创建自定义 TreeView/TreeNode

Question

我需要扩展 TreeNode 类，以便可以向每个节点添加自定义属性（因为 WebForms TreeNode 不包含 Tag 属性）。所以这是我的 CustomTreeNode：

public class CustomTreeNode : TreeNode
{

    public CustomTreeNode()
    {               
    }

    public CustomTreeNode(int nodeId, string nodeType)
    {
        NodeId = nodeId;
        NodeType = nodeType;
    }

    public string NodeType { get; set; }
    public int NodeId { get; set; }
}

如果我创建一个 CustomTreeNode 并将其添加到 TreeView：

CustomTreeNode node = new CustomTreeNode(1, "CustomType");            
treeView.Nodes.Add(node);

然后我会得到一个强制转换异常，执行以下操作：

CustomTreeNode selectedNode = (CustomTreeNode)TreeView.SelectedNode;

因为 TreeView 返回的是 TreeNode，而不是 CustomTreeNode。

我做了一些阅读，看起来我需要扩展 TreeView 类，并重写 CreateNode() 方法以返回 CustomTreeNode 而不是 TreeNode。所以我创建了这个：

public class CustomTreeView : TreeView
{
    protected override TreeNode CreateNode()
    {
        return new CustomTreeNode();
    }
}

但是，问题是 CreateNode() 不接受任何参数，因此您必须调用 CustomTreeNode 类的空构造函数。所以当我在上面创建我的 CustomTreeNode 时，当我从 CustomTreeView 中取回它时，nodeId 和 nodeType 值已经丢失，因为空构造函数返回一个没有任何值的节点。

非常感谢任何帮助。

Answer 1

这是我想出的（专家，欢迎提出任何建议）。在后面的代码中实例化 CustomTreeNodes 并通过 setter 设置属性。修改您的 CustomTreeNode 类以将值保留在 ViewState 中。您的自定义树视图的CreateNode 返回的节点将加载 ViewState 信息。

TreeNode 类：

[DefaultProperty("Text")]
[ToolboxData("<{0}:CustomTreeNode runat=server></{0}:CustomTreeNode>")]
public class CustomTreeNode : TreeNode
{
    private const int NODE_TYPE = 1;
    private const int NODE_ID = 2;

    public string NodeType { get; set; }
    public int NodeId { get; set; }

    protected override void LoadViewState(Object savedState)
    {
        if (savedState != null)
        {
            object[] myState = (object[])savedState;
            if (myState[0] != null)
                base.LoadViewState(myState[0]);
            if (myState[NODE_TYPE] != null)
                this.NodeType = (string)myState[NODE_TYPE];
            if (myState[NODE_ID] != null)
                this.NodeId = (int)myState[NODE_ID];

        }
    }

    protected override Object SaveViewState()
    {
        object baseState = base.SaveViewState();
        object[] allStates = new object[3];
        allStates[0] = baseState;
        allStates[NODE_TYPE] = this.NodeType;
        allStates[NODE_ID] = this.NodeId;

        return allStates;
    }
}

TreeView 类：

[DefaultProperty("Text")]
[ToolboxData("<{0}:CustomTreeView runat=server></{0}:CustomTreeView>")]
public class CustomTreeView : TreeView
{
    protected override TreeNode CreateNode()
    {
        // Tree node will get its members populated with the data from VIEWSTATE
        return new CustomTreeNode();
    }
}

简单的 .aspx 文件（假设您的自定义控件定义在程序集“Foo”和命名空间“Bar”中：

<%@ Register TagPrefix="customControl" Assembly="Foo" Namespace="Bar"  %>

<customControl:CustomTreeView ID="sampleTree" 
    runat="server" onselectednodechanged="sampleTree_SelectedNodeChanged"></customControl:CustomTreeView>
<asp:Label ID="lblSelectedNode" runat="server" ></asp:Label>

代码隐藏：

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            PopulateTree();
        }
    }

    private void PopulateTree()
    {
        sampleTree.Nodes.Clear();
        CustomTreeNode root = new CustomTreeNode();
        root.Value = "root node";

        sampleTree.Nodes.Add(root);

        // Creating some fake nodes (you would of course be using real data)
        for (int i = 0; i < 10; i++)
        {
            CustomTreeNode child = new CustomTreeNode();
            child.NodeId = i;               // Saved in ViewState
            child.NodeType = "Type " + i;   // Saved in ViewState
            child.Value = child.NodeType;
            root.ChildNodes.Add(child);
        }
    }

    protected void sampleTree_SelectedNodeChanged(object sender, EventArgs e)
    {
        CustomTreeView cTreeView = (CustomTreeView) sender;
        lblSelectedNode.Text = ((CustomTreeNode)cTreeView.SelectedNode).NodeType;
    }