A LinearLayout subclass that can be collapsed and expanded in an animated fashion. Relies on NineOldAndroids for animation.

CollapsableLinearLayout.java

package com.animatedpiechart;

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.ViewGroup;
import android.view.animation.AccelerateDecelerateInterpolator;
import android.view.animation.Interpolator;
import android.widget.LinearLayout;

import com.nineoldandroids.animation.Animator;
import com.nineoldandroids.animation.AnimatorListenerAdapter;
import com.nineoldandroids.animation.IntEvaluator;
import com.nineoldandroids.animation.ValueAnimator;

public class CollapsableLinearLayout extends LinearLayout {

    private class HeightEvaluator extends IntEvaluator {
		@Override
		public Integer evaluate(float fraction, Integer startValue, Integer endValue) {
			int height = super.evaluate(fraction, startValue, endValue);
			ViewGroup.LayoutParams params = getLayoutParams();
			params.height = height;
			setLayoutParams(params);
			return height;
		}
	}

	private ValueAnimator animator;
	private Interpolator interpolator = new AccelerateDecelerateInterpolator();

	private boolean animating;

	private int expandedHeight;

	private long duration = 600;

	public CollapsableLinearLayout(Context context) {
		super(context);
		onInit();
	}

	public CollapsableLinearLayout(Context context, AttributeSet attrs) {
		super(context, attrs);
		onInit();
	}

	public CollapsableLinearLayout(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		onInit();
	}

	protected void onInit() {
	}

	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev) {
		// consume all touch events when animating
		if (animating) {
			return true;
		}
		return super.onInterceptTouchEvent(ev);
	}

	@Override
	protected void onSizeChanged(int w, int h, int oldw, int oldh) {
		super.onSizeChanged(w, h, oldw, oldh);
		if ((w != oldw || h != oldh) && !animating && h != 0) {
			expandedHeight = h;
		}
	}

	public void setAnimationDuration(long duration) {
		this.duration = duration;
	}

	public long getAnimationDuration() {
		return duration;
	}

	public void setInterpolator(Interpolator interpolator) {
		this.interpolator = interpolator;
	}

	public Interpolator getInterpolator() {
		return interpolator;
	}

	public void expand() {
		if (getHeight() != expandedHeight) {
			animateHeight(0, expandedHeight);
		}
	}

	public void collapse() {
		if (getHeight() != 0) {
			animateHeight(expandedHeight, 0);
		}
	}

	private void animateHeight(int startHeight, int endHeight) {
		long previousAnimationPlayTime = -1;
		if (animator != null && animator.isRunning()) {
			previousAnimationPlayTime = animator.getCurrentPlayTime();
			animator.cancel();
		}
		animator = ValueAnimator.ofObject(new HeightEvaluator(), startHeight, endHeight);
		animator.setInterpolator(interpolator);
		animator.setDuration(duration);
		animator.addListener(new AnimatorListenerAdapter() {
			@Override
			public void onAnimationStart(Animator animation) {
				animating = true;
			}

			@Override
			public void onAnimationEnd(Animator animation) {
				animating = false;
			}
		});
		animator.start();
		if (previousAnimationPlayTime != -1) {
			animator.setCurrentPlayTime(duration - previousAnimationPlayTime);
		}
	}

	@Override
	protected void onLayout(boolean changed, int l, int t, int r, int b) {
		// We don't want children to move during animation.
		// Also, don't layout children if our height is zero.
		if (!animating && t != b) {
			super.onLayout(changed, l, t, r, b);
		}
	}
}