DxTreeList.CustomizeElement Event

Allows you to customize TreeList cells and rows according to their values.

Namespace: DevExpress.Blazor

Assembly: DevExpress.Blazor.v24.2.dll

NuGet Package: DevExpress.Blazor

Declaration

[Parameter]
public Action<TreeListCustomizeElementEventArgs> CustomizeElement { get; set; }

Parameters

Type	Description
TreeListCustomizeElementEventArgs	An object that defines data for this event.

Remarks

The CustomizeElement event fires each time the TreeList component is re-rendered, for instance when you update data from an asynchronous data source or call the AutoFitColumnWidths() method.

The event fires for most TreeList elements. Use the ElementType, VisibleIndex, and Column event arguments to get information about the processed element.

The CssClass, Style, and Attributes event arguments allow you to customize element settings.

Task-Based Examples

Customize Appearance and Display a Custom Tooltip

The following code customizes the appearance of TreeList elements that meet the following criteria:

• Rows that have child rows are highlighted.
• Cells in March Change and September Change columns that display values larger than 5% are colored green.
• Cells in March Change and September Change columns that display negative values are colored red.

Run Demo: Conditional Formatting

<DxTreeList Data="Data"
            KeyFieldName="ID"
            ParentKeyFieldName="RegionID"
            CustomizeElement="TreeList_CustomizeElement">
    <Columns>
        <DxTreeListDataColumn FieldName="Region" />
        <DxTreeListDataColumn FieldName="MarchSales" DisplayFormat="c0" />
        <DxTreeListDataColumn FieldName="SeptemberSales" DisplayFormat="c0" />
        <DxTreeListDataColumn FieldName="MarchChange" DisplayFormat="p2" />
        <DxTreeListDataColumn FieldName="SeptemberChange" DisplayFormat="p2" />
        <DxTreeListDataColumn FieldName="MarketShare" DisplayFormat="p0" />
    </Columns>
</DxTreeList>

@code {
    object Data { get; set; }

    protected override void OnInitialized () {
        Data = SalesByRegionDataProvider.GenerateData();
    }

    void TreeList_CustomizeElement(TreeListCustomizeElementEventArgs e) {
        if(e.ElementType == TreeListElementType.DataRow 
                         && (int)e.TreeList.GetRowValue(e.VisibleIndex, "RegionID") == 0) {
            e.CssClass = "parent-region-row";
        }
        if(e.ElementType == TreeListElementType.DataCell && e.Column is ITreeListDataColumn dataColumn) {
            if(dataColumn.FieldName == "MarchChange" || dataColumn.FieldName == "SeptemberChange") {
                var value = (decimal)e.TreeList.GetRowValue(e.VisibleIndex, dataColumn.FieldName);
                if(value > 0.05M) {
                    e.CssClass = "win-threshold";
                }
                else if(value < 0) {
                    e.CssClass = "loss-threshold";
                }
            }
        }
    }
}

.parent-region-row {
    background-color: color-mix(in srgb, var(--bs-gray-300), transparent 50%);
}
td.loss-threshold {
    background-color: rgba(245, 198, 203, 0.5);
}
td.win-threshold {
    background-color: rgba(198, 245, 203, 0.5);
}

Highlight Modified Cells

View Example: Implement Batch Data Editing Using Entity Framework Core Run Demo: Batch Edit

<div>
    <DxTreeList @ref="TreeList"
                Data="DataSource"
                KeyFieldName="Id"
                ParentKeyFieldName="ParentId"
                EditMode="TreeListEditMode.EditCell"
                EditModelSaving="TreeList_EditModelSaving"
                CustomizeElement="TreeList_CustomizeElement"
                CustomizeEditModel="TreeList_CustomizeEditModel">
        <Columns>
            <DxTreeListDataColumn FieldName="Name" Caption="Task" />
            <DxTreeListDataColumn FieldName="StartDate" />
            <DxTreeListDataColumn FieldName="DueDate" />
            <DxTreeListCommandColumn>
                @* ... *@
            </DxTreeListCommandColumn>
        </Columns>
        @* ... *@
    </DxTreeList>
</div>

@code {
    ITreeList TreeList { get; set; }
    IList<EmployeeTask> DataSource { get; set; }
    @* ... *@
    void TreeList_CustomizeElement(TreeListCustomizeElementEventArgs ea) {
        if(ea.ElementType == TreeListElementType.DataCell) {
            var employee = (EmployeeTask) TreeList.GetDataItem(ea.VisibleIndex);
            var column = (ITreeListDataColumn) ea.Column;
            bool isNew = employee == null;
            if(!isNew && UnsavedChanges.TryGetValue(employee, out var changes)) {
                if(changes.Type == DataChangeType.Addition || changes.ChangedFields.Contains(column.FieldName))
                    ea.CssClass = "treelist-modified-cell";
            }
        }
    }
    @* ... *@
}

Alternate Row Style

This following code sample highlights alternating (odd) rows with a different style to enhance readability:

Run Demo: Alternating Row Style

<DxTreeList Data="Data"
            KeyFieldName="ID"
            ParentKeyFieldName="RegionID"
            CustomizeElement="TreeList_CustomizeElement">
    <Columns>
        <DxTreeListDataColumn FieldName="Region" />
        <DxTreeListDataColumn FieldName="MarchSales" DisplayFormat="c0" />
        <DxTreeListDataColumn FieldName="SeptemberSales" DisplayFormat="c0" />
        <DxTreeListDataColumn FieldName="MarchChange" DisplayFormat="p2" />
        <DxTreeListDataColumn FieldName="SeptemberChange" DisplayFormat="p2" />
        <DxTreeListDataColumn FieldName="MarketShare" DisplayFormat="p0" />
    </Columns>
</DxTreeList>

@code {
    object Data { get; set; }

    protected override void OnInitialized () {
        Data = SalesByRegionDataProvider.GenerateData();
    }

    void TreeList_CustomizeElement(TreeListCustomizeElementEventArgs e) {
        if(e.ElementType == TreeListElementType.DataRow && e.VisibleIndex % 2 == 1) {
            e.CssClass = "alt-item";
        }
    }
}

.alt-item {
    background-color: color-mix(in srgb, var(--bs-gray-300), transparent 50%);
}

Change Focus and Selection Color

<DxTreeList CustomizeElement="TreeList_CustomizeElement" ... />

@code {
    void TreeList_CustomizeElement(TreeListCustomizeElementEventArgs e) {
        if (e.ElementType == TreeListElementType.DataRow && e.TreeList.IsRowSelected(e.VisibleIndex)) {
            e.CssClass = "custom-selection-style";
        }
        if (e.ElementType == TreeListElementType.DataRow && e.TreeList.IsRowFocused(e.VisibleIndex)) {
            e.CssClass = "custom-focus-style";
        }
    }
    // ...
}

Modify Data Cell Paddings

void TreeList_CustomizeElement(TreeListCustomizeElementEventArgs e) {
    if (e.ElementType == TreeListElementType.DataCell) {
        e.Style = "padding: 0px";
    }
}

Conditionally Hide Commands

void TreeList_CustomizeElement(TreeListCustomizeElementEventArgs e) {
    if (e.ElementType == TreeListElementType.CommandCell &&
            (System.Int32)e.TreeList.GetRowValue(e.VisibleIndex, "Status") == 100) {
        e.CssClass = "hidden-item";
    }
}

.hidden-item button {
    visibility: hidden;
}

Modify Column Header Style Based on Sort Settings

void TreeList_CustomizeElement(TreeListCustomizeElementEventArgs e) {
    if (e.ElementType == TreeListElementType.HeaderCell) {
        var column = (DxTreeListDataColumn)e.Column;
        if (column.AllowSort == false)
            e.CssClass = "nonsortable-header";
        else
            e.CssClass = "my-header-cell";
    }
}

.nonsortable-header {
    background-color: red !important;
}
.my-header-cell[aria-sort="ascending"] {
    background-color: green !important;
}
.my-header-cell[aria-sort="descending"] {
    background-color: red !important;
}