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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

  • I am doing something similar when I extend DataGridView, and the WinForms designer gives me the same errors that this project does ...

    The variable 'treeGridNode6' is either undeclared or was never assigned.  


    Could not find type 'AdvancedDataGridView.TreeGridNode'. Please make sure that the assembly that contains this type is referenced. If this type is a part of your development project, make sure that the project has been successfully built.  


    Can anybody suggest a fix?  Thanks
  • I've been enjoying the control, but I'm having trouble getting it to scale well. Having a node with anything more than 20 children quickly becomes unusable (50 nodes takes over 10 seconds to expand). It seems to come down to setting the this.Style.Padding on each cell, instead of using the default. Am I missing something or is creating a style for each cell really expensive?

    Thanks.
  • Thanks for the great code Mark.
    But i had question,when i try to add items more than 1000 items in the tree,it takes extremely long time to update.
    Is there a way the efficiency could be improved.
  • this is really cool.but adding databinding property would be perfect.if anybody had made this, please show the code:) i really need it.
  • Thanks for the great code. How can i add in support for row template. I see from you code, you disabled it in the treegridview object. However, I'd like the ability to control the row height. where can i make the insertions?
  • it is a great code.....is there any way to put check boxes instead of text boxes....I need something like : check Parent node...check all child nodes....
  • Hey Fil. your code. where does it go?
    in line 218 there is an else.

    all the rest
    did any one added Databinding to this?
    i see i am not the only one asking...
  • Is it posible to have grouped columns in the grid. expandable with (+) sign...or something like that..similar like having tree view on the left..i need master detail functionality where the columns are?
  • Your article is prety nice. It's a pity that i didn't see it more later.
  • Just wondering if anyones looked into implementing sorting with this control? and if so how they managed it? Need to implement it for my control and unsure where to start...
  • I need databinding, may be i make this.

    Vary thanks for the this control !

    Best regards to autor !
  • The tree is expanded.

    how do I get the current node?

    I need to get the values on the click or double click...
  • Mark,

    How can I toggle the highlighting on a row with every mouse click?
    I tried to override SetSelectedRowCore with no luck.

  • thanks for code.
    but,i hope VB source
  • Can I have a check box column in this treeGridView control, so that user can select multiple items
    If possible can u send me the code
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