Android ItemTouchHelper 實踐

實作RecyclerView拖動排序和滑動删除，我想到的是  Android ViewDragHelper執行個體 ，或者是第三方庫，當我看了 ToDoList 的時候，發現原來官方已經支援RecyclerView拖動排序與滑動删除，那就是ItemTouchHelper。

簡介

“ItemTouchHelper is a utility class to add swipe to dismiss and drag & drop support to RecyclerView.

It works with a RecyclerView and a Callback class, which configures what type of interactions are enabled and also receives events when user performs these actions.

Depending on which functionality you support, you should override onMove(RecyclerView, ViewHolder, ViewHolder) and / or onSwiped(ViewHolder, int).”

ItemTouchHelper 實作RecyclerView拖動排序和滑動删除，我們需要重寫方法：

int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)      

指定可以支援的拖放和滑動的方向，上下為拖動（drag），左右為滑動（swipe）

onMove(RecyclerView, ViewHolder, ViewHolder)      

滑動操作

onSwiped(ViewHolder, int)      

删掉操作

實踐

依賴

app/build.gradle

compile 'com.android.support:recyclerview-v7:25.0.0'      

效果預覽

線性

網格

ItemTouchHelperCallback

建立ItemTouchHelperCallback繼承ItemTouchHelper.Callback，完整代碼如下：

public class ItemTouchHelperCallback extends ItemTouchHelper.Callback {
    private ItemTouchHelperAdapter itemTouchHelperAdapter;
    private float ALPHA_FULL = 1.0f;

    ItemTouchHelperCallback(ItemTouchHelperAdapter itemTouchHelperAdapter) {
        this.itemTouchHelperAdapter = itemTouchHelperAdapter;
    }

    /**
     * RecyclerView item支援長按進入拖動操作
     */
    @Override
    public boolean isLongPressDragEnabled() {
        return true;
    }

    /**
     * RecyclerView item任意位置觸發啟用滑動操作
     */
    @Override
    public boolean isItemViewSwipeEnabled() {
        return true;
    }

    /**
     * 指定可以支援的拖放和滑動的方向，上下為拖動（drag），左右為滑動（swipe）
     */
    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        if (recyclerView.getLayoutManager() instanceof GridLayoutManager || recyclerView.getLayoutManager() instanceof StaggeredGridLayoutManager) {
            final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
            //不需要滑動
            final int swipeFlags = 0;
            return makeMovementFlags(dragFlags, swipeFlags);
        } else {
            final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
            final int swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;
            return makeMovementFlags(dragFlags, swipeFlags);
        }
    }

    /**
     * 滑動操作
     */
    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
        if (viewHolder.getItemViewType() != target.getItemViewType()) {
            return false;
        }
        // Notify the adapter of the move
        itemTouchHelperAdapter.onItemMove(viewHolder.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

    /**
     * 删掉操作
     */
    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
        itemTouchHelperAdapter.onItemDismiss(viewHolder.getAdapterPosition());
    }

    @Override
    public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
            //自定義滑動動畫
            final float alpha = ALPHA_FULL - 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);
        }
    }

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        // We only want the active item to change
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
            if (viewHolder instanceof ItemTouchHelperViewHolder) {
                // Let the view holder know that this item is being moved or dragged
                ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
                //選中狀态回調
                itemViewHolder.onItemSelected();
            }
        }
        super.onSelectedChanged(viewHolder, actionState);
    }

    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);
        viewHolder.itemView.setAlpha(ALPHA_FULL);
        if (viewHolder instanceof ItemTouchHelperViewHolder) {
            // Tell the view holder it's time to restore the idle state
            ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
            //未選中狀态回調
            itemViewHolder.onItemClear();
        }
    }
}      

attachToRecyclerView

ItemTouchHelperCallback itemTouchHelperCallback = new ItemTouchHelperCallback(recyclerViewAdatper);
itemTouchHelper = new ItemTouchHelper(itemTouchHelperCallback);
itemTouchHelper.attachToRecyclerView(recyclerView);      

源碼