android之RecycleView之ItemTouchHelper 处理拖拽、滑动删除

android之RecycleView之ItemTouchHelper 处理拖拽、滑动删除

与RecycleView和ItemTouchHelper.Callback一起使用

ItemTouchHelper内部包含内部类ItemTouchHelper.Callback

public class ItemTouchHelper extends RecyclerView.ItemDecoration
        implements RecyclerView.OnChildAttachStateChangeListener {

	public abstract static class Callback {

		/** @param viewHolder   正在被拖拽的viewHolder.
		* @param target       被正在拖拽的覆盖的viewHolder
		*                     dragged.*/

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

		/**direction  滑动的方向
		*                   {@link #UP}, {@link #DOWN},
		*                   {@link #LEFT} or {@link #RIGHT}*/

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

		/**makeFlag(ACTION_STATE_IDLE, RIGHT) | makeFlag(ACTION_STATE_SWIPE, LEFT | RIGHT);*/

		public abstract int getMovementFlags(RecyclerView recyclerView,ViewHolder viewHolder);

		/**被RecyclerView's onDraw调用*/

		public void onChildDraw(Canvas c, RecyclerView recyclerView,
        		ViewHolder viewHolder,
        		float dX, float dY, int actionState, boolean isCurrentlyActive) {
    			sUICallback.onDraw(c, recyclerView, viewHolder.itemView, dX, dY, actionState,
            		isCurrentlyActive);
		}

		/**被RecyclerView's onDraw调用，比较少用到*/

		public void onChildDrawOver(Canvas c, RecyclerView recyclerView,
        		ViewHolder viewHolder,
        		float dX, float dY, int actionState, boolean isCurrentlyActive) {
    			sUICallback.onDrawOver(c, recyclerView, viewHolder.itemView, dX, dY, actionState,
            		isCurrentlyActive);
		}

		public boolean isLongPressDragEnabled() {
    			return true;
		}

		public boolean isItemViewSwipeEnabled() {
    			return true;
		}

		/**当拖拽或者滑动改变的时候调用，复写是需调用父类方法*/

		public void onSelectedChanged(ViewHolder viewHolder, int actionState) {
    			if (viewHolder != null) {
        		sUICallback.onSelected(viewHolder.itemView);
    			}
		}

		……

	}

	/**默认Item长按时触发拖拽功能*/

	public void startDrag(ViewHolder viewHolder) {
    		if (!mCallback.hasDragFlag(mRecyclerView, viewHolder)) {
        		Log.e(TAG, "Start drag has been called but swiping is not enabled");
        		return;
    		}
    		if (viewHolder.itemView.getParent() != mRecyclerView) {
        		Log.e(TAG, "Start drag has been called with a view holder which is not a child of "
                		+ "the RecyclerView which is controlled by this ItemTouchHelper.");
        		return;
    		}
    		obtainVelocityTracker();
    		mDx = mDy = 0f;
    		select(viewHolder, ACTION_STATE_DRAG);
	}

	public static interface ViewDropHandler {……}

}

使用：

继承ItemTouchHelper.Callback

public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback {

    public static final float ALPHA_FULL = 1.0f;

    private final ItemTouchHelperAdapter mAdapter;

    public SimpleItemTouchHelperCallback(ItemTouchHelperAdapter adapter) {
        mAdapter = adapter;
    }

    @Override
    public boolean isLongPressDragEnabled() {
        return true;
    }

    @Override
    public boolean isItemViewSwipeEnabled() {
        return true;
    }

    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
            final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
            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);
        }
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder source, RecyclerView.ViewHolder target) {
        if (source.getItemViewType() != target.getItemViewType()) {
            return false;
        }

        // Notify the adapter of the move
        mAdapter.onItemMove(source.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int i) {
        // Notify the adapter of the dismissal
        mAdapter.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) {
            // Fade out the view as it is swiped out of the parent's bounds
            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;
                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) {
            ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
            itemViewHolder.onItemClear();
        }
    }
}