitrary units" in the javadoc for computeVerticalScrollOffset?
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Raffaele Sgarro  
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 More options Oct 6 2012, 10:49 am
From: Raffaele Sgarro <raffaelesga...@gmail.com>
Date: Sat, 6 Oct 2012 07:49:03 -0700 (PDT)
Local: Sat, Oct 6 2012 10:49 am
Subject: What are "arbitrary units" in the javadoc for computeVerticalScrollOffset?
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The documentation for computeVerticalScrollRange() says<http://developer.android.com/reference/android/view/View.html#compute...()>
:

> Compute the vertical range that the vertical scrollbar represents.
> The range is expressed in *arbitrary units* that must be the same as the
> units used by computeVerticalScrollExtent()<http://developer.android.com/reference/android/view/View.html#compute...()>
>  andcomputeVerticalScrollOffset()<http://developer.android.com/reference/android/view/View.html#compute...()>
> .

The same *arbitrary units* are mentioned in the other two methods. Looking
at the sources, this is what I found:

    protected int computeVerticalScrollRange() {
        return getHeight();
    }
    protected int computeVerticalScrollOffset() {
        return mScrollY;
    }
    protected int computeVerticalScrollExtent() {
        return getHeight();
    }

So, what's going on here? getHeight() is documented to return the height of
the view in pixels, and I wander if it makes any sense to measure things in
miles, kilometers, astronomic units... Do they documented it in such a way
to allow subclasses to use percentages or number of items?

In particular, I looked at this methods because I'm implementing a ListView
with a custom background <http://stackoverflow.com/q/12737600/315306>, and
it seems I need to deal with scroll dimensions


 
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Romain Guy  
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 More options Oct 7 2012, 4:40 am
From: Romain Guy <romain...@android.com>
Date: Sun, 7 Oct 2012 01:37:18 -0700
Local: Sun, Oct 7 2012 4:37 am
Subject: Re: [android-developers] What are "arbitrary units" in the javadoc for computeVerticalScrollOffset?
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ListView sometimes uses the "item" unit (total number of items, first
visible item, etc) instead of pixels because it cannot always know the
exact pixel height of all items. You can also use units that come from your
dataset (a map could very well use meters for instance, a graph could use
time or percentage.)

Feel free to use pixels but it's not mandatory. What matters is that all 3
methods use the same unit.
On Oct 6, 2012 7:50 AM, "Raffaele Sgarro" <raffaelesga...@gmail.com> wrote:


 
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