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TreeList DataBound Column

This article explains the basics of showing data in a treelist and the features of its bound columns.

Sections in this article:

Show Data In A TreeList

To show data in a treelist, you must define TreeListColumn instances in the TreeListColumns collection for the fields of the data source you want to show. Their Field parameter defines which property from the model is shown in the column. You can provide the collection of models to the treelist in its Data parameter.

Since the treelist is designed for hierarchical data, you should also define which column will hold the expand/collapse arrow for the child items. It can be any column, not necessarily the first, and you denote it by setting its Expandable parameter to true.

You can read more details on how to tie the treelist to your data fields and child elements in the Data Binding Overview article. It provides information on the features of the model, and describing the parent-child relationships in two different ways.

Provide data to the treelist and choose which columns (fields) to see

@* define data, model and columns for a treelist *@

@using System.ComponentModel.DataAnnotations
@* This Using is for the model class attributes only *@

<TelerikTreeList Data="@Data" Pageable="true" IdField="Id" ParentIdField="ParentId" Width="650px">
    <TreeListColumns>
        <TreeListColumn Field="Name" Expandable="true" Width="320px" />
        <TreeListColumn Field="Id" />
        <TreeListColumn Field="@nameof(Employee.HireDate)" />
    </TreeListColumns>
</TelerikTreeList>

@code {
    public List<Employee> Data { get; set; }

    protected override async Task OnInitializedAsync()
    {
        Data = await GetTreeListData();
    }

    // sample models and data generation

    public class Employee
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
        [Display(Name = "Employee Name")]
        public string Name { get; set; }
        public DateTime HireDate { get; set; }
        public string Team { get; set; } // in this example we don't use this field (in the treelist)
    }

    async Task<List<Employee>> GetTreeListData()
    {
        List<Employee> data = new List<Employee>();

        for (int i = 1; i < 15; i++)
        {
            data.Add(new Employee
            {
                Id = i,
                ParentId = null,
                Name = $"root: {i}",
                HireDate = DateTime.Now.AddYears(-i)
            }); ;

            for (int j = 1; j < 4; j++)
            {
                int currId = i * 100 + j;
                data.Add(new Employee
                {
                    Id = currId,
                    ParentId = i,
                    Name = $"first level child {j} of {i}",
                    HireDate = DateTime.Now.AddDays(-currId)
                });

                for (int k = 1; k < 3; k++)
                {
                    int nestedId = currId * 1000 + k;
                    data.Add(new Employee
                    {
                        Id = nestedId,
                        ParentId = currId,
                        Name = $"second level child {k} of {i} and {currId}",
                        HireDate = DateTime.Now.AddMinutes(-nestedId)
                    }); ;
                }
            }
        }

        return await Task.FromResult(data);
    }
}

You can also use a string for the field name, using the nameof operator is not necessary. For example, the ID column can be defined like this: <TreeListColumn Field="Id" />. The field name is, however, case-sensitive.

The Data collection can be an ObservableCollection, an array, a List - it must only implement IEnumerable.

The TreeList can generate the columns from the model for you.

TreeList Bound Column Parameters

You can use the following properties on the bound columns:

  • Expandable - (defaults to false) - when set to true, the column shows an expand/collapse arrow in front of the value and denotes hierarchy be intending it. You should set this to at least one column of your treelist to showcase the hierarchical nature of the data.

  • Field - (defaults to null) - the name of the field in the data source that the column will render as a string (case-sensitive). You can set its as a plain string (Field="SomeField") or to have .NET extract the field name from the model for flat models (Field=@nameof(MyModelClass.SomeFIeld)).

  • Title - the text that is rendered in the column header. See the Notes below for its behavior.

  • DisplayFormat - the C# format string that is used to render the field value in the cell when the grid is in display mode. Read more in the Column Display Format article.

  • Editable - (defaults to true) - you can set this property to true or false to allow or prevent editing of this field. Defaults to true. To edit data, you also need a CommandColumn.

  • Filterable - (defaults to true) - you can set this to false so a filterable treelist will not let the user filter that particular column.

  • Locked - (defaults to false) - defines whether the column is locked (frozen, pinned).

  • Sortable - (defaults to true) - set it to false so the user cannot sort this column.

  • Reorderable - (defaults to true) - whether the user can drag to reorder this column.

  • Resizable - (defaults to true) - whether the user can resize this column.

  • Width - (defaults to null) - the width of the column. See the Dimensions article. Keep in mind that these are columns in a <table>, so it is often a good practice to leave one column without explicit dimensions so it can accommodate the remaining width and changes to the container size.

  • Visible - (defaults to null) - if this parameter is set to false it hides the column from the TreeList. Accepts both bool and bool? types, and null is treated like true.

  • Template - this property can also be used as an inner tag and it defines the custom cell content that renders instead of the default field value the treelist puts in it.

  • HeaderTemplate - this property can also be used as an inner tag and defines the custom contents of the header cell that you can render instead of the Title.

  • EditorTemplate - this property can also be used as an inner tag and defines a custom input and logic that is used for editing the field.

You can find more examples in the rest of the treelist documentation and in our live demos.

Notes

  • For advanced operations such as filtering and sorting, you must set a Field to the column, and the field it points to must be a string or a value type (such as a number, string, DateTime, boolean).

    • If a Field is not set the column will not allow filtering, sorting and editing for the column.
    • If the Field points to a custom object or something like an IDictionary, errors will be thrown upon those actions because there are no known data operations on non-primitive types in .NET.
    • To bind to nested (complex) models (also called navigation properties), use only the name of the field that holds the child class and its own field. For an example, see the Bind to navigation properties in complex objects article.
  • The treelist skips fields marked with the IgnoreDataMemberAttribute when performing CUD operations. Its presence indicates that this property does not need to be part of the serialized data anyway, and skipping such fields allows Lazy Loading Proxies in EF to work.

  • If you don't set a Title for a column, the treelist will take the [Display(Name = "My Column Title")] data annotation attribute from the model field. If that's not available either, the name of the field will be shown.

  • If the model has a [DisplayFormat(DataFormatString = "{0:C}")] data annotation attribute, the display format will be taken from the format string in the attribute.

  • If you want to prevent data mutation for a specific property you can set the Editable parameter of the TreeListColumn or the [Editable] data annotation attribute to false for the desired model field.

    • Columns generated out of model properties that do not have a setter or it is not accessible (private) will not be editable too.
  • The treelist uses Activator.CreateInstance<TItem>(); to generate a new item when an Insert action is invoked, so the Model should have a Parameterless constructor defined.

You can improve performance by loading child nodes only when the user expands them. Read more in the Load on Demand article.

See Also

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