Store Information Directly in Nodes of a TreeView Control

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Introduction

This article will show you two things that you can do with the Tag property. First, I will show you how to use the Tag property of a control (here a TreeNode) to store information. Then, I will show you how to link controls together with the Tag property, which is used in this article to link DataRenderer to the TreeNode, which should save the data.

Background

The Tag property is defined in the System.Windows.Forms.Control class of the .NET Framework. This is the base class (directly or indirectly) of all the controls in Windows Forms.

The type of the Tag property is object. So you can store all kinds of information that you can think of. Object is the "superclass" of .NET. All other classes are inherited (directly or indirectly) from this class. The primitive data types, like string or int, can always convert to or from an object. This technique is called boxing/unboxing.

Using the Code

When the TreeView control fires the AfterSelect event, the TreeNode information is displayed in a stupid TextBox txtData. The TextBox and the other controls (here only the "Save"-button) were created at runtime and docked on the GroupBox gpData. The "Save" button was added to a Panel actBtnPanel docked to the top. If a TreeNode in the TreeView control tvMain is selected and this selected node has information in the Tag property, then show this in txtData.

For later saving, the TextBox saves a reference to the TreeNode object, where the information should be saved. The created Button btnSave stores a reference to the TextBox object in the Tag property. So it is able to find out the new information that has to be saved.

TextBox txtData = new TextBox();

//The extended information can be stored 
//in the Tag-Property of a TreeNode
if(this.tvMain.SelectedNode.Tag != null)
    txtData.Text = 
         this.tvMain.SelectedNode.Tag.ToString();
    
//Store the TreeNode for saving data later
txtData.Tag = this.tvMain.SelectedNode;

...

Button btnSave = new Button();
btnSave.Text = "Save";
//Store the TextBox-Instance, wich render 
//the Data, in the Tag-Property
//So the Button itself knows, what 
//to save in the TreeNode
btnSave.Tag = txtData;

btnSave.Click += new EventHandler(BtnSaveClick);
                    
//Build GUI
this.gpData.Controls.Add(txtData);
this.gpData.Controls.Add(actBtnPanel);

When the user changes the text in the TextBox txtData and clicks the "Save" button, the button instance itself is passed to the assigned event-handler as sender. Here, the sender was casted to the right type Button. The Tag property of the button has a reference to the Textbox, which has the new content to be saved in TreeNode. The Textbox also has a reference to the TreeNode (in its Tag property), where the information is to be stored. And that's it. In the event-handler now we have all the information and references that are necessary to save the data.

private void BtnSaveClick(object sender, System.EventArgs e)
{
    //the Save-Button
    Button btnSave = sender as Button;
    
    //TextBox, which stores the data
    TextBox txtData = btnSave.Tag as TextBox;
    
    //TreeNode, Destination for saving data
    TreeNode tnDesc = txtData.Tag as TreeNode;
    
    //Only save if data was modified
    if(txtData.Modified)
    {
        tnDesc.Tag = txtData.Text;                    
    }
}

Points of interest

• In this article, you can see that you don't have to save all the interesting objects in the extra-defined reference variables to work with them. The controls themselves can save the information that they need to work with.
• .NET is great and I had a lot of fun programming in C#.

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