Android实现越界回弹效果

public class DampingReboundLayout extends ViewGroup implements NestedScrollingParent3,
        NestedScrollingParent2, NestedScrollingChild3, NestedScrollingChild2, NestedScrollingParent,
        NestedScrollingChild {
 
    private static final float DECELERATE_INTERPOLATION_FACTOR = 2f;
    private float DRAG_RATE = .35f;
    private ValueAnimator valueAnimator;
 
    public void setDragRate(int dragRate) {
        this.DRAG_RATE = dragRate;
    }
 
 
    // Default offset in dips from the top of the view to where the progress spinner should stop
    private static final int DEFAULT_CIRCLE_TARGET = 200;
 
    private View mTarget; // the target of the gesture
 
    // If nested scrolling is enabled, the total amount that needed to be
    // consumed by this as the nested scrolling parent is used in place of the
    // overscroll determined by MOVE events in the onTouch handler
    private float mTotalUnconsumed;
    private final NestedScrollingParentHelper mNestedScrollingParentHelper;
    private final NestedScrollingChildHelper mNestedScrollingChildHelper;
    private final int[] mParentScrollConsumed = new int[2];
    private final int[] mParentOffsetInWindow = new int[2];
 
    // Used for calls from old versions of onNestedScroll to v3 version of onNestedScroll. This only
    // exists to prevent GC costs that are present before API 21.
    private final int[] mNestedScrollingV2ConsumedCompat = new int[2];
    private boolean mNestedScrollInProgress;
 
 
    private float mInitialScroll;
 
    // damping rebound orientation
    //  0: horizontal
    //  1: vertical
    private int dampingReboundOrientation = LinearLayoutCompat.HORIZONTAL;
 
    public void setOrientation(@LinearLayoutCompat.OrientationMode int orientation) {
        dampingReboundOrientation = orientation;
    }
 
    // Target is returning to its start offset because it was cancelled or a
    // refresh was triggered.
    private final DecelerateInterpolator mDecelerateInterpolator;
    private static final int[] LAYOUT_ATTRS = new int[]{
            android.R.attr.enabled
    };
    private int mLinearLayoutViewIndex = -1;
 
 
    /**
     * @see #setLegacyRequestDisallowInterceptTouchEventEnabled
     */
    private boolean mEnableLegacyRequestDisallowInterceptTouch;
 
 
    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
    }
 
 
    /**
     * Simple constructor to use when creating a SwipeRefreshLayout from code.
     *
     * @param context
     */
    public DampingReboundLayout(@NonNull Context context) {
        this(context, null);
    }
 
    /**
     * Constructor that is called when inflating SwipeRefreshLayout from XML.
     *
     * @param context
     * @param attrs
     */
    public DampingReboundLayout(@NonNull Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }
 
    public DampingReboundLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
 
        setWillNotDraw(false);
        mDecelerateInterpolator = new DecelerateInterpolator(DECELERATE_INTERPOLATION_FACTOR);
 
        final DisplayMetrics metrics = getResources().getDisplayMetrics();
 
        setChildrenDrawingOrderEnabled(true);
        // the absolute offset has to take into account that the circle starts at an offset
        mNestedScrollingParentHelper = new NestedScrollingParentHelper(this);
 
        mNestedScrollingChildHelper = new NestedScrollingChildHelper(this);
        setNestedScrollingEnabled(true);
 
        final TypedArray a = context.obtainStyledAttributes(attrs, LAYOUT_ATTRS);
        setEnabled(a.getBoolean(0, true));
        a.recycle();
    }
 
    @Override
    protected int getChildDrawingOrder(int childCount, int i) {
        if (mLinearLayoutViewIndex < 0) {
            return i;
        } else if (i == childCount - 1) {
            // Draw the selected child last
            return mLinearLayoutViewIndex;
        } else if (i >= mLinearLayoutViewIndex) {
            // Move the children after the selected child earlier one
            return i + 1;
        } else {
            // Keep the children before the selected child the same
            return i;
        }
    }
 
 
    private void ensureTarget() {
        // Don't bother getting the parent height if the parent hasn't been laid
        // out yet.
        if (mTarget == null) {
            mTarget = getChildAt(0);
        }
    }
 
 
    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        final int width = getMeasuredWidth();
        final int height = getMeasuredHeight();
        if (getChildCount() == 0) {
            return;
        }
        if (mTarget == null) {
            ensureTarget();
        }
        if (mTarget == null) {
            return;
        }
        final View child = mTarget;
        final int childLeft = getPaddingLeft();
        final int childTop = getPaddingTop();
        final int childWidth = width - getPaddingLeft() - getPaddingRight();
        final int childHeight = height - getPaddingTop() - getPaddingBottom();
        child.layout(childLeft, childTop, childLeft + childWidth, childTop + childHeight);
    }
 
    @Override
    public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mTarget == null) {
            ensureTarget();
        }
        if (mTarget == null) {
            return;
        }
        mTarget.measure(MeasureSpec.makeMeasureSpec(
                getMeasuredWidth() - getPaddingLeft() - getPaddingRight(),
                MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(
                getMeasuredHeight() - getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY));
    }
 
    /**
     * @return Whether it is possible for the child view of this layout to
     * scroll up. Override this if the child view is a custom view.
     */
    public boolean canChildScrollUp() {
        if (mTarget instanceof ListView) {
            return ListViewCompat.canScrollList((ListView) mTarget, -1);
        }
        return dampingReboundOrientation == 1 ? mTarget.canScrollVertically(-1) : mTarget.canScrollHorizontally(-1);
    }
 
    public boolean canChildScrollDown() {
        if (mTarget instanceof ListView) {
            return ListViewCompat.canScrollList((ListView) mTarget, 1);
        }
        return dampingReboundOrientation == 1 ? mTarget.canScrollVertically(1) : mTarget.canScrollHorizontally(1);
    }
 
 
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        ensureTarget();
        final int action = ev.getActionMasked();
        int pointerIndex;
 
        if (!isEnabled() || canChildScrollUp() || canChildScrollDown() || mNestedScrollInProgress) {
            // Fail fast if we're not in a state where a swipe is possible
            return false;
        }
 
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                if (dampingReboundOrientation == 1) {
                    mInitialScroll = ev.getY();
                } else {
                    mInitialScroll = ev.getX();
                }
                break;
 
            case MotionEvent.ACTION_MOVE:
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                break;
            default:
        }
        return super.onInterceptTouchEvent(ev);
    }
 
    /**
     * Enables the legacy behavior of {@link #requestDisallowInterceptTouchEvent} from before
     * 1.1.0-alpha03, where the request is neither honored, nor propagated up to its parents,
     * in either of the following two cases:
     * <ul>
     *     <li>The child as an {@link AbsListView} and the runtime is API < 21</li>
     *     <li>The child has nested scrolling disabled</li>
     * </ul>
     * Use this method <em>only</em> if your application:
     * <ul>
     *     <li>is upgrading SwipeRefreshLayout from &lt; 1.1.1 to &gt;= 1.1.0-alpha03</li>
     *     <li>has a SwipeRefreshLayout, or its parent, that no longer responds to touch events
     *     when it should</li>
     *     <li>setting this method to {@code true} fixes that issue</li>
     * </ul>
     *
     * @param enabled {@code true} to enable the legacy behavior, {@code false} for default behavior
     * @deprecated Only use this method if the changes introduced in
     * {@link #requestDisallowInterceptTouchEvent} in version 1.1.0-alpha03 and 1.1.1
     * are breaking your application.
     */
    @Deprecated
    public void setLegacyRequestDisallowInterceptTouchEventEnabled(boolean enabled) {
        mEnableLegacyRequestDisallowInterceptTouch = enabled;
    }
 
    @Override
    public void requestDisallowInterceptTouchEvent(boolean b) {
        if (mEnableLegacyRequestDisallowInterceptTouch
                && ((android.os.Build.VERSION.SDK_INT < 21 && mTarget instanceof AbsListView)
                || (mTarget != null && !ViewCompat.isNestedScrollingEnabled(mTarget)))) {
            // Legacy behavior: if this is a List < L or another view that doesn't support
            // nested scrolling, ignore this request so that the vertical scroll event
            // isn't stolen
            return;
        }
        super.requestDisallowInterceptTouchEvent(b);
    }
 
    // NestedScrollingParent 3
 
    @Override
    public void onNestedScroll(@NonNull View target, int dxConsumed, int dyConsumed,
                               int dxUnconsumed, int dyUnconsumed, @ViewCompat.NestedScrollType int type,
                               @NonNull int[] consumed) {
        if (type != ViewCompat.TYPE_TOUCH) {
            return;
        }
 
        int consumedBeforeParents = dampingReboundOrientation == 1 ? consumed[1] : consumed[0];
        dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed,
                mParentOffsetInWindow, type, consumed);
        int consumedByParents = (dampingReboundOrientation == 1 ? consumed[1] : consumed[0]) - consumedBeforeParents;
        int unconsumedAfterParents = dampingReboundOrientation == 1 ? dyUnconsumed : dxUnconsumed - consumedByParents;
 
        // There are two reasons why scroll distance may be totally consumed.  1) All of the nested
        // scrolling parents up the hierarchy implement NestedScrolling3 and consumed all of the
        // distance or 2) at least 1 nested scrolling parent doesn't implement NestedScrolling3 and
        // for comparability reasons, we are supposed to act like they have.
        //
        // We must assume 2) is the case because we have no way of determining that it isn't, and
        // therefore must fallback to a previous hack that was done before nested scrolling 3
        // existed.
        int remainingDistanceToScroll;
        if (unconsumedAfterParents == 0) {
            // The previously implemented hack is to see how far we were offset and assume that that
            // distance is equal to how much all of our parents consumed.
            remainingDistanceToScroll = dampingReboundOrientation == 1 ? (dyUnconsumed + mParentOffsetInWindow[1]) : dxUnconsumed + mParentOffsetInWindow[0];
        } else {
            remainingDistanceToScroll = unconsumedAfterParents;
        }
 
 
        // Not sure why we have to make sure the child can't scroll up... but seems dangerous to
        // remove.
        if (remainingDistanceToScroll < 0 && !canChildScrollUp()) {
            mTotalUnconsumed += Math.abs(remainingDistanceToScroll);
            moveSpinner(mTotalUnconsumed);
            // If we've gotten here, we need to consume whatever is left to consume, which at this
            // point is either equal to 0, or remainingDistanceToScroll.
            if (dampingReboundOrientation == 1) {
                consumed[1] += unconsumedAfterParents;
            } else {
                consumed[0] += unconsumedAfterParents;
            }
 
        }
        if (remainingDistanceToScroll > 0 && !canChildScrollDown()) {
            mTotalUnconsumed -= Math.abs(remainingDistanceToScroll);
            moveSpinner(mTotalUnconsumed);
            // If we've gotten here, we need to consume whatever is left to consume, which at this
            // point is either equal to 0, or remainingDistanceToScroll.
            if (dampingReboundOrientation == 1) {
                consumed[1] -= unconsumedAfterParents;
            } else {
                consumed[0] -= unconsumedAfterParents;
            }
 
        }
    }
 
    // NestedScrollingParent 2
 
    @Override
    public boolean onStartNestedScroll(View child, View target, int axes, int type) {
        if (type == ViewCompat.TYPE_TOUCH) {
            return onStartNestedScroll(child, target, axes);
        } else {
            return false;
        }
    }
 
    @Override
    public void onNestedScrollAccepted(View child, View target, int axes, int type) {
        // Should always be true because onStartNestedScroll returns false for all type !=
        // ViewCompat.TYPE_TOUCH, but check just in case.
        if (type == ViewCompat.TYPE_TOUCH) {
            onNestedScrollAccepted(child, target, axes);
        }
    }
 
    @Override
    public void onStopNestedScroll(View target, int type) {
        // Should always be true because onStartNestedScroll returns false for all type !=
        // ViewCompat.TYPE_TOUCH, but check just in case.
        if (type == ViewCompat.TYPE_TOUCH) {
            onStopNestedScroll(target);
        }
    }
 
    @Override
    public void onNestedScroll(View target, int dxConsumed, int dyConsumed, int dxUnconsumed,
                               int dyUnconsumed, int type) {
        onNestedScroll(target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, type,
                mNestedScrollingV2ConsumedCompat);
    }
 
    @Override
    public void onNestedPreScroll(View target, int dx, int dy, int[] consumed, int type) {
        // Should always be true because onStartNestedScroll returns false for all type !=
        // ViewCompat.TYPE_TOUCH, but check just in case.
        if (type == ViewCompat.TYPE_TOUCH) {
            onNestedPreScroll(target, dx, dy, consumed);
        }
    }
 
    // NestedScrollingParent 1
 
    @Override
    public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {
        return isEnabled() && dampingReboundOrientation == 1 ? (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 1 : (nestedScrollAxes & ViewCompat.SCROLL_AXIS_HORIZONTAL) != 2;
    }
 
    @Override
    public void onNestedScrollAccepted(View child, View target, int axes) {
        // Reset the counter of how much leftover scroll needs to be consumed.
        mNestedScrollingParentHelper.onNestedScrollAccepted(child, target, axes);
        // Dispatch up to the nested parent
        startNestedScroll(axes & (dampingReboundOrientation == 1 ? ViewCompat.SCROLL_AXIS_VERTICAL : ViewCompat.SCROLL_AXIS_HORIZONTAL));
        mTotalUnconsumed = 0;
        mNestedScrollInProgress = true;
    }
 
    @Override
    public void onNestedPreScroll(View target, int dx, int dy, int[] consumed) {
        // If we are in the middle of consuming, a scroll, then we want to move the spinner back up
        // before allowing the list to scroll
        if (dampingReboundOrientation == 1) {
            if (dy > 0 && mTotalUnconsumed > 0 || dy < 0 && mTotalUnconsumed < 0) {
                if (dy > mTotalUnconsumed) {
                    consumed[1] = (int) mTotalUnconsumed;
                    mTotalUnconsumed = 0;
                } else {
                    mTotalUnconsumed -= dy;
                    consumed[1] = dy;
                }
                moveSpinner(mTotalUnconsumed);
            }
        } else {
            if (dx > 0 && mTotalUnconsumed > 0 || dx < 0 && mTotalUnconsumed < 0) {
                if (dx > mTotalUnconsumed) {
                    consumed[0] = (int) mTotalUnconsumed;
                    mTotalUnconsumed = 0;
                } else {
                    mTotalUnconsumed -= dx;
                    consumed[0] = dx;
                }
                moveSpinner(mTotalUnconsumed);
            }
        }
 
 
        // If a client layout is using a custom start position for the circle
        // view, they mean to hide it again before scrolling the child view
        // If we get back to mTotalUnconsumed == 0 and there is more to go, hide
        // the circle so it isn't exposed if its blocking content is moved
 
        // Now let our nested parent consume the leftovers
        final int[] parentConsumed = mParentScrollConsumed;
        if (dispatchNestedPreScroll(dx - consumed[0], dy - consumed[1], parentConsumed, null)) {
            consumed[0] += parentConsumed[0];
            consumed[1] += parentConsumed[1];
        }
    }
 
    @Override
    public int getNestedScrollAxes() {
        return mNestedScrollingParentHelper.getNestedScrollAxes();
    }
 
    @Override
    public void onStopNestedScroll(View target) {
        mNestedScrollingParentHelper.onStopNestedScroll(target);
        mNestedScrollInProgress = false;
        // Finish the spinner for nested scrolling if we ever consumed any
        // unconsumed nested scroll
        if (mTotalUnconsumed != 0) {
            finishSpinner();
            mTotalUnconsumed = 0;
        }
        // Dispatch up our nested parent
        stopNestedScroll();
    }
 
    @Override
    public void onNestedScroll(final View target, final int dxConsumed, final int dyConsumed,
                               final int dxUnconsumed, final int dyUnconsumed) {
        onNestedScroll(target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed,
                ViewCompat.TYPE_TOUCH, mNestedScrollingV2ConsumedCompat);
    }
 
    @Override
    public boolean onNestedPreFling(View target, float velocityX, float velocityY) {
        return dispatchNestedPreFling(velocityX, velocityY);
    }
 
    @Override
    public boolean onNestedFling(View target, float velocityX, float velocityY,
                                 boolean consumed) {
        return dispatchNestedFling(velocityX, velocityY, consumed);
    }
 
    // NestedScrollingChild 3
 
    @Override
    public void dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed,
                                     int dyUnconsumed, @Nullable int[] offsetInWindow, @ViewCompat.NestedScrollType int type,
                                     @NonNull int[] consumed) {
        if (type == ViewCompat.TYPE_TOUCH) {
            mNestedScrollingChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed,
                    dyUnconsumed, offsetInWindow, type, consumed);
        }
    }
 
    // NestedScrollingChild 2
 
    @Override
    public boolean startNestedScroll(int axes, int type) {
        return type == ViewCompat.TYPE_TOUCH && startNestedScroll(axes);
    }
 
    @Override
    public void stopNestedScroll(int type) {
        if (type == ViewCompat.TYPE_TOUCH) {
            stopNestedScroll();
        }
    }
 
    @Override
    public boolean hasNestedScrollingParent(int type) {
        return type == ViewCompat.TYPE_TOUCH && hasNestedScrollingParent();
    }
 
    @Override
    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed,
                                        int dyUnconsumed, int[] offsetInWindow, int type) {
        return type == ViewCompat.TYPE_TOUCH && mNestedScrollingChildHelper.dispatchNestedScroll(
                dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed, offsetInWindow, type);
    }
 
    @Override
    public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow,
                                           int type) {
        return type == ViewCompat.TYPE_TOUCH && dispatchNestedPreScroll(dx, dy, consumed,
                offsetInWindow);
    }
 
    // NestedScrollingChild 1
 
    @Override
    public void setNestedScrollingEnabled(boolean enabled) {
        mNestedScrollingChildHelper.setNestedScrollingEnabled(enabled);
    }
 
    @Override
    public boolean isNestedScrollingEnabled() {
        return mNestedScrollingChildHelper.isNestedScrollingEnabled();
    }
 
    @Override
    public boolean startNestedScroll(int axes) {
        return mNestedScrollingChildHelper.startNestedScroll(axes);
    }
 
    @Override
    public void stopNestedScroll() {
        mNestedScrollingChildHelper.stopNestedScroll();
    }
 
    @Override
    public boolean hasNestedScrollingParent() {
        return mNestedScrollingChildHelper.hasNestedScrollingParent();
    }
 
    @Override
    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed,
                                        int dyUnconsumed, int[] offsetInWindow) {
        return mNestedScrollingChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed,
                dxUnconsumed, dyUnconsumed, offsetInWindow);
    }
 
    @Override
    public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
        return mNestedScrollingChildHelper.dispatchNestedPreScroll(
                dx, dy, consumed, offsetInWindow);
    }
 
    @Override
    public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
        return mNestedScrollingChildHelper.dispatchNestedFling(velocityX, velocityY, consumed);
    }
 
    @Override
    public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
        return mNestedScrollingChildHelper.dispatchNestedPreFling(velocityX, velocityY);
    }
 
 
    private void moveSpinner(float overScrollTop) {
        float scroll = overScrollTop * DRAG_RATE;
        if (dampingReboundOrientation == 1) {
            if (scroll > getHeight() / 2f) {
                scroll = getHeight() / 2f;
            }
            if (scroll < -getHeight() / 2f) {
                scroll = -getHeight() / 2f;
            }
            mTarget.setTranslationY(scroll);
        } else {
            if (scroll > getWidth() / 2f) {
                scroll = getWidth() / 2f;
            }
            if (scroll < -getWidth() / 2f) {
                scroll = -getWidth() / 2f;
            }
            mTarget.setTranslationX(scroll);
        }
 
 
    }
 
 
    private void finishSpinner() {
        animateOffsetToStartPosition();
    }
 
 
    private void animateOffsetToStartPosition() {
        valueAnimator = ValueAnimator.ofFloat(dampingReboundOrientation == 1 ? mTarget.getTranslationY() : mTarget.getTranslationX(), 0);
        valueAnimator.setDuration(500);
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                if (mTarget != null && animation != null) {
                    if (dampingReboundOrientation == 1) {
                        mTarget.setTranslationY((Float) animation.getAnimatedValue());
                    } else {
                        mTarget.setTranslationX((Float) animation.getAnimatedValue());
                    }
                }
            }
        });
        valueAnimator.setInterpolator(mDecelerateInterpolator);
        valueAnimator.start();
    }
 
 
    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        final int action = ev.getActionMasked();
        int pointerIndex = -1;
        if (!isEnabled() || canChildScrollUp() || canChildScrollDown() || mNestedScrollInProgress) {
            // Fail fast if we're not in a state where a swipe is possible
            return false;
        }
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                break;
 
            case MotionEvent.ACTION_MOVE: {
                final float y = ev.getY();
                final float overScrollTop = (y - mInitialScroll);
                // While the spinner is being dragged down, our parent shouldn't try
                // to intercept touch events. It will stop the drag gesture abruptly.
                getParent().requestDisallowInterceptTouchEvent(true);
                moveSpinner(overScrollTop);
                break;
            }
            case MotionEvent.ACTION_UP: {
                finishSpinner();
                return false;
            }
            case MotionEvent.ACTION_CANCEL:
                return false;
        }
 
        return true;
    }
 
}