Android中关于ItemTouchHelper的使用分析

• ItemTouchHelper 是什么

这是一个帮助RecyclerView添加滑动删除和拖放的帮助类。

使用时与RecyclerView、ItemTouchHelper.CallBack一起使用，配置相应的类型接受相应的事件。

其中两个重要需要覆盖的方法 onMove移动 和 onSwiped滑动。

可以使用任何的LayoutManager。

google开放了墙内可以访问的开发者网站,下面是关于ItemTouchHelper的官方介绍地址
https://developer.android.google.cn/reference/android/support/v7/widget/helper/ItemTouchHelper.html

• 如何使用

创建一个ItemTouchHelper并关联RecyclerView

ItemTouchHelper touchHelper = new ItemTouchHelper(new ItemTouchHelper.Callback(){...});
touchHelper.attachToRecyclerView(recyclerView);

Callback的内容

ItemTouchHelper.Callback callback = new ItemTouchHelper.Callback() {

    /**
     * 设置view的操作动作
     */
    @Override
    public int getMovementFlags(RecyclerView recyclerView, ViewHolder viewHolder) {
        int dragFlags;
        int swipeFlags;

        if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
             /* grid风格可以上下左右拖放 */
            dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
            swipeFlags = ItemTouchHelper.ACTION_STATE_IDLE;

        } else if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {
            /* list风格可以左右滑动 */
            dragFlags = ItemTouchHelper.ACTION_STATE_IDLE;
            swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;

        } else {
            dragFlags = ItemTouchHelper.ACTION_STATE_IDLE;
            swipeFlags = ItemTouchHelper.ACTION_STATE_IDLE;
        }

        return makeMovementFlags(dragFlags, swipeFlags);
    }

    /**
     * view移动
     */
    @Override
    public boolean onMove(RecyclerView recyclerView, ViewHolder viewHolder, ViewHolder target) {
        // 原位置
        int oldPosition = viewHolder.getAdapterPosition();
        // 目标位置
        int targetPosition = target.getAdapterPosition();
        // adapter处理数据
        adapter.onItemMoved(oldPosition, targetPosition);
        return false;
    }

    /**
     * view滑动
     */
    @Override
    public void onSwiped(ViewHolder viewHolder, int direction) {
        // 直接删除
        adapter.removeItem(viewHolder);
    }

    /**
     * 是否可滑动
     */
    @Override
    public boolean isItemViewSwipeEnabled() {
        return true;
    }

    /**
     * 是否可长按拖放
     */
    @Override
    public boolean isLongPressDragEnabled() {
        // 单独拦截Item的点击长按事件,此处返回false
        return false;
    }

    /**
     * view移动中
     */
    @Override
    public void onChildDraw(Canvas c, RecyclerView recyclerView, ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
            // 左右滑动时设置透明度
            final float alpha = 1 - Math.abs(dX) / (float) viewHolder.itemView.getWidth();
            viewHolder.itemView.setAlpha(alpha);
            viewHolder.itemView.setTranslationX(dX);
        } else {
            super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
        }
    }

    /**
     * view被选中
     */
    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
            viewHolder.itemView.setBackgroundColor(Color.LTGRAY);
        }
        super.onSelectedChanged(viewHolder, actionState);
    }

    /**
     * 操作完毕
     */
    @Override
    public void clearView(RecyclerView recyclerView, ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);
        viewHolder.itemView.setAlpha(1.0f);
        viewHolder.itemView.setBackgroundColor(Color.WHITE);
    }

    /**
     * 目标是否可被放入
     */
    @Override
    public boolean canDropOver(RecyclerView recyclerView, ViewHolder current, ViewHolder target) {
        return adapter.onItemDrag(target.getAdapterPosition());
    }
};

adapter中的移动操作

@Override
public void onItemMoved(int form, int target) {
    if (form < target) {
        // 向后
        for (int i = form; i < target; i++) {
            Collections.swap(data, i, i + 1);
        }
    } else {
        // 向前
        for (int i = form; i > target; i--) {
            Collections.swap(data, i, i - 1);
        }
    }
    notifyItemMoved(form, target);
}

Item监听事件帮助类

package cn.cyan.dragrecyclerview;

import android.support.v4.view.GestureDetectorCompat;
import android.support.v7.widget.RecyclerView;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;

public class HoldTouchHelper {

private RecyclerView recyclerView;
private OnItemTouchEvent onItemTouchEvent;
private GestureDetectorCompat detector;

private HoldTouchHelper(RecyclerView view, OnItemTouchEvent event) {
    this.recyclerView = view;
    this.onItemTouchEvent = event;

    GestureDetector.SimpleOnGestureListener simpleOnGestureListener = new GestureDetector.SimpleOnGestureListener() {
        @Override
        public boolean onSingleTapUp(MotionEvent e) {
            if (onItemTouchEvent != null) {
                View child = recyclerView.findChildViewUnder(e.getX(), e.getY());
                if (child != null) {
                    RecyclerView.ViewHolder vh = recyclerView.getChildViewHolder(child);
                    onItemTouchEvent.onItemClick(recyclerView, vh, vh.getAdapterPosition());
                }
            }
            return true;
        }

        @Override
        public void onLongPress(MotionEvent e) {
            View child = recyclerView.findChildViewUnder(e.getX(), e.getY());
            if (child != null) {
                RecyclerView.ViewHolder vh = recyclerView.getChildViewHolder(child);
                onItemTouchEvent.onLongPress(recyclerView, vh, vh.getAdapterPosition());
            }
        }
    };

    detector = new GestureDetectorCompat(recyclerView.getContext(), simpleOnGestureListener);

    RecyclerView.OnItemTouchListener onItemTouchListener = new RecyclerView.OnItemTouchListener() {
        @Override
        public boolean onInterceptTouchEvent(RecyclerView rv, MotionEvent e) {
            detector.onTouchEvent(e);
            return false;
        }

        @Override
        public void onTouchEvent(RecyclerView rv, MotionEvent e) {
            detector.onTouchEvent(e);
        }

        @Override
        public void onRequestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        }
    };
    recyclerView.addOnItemTouchListener(onItemTouchListener);
}

public interface OnItemTouchEvent {
    void onLongPress(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, int position);

    void onItemClick(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, int position);
}

public static void bind(RecyclerView view, OnItemTouchEvent event) {
    new HoldTouchHelper(view, event);
}
}

Demo https://github.com/bcqq/Android-DragRecyclerView