Controls / GridView / Hierarchical Grid

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Load Data on Demand in Self Referencing Hierarchy

Load On Demand

RadGridView currently offers Load On Demand feature in hierarchy mode. Fetching data from the source on demand is a common technique to enhance the performance of applications which use large datasource.In this mode client can handle the RowSourceNeeded event and create manually the child rows for the expanded template. More information about the Load on Demand Hierarchy is available here.

Self Reference

The self-reference mode allows to build a hierarchy using a flat collection of objects, by defining a relation. In self-reference hierarchy the RadGridView needs all the data and based on the primary and foreign keys, it builds up the hierarchy levels. More information about the Self Reference Hierarchy is available here.

Load on Demand in Self-Reference Hierarchy

Load on Demand in Self-Reference Hierarchy is a new mehanism that combines the Load on Demand and Self Reference features. Thus, users can achieve a hierarchy in self referance mode while loading the data on demand, at a later moment when it is requested. The data is populated in the RowSourceNeeded event of RadGridView.

gridview-hirarchical-grid-hierarchy-load-on-demand-self-ref.PNG

How to use

The following information is required to implement the Load on Demand in Self-Reference grid, in order to visualize the data properly using this approach:

  • Information for rows on the top level(master template) of the self-reference hierarchy should be provided. This feature supporst only unbound mode of RadGridView.
  • Information about which of the top level rows can be expanded is also required so that the grid should properly show an expander icon.
  • When this data in the bullets above is provided, then the RowSourceNeeded event will trigger to provide manually the expanded levels with data.

You need to follow these steps to get the load on demand in self-referencing hierarchy working:

1. Add desired columns to unbound RadGridView.

2. Add relation that represents the hierarchy structure. 

private void SetupSelfReferenceLoadOnDemandGrid()
{
    this.radGridView1.RowSourceNeeded += new GridViewRowSourceNeededEventHandler(RadGridView1_RowSourceNeeded);
    this.radGridView1.AutoSizeColumnsMode = GridViewAutoSizeColumnsMode.Fill;
    this.radGridView1.AllowAddNewRow = false;

    GridViewDataColumn col = new GridViewDecimalColumn(typeof(int), "ID", "ID") { IsVisible = false };
    this.radGridView1.Columns.Add(col);
    col = new GridViewDecimalColumn(typeof(int), "ParentID", "ParentID") { IsVisible = false };
    this.radGridView1.Columns.Add(col);
    col = new GridViewTextBoxColumn("Name", "Name");
    this.radGridView1.Columns.Add(col);
    col = new GridViewDateTimeColumn("Date", "Date");
    this.radGridView1.Columns.Add(col);
    col = new GridViewTextBoxColumn("Type", "Type");
    this.radGridView1.Columns.Add(col);
    col = new GridViewDecimalColumn(typeof(int), "Size", "Size");
    this.radGridView1.Columns.Add(col);

    // Load on demand
    this.radGridView1.Relations.AddSelfReferenceLoadOnDemand(this.radGridView1.MasterTemplate, "ID", "ParentID");
}

3. Handle the RowsourceNeeded event to populate the data for each row.

private void RadGridView1_RowSourceNeeded(object sender, GridViewRowSourceNeededEventArgs e)
{
    if (e.ParentRow == null)
    {
        // First level of hierarchy
        var data = GetData(-1);
        foreach (var item in data)
        {
            GridViewHierarchyRowInfo row = new GridViewHierarchyRowInfo(e.Template.MasterViewInfo);
            row.Tag = item;
            row.Cells["ID"].Value = item.Id;
            row.Cells["ParentID"].Value = item.ParentId;
            row.Cells["Name"].Value = item.Name;
            row.Cells["Date"].Value = item.Date;
            row.Cells["Type"].Value = item.Type;
            row.Cells["Size"].Value = item.Size;

            // Setting this property will create Fully lazy mode for load on demand.
            row.IsExpandable = item.IsExpandable;
            e.SourceCollection.Add(row);
        }
    }
    else
    {
        FileSystemItem parentItem = e.ParentRow.Tag as FileSystemItem;
        if (parentItem.Type == "Folder")
        {
            var data = GetData(parentItem.Id);
            foreach (var item in data)
            {
                GridViewHierarchyRowInfo row = new GridViewHierarchyRowInfo(e.Template.MasterViewInfo);
                row.Tag = item;
                row.Cells["ID"].Value = item.Id;
                row.Cells["ParentID"].Value = item.ParentId;
                row.Cells["Name"].Value = item.Name;
                row.Cells["Date"].Value = item.Date;
                row.Cells["Type"].Value = item.Type;
                row.Cells["Size"].Value = item.Size;

                'Setting this property will create Fully lazy mode for load on demand.
                row.IsExpandable = item.IsExpandable;
                e.SourceCollection.Add(row);
            }
        }
    }
}

4. Load data that is passed in the RowSourceNeeded event.


private static List<FileSystemItem> GetData(int parentId)
{
    var collection = new List<FileSystemItem>();
    if (parentId < 0)
    {
        collection.Add(new FileSystemItem(1, null, "MyDocuments", DateTime.Now, "Folder", 1024, true));
        collection.Add(new FileSystemItem(4, null, "Windows", DateTime.Now, "Folder", 10240, false));
        collection.Add(new FileSystemItem(5, null, "Users", DateTime.Now, "Folder", 5120, true));
        collection.Add(new FileSystemItem(9, null, "Library", DateTime.Now, "Folder", 3260, true));
        collection.Add(new FileSystemItem(11, null, "Music", DateTime.Now, "Folder", 3680, true));
    }
    else if (parentId == 1)
    {
        collection.Add(new FileSystemItem(2, 1, "Salaries.xlsx", DateTime.Now, "File", 1, false));
        collection.Add(new FileSystemItem(3, 1, "RecesionAnalysis.xlsx", DateTime.Now, "File", 1, false));
    }
    else if (parentId == 5)
    {
        collection.Add(new FileSystemItem(6, 5, "Administrator", DateTime.Now, "Folder", 1512, false));
        collection.Add(new FileSystemItem(7, 5, "Guest", DateTime.Now, "Folder", 2515, false));
        collection.Add(new FileSystemItem(8, 5, "User", DateTime.Now, "Folder", 3512, false));
    }
    else if (parentId == 9)
    {
        collection.Add(new FileSystemItem(10, 9, "Program", DateTime.Now, "Folder", 512, false));
    }
    else if (parentId == 11)
    {
        collection.Add(new FileSystemItem(12, 11, "Podcasts", DateTime.Now, "Folder", 320, false));
        collection.Add(new FileSystemItem(13, 11, "Alternative", DateTime.Now, "Folder", 690, false));
        collection.Add(new FileSystemItem(14, 11, "Rock", DateTime.Now, "Folder", 715, false));
        collection.Add(new FileSystemItem(15, 11, "Classic", DateTime.Now, "Folder", 1060, false));
    }

    return collection;
}

public class FileSystemItem
{
    public FileSystemItem(int id, int? parentId, string name, DateTime date, string type, int size, bool isExpandable)
    {
        this.Id = id;
        this.ParentId = parentId;
        this.Name = name;
        this.Date = date;
        this.Type = type;
        this.Size = size;
        this.IsExpandable = isExpandable;
    }
    public int Id { get; set; }
    public int? ParentId { get; set; }
    public string Name { get; set; }
    public DateTime Date { get; set; }
    public string Type { get; set; }
    public int Size { get; set; }
    public bool IsExpandable { get; set; }
}

Full example in C# and VB is available in our Demo >> RadGridView >> Hierarchy examples.

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