安卓RecyclerView通过ItemTouchHelper实现侧滑拖拽功能

package com.android.ItemTouchHelper.helper; import android.animation.Animator; import android.animation.AnimatorListenerAdapter; import android.animation.ObjectAnimator; import android.animation.ValueAnimator; import android.content.res.Resources; import android.graphics.Canvas; import android.graphics.Rect; import android.os.Build; import android.support.annotation.Nullable; import android.support.v4.view.GestureDetectorCompat; import android.support.v4.view.ViewCompat; import android.support.v7.widget.LinearLayoutManager; import android.support.v7.widget.RecyclerView; import android.support.v7.widget.RecyclerView.OnItemTouchListener; import android.support.v7.widget.RecyclerView.ViewHolder; import android.support.v7.widget.helper.ItemTouchUIUtil; import android.view.GestureDetector; import android.view.HapticFeedbackConstants; 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.AccelerateDecelerateInterpolator; import android.view.animation.Interpolator; import com.android.ItemTouchHelper.R; import com.android.ItemTouchHelper.util.Console; import java.util.ArrayList; import java.util.List; //这个控件的拖拽还有BUG，有时交换元素时，元素会消失 //主要通过Demo来读源码流程，细节上不要太较真 @SuppressWarnings("all") public class ItemTouchHelper extends RecyclerView.ItemDecoration implements RecyclerView.OnChildAttachStateChangeListener { /** * Up direction, used for swipe & drag control. */ public static final int UP = 1; /** * Down direction, used for swipe & drag control. */ public static final int DOWN = 1 << 1; /** * Left direction, used for swipe & drag control. */ public static final int LEFT = 1 << 2; /** * Right direction, used for swipe & drag control. */ public static final int RIGHT = 1 << 3; // If you change these relative direction values, update Callback#convertToAbsoluteDirection, // Callback#convertToRelativeDirection. /** * Horizontal start direction. Resolved to LEFT or RIGHT depending on RecyclerView's layout * direction. Used for swipe & drag control. */ public static final int START = LEFT << 2; /** * Horizontal end direction. Resolved to LEFT or RIGHT depending on RecyclerView's layout * direction. Used for swipe & drag control. */ public static final int END = RIGHT << 2; /** * ItemTouchHelper is in idle state. At this state, either there is no related motion event by * the user or latest motion events have not yet triggered a swipe or drag. */ public static final int ACTION_STATE_IDLE = 0; /** * A View is currently being swiped. */ public static final int ACTION_STATE_SWIPE = 1; /** * A View is currently being dragged. */ public static final int ACTION_STATE_DRAG = 2; /** * Animation type for views which are swiped successfully. */ public static final int ANIMATION_TYPE_SWIPE_SUCCESS = 1 << 1; /** * Animation type for views which are not completely swiped thus will animate back to their * original position. */ public static final int ANIMATION_TYPE_SWIPE_CANCEL = 1 << 2; /** * Animation type for views that were dragged and now will animate to their final position. */ public static final int ANIMATION_TYPE_DRAG = 1 << 3; static final int ACTIVE_POINTER_ID_NONE = -1; static final int DIRECTION_FLAG_COUNT = 8; private static final int ACTION_MODE_IDLE_MASK = (1 << DIRECTION_FLAG_COUNT) - 1; static final int ACTION_MODE_SWIPE_MASK = ACTION_MODE_IDLE_MASK << DIRECTION_FLAG_COUNT; static final int ACTION_MODE_DRAG_MASK = ACTION_MODE_SWIPE_MASK << DIRECTION_FLAG_COUNT; /** * The unit we are using to track velocity */ private static final int PIXELS_PER_SECOND = 1000; /** * Views, whose state should be cleared after they are detached from RecyclerView. * This is necessary after swipe dismissing an item. We wait until animator finishes its job * to clean these views. */ final List<View> mPendingCleanup = new ArrayList<View>(); /** * Re-use array to calculate dx dy for a ViewHolder */ private final float[] mTmpPosition = new float[2]; /** * Currently selected view holder */ ViewHolder mSelected = null; ViewHolder mPreOpened = null; /** * The reference coordinates for the action start. For drag & drop, this is the time long * press is completed vs for swipe, this is the initial touch point. */ float mInitialTouchX; float mInitialTouchY; /** * Set when ItemTouchHelper is assigned to a RecyclerView. */ float mSwipeEscapeVelocity; /** * Set when ItemTouchHelper is assigned to a RecyclerView. */ float mMaxSwipeVelocity; /** * The diff between the last event and initial touch. */ float mDx; float mDy; /** * The coordinates of the selected view at the time it is selected. We record these values * when action starts so that we can consistently position it even if LayoutManager moves the * View. */ float mSelectedStartX; float mSelectedStartY; /** * The pointer we are tracking. */ int mActivePointerId = ACTIVE_POINTER_ID_NONE; /** * Developer callback which controls the behavior of ItemTouchHelper. */ Callback mCallback; /** * Current mode. */ int mActionState = ACTION_STATE_IDLE; /** * The direction flags obtained from unmasking * {@link Callback#getAbsoluteMovementFlags(RecyclerView, ViewHolder)} for the current * action state. */ int mSelectedFlags; /** * When a View is dragged or swiped and needs to go back to where it was, we create a Recover * Animation and animate it to its location using this custom Animator, instead of using * framework Animators. * Using framework animators has the side effect of clashing with ItemAnimator, creating * jumpy UIs. */ List<RecoverAnimation> mRecoverAnimations = new ArrayList<RecoverAnimation>(); private int mSlop; RecyclerView mRecyclerView; /** * When user drags a view to the edge, we start scrolling the LayoutManager as long as View * is partially out of bounds. */ //REMARK => 手指移到控件以外时，仍然继续拖拽 //这只是个细节功能，没有也不影响控件使用 final Runnable mScrollRunnable = new Runnable() { @Override public void run() { // if (mSelected != null && scrollIfNecessary()) { // if (mSelected != null) { //it might be lost during scrolling // moveIfNecessary(mSelected); // } // mRecyclerView.removeCallbacks(mScrollRunnable); // ViewCompat.postOnAnimation(mRecyclerView, this); // } } }; /** * Used for detecting fling swipe */ VelocityTracker mVelocityTracker; //re-used list for selecting a swap target private List<ViewHolder> mSwapTargets; //re used for for sorting swap targets private List<Integer> mDistances; /** * If drag & drop is supported, we use child drawing order to bring them to front. */ private RecyclerView.ChildDrawingOrderCallback mChildDrawingOrderCallback = null; /** * This keeps a reference to the child dragged by the user. Even after user stops dragging,