match button to scaled imageview

Question

For a layout in a prototype I need a button that overlays a section (an inner rectangle) of an ImageView with an image that is scaled-up preserving aspect ratio. Is there some way to overlay the button over the imageview with defined margins, then scale up this combination preserving the margins? I tried putting both in an additional relativelayout, but the child elements did not scale within the relativelayout (like 2 UIViews might scale when scaling the parent UIView). I also tried hooking into the imageview using adjustViewBounds to shrink the imageview to the scaled-up image, but this didn't work either.

Here is the current layout

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="0dp"
    tools:context=".MainActivity" >
        <ImageView
            android:id="@+id/placeholderImage"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:src="@drawable/placeholder"
            android:padding="0dp"
            android:adjustViewBounds="true"/>
        <Button
            android:id="@+id/btn"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:background="@android:color/darker_gray"
            android:onClick="show"/>
</RelativeLayout>

did you try by adding weight to layouts? layout_weight=1 etc — Saqib, Jan 10 '14 at 19:14

score 0 · Accepted Answer · edited May 23 '17 at 11:49

I ended up doing this programmatically using some of the answers here: Find the position of a bitmap...

To summarize the approach:

in onCreate use a globalLayoutListener
in the onGlobalLayout callback, get the scale of the drawable using getImageMatrix, then getValues. Since I'm maintaining aspect ratio either MSCALE_X or MSCALE_Y will work.
get the bounds of the drawable, which will vary from the resource png's dimensions due to pre-scaling for target density. Since the resource png's size is known, compute this 'prescale' and multiply by the Matrix scale to get totalScale
apply totalScale to the button size and offsets using LayoutParams.

match button to scaled imageview

1 Answers1