Android--利用ItemTouchHelper实现RecyclerView的侧滑删除

    @Override
    public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        if (dY != 0 && dX == 0) {//因为我们只关注侧滑，而侧滑条件是dX！=0&&dY ==0，所以其他的情况调用ItemTouchUIUtilImpl的方法
            super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
        }

        if (iMoveAndSwipeCallback != null) {
            iMoveAndSwipeCallback.onChildDraw(viewHolder, dX, dY);
        }
    }

    @Override
    public void onChildDraw(RecyclerView.ViewHolder viewHolder, float dX, float dY) {
        MyAdapter.MyViewHolder myViewHolder = (MyAdapter.MyViewHolder) viewHolder;
        //最大偏移不超过删除布局宽度
        if (dX < -myViewHolder.ll_remove.getWidth()) {
            dX = -myViewHolder.ll_remove.getWidth();
        }
        myViewHolder.tv.setTranslationX(dX);
    }

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="70dp"
    android:orientation="horizontal">


    <LinearLayout
        android:id="@+id/ll_remove"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="right"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/tv_remove"
            android:layout_width="100dp"
            android:layout_height="match_parent"
            android:background="@android:color/holo_red_light"
            android:gravity="center"
            android:text="remove"
            android:textColor="@android:color/white" />

        <TextView
            android:id="@+id/tv_cancel"
            android:layout_width="100dp"
            android:layout_height="match_parent"
            android:background="@android:color/holo_blue_bright"
            android:gravity="center"
            android:text="cancel"
            android:textColor="@android:color/white" />

    </LinearLayout>
    
    <TextView
        android:id="@+id/tv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorPrimary"
        android:gravity="center"
        android:textColor="@android:color/white" />

</FrameLayout>

    private final RecyclerView.OnItemTouchListener mOnItemTouchListener = new RecyclerView.OnItemTouchListener() {
        private boolean onClick;

        @Override
        public boolean onInterceptTouchEvent(RecyclerView recyclerView, MotionEvent event) {
            mGestureDetector.onTouchEvent(event);
            if (DEBUG) {
                Log.d(TAG, "intercept: x:" + event.getX() + ",y:" + event.getY() + ", " + event);
            }
            final int action = event.getActionMasked();
            if (action == MotionEvent.ACTION_DOWN) {
                mActivePointerId = event.getPointerId(0);
                mInitialTouchX = event.getX();
                mInitialTouchY = event.getY();
                //记录ACTION_DOWN的位置
                mDownX = event.getX();
                mDownY = event.getY();
                onClick = true;

                obtainVelocityTracker();
                if (mSelected == null) {
                    final RecoverAnimation animation = findAnimation(event);
                    if (animation != null) {
                        mInitialTouchX -= animation.mX;
                        mInitialTouchY -= animation.mY;
                        endRecoverAnimation(animation.mViewHolder, true);
                        if (mPendingCleanup.remove(animation.mViewHolder.itemView)) {
                            mCallback.clearView(mRecyclerView, animation.mViewHolder);
                        }
                        select(animation.mViewHolder, animation.mActionState);
                        updateDxDy(event, mSelectedFlags, 0);
                    }
                }
            } else if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
                mActivePointerId = ACTIVE_POINTER_ID_NONE;
                if (action == MotionEvent.ACTION_UP) {
                    //点击事件
                    click(event);
                }
                select(null, ACTION_STATE_IDLE);
            } else if (mActivePointerId != ACTIVE_POINTER_ID_NONE) {
                // in a non scroll orientation, if distance change is above threshold, we
                // can select the item
                final int index = event.findPointerIndex(mActivePointerId);
                if (DEBUG) {
                    Log.d(TAG, "pointer index " + index);
                }
                if (index >= 0) {
                    checkSelectForSwipe(action, event, index);
                }
            }

            //处理下move事件
            if (action == MotionEvent.ACTION_MOVE) {
                //移动了，就解除点击
                final float dx = event.getX(mActivePointerId) - mDownX;
                final float dy = event.getY(mActivePointerId) - mDownY;
                final float absDx = Math.abs(dx);
                final float absDy = Math.abs(dy);

                if (absDx > mSlop || absDy > mSlop) {
                    onClick = false;
                }
            }


            if (mVelocityTracker != null) {
                mVelocityTracker.addMovement(event);
            }
            return mSelected != null;
        }

        @Override
        public void onTouchEvent(RecyclerView recyclerView, MotionEvent event) {
            mGestureDetector.onTouchEvent(event);
            if (DEBUG) {
                Log.d(TAG,
                        "on touch: x:" + mInitialTouchX + ",y:" + mInitialTouchY + ", :" + event);
            }
            if (mVelocityTracker != null) {
                mVelocityTracker.addMovement(event);
            }
            if (mActivePointerId == ACTIVE_POINTER_ID_NONE) {
                return;
            }
            final int action = event.getActionMasked();
            final int activePointerIndex = event.findPointerIndex(mActivePointerId);
            if (activePointerIndex >= 0) {
                checkSelectForSwipe(action, event, activePointerIndex);
            }
            ViewHolder viewHolder = mSelected;
            if (viewHolder == null) {
                return;
            }
            switch (action) {
                case MotionEvent.ACTION_MOVE: {
                    // Find the index of the active pointer and fetch its position
                    if (activePointerIndex >= 0) {
                        updateDxDy(event, mSelectedFlags, activePointerIndex);
                        moveIfNecessary(viewHolder);
                        mRecyclerView.removeCallbacks(mScrollRunnable);
                        mScrollRunnable.run();
                        mRecyclerView.invalidate();
                    }
                    break;
                }
                case MotionEvent.ACTION_CANCEL:
                    if (mVelocityTracker != null) {
                        mVelocityTracker.clear();
                    }
                    // fall through
                case MotionEvent.ACTION_UP:
                    //点击事件
                    click(event);
                    select(null, ACTION_STATE_IDLE);
                    mActivePointerId = ACTIVE_POINTER_ID_NONE;
                    break;
                case MotionEvent.ACTION_POINTER_UP: {
                    onClick = false;
                    final int pointerIndex = event.getActionIndex();
                    final int pointerId = event.getPointerId(pointerIndex);
                    if (pointerId == mActivePointerId) {
                        // This was our active pointer going up. Choose a new
                        // active pointer and adjust accordingly.
                        final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                        mActivePointerId = event.getPointerId(newPointerIndex);
                        updateDxDy(event, mSelectedFlags, pointerIndex);
                    }
                    break;
                }

                default:
                    onClick = false;
                    break;
            }
        }

        /**
         * 点击事件处理
         * @param event
         */
        private void click(MotionEvent event) {
            if (onClick && mSelected != null) {//抬起时，调用点击
                View view = mSelected.itemView;
                if (view instanceof ViewGroup) {
                    view = findView((ViewGroup) mSelected.itemView, event.getRawX(), event.getRawY());
                }

                if (view != null) {
                    view.performClick();
                }
            }
            onClick = false;
        }

        /**
         * 找到被点击的View
         *
         * @param parent
         * @param x
         * @param y
         * @return
         */
        private View findView(ViewGroup parent, float x, float y) {
            int count = parent.getChildCount();
            for (int i = 0; i < count; i++) {
                View view = parent.getChildAt(i);
                //如果是组件，并可见的话
                if (view instanceof ViewGroup && view.getVisibility() == View.VISIBLE) {
                    //递归调用
                    View child = findView((ViewGroup) view, x, y);
                    if (child != null) {
                        return child;
                    }
                }

                //如果在可点击区域内，又是控件的话
                if (isInRegion(view, x, y) && view.getVisibility() == View.VISIBLE) {
                    return view;
                }
            }

            //没有child的情况，判断下有没有在可点击区域内
            if (isInRegion(parent, x, y) && parent.getVisibility() == View.VISIBLE) {
                return parent;
            }

            return null;
        }

        /**
         * 判断点击位置是否在区域内
         * @param child
         * @param x
         * @param y
         * @return
         */
        private boolean isInRegion(View child, float x, float y) {
            Rect rect = new Rect();
            //获取在屏幕全局的区域
            child.getGlobalVisibleRect(rect);
            if (rect.contains((int) x, (int) y) && ViewCompat.hasOnClickListeners(child) &&
                    child.getVisibility() == View.VISIBLE) {
                return true;
            }
            return false;
        }


        @Override
        public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
            if (!disallowIntercept) {
                return;
            }
            select(null, ACTION_STATE_IDLE);
        }
    };

    /**
     * 之前侧滑的ViewHolder
     */
    ViewHolder mPreSelected = null;

                final RecoverAnimation rv = new RecoverAnimation(prevSelected, animationType,
                        prevActionState, currentTranslateX, currentTranslateY,
                        targetTranslateX, targetTranslateY) {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        super.onAnimationEnd(animation);
                        if (this.mOverridden) {
                            return;
                        }
                        if (swipeDir <= 0) {
                            // this is a drag or failed swipe. recover immediately
                            mCallback.clearView(mRecyclerView, prevSelected);
                            // full cleanup will happen on onDrawOver
                        } else {
                            // wait until remove animation is complete.
                            mPendingCleanup.add(prevSelected.itemView);
                            //记录
                            mPreSelected = prevSelected;
                            mIsPendingCleanup = true;
                            if (swipeDir > 0) {
                                // Animation might be ended by other animators during a layout.
                                // We defer callback to avoid editing adapter during a layout.
                                postDispatchSwipe(this, swipeDir);
                            }
                        }
                        // removed from the list after it is drawn for the last time
                        if (mOverdrawChild == prevSelected.itemView) {
                            removeChildDrawingOrderCallbackIfNecessary(prevSelected.itemView);
                        }
                    }
                };

    /**
     * 关闭动画
     */
    private void closeOpenedPreItem() {
        final View view = mCallback.getItemFrontView(mPreSelected);
        if (mPreSelected == null || view == null) return;
        ObjectAnimator objectAnimator = ObjectAnimator.ofFloat(view, "translationX", view.getTranslationX(), 0f);
        objectAnimator.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationStart(Animator animation) {
                super.onAnimationStart(animation);
                if (mPreSelected != null) mCallback.clearView(mRecyclerView, mPreSelected);
                if (mPreSelected != null) mPendingCleanup.remove(mPreSelected.itemView);
                endRecoverAnimation(mPreSelected, true);
                mPreSelected = mSelected;
            }

            @Override
            public void onAnimationEnd(Animator animation) {
                super.onAnimationEnd(animation);
            }
        });
        objectAnimator.setInterpolator(new AccelerateDecelerateInterpolator());
        objectAnimator.start();
    }

    public void attachToRecyclerView(@Nullable RecyclerView recyclerView) {
        if (mRecyclerView == recyclerView) {
            return; // nothing to do
        }
        if (mRecyclerView != null) {
            destroyCallbacks();
        }
        mRecyclerView = recyclerView;
        if (mRecyclerView != null) {
            final Resources resources = recyclerView.getResources();
            mSwipeEscapeVelocity = resources
                    .getDimension(R.dimen.item_touch_helper_swipe_escape_velocity);
            mMaxSwipeVelocity = resources
                    .getDimension(R.dimen.item_touch_helper_swipe_escape_max_velocity);
            //添加滑动监听
            mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
                @Override
                public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                    super.onScrollStateChanged(recyclerView, newState);
                    if (newState == RecyclerView.SCROLL_STATE_DRAGGING && mPreSelected != null) {
                        closeOpenedPreItem();
                    }
                }
            });
            setupCallbacks();
        }
    }

    /**
     * Checks whether we should select a View for swiping.
     */
    boolean checkSelectForSwipe(int action, MotionEvent motionEvent, int pointerIndex) {
        if (mSelected != null || action != MotionEvent.ACTION_MOVE
                || mActionState == ACTION_STATE_DRAG || !mCallback.isItemViewSwipeEnabled()) {
            return false;
        }
        if (mRecyclerView.getScrollState() == RecyclerView.SCROLL_STATE_DRAGGING) {
            return false;
        }
        final ViewHolder vh = findSwipedView(motionEvent);
        if (vh == null) {
            return false;
        }
        final int movementFlags = mCallback.getAbsoluteMovementFlags(mRecyclerView, vh);

        final int swipeFlags = (movementFlags & ACTION_MODE_SWIPE_MASK)
                >> (DIRECTION_FLAG_COUNT * ACTION_STATE_SWIPE);

        if (swipeFlags == 0) {
            return false;
        }

        // mDx and mDy are only set in allowed directions. We use custom x/y here instead of
        // updateDxDy to avoid swiping if user moves more in the other direction
        final float x = motionEvent.getX(pointerIndex);
        final float y = motionEvent.getY(pointerIndex);

        // Calculate the distance moved
        final float dx = x - mInitialTouchX;
        final float dy = y - mInitialTouchY;
        // swipe target is chose w/o applying flags so it does not really check if swiping in that
        // direction is allowed. This why here, we use mDx mDy to check slope value again.
        final float absDx = Math.abs(dx);
        final float absDy = Math.abs(dy);

        if (absDx < mSlop && absDy < mSlop) {
            return false;
        }
        if (absDx > absDy) {
            if (dx < 0 && (swipeFlags & LEFT) == 0) {
                return false;
            }
            if (dx > 0 && (swipeFlags & RIGHT) == 0) {
                return false;
            }
        } else {
            if (dy < 0 && (swipeFlags & UP) == 0) {
                return false;
            }
            if (dy > 0 && (swipeFlags & DOWN) == 0) {
                return false;
            }
        }
        mDx = mDy = 0f;
        mActivePointerId = motionEvent.getPointerId(0);
        select(vh, ACTION_STATE_SWIPE);

        if (mPreSelected != null && mPreSelected != vh && mPreSelected != null) {
            closeOpenedPreItem();
        }
        return true;
    }