ScrollView2D.java

/*
 * Copyright (C) 2006 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.
 */
/*
 * Revised 5/19/2010 by GORGES
 * Now supports two-dimensional view scrolling
 * http://GORGES.us
 */
 
package com.freerdp.freerdpcore.presentation;
 
import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.FocusFinder;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.animation.AnimationUtils;
import android.widget.FrameLayout;
import android.widget.LinearLayout;
import android.widget.Scroller;
import android.widget.TextView;
 
import java.util.List;
 
public class ScrollView2D extends FrameLayout
{
 
  static final int ANIMATED_SCROLL_GAP = 250;
  static final float MAX_SCROLL_FACTOR = 0.5f;
  private final Rect mTempRect = new Rect();
  private ScrollView2DListener scrollView2DListener = null;
  private long mLastScroll;
  private Scroller mScroller;
  private boolean scrollEnabled = true;
  private boolean mTwoDScrollViewMovedFocus;
  private float mLastMotionY;
  private float mLastMotionX;
  private boolean mIsLayoutDirty = true;
  private View mChildToScrollTo = null;
  private boolean mIsBeingDragged = false;
  private VelocityTracker mVelocityTracker;
  private int mTouchSlop;
  private int mMinimumVelocity;
  private int mMaximumVelocity;
  public ScrollView2D(Context context)
  {
    super(context);
    initTwoDScrollView();
  }
 
  public ScrollView2D(Context context, AttributeSet attrs)
  {
    super(context, attrs);
    initTwoDScrollView();
  }
 
  public ScrollView2D(Context context, AttributeSet attrs, int defStyle)
  {
    super(context, attrs, defStyle);
    initTwoDScrollView();
  }
 
  @Override protected float getTopFadingEdgeStrength()
  {
    if (getChildCount() == 0)
    {
      return 0.0f;
    }
    final int length = getVerticalFadingEdgeLength();
    if (getScrollY() < length)
    {
      return getScrollY() / (float)length;
    }
    return 1.0f;
  }
 
  @Override protected float getBottomFadingEdgeStrength()
  {
    if (getChildCount() == 0)
    {
      return 0.0f;
    }
    final int length = getVerticalFadingEdgeLength();
    final int bottomEdge = getHeight() - getPaddingBottom();
    final int span = getChildAt(0).getBottom() - getScrollY() - bottomEdge;
    if (span < length)
    {
      return span / (float)length;
    }
    return 1.0f;
  }
 
  @Override protected float getLeftFadingEdgeStrength()
  {
    if (getChildCount() == 0)
    {
      return 0.0f;
    }
    final int length = getHorizontalFadingEdgeLength();
    if (getScrollX() < length)
    {
      return getScrollX() / (float)length;
    }
    return 1.0f;
  }
 
  @Override protected float getRightFadingEdgeStrength()
  {
    if (getChildCount() == 0)
    {
      return 0.0f;
    }
    final int length = getHorizontalFadingEdgeLength();
    final int rightEdge = getWidth() - getPaddingRight();
    final int span = getChildAt(0).getRight() - getScrollX() - rightEdge;
    if (span < length)
    {
      return span / (float)length;
    }
    return 1.0f;
  }
 
  public void setScrollEnabled(boolean enable)
  {
    scrollEnabled = enable;
  }
 
  public int getMaxScrollAmountVertical()
  {
    return (int)(MAX_SCROLL_FACTOR * getHeight());
  }
 
  public int getMaxScrollAmountHorizontal()
  {
    return (int)(MAX_SCROLL_FACTOR * getWidth());
  }
 
  private void initTwoDScrollView()
  {
    mScroller = new Scroller(getContext());
    setFocusable(true);
    setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
    setWillNotDraw(false);
    final ViewConfiguration configuration = ViewConfiguration.get(getContext());
    mTouchSlop = configuration.getScaledTouchSlop();
    mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
    mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
  }
 
  @Override public void addView(View child)
  {
    if (getChildCount() > 0)
    {
      throw new IllegalStateException("TwoDScrollView can host only one direct child");
    }
    super.addView(child);
  }
 
  @Override public void addView(View child, int index)
  {
    if (getChildCount() > 0)
    {
      throw new IllegalStateException("TwoDScrollView can host only one direct child");
    }
    super.addView(child, index);
  }
 
  @Override public void addView(View child, ViewGroup.LayoutParams params)
  {
    if (getChildCount() > 0)
    {
      throw new IllegalStateException("TwoDScrollView can host only one direct child");
    }
    super.addView(child, params);
  }
 
  @Override public void addView(View child, int index, ViewGroup.LayoutParams params)
  {
    if (getChildCount() > 0)
    {
      throw new IllegalStateException("TwoDScrollView can host only one direct child");
    }
    super.addView(child, index, params);
  }
 
  private boolean canScroll()
  {
    if (!scrollEnabled)
      return false;
    View child = getChildAt(0);
    if (child != null)
    {
      int childHeight = child.getHeight();
      int childWidth = child.getWidth();
      return (getHeight() < childHeight + getPaddingTop() + getPaddingBottom()) ||
          (getWidth() < childWidth + getPaddingLeft() + getPaddingRight());
    }
    return false;
  }
 
  @Override public boolean dispatchKeyEvent(KeyEvent event)
  {
    // Let the focused view and/or our descendants get the key first
    boolean handled = super.dispatchKeyEvent(event);
    if (handled)
    {
      return true;
    }
    return executeKeyEvent(event);
  }
 
  public boolean executeKeyEvent(KeyEvent event)
  {
    mTempRect.setEmpty();
    if (!canScroll())
    {
      if (isFocused())
      {
        View currentFocused = findFocus();
        if (currentFocused == this)
          currentFocused = null;
        View nextFocused =
            FocusFinder.getInstance().findNextFocus(this, currentFocused, View.FOCUS_DOWN);
        return nextFocused != null && nextFocused != this &&
            nextFocused.requestFocus(View.FOCUS_DOWN);
      }
      return false;
    }
    boolean handled = false;
    if (event.getAction() == KeyEvent.ACTION_DOWN)
    {
      switch (event.getKeyCode())
      {
        case KeyEvent.KEYCODE_DPAD_UP:
          if (!event.isAltPressed())
          {
            handled = arrowScroll(View.FOCUS_UP, false);
          }
          else
          {
            handled = fullScroll(View.FOCUS_UP, false);
          }
          break;
        case KeyEvent.KEYCODE_DPAD_DOWN:
          if (!event.isAltPressed())
          {
            handled = arrowScroll(View.FOCUS_DOWN, false);
          }
          else
          {
            handled = fullScroll(View.FOCUS_DOWN, false);
          }
          break;
        case KeyEvent.KEYCODE_DPAD_LEFT:
          if (!event.isAltPressed())
          {
            handled = arrowScroll(View.FOCUS_LEFT, true);
          }
          else
          {
            handled = fullScroll(View.FOCUS_LEFT, true);
          }
          break;
        case KeyEvent.KEYCODE_DPAD_RIGHT:
          if (!event.isAltPressed())
          {
            handled = arrowScroll(View.FOCUS_RIGHT, true);
          }
          else
          {
            handled = fullScroll(View.FOCUS_RIGHT, true);
          }
          break;
      }
    }
    return handled;
  }
 
  @Override public boolean onInterceptTouchEvent(MotionEvent ev)
  {
    /*
     * This method JUST determines whether we want to intercept the motion.
     * If we return true, onMotionEvent will be called and we do the actual
     * scrolling there.
     *
     * Shortcut the most recurring case: the user is in the dragging
     * state and he is moving his finger.  We want to intercept this
     * motion.
     */
    final int action = ev.getAction();
    if ((action == MotionEvent.ACTION_MOVE) && (mIsBeingDragged))
    {
      return true;
    }
    if (!canScroll())
    {
      mIsBeingDragged = false;
      return false;
    }
    final float y = ev.getY();
    final float x = ev.getX();
    switch (action)
    {
      case MotionEvent.ACTION_MOVE:
        /*
         * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
         * whether the user has moved far enough from his original down touch.
         */
        /*
         * Locally do absolute value. mLastMotionY is set to the y value
         * of the down event.
         */
        final int yDiff = (int)Math.abs(y - mLastMotionY);
        final int xDiff = (int)Math.abs(x - mLastMotionX);
        if (yDiff > mTouchSlop || xDiff > mTouchSlop)
        {
          mIsBeingDragged = true;
        }
        break;
 
      case MotionEvent.ACTION_DOWN:
        /* Remember location of down touch */
        mLastMotionY = y;
        mLastMotionX = x;
 
        /*
         * If being flinged and user touches the screen, initiate drag;
         * otherwise don't.  mScroller.isFinished should be false when
         * being flinged.
         */
        mIsBeingDragged = !mScroller.isFinished();
        break;
 
      case MotionEvent.ACTION_CANCEL:
      case MotionEvent.ACTION_UP:
        /* Release the drag */
        mIsBeingDragged = false;
        break;
    }
 
    /*
     * The only time we want to intercept motion events is if we are in the
     * drag mode.
     */
    return mIsBeingDragged;
  }
 
  @Override public boolean onTouchEvent(MotionEvent ev)
  {
 
    if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0)
    {
      // Don't handle edge touches immediately -- they may actually belong to one of our
      // descendants.
      return false;
    }
 
    if (!canScroll())
    {
      return false;
    }
 
    if (mVelocityTracker == null)
    {
      mVelocityTracker = VelocityTracker.obtain();
    }
    mVelocityTracker.addMovement(ev);
 
    final int action = ev.getAction();
    final float y = ev.getY();
    final float x = ev.getX();
 
    switch (action)
    {
      case MotionEvent.ACTION_DOWN:
        /*
         * If being flinged and user touches, stop the fling. isFinished
         * will be false if being flinged.
         */
        if (!mScroller.isFinished())
        {
          mScroller.abortAnimation();
        }
 
        // Remember where the motion event started
        mLastMotionY = y;
        mLastMotionX = x;
        break;
      case MotionEvent.ACTION_MOVE:
        // Scroll to follow the motion event
        int deltaX = (int)(mLastMotionX - x);
        int deltaY = (int)(mLastMotionY - y);
        mLastMotionX = x;
        mLastMotionY = y;
 
        if (deltaX < 0)
        {
          if (getScrollX() < 0)
          {
            deltaX = 0;
          }
        }
        else if (deltaX > 0)
        {
          final int rightEdge = getWidth() - getPaddingRight();
          final int availableToScroll =
              getChildAt(0).getRight() - getScrollX() - rightEdge;
          if (availableToScroll > 0)
          {
            deltaX = Math.min(availableToScroll, deltaX);
          }
          else
          {
            deltaX = 0;
          }
        }
        if (deltaY < 0)
        {
          if (getScrollY() < 0)
          {
            deltaY = 0;
          }
        }
        else if (deltaY > 0)
        {
          final int bottomEdge = getHeight() - getPaddingBottom();
          final int availableToScroll =
              getChildAt(0).getBottom() - getScrollY() - bottomEdge;
          if (availableToScroll > 0)
          {
            deltaY = Math.min(availableToScroll, deltaY);
          }
          else
          {
            deltaY = 0;
          }
        }
        if (deltaY != 0 || deltaX != 0)
          scrollBy(deltaX, deltaY);
        break;
      case MotionEvent.ACTION_UP:
        final VelocityTracker velocityTracker = mVelocityTracker;
        velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
        int initialXVelocity = (int)velocityTracker.getXVelocity();
        int initialYVelocity = (int)velocityTracker.getYVelocity();
        if ((Math.abs(initialXVelocity) + Math.abs(initialYVelocity) > mMinimumVelocity) &&
            getChildCount() > 0)
        {
          fling(-initialXVelocity, -initialYVelocity);
        }
        if (mVelocityTracker != null)
        {
          mVelocityTracker.recycle();
          mVelocityTracker = null;
        }
    }
    return true;
  }
 
  private View findFocusableViewInMyBounds(final boolean topFocus, final int top,
                                           final boolean leftFocus, final int left,
                                           View preferredFocusable)
  {
    /*
     * The fading edge's transparent side should be considered for focus
     * since it's mostly visible, so we divide the actual fading edge length
     * by 2.
     */
    final int verticalFadingEdgeLength = getVerticalFadingEdgeLength() / 2;
    final int topWithoutFadingEdge = top + verticalFadingEdgeLength;
    final int bottomWithoutFadingEdge = top + getHeight() - verticalFadingEdgeLength;
    final int horizontalFadingEdgeLength = getHorizontalFadingEdgeLength() / 2;
    final int leftWithoutFadingEdge = left + horizontalFadingEdgeLength;
    final int rightWithoutFadingEdge = left + getWidth() - horizontalFadingEdgeLength;
 
    if ((preferredFocusable != null) &&
        (preferredFocusable.getTop() < bottomWithoutFadingEdge) &&
        (preferredFocusable.getBottom() > topWithoutFadingEdge) &&
        (preferredFocusable.getLeft() < rightWithoutFadingEdge) &&
        (preferredFocusable.getRight() > leftWithoutFadingEdge))
    {
      return preferredFocusable;
    }
    return findFocusableViewInBounds(topFocus, topWithoutFadingEdge, bottomWithoutFadingEdge,
                                     leftFocus, leftWithoutFadingEdge, rightWithoutFadingEdge);
  }
 
  private View findFocusableViewInBounds(boolean topFocus, int top, int bottom, boolean leftFocus,
                                         int left, int right)
  {
    List<View> focusables = getFocusables(View.FOCUS_FORWARD);
    View focusCandidate = null;
 
    /*
     * A fully contained focusable is one where its top is below the bound's
     * top, and its bottom is above the bound's bottom. A partially
     * contained focusable is one where some part of it is within the
     * bounds, but it also has some part that is not within bounds.  A fully contained
     * focusable is preferred to a partially contained focusable.
     */
    boolean foundFullyContainedFocusable = false;
 
    int count = focusables.size();
    for (int i = 0; i < count; i++)
    {
      View view = focusables.get(i);
      int viewTop = view.getTop();
      int viewBottom = view.getBottom();
      int viewLeft = view.getLeft();
      int viewRight = view.getRight();
 
      if (top < viewBottom && viewTop < bottom && left < viewRight && viewLeft < right)
      {
        /*
         * the focusable is in the target area, it is a candidate for
         * focusing
         */
        final boolean viewIsFullyContained = (top < viewTop) && (viewBottom < bottom) &&
                                             (left < viewLeft) && (viewRight < right);
        if (focusCandidate == null)
        {
          /* No candidate, take this one */
          focusCandidate = view;
          foundFullyContainedFocusable = viewIsFullyContained;
        }
        else
        {
          final boolean viewIsCloserToVerticalBoundary =
              (topFocus && viewTop < focusCandidate.getTop()) ||
              (!topFocus && viewBottom > focusCandidate.getBottom());
          final boolean viewIsCloserToHorizontalBoundary =
              (leftFocus && viewLeft < focusCandidate.getLeft()) ||
              (!leftFocus && viewRight > focusCandidate.getRight());
          if (foundFullyContainedFocusable)
          {
            if (viewIsFullyContained && viewIsCloserToVerticalBoundary &&
                viewIsCloserToHorizontalBoundary)
            {
              /*
               * We're dealing with only fully contained views, so
               * it has to be closer to the boundary to beat our
               * candidate
               */
              focusCandidate = view;
            }
          }
          else
          {
            if (viewIsFullyContained)
            {
              /* Any fully contained view beats a partially contained view */
              focusCandidate = view;
              foundFullyContainedFocusable = true;
            }
            else if (viewIsCloserToVerticalBoundary && viewIsCloserToHorizontalBoundary)
            {
              /*
               * Partially contained view beats another partially
               * contained view if it's closer
               */
              focusCandidate = view;
            }
          }
        }
      }
    }
    return focusCandidate;
  }
 
  public boolean fullScroll(int direction, boolean horizontal)
  {
    if (!horizontal)
    {
      boolean down = direction == View.FOCUS_DOWN;
      int height = getHeight();
      mTempRect.top = 0;
      mTempRect.bottom = height;
      if (down)
      {
        int count = getChildCount();
        if (count > 0)
        {
          View view = getChildAt(count - 1);
          mTempRect.bottom = view.getBottom();
          mTempRect.top = mTempRect.bottom - height;
        }
      }
      return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom, 0, 0, 0);
    }
    else
    {
      boolean right = direction == View.FOCUS_DOWN;
      int width = getWidth();
      mTempRect.left = 0;
      mTempRect.right = width;
      if (right)
      {
        int count = getChildCount();
        if (count > 0)
        {
          View view = getChildAt(count - 1);
          mTempRect.right = view.getBottom();
          mTempRect.left = mTempRect.right - width;
        }
      }
      return scrollAndFocus(0, 0, 0, direction, mTempRect.top, mTempRect.bottom);
    }
  }
 
  private boolean scrollAndFocus(int directionY, int top, int bottom, int directionX, int left,
                                 int right)
  {
    boolean handled = true;
    int height = getHeight();
    int containerTop = getScrollY();
    int containerBottom = containerTop + height;
    boolean up = directionY == View.FOCUS_UP;
    int width = getWidth();
    int containerLeft = getScrollX();
    int containerRight = containerLeft + width;
    boolean leftwards = directionX == View.FOCUS_UP;
    View newFocused = findFocusableViewInBounds(up, top, bottom, leftwards, left, right);
    if (newFocused == null)
    {
      newFocused = this;
    }
    if ((top >= containerTop && bottom <= containerBottom) ||
        (left >= containerLeft && right <= containerRight))
    {
      handled = false;
    }
    else
    {
      int deltaY = up ? (top - containerTop) : (bottom - containerBottom);
      int deltaX = leftwards ? (left - containerLeft) : (right - containerRight);
      doScroll(deltaX, deltaY);
    }
    if (newFocused != findFocus() && newFocused.requestFocus(directionY))
    {
      mTwoDScrollViewMovedFocus = true;
      mTwoDScrollViewMovedFocus = false;
    }
    return handled;
  }
 
  public boolean arrowScroll(int direction, boolean horizontal)
  {
    View currentFocused = findFocus();
    if (currentFocused == this)
      currentFocused = null;
    View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);
    final int maxJump =
        horizontal ? getMaxScrollAmountHorizontal() : getMaxScrollAmountVertical();
 
    if (!horizontal)
    {
      if (nextFocused != null)
      {
        nextFocused.getDrawingRect(mTempRect);
        offsetDescendantRectToMyCoords(nextFocused, mTempRect);
        int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
        doScroll(0, scrollDelta);
        nextFocused.requestFocus(direction);
      }
      else
      {
        // no new focus
        int scrollDelta = maxJump;
        if (direction == View.FOCUS_UP && getScrollY() < scrollDelta)
        {
          scrollDelta = getScrollY();
        }
        else if (direction == View.FOCUS_DOWN)
        {
          if (getChildCount() > 0)
          {
            int daBottom = getChildAt(0).getBottom();
            int screenBottom = getScrollY() + getHeight();
            if (daBottom - screenBottom < maxJump)
            {
              scrollDelta = daBottom - screenBottom;
            }
          }
        }
        if (scrollDelta == 0)
        {
          return false;
        }
        doScroll(0, direction == View.FOCUS_DOWN ? scrollDelta : -scrollDelta);
      }
    }
    else
    {
      if (nextFocused != null)
      {
        nextFocused.getDrawingRect(mTempRect);
        offsetDescendantRectToMyCoords(nextFocused, mTempRect);
        int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
        doScroll(scrollDelta, 0);
        nextFocused.requestFocus(direction);
      }
      else
      {
        // no new focus
        int scrollDelta = maxJump;
        if (direction == View.FOCUS_UP && getScrollY() < scrollDelta)
        {
          scrollDelta = getScrollY();
        }
        else if (direction == View.FOCUS_DOWN)
        {
          if (getChildCount() > 0)
          {
            int daBottom = getChildAt(0).getBottom();
            int screenBottom = getScrollY() + getHeight();
            if (daBottom - screenBottom < maxJump)
            {
              scrollDelta = daBottom - screenBottom;
            }
          }
        }
        if (scrollDelta == 0)
        {
          return false;
        }
        doScroll(direction == View.FOCUS_DOWN ? scrollDelta : -scrollDelta, 0);
      }
    }
    return true;
  }
 
  private void doScroll(int deltaX, int deltaY)
  {
    if (deltaX != 0 || deltaY != 0)
    {
      smoothScrollBy(deltaX, deltaY);
    }
  }
 
  public final void smoothScrollBy(int dx, int dy)
  {
    long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
    if (duration > ANIMATED_SCROLL_GAP)
    {
      mScroller.startScroll(getScrollX(), getScrollY(), dx, dy);
      awakenScrollBars(mScroller.getDuration());
      invalidate();
    }
    else
    {
      if (!mScroller.isFinished())
      {
        mScroller.abortAnimation();
      }
      scrollBy(dx, dy);
    }
    mLastScroll = AnimationUtils.currentAnimationTimeMillis();
  }
 
  public final void smoothScrollTo(int x, int y)
  {
    smoothScrollBy(x - getScrollX(), y - getScrollY());
  }
 
  @Override protected int computeVerticalScrollRange()
  {
    int count = getChildCount();
    return count == 0 ? getHeight() : (getChildAt(0)).getBottom();
  }
 
  @Override protected int computeHorizontalScrollRange()
  {
    int count = getChildCount();
    return count == 0 ? getWidth() : (getChildAt(0)).getRight();
  }
 
  @Override
  protected void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)
  {
    ViewGroup.LayoutParams lp = child.getLayoutParams();
    int childWidthMeasureSpec;
    int childHeightMeasureSpec;
 
    childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
                                                getPaddingLeft() + getPaddingRight(), lp.width);
    childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
 
    child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
  }
 
  @Override
  protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed,
                                         int parentHeightMeasureSpec, int heightUsed)
  {
    final MarginLayoutParams lp = (MarginLayoutParams)child.getLayoutParams();
    final int childWidthMeasureSpec =
        MeasureSpec.makeMeasureSpec(lp.leftMargin + lp.rightMargin, MeasureSpec.UNSPECIFIED);
    final int childHeightMeasureSpec =
        MeasureSpec.makeMeasureSpec(lp.topMargin + lp.bottomMargin, MeasureSpec.UNSPECIFIED);
 
    child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
  }
 
  @Override public void computeScroll()
  {
    if (mScroller.computeScrollOffset())
    {
      // This is called at drawing time by ViewGroup.  We don't want to
      // re-show the scrollbars at this point, which scrollTo will do,
      // so we replicate most of scrollTo here.
      //
      //         It's a little odd to call onScrollChanged from inside the drawing.
      //
      //         It is, except when you remember that computeScroll() is used to
      //         animate scrolling. So unless we want to defer the onScrollChanged()
      //         until the end of the animated scrolling, we don't really have a
      //         choice here.
      //
      //         I agree.  The alternative, which I think would be worse, is to post
      //         something and tell the subclasses later.  This is bad because there
      //         will be a window where mScrollX/Y is different from what the app
      //         thinks it is.
      //
      int oldX = getScrollX();
      int oldY = getScrollY();
      int x = mScroller.getCurrX();
      int y = mScroller.getCurrY();
      if (getChildCount() > 0)
      {
        View child = getChildAt(0);
        scrollTo(
            clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth()),
            clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(),
                  child.getHeight()));
      }
      else
      {
        scrollTo(x, y);
      }
      if (oldX != getScrollX() || oldY != getScrollY())
      {
        onScrollChanged(getScrollX(), getScrollY(), oldX, oldY);
      }
 
      // Keep on drawing until the animation has finished.
      postInvalidate();
    }
  }
 
  private void scrollToChild(View child)
  {
    child.getDrawingRect(mTempRect);
    /* Offset from child's local coordinates to TwoDScrollView coordinates */
    offsetDescendantRectToMyCoords(child, mTempRect);
    int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
    if (scrollDelta != 0)
    {
      scrollBy(0, scrollDelta);
    }
  }
 
  private boolean scrollToChildRect(Rect rect, boolean immediate)
  {
    final int delta = computeScrollDeltaToGetChildRectOnScreen(rect);
    final boolean scroll = delta != 0;
    if (scroll)
    {
      if (immediate)
      {
        scrollBy(0, delta);
      }
      else
      {
        smoothScrollBy(0, delta);
      }
    }
    return scroll;
  }
 
  protected int computeScrollDeltaToGetChildRectOnScreen(Rect rect)
  {
    if (getChildCount() == 0)
      return 0;
    int height = getHeight();
    int screenTop = getScrollY();
    int screenBottom = screenTop + height;
    int fadingEdge = getVerticalFadingEdgeLength();
    // leave room for top fading edge as long as rect isn't at very top
    if (rect.top > 0)
    {
      screenTop += fadingEdge;
    }
 
    // leave room for bottom fading edge as long as rect isn't at very bottom
    if (rect.bottom < getChildAt(0).getHeight())
    {
      screenBottom -= fadingEdge;
    }
    int scrollYDelta = 0;
    if (rect.bottom > screenBottom && rect.top > screenTop)
    {
      // need to move down to get it in view: move down just enough so
      // that the entire rectangle is in view (or at least the first
      // screen size chunk).
      if (rect.height() > height)
      {
        // just enough to get screen size chunk on
        scrollYDelta += (rect.top - screenTop);
      }
      else
      {
        // get entire rect at bottom of screen
        scrollYDelta += (rect.bottom - screenBottom);
      }
 
      // make sure we aren't scrolling beyond the end of our content
      int bottom = getChildAt(0).getBottom();
      int distanceToBottom = bottom - screenBottom;
      scrollYDelta = Math.min(scrollYDelta, distanceToBottom);
    }
    else if (rect.top < screenTop && rect.bottom < screenBottom)
    {
      // need to move up to get it in view: move up just enough so that
      // entire rectangle is in view (or at least the first screen
      // size chunk of it).
 
      if (rect.height() > height)
      {
        // screen size chunk
        scrollYDelta -= (screenBottom - rect.bottom);
      }
      else
      {
        // entire rect at top
        scrollYDelta -= (screenTop - rect.top);
      }
 
      // make sure we aren't scrolling any further than the top our content
      scrollYDelta = Math.max(scrollYDelta, -getScrollY());
    }
    return scrollYDelta;
  }
 
  @Override public void requestChildFocus(View child, View focused)
  {
    if (!mTwoDScrollViewMovedFocus)
    {
      if (!mIsLayoutDirty)
      {
        scrollToChild(focused);
      }
      else
      {
        // The child may not be laid out yet, we can't compute the scroll yet
        mChildToScrollTo = focused;
      }
    }
    super.requestChildFocus(child, focused);
  }
 
  @Override
  protected boolean onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect)
  {
    // convert from forward / backward notation to up / down / left / right
    // (ugh).
    if (direction == View.FOCUS_FORWARD)
    {
      direction = View.FOCUS_DOWN;
    }
    else if (direction == View.FOCUS_BACKWARD)
    {
      direction = View.FOCUS_UP;
    }
 
    final View nextFocus = previouslyFocusedRect == null
                               ? FocusFinder.getInstance().findNextFocus(this, null, direction)
                               : FocusFinder.getInstance().findNextFocusFromRect(
                                     this, previouslyFocusedRect, direction);
 
    if (nextFocus == null)
    {
      return false;
    }
 
    return nextFocus.requestFocus(direction, previouslyFocusedRect);
  }
 
  @Override
  public boolean requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate)
  {
    // offset into coordinate space of this scroll view
    rectangle.offset(child.getLeft() - child.getScrollX(), child.getTop() - child.getScrollY());
    return scrollToChildRect(rectangle, immediate);
  }
 
  @Override public void requestLayout()
  {
    mIsLayoutDirty = true;
    super.requestLayout();
  }
 
  @Override protected void onLayout(boolean changed, int l, int t, int r, int b)
  {
    super.onLayout(changed, l, t, r, b);
    mIsLayoutDirty = false;
    // Give a child focus if it needs it
    if (mChildToScrollTo != null && isViewDescendantOf(mChildToScrollTo, this))
    {
      scrollToChild(mChildToScrollTo);
    }
    mChildToScrollTo = null;
 
    // Calling this with the present values causes it to re-clam them
    scrollTo(getScrollX(), getScrollY());
  }
 
  @Override protected void onSizeChanged(int w, int h, int oldw, int oldh)
  {
    super.onSizeChanged(w, h, oldw, oldh);
 
    View currentFocused = findFocus();
    if (null == currentFocused || this == currentFocused)
      return;
 
    // If the currently-focused view was visible on the screen when the
    // screen was at the old height, then scroll the screen to make that
    // view visible with the new screen height.
    currentFocused.getDrawingRect(mTempRect);
    offsetDescendantRectToMyCoords(currentFocused, mTempRect);
    int scrollDeltaX = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
    int scrollDeltaY = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
    doScroll(scrollDeltaX, scrollDeltaY);
  }
 
  private boolean isViewDescendantOf(View child, View parent)
  {
    if (child == parent)
    {
      return true;
    }
 
    final ViewParent theParent = child.getParent();
    return (theParent instanceof ViewGroup) && isViewDescendantOf((View)theParent, parent);
  }
 
  public void fling(int velocityX, int velocityY)
  {
    if (getChildCount() > 0)
    {
      int height = getHeight() - getPaddingBottom() - getPaddingTop();
      int bottom = getChildAt(0).getHeight();
      int width = getWidth() - getPaddingRight() - getPaddingLeft();
      int right = getChildAt(0).getWidth();
 
      mScroller.fling(getScrollX(), getScrollY(), velocityX, velocityY, 0, right - width, 0,
                      bottom - height);
 
      final boolean movingDown = velocityY > 0;
      final boolean movingRight = velocityX > 0;
 
      View newFocused = findFocusableViewInMyBounds(
          movingRight, mScroller.getFinalX(), movingDown, mScroller.getFinalY(), findFocus());
      if (newFocused == null)
      {
        newFocused = this;
      }
 
      if (newFocused != findFocus() &&
          newFocused.requestFocus(movingDown ? View.FOCUS_DOWN : View.FOCUS_UP))
      {
        mTwoDScrollViewMovedFocus = true;
        mTwoDScrollViewMovedFocus = false;
      }
 
      awakenScrollBars(mScroller.getDuration());
      invalidate();
    }
  }
 
  public void scrollTo(int x, int y)
  {
    // we rely on the fact the View.scrollBy calls scrollTo.
    if (getChildCount() > 0)
    {
      View child = getChildAt(0);
      x = clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth());
      y = clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(), child.getHeight());
      if (x != getScrollX() || y != getScrollY())
      {
        super.scrollTo(x, y);
      }
    }
  }
 
  private int clamp(int n, int my, int child)
  {
    if (my >= child || n < 0)
    {
      /* my >= child is this case:
       *                    |--------------- me ---------------|
       *     |------ child ------|
       * or
       *     |--------------- me ---------------|
       *            |------ child ------|
       * or
       *     |--------------- me ---------------|
       *                                  |------ child ------|
       *
       * n < 0 is this case:
       *     |------ me ------|
       *                    |-------- child --------|
       *     |-- mScrollX --|
       */
      return 0;
    }
    if ((my + n) > child)
    {
      /* this case:
       *                    |------ me ------|
       *     |------ child ------|
       *     |-- mScrollX --|
       */
      return child - my;
    }
    return n;
  }
 
  public void setScrollViewListener(ScrollView2DListener scrollViewListener)
  {
    this.scrollView2DListener = scrollViewListener;
  }
 
  @Override protected void onScrollChanged(int x, int y, int oldx, int oldy)
  {
    super.onScrollChanged(x, y, oldx, oldy);
    if (scrollView2DListener != null)
    {
      scrollView2DListener.onScrollChanged(this, x, y, oldx, oldy);
    }
  }
 
  // interface to receive notifications when the view is scrolled
  public interface ScrollView2DListener {
    abstract void onScrollChanged(ScrollView2D scrollView, int x, int y, int oldx, int oldy);
  }
}