Android: Expand/collapse animation

Question

Let\'s say I have a vertical linearLayout with :

[v1]
[v2]

By default v1 has visibily = GONE. I would like to show v1 with an expand animat

Answer 1

Adding to Tom Esterez's excellent answer and Erik B's excellent update to it, I thought I'd post my own take, compacting the expand and contract methods into one. This way, you could for example have an action like this...

button.setOnClickListener(v -> expandCollapse(view));

... which calls the method below and letting it figure out what to do after each onClick()...

public static void expandCollapse(View view) {

    boolean expand = view.getVisibility() == View.GONE;
    Interpolator easeInOutQuart = PathInterpolatorCompat.create(0.77f, 0f, 0.175f, 1f);

    view.measure(
        View.MeasureSpec.makeMeasureSpec(((View) view.getParent()).getWidth(), View.MeasureSpec.EXACTLY),
        View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED)
    );

    int height = view.getMeasuredHeight();
    int duration = (int) (height/view.getContext().getResources().getDisplayMetrics().density);

    Animation animation = new Animation() {
        @Override protected void applyTransformation(float interpolatedTime, Transformation t) {
            if (expand) {
                view.getLayoutParams().height = 1;
                view.setVisibility(View.VISIBLE);
                if (interpolatedTime == 1) {
                    view.getLayoutParams().height = ViewGroup.LayoutParams.WRAP_CONTENT;
                } else {
                    view.getLayoutParams().height = (int) (height * interpolatedTime);
                }
                view.requestLayout();
            } else {
                if (interpolatedTime == 1) {
                    view.setVisibility(View.GONE);
                } else {
                    view.getLayoutParams().height = height - (int) (height * interpolatedTime);
                    view.requestLayout();
                }
            }
        }
        @Override public boolean willChangeBounds() {
            return true;
        }
    };

    animation.setInterpolator(easeInOutQuart);
    animation.setDuration(duration);
    view.startAnimation(animation);

}