创建自定义 TreeView/TreeNode [英] Creating custom TreeView/TreeNode

问题描述

我需要扩展 TreeNode 类，以便我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:

I need to extend the TreeNode class such that I can add custom properties to each node (seeing as WebForms TreeNode doesn't include the Tag property). So this is my 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:

If I create a CustomTreeNode and add it to a TreeView:

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

然后我会在执行以下操作时遇到强制转换异常:

I would then get a casting exception doing the following:

CustomTreeNode selectedNode = (CustomTreeNode)TreeView.SelectedNode;

因为 TreeView 返回的是 TreeNode，而不是 CustomTreeNode.

because TreeView returns a TreeNode, not a CustomTreeNode.

我已经阅读了一些资料，看起来我需要扩展 TreeView 类，并覆盖 CreateNode() 方法以返回 CustomTreeNode 而不是 TreeNode.所以我创建了这个:

I've done some reading, and it looks like I need to extend the TreeView class, and override the CreateNode() method to return CustomTreeNode instead of TreeNode. So I created this:

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

然而，问题是 CreateNode() 不接受任何参数，因此您必须为 CustomTreeNode 类调用空构造函数.所以当我在上面创建我的 CustomTreeNode 时，当我从 CustomTreeView 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.

The problem is however, CreateNode() doesn't take any arguments, so you have to have call the empty constructor for the CustomTreeNode class. So when I created my CustomTreeNode above, when I get it back from the CustomTreeView, the nodeId and nodeType values have been lost because the empty constructor returns a node without any values.

非常感谢任何帮助.

推荐答案

这就是我想出来的(专家，欢迎任何建议).在后面的代码中实例化 CustomTreeNode 并通过 setter 设置属性.修改您的 CustomTreeNode 类以将值保留在 ViewState 中.自定义树视图的 CreateNode 返回的节点将加载 ViewState 信息.

This is what I came up with (experts, any advice welcomed). Instantiate the CustomTreeNodes in your code behind and set the properties via setters. Modify your CustomTreeNode class to persist the values in ViewState. The node returned by your custom tree view's CreateNode will load the ViewState information.

TreeNode 类:

TreeNode class:

[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:

TreeView class:

[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在程序集Foo"和命名空间Bar"中定义:

Simple .aspx file (Assuming that your custom control is defined in an assembly "Foo" and a namespace "Bar":

<%@ 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;
    }

这篇关于创建自定义 TreeView/TreeNode的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！