AspectRatioImageView.java

import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.widget.ImageView;

/**
 * TODO: Add a class header comment!
 */
public class AspectRatioImageView extends ImageView {

    private float mAspectRatio;

    public AspectRatioImageView(Context context) {
        this(context, null);
    }

    public AspectRatioImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public AspectRatioImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.AspectRatioImageView);
        mAspectRatio = a.getFloat(R.styleable.AspectRatioImageView_aspect_ratio, -1);
        a.recycle();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mAspectRatio > 0) {
            int width = getMeasuredWidth();
            int height = (int) (width * mAspectRatio);
            setMeasuredDimension(width, height);
        }
    }
}

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="AspectRatioImageView">
        <attr name="aspect_ratio" format="float" />
    </declare-styleable>
</resources>