Set size of ImageView in px at runtime

I want to put 8 image thumbs in one horizontal line, using the whole available width.
The images are retrieved from a webservice which lets me specify the dimensions.
I tried the following:

int widthPx = container.getWidth();
LinearLayout thumbs = (LinearLayout)curView.findViewById(R.id.thumbs);
    for(int i=0; i<pics.length; i++) {
        ImageView iv = new ImageView(mContextt);

        int thumbSize = widthPx / 8;

        try {
            String url = "http://someurl/" + pics[i] + "&width=" + thumbSize  + "&height=" + thumbSize;
            URL imgUrl = new URL(url);
            Drawable imgD = Drawable.createFromStream(imgUrl.openStream(), "src");
            iv.setImageDrawable(imgD);
        }
        catch (Exception e) {
            Log.e(TAG, "loading image failed");
            e.printStackTrace();
        }

        thumbs.addView(iv);
    }

The LinearLayout thumbs has android:layout_width="fill_parent set. The thumbs produced by this code are significantly smaller then 1/8 of the width. Why is this? What would be the correct way?

Update:
This code is inside onCreateView of a Fragment. While my width value is calculated based on the root-view and is correct, thumbs.getWidth() returns 0, although the view is inflated before and should also have a width of 480 because of layout_width is set to fill_parent. I'm not sure if that's a problem.

Is my assumption correct that the layout of the created ImageViews is set to wrap_content by default? If not, how to set this with Java code?