DoubleSwipeDetector.cs

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;

using Android.Runtime;
using Android.Content;
using Android.Util;
using Android.Views;

namespace FriendTab
{
  public class DoubleSwipeDetector
	{
		public interface IOnScaleGestureListener {

			bool OnScale(DoubleSwipeDetector detector);

			bool OnScaleBegin(DoubleSwipeDetector detector);

			void OnScaleEnd(DoubleSwipeDetector detector);
		}

		public class SimpleOnScaleGestureListener : IOnScaleGestureListener {

			public bool OnScale(DoubleSwipeDetector detector) {
				return false;
			}

			public bool OnScaleBegin(DoubleSwipeDetector detector) {
				return true;
			}

			public void OnScaleEnd(DoubleSwipeDetector detector) {
				// Intentionally empty
			}
		}

		private static float PRESSURE_THRESHOLD = 0.67f;

		private Context mContext;
		private IOnScaleGestureListener mListener;
		private bool mGestureInProgress;

		private MotionEvent mPrevEvent;
		private MotionEvent mCurrEvent;

		private float mFocusX;
		private float mFocusY;
		private float mPrevFingerDiffX;
		private float mPrevFingerDiffY;
		private float mCurrFingerDiffX;
		private float mCurrFingerDiffY;
		private float mCurrLen;
		private float mPrevLen;
		private float mScaleFactor;
		private float mCurrPressure;
		private float mPrevPressure;
		private long mTimeDelta;

		private bool mInvalidGesture;

		// Pointer IDs currently responsible for the two fingers controlling the gesture
		private int mActiveId0;
		private int mActiveId1;
		private bool mActive0MostRecent;

		public DoubleSwipeDetector (Context context, IOnScaleGestureListener listener) {
			mContext = context;
			mListener = listener;
		}

		public bool OnTouchEvent (MotionEvent evt) {
			var action = evt.ActionMasked;

			if (action == MotionEventActions.Down) {
				reset(); // Start fresh
			}

			bool handled = true;
			if (mInvalidGesture) {
				handled = false;
			} else if (!mGestureInProgress) {
				switch (action) {
				case MotionEventActions.Down: {
					mActiveId0 = evt.GetPointerId(0);
					mActive0MostRecent = true;
				}
					break;

				case MotionEventActions.Up:
					reset();
					break;

				case MotionEventActions.PointerDown: {
					// We have a new multi-finger gesture
					if (mPrevEvent != null) mPrevEvent.Recycle();
					mPrevEvent = MotionEvent.Obtain(evt);
					mTimeDelta = 0;

					int index1 = evt.ActionIndex;
					int index0 = evt.FindPointerIndex(mActiveId0);
					mActiveId1 = evt.GetPointerId(index1);
					if (index0 < 0 || index0 == index1) {
						// Probably someone sending us a broken evt stream.
						index0 = findNewActiveIndex(evt, mActiveId1, -1);
						mActiveId0 = evt.GetPointerId(index0);
					}
					mActive0MostRecent = false;

					setContext(evt);

					mGestureInProgress = mListener.OnScaleBegin(this);
					break;
				}
				}
			} else {
				// Transform gesture in progress - attempt to handle it
				switch (action) {
				case MotionEventActions.Down: {
					// End the old gesture and begin a new one with the most recent two fingers.
					mListener.OnScaleEnd(this);
					int oldActive0 = mActiveId0;
					int oldActive1 = mActiveId1;
					reset();

					mPrevEvent = MotionEvent.Obtain(evt);
					mActiveId0 = mActive0MostRecent ? oldActive0 : oldActive1;
					mActiveId1 = evt.GetPointerId(evt.ActionIndex);
					mActive0MostRecent = false;

					int index0 = evt.FindPointerIndex (mActiveId0);
					if (index0 < 0 || mActiveId0 == mActiveId1) {
						index0 = findNewActiveIndex(evt, mActiveId1, -1);
						mActiveId0 = evt.GetPointerId(index0);
					}

					setContext(evt);

					mGestureInProgress = mListener.OnScaleBegin(this);
				}
					break;

				case MotionEventActions.PointerUp: {
					int pointerCount = evt.PointerCount;
					int actionIndex = evt.ActionIndex;
					int actionId = evt.GetPointerId(actionIndex);

					bool gestureEnded = false;
					if (pointerCount > 2) {
						if (actionId == mActiveId0) {
							int newIndex = findNewActiveIndex(evt, mActiveId1, actionIndex);
							if (newIndex >= 0) {
								mListener.OnScaleEnd(this);
								mActiveId0 = evt.GetPointerId(newIndex);
								mActive0MostRecent = true;
								mPrevEvent = MotionEvent.Obtain(evt);
								setContext(evt);
							mGestureInProgress = mListener.OnScaleBegin(this);
							} else {
								gestureEnded = true;
							}
						} else if (actionId == mActiveId1) {
							int newIndex = findNewActiveIndex(evt, mActiveId0, actionIndex);
							if (newIndex >= 0) {
								mListener.OnScaleEnd(this);
								mActiveId1 = evt.GetPointerId(newIndex);
								mActive0MostRecent = false;
								mPrevEvent = MotionEvent.Obtain(evt);
								setContext(evt);
								mGestureInProgress = mListener.OnScaleBegin(this);
							} else {
								gestureEnded = true;
							}
						}
						mPrevEvent.Recycle();
						mPrevEvent = MotionEvent.Obtain(evt);
						setContext(evt);
					} else {
						gestureEnded = true;
					}

					if (gestureEnded) {
						// Gesture ended
						setContext(evt);

						// Set focus point to the remaining finger
						int activeId = actionId == mActiveId0 ? mActiveId1 : mActiveId0;
						int index = evt.FindPointerIndex(activeId);
						mFocusX = evt.GetX(index);
						mFocusY = evt.GetY(index);

						mListener.OnScaleEnd(this);
						reset();
						mActiveId0 = activeId;
						mActive0MostRecent = true;
					}
				}
					break;

				case MotionEventActions.Cancel:
					mListener.OnScaleEnd(this);
					reset();
					break;

				case MotionEventActions.Up:
					reset();
					break;

				case MotionEventActions.Move: {
					setContext(evt);

					// Only accept the evt if our relative pressure is within
					// a certain limit - this can help filter shaky data as a
					// finger is lifted.
					if (mCurrPressure / mPrevPressure > PRESSURE_THRESHOLD) {
						bool updatePrevious = mListener.OnScale(this);

						if (updatePrevious) {
							mPrevEvent.Recycle();
							mPrevEvent = MotionEvent.Obtain(evt);
						}
					}
				}
					break;
				}
			}

			return handled;
		}

		private int findNewActiveIndex(MotionEvent ev, int otherActiveId, int removedPointerIndex) {
			int pointerCount = ev.PointerCount;

			// It's ok if this isn't found and returns -1, it simply won't match.
			int otherActiveIndex = ev.FindPointerIndex(otherActiveId);

			// Pick a new id and update tracking state.
			for (int i = 0; i < pointerCount; i++) {
				if (i != removedPointerIndex && i != otherActiveIndex) {
					return i;
				}
			}
			return -1;
		}

		private void setContext(MotionEvent curr) {
			if (mCurrEvent != null) {
				mCurrEvent.Recycle();
			}
			mCurrEvent = MotionEvent.Obtain(curr);

			mCurrLen = -1;
			mPrevLen = -1;
			mScaleFactor = -1;

			MotionEvent prev = mPrevEvent;

			int prevIndex0 = prev.FindPointerIndex(mActiveId0);
			int prevIndex1 = prev.FindPointerIndex(mActiveId1);
			int currIndex0 = curr.FindPointerIndex(mActiveId0);
			int currIndex1 = curr.FindPointerIndex(mActiveId1);

			if (prevIndex0 < 0 || prevIndex1 < 0 || currIndex0 < 0 || currIndex1 < 0) {
				mInvalidGesture = true;
				if (mGestureInProgress) {
					mListener.OnScaleEnd(this);
				}
				return;
			}

			float px0 = prev.GetX(prevIndex0);
			float py0 = prev.GetY(prevIndex0);
			float px1 = prev.GetX(prevIndex1);
			float py1 = prev.GetY(prevIndex1);
			float cx0 = curr.GetX(currIndex0);
			float cy0 = curr.GetY(currIndex0);
			float cx1 = curr.GetX(currIndex1);
			float cy1 = curr.GetY(currIndex1);

			float pvx = px1 - px0;
			float pvy = py1 - py0;
			float cvx = cx1 - cx0;
			float cvy = cy1 - cy0;
			mPrevFingerDiffX = pvx;
			mPrevFingerDiffY = pvy;
			mCurrFingerDiffX = cvx;
			mCurrFingerDiffY = cvy;

			mFocusX = cx0 + cvx * 0.5f;
			mFocusY = cy0 + cvy * 0.5f;
			mTimeDelta = curr.EventTime - prev.EventTime;
			mCurrPressure = curr.GetPressure(currIndex0) + curr.GetPressure(currIndex1);
			mPrevPressure = prev.GetPressure(prevIndex0) + prev.GetPressure(prevIndex1);
		}

		private void reset() {
			if (mPrevEvent != null) {
				mPrevEvent.Recycle();
				mPrevEvent = null;
			}
			if (mCurrEvent != null) {
				mCurrEvent.Recycle();
				mCurrEvent = null;
			}
			mGestureInProgress = false;
			mActiveId0 = -1;
			mActiveId1 = -1;
			mInvalidGesture = false;
		}

		public bool IsInProgress {
			get {
				return mGestureInProgress;
			}
		}

		public float FocusX {
			get {
				return mFocusX;
			}
		}

		public float FocusY {
			get {
				return mFocusY;
			}
		}

		public float CurrentSpan {
			get {
				if (mCurrLen == -1) {
					float cvx = mCurrFingerDiffX;
					float cvy = mCurrFingerDiffY;
					mCurrLen = (float)Math.Sqrt (cvx * cvx + cvy * cvy);
				}
				return mCurrLen;
			}
		}

		public float CurrentSpanX {
			get {
				return mCurrFingerDiffX;
			}
		}

		public float CurrentSpanY {
			get {
				return mCurrFingerDiffY;
			}
		}

		public float PreviousSpan {
			get {
				if (mPrevLen == -1) {
					float pvx = mPrevFingerDiffX;
					float pvy = mPrevFingerDiffY;
					mPrevLen = (float)Math.Sqrt (pvx * pvx + pvy * pvy);
				}
				return mPrevLen;
			}
		}

		public float PreviousSpanX {
			get {
				return mPrevFingerDiffX;
			}
		}

		public float PreviousSpanY {
			get {
				return mPrevFingerDiffY;
			}
		}

		public float ScaleFactor {
			get {
				if (mScaleFactor == -1) {
					mScaleFactor = CurrentSpan / PreviousSpan;
				}
				return mScaleFactor;
			}
		}

		public long TimeDelta {
			get {
				return mTimeDelta;
			}
		}

		public long EventTime {
			get {
				return mCurrEvent.EventTime;
			}
		}
	}
}

ExpandableListView.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Util;
using Android.Views;
using Android.Widget;

namespace Foo
{
  public class ExpandableListView : ListView, ExpandHelper.Callback
	{
		ExpandHelper expandHelper;
		bool expandoRequested;

		public ExpandableListView (Context context) :
			base (context)
		{
			Initialize ();
		}

		public ExpandableListView (Context context, IAttributeSet attrs) :
			base (context, attrs)
		{
			Initialize ();
		}

		public ExpandableListView (Context context, IAttributeSet attrs, int defStyle) :
			base (context, attrs, defStyle)
		{
			Initialize ();
		}

		void Initialize ()
		{
			Focusable = false;
			FocusableInTouchMode = false;
			DescendantFocusability = DescendantFocusability.BlockDescendants;
			LongClickable = false;
			Clickable = false;
			SetSelector (Android.Resource.Color.Transparent);
			expandHelper = new ExpandHelper (Context, this, 0, ActivityItemAdapter.MapHeight);
			expandHelper.SetEventSource (this);
		}

		public override bool OnInterceptTouchEvent (MotionEvent ev)
		{
			expandoRequested = expandHelper.OnInterceptTouchEvent (ev);
			return expandoRequested;
		}

		public override bool OnTouchEvent (MotionEvent e)
		{
			expandHelper.OnTouchEvent (e);
			return expandHelper.Progressing || e.PointerCount == 2 || base.OnTouchEvent (e);
		}

		public View GetChildAtRawPosition (float x, float y)
		{
			var index = GetItemPositionFromRawYCoordinates ((int)y);
			if (index == -1)
				return null;
			var view = GetChildAt (index);
			return view.FindViewById (Resource.Id.MapPicture);
		}

		public View GetChildAtPosition (float x, float y)
		{
			return GetChildAtRawPosition (x, y);
		}

		public bool CanChildBeExpanded (View v)
		{
			var activityItem = GetActivityItemFromChildView (v);
			return activityItem != null && activityItem.Expandable;
		}

		public bool SetUserExpandedChild (View v, bool userxpanded)
		{
			var activityItem = GetActivityItemFromChildView (v);
			if (activityItem != null)
				activityItem.Expanded = userxpanded;
			return activityItem != null;
		}

		ActivityItem GetActivityItemFromChildView (View v)
		{
			ActivityItem item = v as ActivityItem;
			if (item != null)
				return item;
			var parent = v.Parent;
			while (parent != null && (item = parent as ActivityItem) == null)
				parent = parent.Parent;
			return item;
		}

		int GetItemPositionFromRawYCoordinates (int rawY)
		{
			int total = LastVisiblePosition - FirstVisiblePosition + 1;

			int[] coords = new int[2];
			for (int i = 0; i < total; i++) {
				var child = GetChildAt (i);
				child.GetLocationOnScreen (coords);
				int top = coords[1];
				int bottom = top + child.Height;
				if ((rawY >= top) && (rawY <= bottom))
					return i;
			}

			return -1;
		}
	}
}

ExpandHelper.cs

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;

using Android.Animation;
using Android.Content;
using Android.Views;
using Android.Util;

namespace Foo
{
  public class ExpandHelper : Java.Lang.Object
	{
		public interface Callback
		{
			View GetChildAtRawPosition(float x, float y);
			View GetChildAtPosition(float x, float y);
			bool CanChildBeExpanded(View v);
			bool SetUserExpandedChild(View v, bool userxpanded);
		}

		const string Tag = "ExpandHelper";
		protected const bool Debug = false;
		const long ExpandDuration = 250;
		const long GlowDuration = 150;

		// Set to false to disable focus-based gestures (two-finger pull).
		const bool UseDrag = true;
		// Set to false to disable scale-based gestures (both horizontal and vertical).
		const bool UseSpan = false;
		// Both gestures types may be active at the same time.
		// At least one gesture type should be active.
		// A variant of the screwdriver gesture will emerge from either gesture type.

		// amount of overstretch for maximum brightness expressed in U
		// 2f: maximum brightness is stretching a 1U to 3U, or a 4U to 6U
		const float StretchInterval = 2f;

		// level of glow for a touch, without overstretch
		// overstretch fills the range (GLOW_BASE, 1.0]
		const float GlowBase = 0.5f;

		Context context;

		bool stretching;
		View eventSource;
		View currView;
		View currViewTopGlow;
		View currViewBottomGlow;
		float oldHeight;
		float naturalHeight;
		float initialTouchFocusY;
		float initialTouchSpan;
		Callback callback;
		DoubleSwipeDetector detector;
		ViewScaler scaler;
		//ObjectAnimator scaleAnimation;
		ValueAnimator scaleAnimation;
		AnimatorSet glowAnimationSet;
		ObjectAnimator glowTopAnimation;
		ObjectAnimator glowBottomAnimation;

		int smallSize;
		int largeSize;
		float maximumStretch;

		GravityFlags gravity;

		class ViewScaler
		{
			View mView;
			ViewGroup.LayoutParams pars;

			public ViewScaler() {}

			public void SetView(View v)
			{
				mView = v;
				pars = v.LayoutParameters;
			}

			public float Height {
				get {
					int height = mView.LayoutParameters.Height;
					if (height < 0) {
						height = mView.MeasuredHeight;
					}
					return (float) height;
				}
				set {
					mView.Visibility = value == 0 ? ViewStates.Invisible : ViewStates.Visible;
					pars.Height = (int)value;
					mView.RequestLayout ();
				}
			}

			public int GetNaturalHeight (int maximum)
			{
				ViewGroup.LayoutParams lp = mView.LayoutParameters;
				int oldHeight = lp.Height;
				lp.Height = ViewGroup.LayoutParams.WrapContent;
				mView.LayoutParameters = lp;
				mView.Measure (
					View.MeasureSpec.MakeMeasureSpec(mView.MeasuredWidth, MeasureSpecMode.Exactly),
					View.MeasureSpec.MakeMeasureSpec(maximum, MeasureSpecMode.AtMost));
				lp.Height = oldHeight;
				mView.LayoutParameters = lp;
				var height = mView.MeasuredHeight;
				return height;
			}
		}

		class AnimatorListener : AnimatorListenerAdapter
		{
			public override void OnAnimationStart(Animator animation)
			{
				View target = (View) ((ObjectAnimator) animation).Target;
				if (target.Alpha <= 0.0f)
					target.Visibility = ViewStates.Visible;
			}

			public override void OnAnimationEnd(Animator animation)
			{
				View target = (View) ((ObjectAnimator) animation).Target;
				if (target.Alpha <= 0.0f)
					target.Visibility = ViewStates.Invisible;
			}
		}

		class GestureDetector : DoubleSwipeDetector.IOnScaleGestureListener
		{
			ExpandHelper parent;

			public GestureDetector (ExpandHelper parent)
			{
				this.parent = parent;
			}

			public bool OnScaleBegin (DoubleSwipeDetector detector)
			{
				float x = detector.FocusX;
				float y = detector.FocusY;

				View v = null;
				if (parent.eventSource != null) {
					int[] location = new int[2];
					parent.eventSource.GetLocationOnScreen(location);
					x += (float) location[0];
					y += (float) location[1];
					v = parent.callback.GetChildAtRawPosition(x, y);
				} else {
					v = parent.callback.GetChildAtPosition(x, y);
				}

				// your fingers have to be somewhat close to the bounds of the view in question
				parent.initialTouchFocusY = detector.FocusY;
				parent.initialTouchSpan = Math.Abs(detector.CurrentSpan);

				parent.stretching = parent.InitScale(v);
				return parent.stretching;
			}

			public bool OnScale (DoubleSwipeDetector detector)
			{
				// are we scaling or dragging?
				float span = Math.Abs(detector.CurrentSpan) - parent.initialTouchSpan;
				span *= UseSpan ? 1f : 0f;
				float drag = detector.FocusY - parent.initialTouchFocusY;
				drag *= UseDrag ? 1f : 0f;
				drag *= parent.gravity == GravityFlags.Bottom ? -1f : 1f;
				float pull = Math.Abs(drag) + Math.Abs(span) + 1f;
				float hand = drag * Math.Abs(drag) / pull + span * Math.Abs(span) / pull;

				hand = hand + parent.oldHeight;
				float target = hand;

				hand = hand < parent.smallSize ? parent.smallSize : (hand > parent.largeSize ? parent.largeSize : hand);
				hand = hand > parent.naturalHeight ? parent.naturalHeight : hand;

				parent.scaler.Height = hand;

				// glow if overscale
				float stretch = (float) Math.Abs((target - hand) / parent.maximumStretch);
				float strength = 1f / (1f + (float) Math.Pow(Math.E, -1 * ((8f * stretch) - 5f)));
				parent.SetGlow(GlowBase + strength * (1f - GlowBase));
				return true;
			}

			public void OnScaleEnd(DoubleSwipeDetector detector)
			{
				parent.FinishScale(false);
			}
		}

		public ExpandHelper(Context context, Callback callback, int small, int large) {
			this.smallSize = small;
			this.maximumStretch = Math.Max (smallSize, 1) * StretchInterval;
			this.largeSize = large;
			this.context = context;
			this.callback = callback;
			this.scaler = new ViewScaler();
			this.gravity = GravityFlags.Top;

			//this.scaleAnimation = ObjectAnimator.OfFloat (scaler, "Height", 0f);
			this.scaleAnimation = ValueAnimator.OfFloat (0f);
			this.scaleAnimation.Update += (sender, e) => scaler.Height = (float)e.Animation.AnimatedValue;
			this.scaleAnimation.SetDuration (ExpandDuration);

			AnimatorListenerAdapter glowVisibilityController = new AnimatorListener ();
			glowTopAnimation = ObjectAnimator.OfFloat (null, "alpha", 0f);
			glowTopAnimation.AddListener (glowVisibilityController);
			glowBottomAnimation = ObjectAnimator.OfFloat (null, "alpha", 0f);
			glowBottomAnimation.AddListener (glowVisibilityController);
			glowAnimationSet = new AnimatorSet();
			glowAnimationSet.Play (glowTopAnimation).With(glowBottomAnimation);
			glowAnimationSet.SetDuration(GlowDuration);

			detector = new DoubleSwipeDetector(context, new GestureDetector (this));
		}

		public bool Progressing {
			get {
				return detector.IsInProgress;
			}
		}

		public void SetEventSource (View eventSource)
		{
			this.eventSource = eventSource;
		}

		public void SetGravity (GravityFlags gravity)
		{
			this.gravity = gravity;
		}

		public void SetGlow (float glow)
		{
			if (!glowAnimationSet.IsRunning || glow == 0f) {
				if (glowAnimationSet.IsRunning) {
					glowAnimationSet.Cancel ();
				}
				if (currViewTopGlow != null && currViewBottomGlow != null) {
					if (glow == 0f || currViewTopGlow.Alpha == 0f) { 
						// animate glow in and out
						glowTopAnimation.SetTarget(currViewTopGlow);
						glowBottomAnimation.SetTarget(currViewBottomGlow);
						glowTopAnimation.SetFloatValues(glow);
						glowBottomAnimation.SetFloatValues(glow);
						glowAnimationSet.SetupStartValues();
						glowAnimationSet.Start();
					} else {
						// set it explicitly in reponse to touches.
						currViewTopGlow.Alpha = glow;
						currViewBottomGlow.Alpha = glow;
						HandleGlowVisibility();
					}
				}
			}
		}

		void HandleGlowVisibility ()
		{
			currViewTopGlow.Visibility = currViewTopGlow.Alpha <= 0.0f ? ViewStates.Invisible : ViewStates.Visible;
			currViewBottomGlow.Visibility = currViewBottomGlow.Alpha <= 0.0f ? ViewStates.Invisible : ViewStates.Visible;
		}

		public bool OnInterceptTouchEvent (MotionEvent ev)
		{
			stretching = detector.OnTouchEvent(ev);
			return stretching;
		}

		public bool OnTouchEvent (MotionEvent ev)
		{
			var action = ev.Action;
			if (stretching)
				detector.OnTouchEvent(ev);
			switch (action) {
			case MotionEventActions.Up:
			case MotionEventActions.Cancel:
				stretching = false;
				ClearView();
				break;
			}
			return true;
		}

		bool InitScale (View v)
		{
			if (v != null) {
				stretching = true;
				SetView(v);
				SetGlow(GlowBase);
				scaler.SetView(v);
				oldHeight = scaler.Height;
				if (callback.CanChildBeExpanded(v))
					naturalHeight = scaler.GetNaturalHeight(largeSize);
				else
					naturalHeight = oldHeight;
				v.Parent.RequestDisallowInterceptTouchEvent (true);
			}
			return stretching;
		}

		void FinishScale (bool force) {
			float h = scaler.Height;
			bool wasClosed = (oldHeight == smallSize);
			if (wasClosed) {
				h = (force || h > smallSize) ? naturalHeight : smallSize;
			} else {
				h = (force || h < naturalHeight) ? smallSize : naturalHeight;
			}
			if (scaleAnimation.IsRunning) {
				scaleAnimation.Cancel();
			}
			scaleAnimation.SetFloatValues (scaler.Height, h);
			scaleAnimation.Start();
			stretching = false;
			SetGlow(0f);
			callback.SetUserExpandedChild(currView, h == naturalHeight);

			ClearView();
		}

		void ClearView ()
		{
			currView = null;
			currViewTopGlow = null;
			currViewBottomGlow = null;
		}

		void SetView (View v)
		{
			currView = v;
			ViewGroup g = v as ViewGroup;
			if (g == null)
				g = v.Parent.Parent as ViewGroup;
			if (g != null) {
				currViewTopGlow = g.FindViewById(Resource.Id.TopGlow);
				currViewBottomGlow = g.FindViewById(Resource.Id.BottomGlow);
			}
		}
	}
}

Hello..

Your example of Expandable Listview is so good.

I want to implement functionality same like you. so can you please provide me some more code. so i can implement this kind of functionality .

Thanks
Harshad

@garuma Can you please help me use your ExpandableListView? I read your article over at http://blog.xamarin.com/mfa-tricks-2-2-fingers-expandable-layout/ but there seems to be a lot left out. Where do we place the .cs files? In the root directory of our project? In the resources folder? How do we add the ExpandableListView control to our Layout? Also, the links to the glow images you posted are not working. GitHub just keeps loading and loading but never starts the download for the images. Any help would be greatly appreciated!