实现树的拖动,从一个节点到令一节点, 可以自动的判断是否可以添加或介绍,是学习树拖拽的好参考-Drag the realization of the tree from one node to make a node, you can automatically determine whether you can add or introduction, is to learn from the tree drag the good reference

VC Tree树状节点拖动示例，精选学习源码，很好的参考资料。-VC Tree tree node drag example, select learning source code, a good reference.