NestedAppBarLayout, make AppBarLayout scrollable in CoordinatorLayout, merge code from NestedScrollView, lots of thing to improve...

NestedAppBarLayout.java

import android.content.Context;
import android.support.annotation.NonNull;
import android.support.design.widget.AppBarLayout;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.NestedScrollingChild;
import android.support.v4.view.NestedScrollingChildHelper;
import android.support.v4.view.VelocityTrackerCompat;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ScrollerCompat;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.ViewConfiguration;
import android.view.ViewParent;

public class NestedAppBarLayout extends AppBarLayout implements NestedScrollingChild {

    private static final String TAG = "NestedAppBarLayout";

    private ScrollerCompat mScroller;

    /**
     * Position of the last motion event.
     */
    private int mLastMotionY;

    /**
     * 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;

    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;

    /**
     * Used during scrolling to retrieve the new offset within the window.
     */
    private final int[] mScrollOffset = new int[2];
    private int mNestedYOffset;

    /**
     * Sentinel value for no current active pointer.
     * Used by {@link #mActivePointerId}.
     */
    private static final int INVALID_POINTER = -1;

    private final NestedScrollingChildHelper mChildHelper;

    public NestedAppBarLayout(Context context) {
        this(context, null);
    }

    public NestedAppBarLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

        initScrollView();

        mChildHelper = new NestedScrollingChildHelper(this);

        // ...because why else would you be using this widget?
        setNestedScrollingEnabled(true);
    }

    // NestedScrollingChild

    @Override
    public void setNestedScrollingEnabled(boolean enabled) {
        mChildHelper.setNestedScrollingEnabled(enabled);
    }

    @Override
    public boolean isNestedScrollingEnabled() {
        return mChildHelper.isNestedScrollingEnabled();
    }

    @Override
    public boolean startNestedScroll(int axes) {
        return mChildHelper.startNestedScroll(axes);
    }

    @Override
    public void stopNestedScroll() {
        mChildHelper.stopNestedScroll();
    }

    @Override
    public boolean hasNestedScrollingParent() {
        return mChildHelper.hasNestedScrollingParent();
    }

    @Override
    public boolean dispatchNestedScroll(int dxConsumed, int dyConsumed, int dxUnconsumed,
                                        int dyUnconsumed, int[] offsetInWindow) {
        return mChildHelper.dispatchNestedScroll(dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed,
                offsetInWindow);
    }

    @Override
    public boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed, int[] offsetInWindow) {
        return mChildHelper.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow);
    }

    @Override
    public boolean dispatchNestedFling(float velocityX, float velocityY, boolean consumed) {
        return mChildHelper.dispatchNestedFling(velocityX, velocityY, consumed);
    }

    @Override
    public boolean dispatchNestedPreFling(float velocityX, float velocityY) {
        return mChildHelper.dispatchNestedPreFling(velocityX, velocityY);
    }

    private void initScrollView() {
        mScroller = ScrollerCompat.create(getContext());
        setFocusable(true);
        setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
        final ViewConfiguration configuration = ViewConfiguration.get(getContext());
        mTouchSlop = configuration.getScaledTouchSlop();
        mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
    }

    private void initOrResetVelocityTracker() {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        } else {
            mVelocityTracker.clear();
        }
    }

    private void initVelocityTrackerIfNotExists() {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
    }

    private void recycleVelocityTracker() {
        if (mVelocityTracker != null) {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        if (disallowIntercept) {
            recycleVelocityTracker();
        }
        super.requestDisallowInterceptTouchEvent(disallowIntercept);
    }


    @Override
    public boolean onInterceptTouchEvent(@NonNull 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 & MotionEventCompat.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 = MotionEventCompat.findPointerIndex(ev, activePointerId);
                if (pointerIndex == -1) {
                    Log.e(TAG, "Invalid pointerId=" + activePointerId
                            + " in onInterceptTouchEvent");
                    break;
                }

                final int y = (int) MotionEventCompat.getY(ev, pointerIndex);
                final int yDiff = Math.abs(y - mLastMotionY);
                if (yDiff > mTouchSlop) {
                    mIsBeingDragged = true;
                    mLastMotionY = y;
                    initVelocityTrackerIfNotExists();
                    mVelocityTracker.addMovement(ev);
                    mNestedYOffset = 0;
                    final ViewParent parent = getParent();
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent(true);
                    }
                }
                break;
            }

            case MotionEvent.ACTION_DOWN: {

                /*
                 * Remember location of down touch.
                 * ACTION_DOWN always refers to pointer index 0.
                 */
                mLastMotionY = (int) ev.getY();
                mActivePointerId = MotionEventCompat.getPointerId(ev, 0);

                initOrResetVelocityTracker();
                mVelocityTracker.addMovement(ev);
                /*
                * If being flinged and user touches the screen, initiate drag;
                * otherwise don't.  mScroller.isFinished should be false when
                * being flinged.
                */
                mIsBeingDragged = !mScroller.isFinished();
                startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
                break;
            }

            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                /* Release the drag */
                mIsBeingDragged = false;
                mActivePointerId = INVALID_POINTER;
                recycleVelocityTracker();
                stopNestedScroll();
                break;
            case MotionEventCompat.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(@NonNull MotionEvent ev) {
        initVelocityTrackerIfNotExists();

        MotionEvent vtev = MotionEvent.obtain(ev);

        final int actionMasked = MotionEventCompat.getActionMasked(ev);

        if (actionMasked == MotionEvent.ACTION_DOWN) {
            mNestedYOffset = 0;
        }
        vtev.offsetLocation(0, mNestedYOffset);

        switch (actionMasked) {
            case MotionEvent.ACTION_DOWN: {
                if (getChildCount() == 0) {
                    return false;
                }
                if ((mIsBeingDragged = !mScroller.isFinished())) {
                    final ViewParent parent = getParent();
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent(true);
                    }
                }

                /*
                 * 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 = (int) ev.getY();
                mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
                startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
                break;
            }
            case MotionEvent.ACTION_MOVE:
                final int activePointerIndex = MotionEventCompat.findPointerIndex(ev,
                        mActivePointerId);
                if (activePointerIndex == -1) {
                    Log.e(TAG, "Invalid pointerId=" + mActivePointerId + " in onTouchEvent");
                    break;
                }

                final int y = (int) MotionEventCompat.getY(ev, activePointerIndex);
                int deltaY = mLastMotionY - y;
                if (dispatchNestedPreScroll(0, deltaY, null, mScrollOffset)) {
                    vtev.offsetLocation(0, mScrollOffset[1]);
                    mNestedYOffset += mScrollOffset[1];
                }
                if (!mIsBeingDragged && Math.abs(deltaY) > mTouchSlop) {
                    final ViewParent parent = getParent();
                    if (parent != null) {
                        parent.requestDisallowInterceptTouchEvent(true);
                    }
                    mIsBeingDragged = true;
                    if (deltaY > 0) {
                        deltaY -= mTouchSlop;
                    } else {
                        deltaY += mTouchSlop;
                    }
                }
                if (mIsBeingDragged) {
                    // Scroll to follow the motion event
                    mLastMotionY = y - mScrollOffset[1];

                    // Calling overScrollByCompat will call onOverScrolled, which
                    // calls onScrollChanged if applicable.
                    if (!hasNestedScrollingParent()) {
                        // Break our velocity if we hit a scroll barrier.
                        mVelocityTracker.clear();
                    }

                    if (dispatchNestedScroll(0, 0, 0, deltaY, mScrollOffset)) {
                        mLastMotionY -= mScrollOffset[1];
                        vtev.offsetLocation(0, mScrollOffset[1]);
                        mNestedYOffset += mScrollOffset[1];
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
                if (mIsBeingDragged) {
                    final VelocityTracker velocityTracker = mVelocityTracker;
                    velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
                    int initialVelocity = (int) VelocityTrackerCompat.getYVelocity(velocityTracker,
                            mActivePointerId);

                    if ((Math.abs(initialVelocity) > mMinimumVelocity)) {
                        flingWithNestedDispatch(-initialVelocity);
                    }

                    mActivePointerId = INVALID_POINTER;
                    endDrag();
                }
                break;
            case MotionEvent.ACTION_CANCEL:
                if (mIsBeingDragged && getChildCount() > 0) {
                    mActivePointerId = INVALID_POINTER;
                    endDrag();
                }
                break;
            case MotionEventCompat.ACTION_POINTER_DOWN: {
                final int index = MotionEventCompat.getActionIndex(ev);
                mLastMotionY = (int) MotionEventCompat.getY(ev, index);
                mActivePointerId = MotionEventCompat.getPointerId(ev, index);
                break;
            }
            case MotionEventCompat.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                mLastMotionY = (int) MotionEventCompat.getY(ev,
                        MotionEventCompat.findPointerIndex(ev, mActivePointerId));
                break;
        }

        if (mVelocityTracker != null) {
            mVelocityTracker.addMovement(vtev);
        }
        vtev.recycle();
        return true;
    }

    private void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = (ev.getAction() & MotionEventCompat.ACTION_POINTER_INDEX_MASK) >>
                MotionEventCompat.ACTION_POINTER_INDEX_SHIFT;
        final int pointerId = MotionEventCompat.getPointerId(ev, 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 = (int) MotionEventCompat.getY(ev, newPointerIndex);
            mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);
            if (mVelocityTracker != null) {
                mVelocityTracker.clear();
            }
        }
    }

    @Override
    protected int computeVerticalScrollOffset() {
        return Math.max(0, super.computeVerticalScrollOffset());
    }

    /**
     * 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) {
        mScroller.fling(0, 0, 0, velocityY, 0, 0, 0, 0);
    }

    private void flingWithNestedDispatch(int velocityY) {
        if (!dispatchNestedPreFling(0, velocityY)) {
            dispatchNestedFling(0, velocityY, true);
            fling(velocityY);
        }
    }

    private void endDrag() {
        mIsBeingDragged = false;

        recycleVelocityTracker();
    }
}

nice and helpful

Very usefull. Appreciate it!

Fixed a scroll bug I've spent too much time on, thank you!

发现没有效果啊，需要特殊处理什么么？

   <com.tmall.wireless.tangram.example.cc.NestedAppBarLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent">
        
        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#c07"
            app:layout_scrollFlags="scroll|enterAlways" />
    
    </com.tmall.wireless.tangram.example.cc.NestedAppBarLayout>