How to align ImageView to the bottom, fill its width and height, and keep its aspect ratio?

Question

Background

There are various XML attributes for ImageView to scale its content , and various layout views that allow to place views and set their sizes.

Howeve

Answer 1

this is a proof-om-concept custom ImageView, you will need to add missing constructors and perform the Matrix setting whenever ImageView's Drawable changes:

class V extends ImageView {
    public V(Context context) {
        super(context);
        setScaleType(ScaleType.MATRIX);
    }
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        Drawable d = getDrawable();
        if (d != null) {
            Matrix matrix = new Matrix();
            RectF src = new RectF(0, 0, d.getIntrinsicWidth(), d.getIntrinsicHeight());
            RectF dst = new RectF(0, 0, w, h);
            matrix.setRectToRect(src, dst, Matrix.ScaleToFit.CENTER);
            float[] points = {
                    0, d.getIntrinsicHeight()
            };
            matrix.mapPoints(points);
            matrix.postTranslate(0, h - points[1]);
            setImageMatrix(matrix);
        }
    }
}

how it works in short:

• first the Matrix is set by calling Matrix.setRectToRect() with stf == Matrix.ScaleToFit.CENTER, the result is the same as ImageView.ScaleType.FIT_CENTER

• then in order to align the Drawable to the bottom Matrix.mapPoints() is called, it maps the Drawable's left/bottom corner and the result is transformed point as would be seen in the ImageView

• and finally Matrix.postTranslate() translates the MAtrix in Y axis to the ImageView's bottom