贴上一个我自己用过的阻尼滑动的ScrollView，像QQ里面那种滑动效果，尽管不是我写的，可是我认为还能够，贴出来做个记录，实用到的时候免得到处去找。
代码例如以下：
/*
* 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.
*/
import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.FocusFinder;
import android.view.KeyEvent;
import android.view.LayoutInflater;
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.view.animation.OvershootInterpolator;
import android.widget.FrameLayout;
import android.widget.Scroller;
import android.view.View.OnTouchListener;
import java.lang.reflect.Field;
import java.util.List;
/**
* Layout container for a view hierarchy that can be scrolled by the user,
* allowing it to be larger than the physical display. A ScrollView is a
* {@link FrameLayout}, meaning you should place one child in it containing the
* entire contents to scroll; this child may itself be a layout manager with a
* complex hierarchy of objects. A child that is often used is a
* {@link LinearLayout} in a vertical orientation, presenting a vertical array
* of top-level items that the user can scroll through.
*
* <p>
* The {@link TextView} class also takes care of its own scrolling, so does not
* require a ScrollView, but using the two together is possible to achieve the
* effect of a text view within a larger container.
*
* <p>
* ScrollView only supports vertical scrolling.
*/
public class OverScrollView extends FrameLayout implements OnTouchListener
{
private static final String TAG = OverScrollView.class.getName();
static final int ANIMATED_SCROLL_GAP = 250;
static final float MAX_SCROLL_FACTOR = 0.5f;
private static final float SCROLL_RATIO = 0.3f;// 阻尼系数
static final float OVERSHOOT_TENSION = 0.75f;
private long mLastScroll;
private final Rect mTempRect = new Rect();
private Scroller mScroller;
protected Context mContext;
Field mScrollYField;
Field mScrollXField;
boolean hasFailedObtainingScrollFields;
int prevScrollY;
boolean isInFlingMode = false;
DisplayMetrics metrics;
LayoutInflater inflater;
protected View child;
private Runnable overScrollerSpringbackTask;
/**
* Flag to indicate that we are moving focus ourselves. This is so the code
* that watches for focus changes initiated outside this ScrollView knows
* that it does not have to do anything.
*/
private boolean mScrollViewMovedFocus;
/**
* Position of the last motion event.
*/
private float mLastMotionY;
/**
* True when the layout has changed but the traversal has not come through
* yet. Ideally the view hierarchy would keep track of this for us.
*/
private boolean mIsLayoutDirty = true;
/**
* The child to give focus to in the event that a child has requested focus
* while the layout is dirty. This prevents the scroll from being wrong if
* the child has not been laid out before requesting focus.
*/
private View mChildToScrollTo = null;
/**
* True if the user is currently dragging this ScrollView around. This is
* not the same as 'is being flinged', which can be checked by
* mScroller.isFinished() (flinging begins when the user lifts his finger).
*/
private boolean mIsBeingDragged = false;
/**
* Determines speed during touch scrolling
*/
private VelocityTracker mVelocityTracker;
/**
* When set to true, the scroll view measure its child to make it fill the
* currently visible area.
*/
private boolean mFillViewport;
/**
* Whether arrow scrolling is animated.
*/
private boolean mSmoothScrollingEnabled = true;
private int mTouchSlop;
private int mMinimumVelocity;
private int mMaximumVelocity;
/**
* ID of the active pointer. This is used to retain consistency during
* drags/flings if multiple pointers are used.
*/
private int mActivePointerId = INVALID_POINTER;
/**
* Sentinel value for no current active pointer. Used by
* {@link #mActivePointerId}.
*/
private static final int INVALID_POINTER = -1;
public OverScrollView(Context context)
{
this(context, null);
mContext = context;
initBounce();
}
public OverScrollView(Context context, AttributeSet attrs)
{
this(context, attrs, 0);
mContext = context;
initBounce();
}
public OverScrollView(Context context, AttributeSet attrs, int defStyle)
{
super(context, attrs, defStyle);
mContext = context;
initScrollView();
setFillViewport(true);
initBounce();
}
private void initBounce()
{
metrics = this.mContext.getResources().getDisplayMetrics();
// init the bouncy scroller, and make sure the layout is being drawn
// after the top padding
mScroller = new Scroller(getContext(), new OvershootInterpolator(OVERSHOOT_TENSION));
overScrollerSpringbackTask = new Runnable()
{
@Override
public void run()
{
// scroll till after the padding
mScroller.computeScrollOffset();
scrollTo(0, mScroller.getCurrY());
if (!mScroller.isFinished())
{
post(this);
}
}
};
prevScrollY = getPaddingTop();
try
{
mScrollXField = View.class.getDeclaredField("mScrollX");
mScrollYField = View.class.getDeclaredField("mScrollY");
} catch (Exception e)
{
hasFailedObtainingScrollFields = true;
}
}
private void SetScrollY(int value)
{
if (mScrollYField != null)
{
try
{
mScrollYField.setInt(this, value);
} catch (Exception e)
{
}
}
}
private void SetScrollX(int value)
{
if (mScrollXField != null)
{
try
{
mScrollXField.setInt(this, value);
} catch (Exception e)
{
}
}
}
public void initChildPointer()
{
Log.i(TAG,"initChildPointer");
child = getChildAt(0);
child.setPadding(0, 1500, 0, 1500);
}
@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;
}
/**
* @return The maximum amount this scroll view will scroll in response to an
* arrow event.
*/
public int getMaxScrollAmount()
{
return (int) (MAX_SCROLL_FACTOR * (getBottom() - getTop()));
}
private void initScrollView()
{
mScroller = new Scroller(getContext());
setFocusable(true);
setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
setWillNotDraw(false);
final ViewConfiguration configuration = ViewConfiguration.get(mContext);
mTouchSlop = configuration.getScaledTouchSlop();
mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
setOnTouchListener(this);
post(new Runnable()
{
public void run()
{
scrollTo(0, child.getPaddingTop());
}
});
}
@Override
public void addView(View child)
{
if (getChildCount() > 0)
{
throw new IllegalStateException("ScrollView can host only one direct child");
}
super.addView(child);
initChildPointer();
}
@Override
public void addView(View child, int index)
{
if (getChildCount() > 0)
{
throw new IllegalStateException("ScrollView can host only one direct child");
}
super.addView(child, index);
initChildPointer();
}
@Override
public void addView(View child, ViewGroup.LayoutParams params)
{
if (getChildCount() > 0)
{
throw new IllegalStateException("ScrollView can host only one direct child");
}
super.addView(child, params);
initChildPointer();
}
@Override
public void addView(View child, int index, ViewGroup.LayoutParams params)
{
if (getChildCount() > 0)
{
throw new IllegalStateException("ScrollView can host only one direct child");
}
super.addView(child, index, params);
}
/**
* @return Returns true this ScrollView can be scrolled
*/
private boolean canScroll()
{
View child = getChildAt(0);
if (child != null)
{
int childHeight = child.getHeight();
return getHeight() < childHeight + getPaddingTop() + getPaddingBottom();
}
return false;
}
/**
* Indicates whether this ScrollView's content is stretched to fill the
* viewport.
*
* @return True if the content fills the viewport, false otherwise.
*/
public boolean isFillViewport()
{
return mFillViewport;
}
/**
* Indicates this ScrollView whether it should stretch its content height to
* fill the viewport or not.
*
* @param fillViewport
* True to stretch the content's height to the viewport's
* boundaries, false otherwise.
*/
public void setFillViewport(boolean fillViewport)
{
if (fillViewport != mFillViewport)
{
mFillViewport = fillViewport;
requestLayout();
}
}
/**
* @return Whether arrow scrolling will animate its transition.
*/
public boolean isSmoothScrollingEnabled()
{
return mSmoothScrollingEnabled;
}
/**
* Set whether arrow scrolling will animate its transition.
*
* @param smoothScrollingEnabled
* whether arrow scrolling will animate its transition
*/
public void setSmoothScrollingEnabled(boolean smoothScrollingEnabled)
{
mSmoothScrollingEnabled = smoothScrollingEnabled;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
{
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (!mFillViewport)
{
return;
}
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
if (heightMode == MeasureSpec.UNSPECIFIED)
{
return;
}
if (getChildCount() > 0)
{
final View child = getChildAt(0);
int height = getMeasuredHeight();
if (child.getMeasuredHeight() < height)
{
final FrameLayout.LayoutParams lp = (LayoutParams) child.getLayoutParams();
int childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec, getPaddingLeft() + getPaddingRight(), lp.width);
height -= getPaddingTop();
height -= getPaddingBottom();
int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
}
}
@Override
public boolean dispatchKeyEvent(KeyEvent event)
{
// Let the focused view and/or our descendants get the key first
return super.dispatchKeyEvent(event) || executeKeyEvent(event);
}
/**
* You can call this function yourself to have the scroll view perform
* scrolling from a key event, just as if the event had been dispatched to
* it by the view hierarchy.
*
* @param event
* The key event to execute.
* @return Return true if the event was handled, else false.
*/
public boolean executeKeyEvent(KeyEvent event)
{
mTempRect.setEmpty();
if (!canScroll())
{
if (isFocused() && event.getKeyCode() != KeyEvent.KEYCODE_BACK)
{
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);
} else
{
handled = fullScroll(View.FOCUS_UP);
}
break;
case KeyEvent.KEYCODE_DPAD_DOWN:
if (!event.isAltPressed())
{
handled = arrowScroll(View.FOCUS_DOWN);
} else
{
handled = fullScroll(View.FOCUS_DOWN);
}
break;
case KeyEvent.KEYCODE_SPACE:
pageScroll(event.isShiftPressed() ? View.FOCUS_UP : View.FOCUS_DOWN);
break;
}
}
return handled;
}
public boolean inChild(int x, int y)
{
if (getChildCount() > 0)
{
final int scrollY = getScrollY();
final View child = getChildAt(0);
return !(y < child.getTop() - scrollY || y >= child.getBottom() - scrollY || x < child.getLeft() || x >= child.getRight());
}
return false;
}
@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;
}
switch (action & MotionEvent.ACTION_MASK)
{
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 activePointerId = mActivePointerId;
if (activePointerId == INVALID_POINTER)
{
// If we don't have a valid id, the touch down wasn't on
// content.
break;
}
final int pointerIndex = ev.findPointerIndex(activePointerId);
final float y = ev.getY(pointerIndex);
final int yDiff = (int) Math.abs(y - mLastMotionY);
if (yDiff > mTouchSlop)
{
mIsBeingDragged = true;
mLastMotionY = y;
}
break;
}
case MotionEvent.ACTION_DOWN:
{
final float y = ev.getY();
if (!inChild((int) ev.getX(), (int) y))
{
mIsBeingDragged = false;
break;
}
/*
* Remember location of down touch. ACTION_DOWN always refers to
* pointer index 0.
*/
mLastMotionY = y;
mActivePointerId = ev.getPointerId(0);
/*
* 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;
mActivePointerId = INVALID_POINTER;
break;
case MotionEvent.ACTION_POINTER_UP:
onSecondaryPointerUp(ev);
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 (mVelocityTracker == null)
{
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
final int action = ev.getAction();
switch (action & MotionEvent.ACTION_MASK)
{
case MotionEvent.ACTION_DOWN:
{
final float y = ev.getY();
if (!(mIsBeingDragged = inChild((int) ev.getX(), (int) y)))
{
return false;
}
/*
* 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;
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE:
if (mIsBeingDragged)
{
// Scroll to follow the motion event
final int activePointerIndex = ev.findPointerIndex(mActivePointerId);
final float y = ev.getY(activePointerIndex);
final int deltaY = (int) (mLastMotionY - y);
mLastMotionY = y;
if (isOverScrolled())
{
// when overscrolling, move the scroller just half of the
// finger movement, to make it feel like a spring...
scrollBy(0,(int)(deltaY * SCROLL_RATIO));
} else
{
scrollBy(0, deltaY);
}
}
break;
case MotionEvent.ACTION_UP:
if (mIsBeingDragged)
{
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialVelocity = (int) velocityTracker.getYVelocity(mActivePointerId);
if (getChildCount() > 0 && Math.abs(initialVelocity) > mMinimumVelocity)
{
fling(-initialVelocity);
}
mActivePointerId = INVALID_POINTER;
mIsBeingDragged = false;
if (mVelocityTracker != null)
{
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
break;
case MotionEvent.ACTION_CANCEL:
if (mIsBeingDragged && getChildCount() > 0)
{
mActivePointerId = INVALID_POINTER;
mIsBeingDragged = false;
if (mVelocityTracker != null)
{
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
break;
case MotionEvent.ACTION_POINTER_UP:
onSecondaryPointerUp(ev);
break;
}
return true;
}
public boolean isOverScrolled()
{
return (getScrollY() < child.getPaddingTop() || getScrollY() > child.getBottom() - child.getPaddingBottom() - getHeight());
}
private void onSecondaryPointerUp(MotionEvent ev)
{
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId)
{
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
// TODO: Make this decision more intelligent.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastMotionY = ev.getY(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
if (mVelocityTracker != null)
{
mVelocityTracker.clear();
}
}
}
/**
* <p>
* Finds the next focusable component that fits in this View's bounds
* (excluding fading edges) pretending that this View's top is located at
* the parameter top.
* </p>
*
* @param topFocus
* look for a candidate is the one at the top of the bounds if
* topFocus is true, or at the bottom of the bounds if topFocus
* is false
* @param top
* the top offset of the bounds in which a focusable must be
* found (the fading edge is assumed to start at this position)
* @param preferredFocusable
* the View that has highest priority and will be returned if it
* is within my bounds (null is valid)
* @return the next focusable component in the bounds or null if none can be
* found
*/
private View findFocusableViewInMyBounds(final boolean topFocus, final int top, 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 fadingEdgeLength = getVerticalFadingEdgeLength() / 2;
final int topWithoutFadingEdge = top + fadingEdgeLength;
final int bottomWithoutFadingEdge = top + getHeight() - fadingEdgeLength;
if ((preferredFocusable != null) && (preferredFocusable.getTop() < bottomWithoutFadingEdge)
&& (preferredFocusable.getBottom() > topWithoutFadingEdge))
{
return preferredFocusable;
}
return findFocusableViewInBounds(topFocus, topWithoutFadingEdge, bottomWithoutFadingEdge);
}
/**
* <p>
* Finds the next focusable component that fits in the specified bounds.
* </p>
*
* @param topFocus
* look for a candidate is the one at the top of the bounds if
* topFocus is true, or at the bottom of the bounds if topFocus
* is false
* @param top
* the top offset of the bounds in which a focusable must be
* found
* @param bottom
* the bottom offset of the bounds in which a focusable must be
* found
* @return the next focusable component in the bounds or null if none can be
* found
*/
private View findFocusableViewInBounds(boolean topFocus, int top, int bottom)
{
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();
if (top < viewBottom && viewTop < bottom)
{
/*
* the focusable is in the target area, it is a candidate for
* focusing
*/
final boolean viewIsFullyContained = (top < viewTop) && (viewBottom < bottom);
if (focusCandidate == null)
{
/* No candidate, take this one */
focusCandidate = view;
foundFullyContainedFocusable = viewIsFullyContained;
} else
{
final boolean viewIsCloserToBoundary = (topFocus && viewTop < focusCandidate.getTop())
|| (!topFocus && viewBottom > focusCandidate.getBottom());
if (foundFullyContainedFocusable)
{
if (viewIsFullyContained && viewIsCloserToBoundary)
{
/*
* 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 (viewIsCloserToBoundary)
{
/*
* Partially contained view beats another partially
* contained view if it's closer
*/
focusCandidate = view;
}
}
}
}
}
return focusCandidate;
}
/**
* <p>
* Handles scrolling in response to a "page up/down" shortcut press. This
* method will scroll the view by one page up or down and give the focus to
* the topmost/bottommost component in the new visible area. If no component
* is a good candidate for focus, this scrollview reclaims the focus.
* </p>
*
* @param direction
* the scroll direction: {@link android.view.View#FOCUS_UP} to go
* one page up or {@link android.view.View#FOCUS_DOWN} to go one
* page down
* @return true if the key event is consumed by this method, false otherwise
*/
public boolean pageScroll(int direction)
{
boolean down = direction == View.FOCUS_DOWN;
int height = getHeight();
if (down)
{
mTempRect.top = getScrollY() + height;
int count = getChildCount();
if (count > 0)
{
View view = getChildAt(count - 1);
if (mTempRect.top + height > view.getBottom())
{
mTempRect.top = view.getBottom() - height;
}
}
} else
{
mTempRect.top = getScrollY() - height;
if (mTempRect.top < 0)
{
mTempRect.top = 0;
}
}
mTempRect.bottom = mTempRect.top + height;
return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom);
}
/**
* <p>
* Handles scrolling in response to a "home/end" shortcut press. This method
* will scroll the view to the top or bottom and give the focus to the
* topmost/bottommost component in the new visible area. If no component is
* a good candidate for focus, this scrollview reclaims the focus.
* </p>
*
* @param direction
* the scroll direction: {@link android.view.View#FOCUS_UP} to go
* the top of the view or {@link android.view.View#FOCUS_DOWN} to
* go the bottom
* @return true if the key event is consumed by this method, false otherwise
*/
public boolean fullScroll(int direction)
{
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);
}
/**
* <p>
* Scrolls the view to make the area defined by <code>top</code> and
* <code>bottom</code> visible. This method attempts to give the focus to a
* component visible in this area. If no component can be focused in the new
* visible area, the focus is reclaimed by this scrollview.
* </p>
*
* @param direction
* the scroll direction: {@link android.view.View#FOCUS_UP} to go
* upward {@link android.view.View#FOCUS_DOWN} to downward
* @param top
* the top offset of the new area to be made visible
* @param bottom
* the bottom offset of the new area to be made visible
* @return true if the key event is consumed by this method, false otherwise
*/
private boolean scrollAndFocus(int direction, int top, int bottom)
{
boolean handled = true;
int height = getHeight();
int containerTop = getScrollY();
int containerBottom = containerTop + height;
boolean up = direction == View.FOCUS_UP;
View newFocused = findFocusableViewInBounds(up, top, bottom);
if (newFocused == null)
{
newFocused = this;
}
if (top >= containerTop && bottom <= containerBottom)
{
handled = false;
} else
{
int delta = up ?
(top - containerTop) : (bottom - containerBottom);
doScrollY(delta);
}
if (newFocused != findFocus() && newFocused.requestFocus(direction))
{
mScrollViewMovedFocus = true;
mScrollViewMovedFocus = false;
}
return handled;
}
/**
* Handle scrolling in response to an up or down arrow click.
*
* @param direction
* The direction corresponding to the arrow key that was pressed
* @return True if we consumed the event, false otherwise
*/
public boolean arrowScroll(int direction)
{
View currentFocused = findFocus();
if (currentFocused == this)
currentFocused = null;
View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);
final int maxJump = getMaxScrollAmount();
if (nextFocused != null && isWithinDeltaOfScreen(nextFocused, maxJump, getHeight()))
{
nextFocused.getDrawingRect(mTempRect);
offsetDescendantRectToMyCoords(nextFocused, mTempRect);
int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
doScrollY(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;
}
doScrollY(direction == View.FOCUS_DOWN ?
scrollDelta : -scrollDelta);
}
if (currentFocused != null && currentFocused.isFocused() && isOffScreen(currentFocused))
{
// previously focused item still has focus and is off screen, give
// it up (take it back to ourselves)
// (also, need to temporarily force FOCUS_BEFORE_DESCENDANTS so we
// are
// sure to
// get it)
final int descendantFocusability = getDescendantFocusability(); // save
setDescendantFocusability(ViewGroup.FOCUS_BEFORE_DESCENDANTS);
requestFocus();
setDescendantFocusability(descendantFocusability); // restore
}
return true;
}
/**
* @return whether the descendant of this scroll view is scrolled off
* screen.
*/
private boolean isOffScreen(View descendant)
{
return !isWithinDeltaOfScreen(descendant, 0, getHeight());
}
/**
* @return whether the descendant of this scroll view is within delta pixels
* of being on the screen.
*/
private boolean isWithinDeltaOfScreen(View descendant, int delta, int height)
{
descendant.getDrawingRect(mTempRect);
offsetDescendantRectToMyCoords(descendant, mTempRect);
return (mTempRect.bottom + delta) >= getScrollY() && (mTempRect.top - delta) <= (getScrollY() + height);
}
/**
* Smooth scroll by a Y delta
*
* @param delta
* the number of pixels to scroll by on the Y axis
*/
private void doScrollY(int delta)
{
if (delta != 0)
{
if (mSmoothScrollingEnabled)
{
smoothScrollBy(0, delta);
} else
{
scrollBy(0, delta);
}
}
}
/**
* Like {@link View#scrollBy}, but scroll smoothly instead of immediately.
*
* @param dx
* the number of pixels to scroll by on the X axis
* @param dy
* the number of pixels to scroll by on the Y axis
*/
public final void smoothScrollBy(int dx, int dy)
{
if (getChildCount() == 0)
{
// Nothing to do.
return;
}
long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
if (duration > ANIMATED_SCROLL_GAP)
{
final int height = getHeight() - getPaddingBottom() - getPaddingTop();
final int bottom = getChildAt(0).getHeight();
final int maxY = Math.max(0, bottom - height);
final int scrollY = getScrollY();
dy = Math.max(0, Math.min(scrollY + dy, maxY)) - scrollY;
mScroller.startScroll(getScrollX(), scrollY, 0, dy);
invalidate();
} else
{
if (!mScroller.isFinished())
{
mScroller.abortAnimation();
}
scrollBy(dx, dy);
}
mLastScroll = AnimationUtils.currentAnimationTimeMillis();
}
public final void smoothScrollToTop()
{
smoothScrollTo(0, child.getPaddingTop());
}
public final void smoothScrollToBottom()
{
smoothScrollTo(0, child.getHeight() - child.getPaddingTop() - getHeight());
}
/**
* Like {@link #scrollTo}, but scroll smoothly instead of immediately.
*
* @param x
* the position where to scroll on the X axis
* @param y
* the position where to scroll on the Y axis
*/
public final void smoothScrollTo(int x, int y)
{
smoothScrollBy(x - getScrollX(), y - getScrollY());
}
/**
* <p>
* The scroll range of a scroll view is the overall height of all of its
* children.
* </p>
*/
@Override
protected int computeVerticalScrollRange()
{
final int count = getChildCount();
final int contentHeight = getHeight() - getPaddingBottom() - getPaddingTop();
if (count == 0)
{
return contentHeight;
}
return getChildAt(0).getBottom();
}
@Override
protected int computeVerticalScrollOffset()
{
return Math.max(0, super.computeVerticalScrollOffset());
}
@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 = getChildMeasureSpec(parentWidthMeasureSpec, getPaddingLeft() + getPaddingRight() + lp.leftMargin
+ lp.rightMargin + widthUsed, lp.width);
final int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(lp.topMargin + lp.bottomMargin, MeasureSpec.UNSPECIFIED);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
@Override
public void computeScroll()
{
// If android implementation has changed and we cannot obtain mScrollY -
// The default behavior will be applied by the parent.
if (hasFailedObtainingScrollFields)
{
super.computeScroll();
return;
}
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 getScrollX()/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);
x = clamp(x, getWidth() - getPaddingRight() - getPaddingLeft(), child.getWidth());
y = clamp(y, getHeight() - getPaddingBottom() - getPaddingTop(), child.getHeight());
if (x != oldX || y != oldY)
{
SetScrollX(x);
// mScrollX = x;
SetScrollY(y);
// mScrollY = y;
onScrollChanged(x, y, oldX, oldY);
}
}
awakenScrollBars();
// Keep on drawing until the animation has finished.
postInvalidate();
}
}
/**
* Scrolls the view to the given child.
*
* @param child
* the View to scroll to
*/
private void scrollToChild(View child)
{
child.getDrawingRect(mTempRect);
/* Offset from child's local coordinates to ScrollView coordinates */
offsetDescendantRectToMyCoords(child, mTempRect);
int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
if (scrollDelta != 0)
{
scrollBy(0, scrollDelta);
}
}
/**
* If rect is off screen, scroll just enough to get it (or at least the
* first screen size chunk of it) on screen.
*
* @param rect
* The rectangle.
* @param immediate
* True to scroll immediately without animation
* @return true if scrolling was performed
*/
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;
}
/**
* Compute the amount to scroll in the Y direction in order to get a
* rectangle completely on the screen (or, if taller than the screen, at
* least the first screen size chunk of it).
*
* @param rect
* The rect.
* @return The scroll delta.
*/
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 (!mScrollViewMovedFocus)
{
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);
}
/**
* When looking for focus in children of a scroll view, need to be a little
* more careful not to give focus to something that is scrolled off screen.
*
* This is more expensive than the default {@link android.view.ViewGroup}
* implementation, otherwise this behavior might have been made the default.
*/
@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;
}
if (isOffScreen(nextFocus))
{
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());
post(new Runnable()
{
public void run()
{
scrollTo(0, child.getPaddingTop());
}
});
}
@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.
if (isWithinDeltaOfScreen(currentFocused, 0, oldh))
{
currentFocused.getDrawingRect(mTempRect);
offsetDescendantRectToMyCoords(currentFocused, mTempRect);
int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
doScrollY(scrollDelta);
}
}
@Override
protected void onScrollChanged(int leftOfVisibleView, int topOfVisibleView, int oldLeftOfVisibleView, int oldTopOfVisibleView)
{
int displayHeight = getHeight();
int paddingTop = child.getPaddingTop();
int contentBottom = child.getHeight() - child.getPaddingBottom();
if (isInFlingMode)
{
if (topOfVisibleView < paddingTop || topOfVisibleView > contentBottom - displayHeight)
{
if (topOfVisibleView < paddingTop)
{
mScroller.startScroll(0, topOfVisibleView, 0, paddingTop - topOfVisibleView, 1000);
} else if (topOfVisibleView > contentBottom - displayHeight)
{
mScroller.startScroll(0, topOfVisibleView, 0, contentBottom - displayHeight - topOfVisibleView, 1000);
}
// Start animation.
post(overScrollerSpringbackTask);
isInFlingMode = false;
return;
}
}
super.onScrollChanged(leftOfVisibleView, topOfVisibleView, oldLeftOfVisibleView, oldTopOfVisibleView);
}
/**
* Return true if child is an descendant of parent, (or equal to the
* parent).
*/
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);
}
/**
* Fling the scroll view
*
* @param velocityY
* The initial velocity in the Y direction. Positive numbers mean
* that the finger/cursor is moving down the screen, which means
* we want to scroll towards the top.
*/
public void fling(int velocityY)
{
if (getChildCount() > 0)
{
int height = getHeight() - getPaddingBottom() - getPaddingTop();
int bottom = getChildAt(0).getHeight();
mScroller.fling(getScrollX(), getScrollY(), 0, velocityY, 0, 0, 0, Math.max(0, bottom - height));
final boolean movingDown = velocityY > 0;
View newFocused = findFocusableViewInMyBounds(movingDown, mScroller.getFinalY(), findFocus());
if (newFocused == null)
{
newFocused = this;
}
if (newFocused != findFocus() && newFocused.requestFocus(movingDown ? View.FOCUS_DOWN : View.FOCUS_UP))
{
mScrollViewMovedFocus = true;
mScrollViewMovedFocus = false;
}
invalidate();
}
}
/**
* {@inheritDoc}
*
* <p>
* This version also clamps the scrolling to the bounds of our child.
*/
@Override
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 --------|
* |-- getScrollX() --|
*/
return 0;
}
if ((my + n) > child)
{
/*
* this case: |------ me ------| |------ child ------| |--
* getScrollX() --|
*/
return child - my;
}
return n;
}
@Override
public boolean onTouch(View v, MotionEvent event)
{
// Stop scrolling calculation.
mScroller.forceFinished(true);
// Stop scrolling animation.
removeCallbacks(overScrollerSpringbackTask);
if (event.getAction() == MotionEvent.ACTION_UP)
{
return overScrollView();
}
else if (event.getAction() == MotionEvent.ACTION_CANCEL)
{
return overScrollView();
}
return false;
}
private boolean overScrollView()
{
// The height of scroll view, in pixels
int displayHeight = getHeight();
Log.i(TAG , "displayHeight = "+displayHeight);
// The top of content view, in pixels.
int contentTop = child.getPaddingTop();
// The top of content view, in pixels.
int contentBottom = child.getHeight() - child.getPaddingBottom();
// The scrolled top position of scroll view, in pixels.
int currScrollY = getScrollY();
Log.i(TAG , "currScrollY = "+currScrollY);
Log.i(TAG , "contentTop = "+contentTop);
int scrollBy;
// Scroll to content top
if (currScrollY < contentTop)
{
onOverScroll(currScrollY);
scrollBy = contentTop - currScrollY;
} else if (currScrollY + displayHeight > contentBottom)
{
// Scroll to content top
if (child.getHeight() - child.getPaddingTop() - child.getPaddingBottom() < displayHeight)
{
scrollBy = contentTop - currScrollY;
}
// Scroll to content bottom
else
{
scrollBy = contentBottom - displayHeight - currScrollY;
// Log.d(Definitions.LOG_TAG, "scrollBy=" + scrollBy);
}
// fire onOverScroll event, and update scrollBy if a loadingView has
// been added to the scroller.
scrollBy += onOverScroll(currScrollY);
}
// scrolling between the contentTop and contentBottom
else
{
isInFlingMode = true;
return false;
}
mScroller.startScroll(0, currScrollY, 0, scrollBy, 500);
// Start animation.
post(overScrollerSpringbackTask);
prevScrollY = currScrollY;
// consume(to stop fling)
return true;
}
protected int onOverScroll(int scrollY)
{
return 0;
}
}
拿去能够直接用哟