Winform组合ComboBox和TreeView实现ComboTree

最近做Winform项目需要用到类似ComboBox的TreeView控件。

虽然各种第三方控件很多，但是存在各种版本不兼容问题。所以自己写了个简单的ComboTreeView控件。

下图是实现效果：

目前实现的比较简单，能满足我项目中的需求。

此处是项目中的代码简化后的版本，供大家参考。

 using System;
 using System.Collections.Generic;
 using System.Windows.Forms;

 namespace CustomControl.Tree
 {
     public abstract class ComboTreeView<T> : ComboBox where T : class
     {
         protected const int WM_LBUTTONDOWN = 0x0201, WM_LBUTTONDBLCLK = 0x0203;

         protected TreeView treeView;
         protected ToolStripControlHost treeViewHost;
         protected ToolStripDropDown dropDown;
         protected bool dropDownOpen = false;
         protected TreeNode selectedNode;
         protected T toBeSelected;

         public ComboTreeView(TreeView internalTreeView)
         {
             if (null == internalTreeView)
             {
                 throw new ArgumentNullException("internalTreeView");
             }
             this.InitializeControls(internalTreeView);
         }

         public event TreeNodeChangedEventHandler TreeNodeChanged;

         protected virtual void InitializeControls(TreeView internalTreeView)
         {
             this.treeView = internalTreeView;
             this.treeView.BorderStyle = BorderStyle.FixedSingle;
             this.treeView.Margin = new Padding();
             this.treeView.Padding = new Padding();
             this.treeView.AfterExpand += new TreeViewEventHandler(this.WhenAfterExpand);

             this.treeViewHost = new ToolStripControlHost(this.treeView);
             this.treeViewHost.Margin = new Padding();
             this.treeViewHost.Padding = new Padding();
             this.treeViewHost.AutoSize = false;

             this.dropDown = new ToolStripDropDown();
             this.dropDown.Margin = new Padding();
             this.dropDown.Padding = new Padding();
             this.dropDown.AutoSize = false;
             this.dropDown.DropShadowEnabled = true;
             this.dropDown.Items.Add(this.treeViewHost);
             this.dropDown.Closed += new ToolStripDropDownClosedEventHandler(this.OnDropDownClosed);

             this.DropDownWidth = this.Width;
             base.DropDownStyle = ComboBoxStyle.DropDownList;
             base.SizeChanged += new EventHandler(this.WhenComboboxSizeChanged);
         }

         public new ComboBoxStyle DropDownStyle
         {
             get { return base.DropDownStyle; }
             set { base.DropDownStyle = ComboBoxStyle.DropDownList; }
         }

         public virtual TreeNode SelectedNode
         {
             get { return this.selectedNode; }
             private set { this.treeView.SelectedNode = value; }
         }

         public virtual T SelectedNodeData
         {
             get { return (T)base.SelectedItem; }
             set
             {
                 this.toBeSelected = value;
                 this.UpdateComboBox(value);
             }
         }

         protected new int SelectedIndex
         {
             get { return base.SelectedIndex; }
             set { base.SelectedIndex = value; }
         }

         protected new object SelectedItem
         {
             get { return base.SelectedItem; }
             set { base.SelectedItem = value; }
         }

         public virtual string DisplayMember { get; set; } = "Name";

         /// <summary>Gets the internal TreeView control.</summary>
         public virtual TreeView TreeView => this.treeView;

         /// <summary>Gets the collection of tree nodes that are assigned to the tree view control.</summary>
         /// <returns>A <see cref="T:System.Windows.Forms.TreeNodeCollection" /> that represents the tree nodes assigned to the tree view control.</returns>
         public virtual TreeNodeCollection Nodes => this.treeView.Nodes;

         public new int DropDownHeight { get; set; } = ;

         public new int DropDownWidth { get; set; } = ;

         protected virtual void ShowDropDown()
         {
             this.dropDown.Width = this.Width;
             this.dropDown.Height = this.DropDownHeight;
             this.treeViewHost.Width = this.Width;
             this.treeViewHost.Height = this.DropDownHeight;
             this.treeView.Font = this.Font;
             this.dropDown.Focus();
             this.dropDownOpen = true;
             this.dropDown.Show(this, , base.Height);
         }

         protected virtual void HideDropDown()
         {
             this.dropDown.Hide();
             this.dropDownOpen = false;
         }

         protected virtual void ToggleDropDown()
         {
             if (!this.dropDownOpen)
             {
                 this.ShowDropDown();
             }
             else
             {
                 this.HideDropDown();
             }
         }

         protected override void WndProc(ref Message m)
         {
             if ((WM_LBUTTONDOWN == m.Msg) || (WM_LBUTTONDBLCLK == m.Msg))
             {
                 if (!this.Focused)
                 {
                     this.Focus();
                 }
                 this.ToggleDropDown();
             }
             else
             {
                 base.WndProc(ref m);
             }
         }

         protected override void Dispose(bool disposing)
         {
             if (disposing)
             {
                 if (this.dropDown != null)
                 {
                     this.dropDown.Dispose();
                     this.dropDown = null;
                 }
             }
             base.Dispose(disposing);
         }

         protected virtual void WhenTreeNodeChanged(TreeNode newValue)
         {
             if ((null != this.selectedNode) || (null != newValue))
             {
                 bool changed;
                 if ((null != this.selectedNode) && (null != newValue))
                 {
                     changed = (this.selectedNode.GetHashCode() != newValue.GetHashCode());
                 }
                 else
                 {
                     changed = true;
                 }

                 if (changed)
                 {
                     if (null != this.TreeNodeChanged)
                     {
                         try
                         {
                             this.TreeNodeChanged.Invoke(this, new TreeNodeChangedEventArgs(this.selectedNode, newValue));
                         }
                         catch (Exception)
                         {
                             // do nothing
                         }
                     }

                     this.selectedNode = newValue;
                     this.UpdateComboBox(this.GetTreeNodeData(newValue));
                 }
             }
         }

         protected virtual void OnDropDownClosed(object sender, ToolStripDropDownClosedEventArgs e)
         {
             if (null == this.toBeSelected)
             {
                 var selectedNode = this.treeView.SelectedNode;
                 this.WhenTreeNodeChanged(selectedNode);
             }
         }

         protected virtual void UpdateComboBox(T data)
         {
             base.DisplayMember = this.DisplayMember; // update DisplayMember
             if (null != data)
             {
                 this.DataSource = new List<T>() { data };
                 this.SelectedIndex = ;
             }
             else
             {
                 this.DataSource = null;
             }
         }

         protected virtual void WhenAfterExpand(object sender, TreeViewEventArgs e)
         {
             if (null != this.toBeSelected)
             {
                 if (this.SelectChildNode(e.Node.Nodes, this.toBeSelected))
                 {
                     this.toBeSelected = null;
                 }
             }
         }

         protected virtual void WhenComboboxSizeChanged(object sender, EventArgs e)
         {
             this.DropDownWidth = base.Width;
         }

         public virtual bool SelectChildNode(TreeNodeCollection nodes, T data)
         {
             var node = this.FindChildNode(nodes, data);
             if (null != node)
             {
                 this.DoSelectTreeNode(node);
                 return true;
             }
             else
             {
                 return false;
             }
         }

         protected abstract bool Identical(T x, T y);

         protected virtual void DoSelectTreeNode(TreeNode node)
         {
             this.SelectedNode = node;
             this.ExpandTreeNode(node.Parent);
         }

         public virtual TreeNode FindChildNode(TreeNodeCollection nodes, T data)
         {
             foreach (TreeNode node in nodes)
             {
                 var nodeData = this.GetTreeNodeData(node);
                 if (this.Identical(nodeData, data))
                 {
                     return node;
                 }
             }

             return null;
         }

         public virtual void ExpandTreeNode(TreeNode node)
         {
             if (null != node)
             {
                 node.Expand();
                 this.ExpandTreeNode(node.Parent);
             }
         }

         public abstract T GetTreeNodeData(TreeNode node);
     }
 }

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