【RecyclerView】十五、使用 ItemTouchHelper 实现 RecyclerView 拖动排序 ( ItemTouchHelper 简介 )

韩曙亮

发布于 2023-03-28 21:08:56

7730

发布于 2023-03-28 21:08:56

文章被收录于专栏：韩曙亮的移动开发专栏韩曙亮的移动开发专栏

文章目录

一、ItemTouchHelper 简介

官方文档 : https://developer.android.google.cn/reference/kotlin/androidx/recyclerview/widget/ItemTouchHelper

ItemTouchHelper 可以为 RecyclerView 添加滑动删除效果和拖动效果 ;

ItemTouchHelper 需要与 RecyclerView 和 ItemTouchHelper.Callback 结合起来使用 ;

根据想要开发的功能 , 重写不同的方法 ;

如果是想要开发拖动效果相关的功能 , 重写 ItemTouchHelper.Callback 的 onMoved 方法 ;

        public abstract boolean onMove(@NonNull RecyclerView recyclerView,
                @NonNull ViewHolder viewHolder, @NonNull ViewHolder target);

如果想要开发滑动相关效果 , 重写 ItemTouchHelper.Callback 的 onSwiped 方法 ;

public abstract void onSwiped(@NonNull ViewHolder viewHolder, int direction);

ItemTouchHelper 需要与 LayoutManager 布局管理器结合使用 ;

通过继承 ItemTouchHelper.Callback 抽象类 , 或

实现 ItemTouchHelper.Callback 接口 ,

这两个操作自定义 LayoutManager 布局管理器 , 可以达到最优化的效果 ;

看一下 Android 官方定义的线性布局管理器 LinearLayoutManager , 就实现了 ItemTouchHelper.ViewDropHandler 接口 ;

public class LinearLayoutManager extends RecyclerView.LayoutManager implements
        ItemTouchHelper.ViewDropHandler, RecyclerView.SmoothScroller.ScrollVectorProvider {
}

默认情况下 , ItemTouchHelper 移动 item 组件的 translateX 或 translateY 属性 , 为其重新设置位置 ;

开发者可以自定义这些行为通过覆盖 ItemTouchHelper.Callback 的 onChildDraw 和 onChildDrawOver 方法 ;

大多数情况下只需要覆盖 onChildDraw 方法即可 ;

onChildDraw 方法原型 :

public class ItemTouchHelper extends RecyclerView.ItemDecoration
        implements RecyclerView.OnChildAttachStateChangeListener {
	public abstract static class Callback {
        /**
         * Called by ItemTouchHelper on RecyclerView's onDraw callback.
         * <p>
         * If you would like to customize how your View's respond to user interactions, this is
         * a good place to override.
         * <p>
         * Default implementation translates the child by the given <code>dX</code>,
         * <code>dY</code>.
         * ItemTouchHelper also takes care of drawing the child after other children if it is being
         * dragged. This is done using child re-ordering mechanism. On platforms prior to L, this
         * is
         * achieved via {@link android.view.ViewGroup#getChildDrawingOrder(int, int)} and on L
         * and after, it changes View's elevation value to be greater than all other children.)
         *
         * @param c                 The canvas which RecyclerView is drawing its children
         * @param recyclerView      The RecyclerView to which ItemTouchHelper is attached to
         * @param viewHolder        The ViewHolder which is being interacted by the User or it was
         *                          interacted and simply animating to its original position
         * @param dX                The amount of horizontal displacement caused by user's action
         * @param dY                The amount of vertical displacement caused by user's action
         * @param actionState       The type of interaction on the View. Is either {@link
         *                          #ACTION_STATE_DRAG} or {@link #ACTION_STATE_SWIPE}.
         * @param isCurrentlyActive True if this view is currently being controlled by the user or
         *                          false it is simply animating back to its original state.
         * @see #onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int,
         * boolean)
         */
        public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView,
                @NonNull ViewHolder viewHolder,
                float dX, float dY, int actionState, boolean isCurrentlyActive) {
            ItemTouchUIUtilImpl.INSTANCE.onDraw(c, recyclerView, viewHolder.itemView, dX, dY,
                    actionState, isCurrentlyActive);
        }
    }
}

onChildDrawOver 方法原型 :

public class ItemTouchHelper extends RecyclerView.ItemDecoration
        implements RecyclerView.OnChildAttachStateChangeListener {
	public abstract static class Callback {
        /**
         * Called by ItemTouchHelper on RecyclerView's onDraw callback.
         * <p>
         * If you would like to customize how your View's respond to user interactions, this is
         * a good place to override.
         * <p>
         * Default implementation translates the child by the given <code>dX</code>,
         * <code>dY</code>.
         * ItemTouchHelper also takes care of drawing the child after other children if it is being
         * dragged. This is done using child re-ordering mechanism. On platforms prior to L, this
         * is
         * achieved via {@link android.view.ViewGroup#getChildDrawingOrder(int, int)} and on L
         * and after, it changes View's elevation value to be greater than all other children.)
         *
         * @param c                 The canvas which RecyclerView is drawing its children
         * @param recyclerView      The RecyclerView to which ItemTouchHelper is attached to
         * @param viewHolder        The ViewHolder which is being interacted by the User or it was
         *                          interacted and simply animating to its original position
         * @param dX                The amount of horizontal displacement caused by user's action
         * @param dY                The amount of vertical displacement caused by user's action
         * @param actionState       The type of interaction on the View. Is either {@link
         *                          #ACTION_STATE_DRAG} or {@link #ACTION_STATE_SWIPE}.
         * @param isCurrentlyActive True if this view is currently being controlled by the user or
         *                          false it is simply animating back to its original state.
         * @see #onChildDrawOver(Canvas, RecyclerView, ViewHolder, float, float, int,
         * boolean)
         */
        public void onChildDrawOver(@NonNull Canvas c, @NonNull RecyclerView recyclerView,
                ViewHolder viewHolder,
                float dX, float dY, int actionState, boolean isCurrentlyActive) {
            ItemTouchUIUtilImpl.INSTANCE.onDrawOver(c, recyclerView, viewHolder.itemView, dX, dY,
                    actionState, isCurrentlyActive);
        }
    }
}