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Customizing the DataGridView to support expanding/collapsing (ala TreeGridView)

Customizing the DataGridView to support expanding/collapsing (ala TreeGridView)

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One of the first things that I wanted to customize with the DataGridView is to make it support hierarchical data

If you read my first blog post you'll find out that I'm not a developer (anymore). Even though I'm not a developer I still like to take features and customize them to do something really cool. As far as the DataGridView goes, customizing it to support hierarchical data is a much larger task since the structure of the DGV doesn't lend itself to having different column sets, so, I decided I'd settled for a tree like structure.

Think of a TreeView combined with a ListView and that is basically what I wanted to go with.

NOTE: This code is not supported by Microsoft and is provided "as-is". This code it not meant to show "best practices", but just showing a concept.

NOTE: This control is written to require Visual Styles to be enabled on your computer. You'll need to modify it if you want to run the TreeGridView without visual styles. Some people have been able to modify the code to run without Visual Styles. See this post for details.

Original Code: http://www.windowsforms.net/blogs/markrideout/treegridview.zip

Here is a picture:

Anyway. The basic part of creating a DataGridView that can expand and collapse is to dynamically add and remove rows. That was the easy part. To make this really usable and extendable, I decided to add a lot code and make this easier to use. Here are some details:

Design

I wanted to ensure that the design of the TreeGridView supported normal TreeView type properties and features, so creating necessary classes to create the “tree view” experience wa necessary (see object model for more details).

Custom Painting – Painting an image in a cell is easy, but ensuring that the text from the DataGridViewTextBoxCell didn’t overlap the image took a bit of work. Using the Padding feature of the DataGridViewCellStyle, I add padding to the left side of the cell to account for the text and the indentation. This padding affects the painting and behavior of the text box cell, so editing a text cell correctly positions the editing control.

Siting/Unsiting a node – Since I don’t want to set padding and styling except when a node is actually displayed. When the node is displayed or in the grid, it is sited. When the node is sited I set all the necessary properties.

Unbound – Since expanding and collapsing is based upon dynamically adding and removing rows from the grid, I decided that unbound mode would be the best way to go with this. I’ve hidden the “databinding” properties and the virtual mode property since this doesn’t support those features.

Edit Mode – One thing that I had to deal with is that double-clicking a cell enters edit mode. This double-click occurs regardless of the padding, so double-click on the +\- symbol causes the control to enter edit mode. Edit also enters if you single click on a cell that already has focus. So, to deal with this I turn edit mode to be enabled only through programmatic means. I have code to handle the F2 key to enter edit mode. There are other ways to solve this, but I went with the F2 approach.

Object model structure

TreeGridNode - Just like a tree view, I wanted to have the concept of a node. I made the nodes class derive from a DataGridViewRow since a node in the list is the same as a row, just with a bit more info.

Here are some properties:

Nodes – Again, like the treeview, a node has children, so there is a Nodes property that returns child nodes. One of the challenges in coding this is to know when a node is actually a row or when it is just a node. A node is a row when it is in the grid, otherwise it is just a node.

IsSited – A node is “sited” when it is contained in the grid as a row. The Sited property is true in this case. There are a set of protected virtual methods on the TreeGridView class (SiteNode and UnSiteNode).

ImageIndex – Image index for the node’s image. Only used when an ImageList is associated with the TreeGridView.

Image – Image associated with the node. Sets or gets the image. When an ImageList is associated with the TreeGridView and an ImageIndex is set then this returns an image from the ImageList. You can set the Image property to an image if you aren’t using an ImageList.

Cells – Returns the cells for the given node. This wasn’t easy to do since accessing the cells for a node (or row) when the node isn’t sited. Using the DataGridView’s CreateCells method I can get the correct cells collection when the node isn’t in the grid.

TreeGridCell/Column – This is a special DataGridView cell that derives from the DataGridViewTextBoxCell. The main thing that this custom cell class does is to customize the cell drawing to make it look like a tree node. That means that it draws the node’s image and the +/- icons and the tree lines. The custom cell also is where a node detects when you click the mouse to expand or collapse a node. NOTE: A lot more work can be done to correctly detect that the mouse is directly over the +/- image. Right now I’m not doing that.

TreeGridView – This class derives from the DataGridView control. Many things are done in this class. Nodes are sited/unsited in the grid as actual rows. Somce DataGridView Properties are hidden since they do not apply.

Here are some properties:

VirtualNodes – One of the common things done with a normal TreeView is to dynamically add child nodes when the user is expanding the parent. With the normal TreeView usres add temp child nodes to get the + sign and support expanding, then remove the temp node later. With the VirtualNodes property, the TreeGridView always displays a + sign next to a node, even if the node doesn’t have any children. Then, by handling the Expanding event you can dynamically add child nodes.

ImageList – ImageList associated with the TreeGridView

Nodes – Identifies the root nodes.

ShowLines – Determines if the TreeGridView shows lines between nodes.

CurrentNode – Identifies the node that has focus.

Here are some events:

Expanding – Again, like the treeview, this event occurs before a node is starting to expand. You can add nodes in this event to fill in more details of a child node collection. When the VirtualNodes property is true, the TreeGridView will display the node with a + sign next to it even when it doesn’t have any children. Handling the Expanding event is where you would dynamically add new child nodes.

Expanded – After a node is expanded.

Collapsing – Before a node is being collapsed

Collapsed – After a node has been collapsed.

I’ve included a simple test app that creates a news group reader looking list that supports expanding and collapsing.

Let me know what you think and how you've used this in your project!

-mark

  • Good work!
    Can I have it in  2003 version?
    Thanks.
  • The Tag property of a TreeNodeCell does'nt work. I've added a new TreeNodeCell programmetically and set its Tag property to some integer and tried to get that it returns null
  • Hello,

    I had a similar idea some time ago and here is the result: Hierarchical DataGridView. Component works in a similar way - instead of a node collection it uses data in System.Data.DataTable to represent hierarchically organized data.


    Regards,
    Rasinec Ninoslav
    ApplicationAspect.com
  • Very nice. What about databinding, did anybody made it?
  • First of all, Great job.
    I'm tring to implement sort, I've though about using the
    level of a node and the SortCompare event (only values with the same level will be sorted), my question is, how can I get the node of a row from the RowIndex property?

    thanks...
  • Hi,

    Who solved the error :

    Unable to cast object of type 'System.Windows.Forms.DataGridViewTextBoxCell' to type 'AdvancedDataGridView.TreeGridCell'.

    Thank you

  • Hi,

    Is it possible to create a custom datagrid with the feature of expandable columns like expandable rows? Using that a user can expand and collapse the columns to edit the data.

    I am searching this for a long time.

    Please give me your valuable feedback.

    Thanks,

    Natraj

  • Looks Good. But is it compatable with Framework 1.1. I am using VS.NET 2003 and i am not able to add this control in my project. getting following error message.

    "ExpandableGridView.dll not a Microsoft .NET module"

  • hi. I want to ask question about code copyright? What does is mean?

    Can I use in commercial application with microsoft visual c# 2005 express edition?

  • In order to fix the error that most people are receiving you have to goto the properties for the treegridview and then click on columns.  It automatically defaults to DataGridTextboxColumn for ColumnType.  You need to change this to TreeGridColumn.  Took me a minute to figure out as well.

  • For those who are encountering the following error:

    Unable to cast object of type 'System.Windows.Forms.DataGridViewTextBoxCell' to type 'AdvancedDataGridView.TreeGridCell'

    I'm only dealing with text but I accidentally selected a Column Type of System.Windows.Forms.DataGridViewTextBoxColumn instead of AdvancedDataGridView.TreeGridColumn  once i changed it to TreeGridColumn, walla.

    This fixed it for me.  I'm using this in a VB.Net Project.

    Hope this helps

    Justified

  • I wanted to use the control in windows 2000, without the XP Visual Styles, so I made some changes, based on another project I found here:

    http://www.codeproject.com/cs/miscctrl/XPCollapsGroupBox.asp

    The changes are:

    In the TreeGridView.cs instead of the 2 rows:

    internal VisualStyleRenderer rOpen = new VisualStyleRenderer(VisualStyleElement.TreeView.Glyph.Opened);

    //internal VisualStyleRenderer rClosed = new VisualStyleRenderer(VisualStyleElement.TreeView.Glyph.Closed);

    I have:

    internal Graphics rOpen ;

    internal Graphics rClosed ;

    In the TreeGridCell.cs

    Instead of :

    // Paint node glyphs

                   if (node.IsExpanded)

                        node._grid.rOpen.DrawBackground(graphics, new Rectangle(glyphRect.X, glyphRect.Y + (glyphRect.Height / 2) - 4, 10, 10));              

                   else

                        node._grid.rClosed.DrawBackground(graphics, new Rectangle(glyphRect.X, glyphRect.Y + (glyphRect.Height / 2) - 4, 10, 10));

    I have:

    // Paint node glyphs

                   if (node.IsExpanded)

                   {

                       node._grid.rOpen = graphics;

                       node._grid.rOpen.DrawImage(Properties.Resources.minus, new Rectangle(glyphRect.X, glyphRect.Y + (glyphRect.Height / 2) - 4, 10, 10));

                   }

                   else

                   {

                       node._grid.rClosed = graphics;

                       node._grid.rClosed.DrawImage(Properties.Resources.plus, new Rectangle(glyphRect.X, glyphRect.Y + (glyphRect.Height / 2) - 4, 10, 10));

                   }

    For the last code snippet I added 2 images to the project resources. The images could be found in the project I mentions its url in the beginning.

  • i added the ExpandableGridView.dll in my vbdot ent project, but i am not able to add the Refernce of C# classes required into my vb project. how to do it ?

  • I've mananged to get a datagridview working very well with grouping as well as expanding and collapsing icons in the grid.

    The grouping has a category as the parent and descriptions... price... etc... as children with an item count in the Parent.

    Looks like this sort of in the DataGridView:

    Some Category (Plus Item Count)

                Descritpion        Price        Sold

    Some Category #2 (Plus Item Count)

                Descritpion        Price        Sold

    etc...

    It also has all the trimings with row delete... notes addition from a currentcell doubleclick which i'd be happy to share if anyone is interested.

    I have been trying to implement a DragDrop and having major trouble maintaining the above group when I move the rows in the DataGridView. I need to keep the Parent/Children relationship when the rows are moved in the DataGridView.

    Has anyone done this before that can offer the right way to go about solving the above? Have sample code to illustrate???

    Any help would be greatly appreciated... Thank you in advance.

    Thanks,

    BillB

  • I got an error:

    Object reference not set to an instance of an object.

    Site: Void UnSiteNode

           TreeGridView.UnSiteNode(TreeGridNode node)

           TreeGridView.Dispose(Boolean disposing)

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