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- VB NET 2010 POPULATE TREEVIEW WITH DIRECTORY STRUCTURE HOW TO
- VB NET 2010 POPULATE TREEVIEW WITH DIRECTORY STRUCTURE UPDATE
- VB NET 2010 POPULATE TREEVIEW WITH DIRECTORY STRUCTURE CODE
If iE.Current IsNot Nothing Then Dim r As DbDataRecord = CType(iE.Current, DbDataRecord)
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Here we get a data enumerator to fill out the root nodes: Having done that, we want to create a SQLDbDataReader or OleDbDataReader object and return an IEnumerator by calling GetEnumerator on it. DataReader and IEnumerator are very fast, read-only, forward-only recordset-like objects perfect for just this sort of thing.Īssume we have opened a query against the database that either reads the records to initialize the treeview with the root nodes or one that uses a parameter or stored procedure argument to fill the children of a selected node. We will be using the IEnumerator object to iterate through the records, filling the Treeview nodes. One is that you are familiar with opening Access or SQL Server databases using ADO.NET.
VB NET 2010 POPULATE TREEVIEW WITH DIRECTORY STRUCTURE CODE
These code snippets will not compile as is. This is the database table scheme I often use to represent hierarchical relationships. With transaction processing, undos are available to the user, and strongly recommended.
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VB NET 2010 POPULATE TREEVIEW WITH DIRECTORY STRUCTURE UPDATE
It's powerful, for example, one could allow the user to drag/drop folders as in Windows explorer and all that would be required is a single record update in the database to effect the operation. What is instructive is the database table scheme to represent folder relationships-a methodology I have been using for some time, and one that is demonstrated in this article.
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Note that the author is using ASP.NET, and is using the table adapter scheme in ADO.NET, which I consider overkill for simply filling out nodes, unless the developer intends to allow the user to edit and save the node labels. One can search the internet for code snippets dealing with recursive methods that fill out the entire tree, one is here. There are plenty of good articles on the net to learn this.
VB NET 2010 POPULATE TREEVIEW WITH DIRECTORY STRUCTURE HOW TO
It is beyond the scope of the article to teach the reader how to use ADO.NET to do what is presented. Since this my first submission, I will not attempt to include working code or a project sample, just code snippets to demonstrate the method. This duplicates the behavior of the Windows Explorer tree while browsing local drives. I have made changes to the code to load one level ahead-the algorithms now load the grandchildren of the node being selected. Selective recursion on an expanded node might be an option or deciding to recurse based on the number of records returned by a query, and I welcome any comments on that topic. I deemed this behavior acceptable for the application I was writing, since the source database contains thousands of records. You do not get an indication of possible node expansion (+ symbol) until you actually click on it. This is the behavior one encounters when you are using Windows explorer's tree to browse network shares. What I needed was a fast, lightweight method to fill the nodes in a tree dynamically as the user clicks on them (also known as load or populate on demand). What I have found is either old code dealing with the COM Treeview control, or articles written using recursive algorithms (which are cool, BTW). NET Treeview control except on CodeProject. There is not a lot of documentation dealing with the use of the.