How to Use JavaScript in ASP.NET Core to Dynamically Add Custom Templates to the DevExpress TabPanel

Using JavaScript to Dynamically Populate DevExpress TabPanel Templates

When working with ASP.NET Core and DevExpress components, developers often encounter the need to dynamically inject content into UI elements such as the dxTabPanel. However, a common issue arises where the correct number of tabs is created, but the tab content remains empty, frustrating development efforts.

The challenge occurs when templates defined in the Razor views fail to load correctly within the tab panel at runtime. This article addresses how to populate DevExpress TabPanel templates dynamically using JavaScript. We will explore a practical solution to ensure that content is displayed correctly inside each tab.

By examining a scenario with two templates—`employeeListTemplate` and `addEditEmployeeTemplate`—we aim to resolve the problem of missing tab content. You will learn how to parse template data and bind them to your TabPanel through JavaScript.

In the following sections, we will walk you through the steps involved in creating and rendering templates dynamically using JavaScript. Additionally, we will highlight potential pitfalls to avoid while dealing with DevExpress components in your ASP.NET Core projects.

Understanding Dynamic TabPanel Template Management in ASP.NET Core with DevExpress

The scripts provided in this example aim to dynamically populate a DevExpress TabPanel by using JavaScript in an ASP.NET Core environment. The challenge arises when the templates, which are defined within the Razor view, do not automatically display within the tabs despite being correctly added. This solution ensures that templates like `employeeListTemplate` and `addEditEmployeeTemplate` are correctly loaded and rendered by manipulating the TabPanel’s items property using JavaScript.

The key function, `populateTabPanel`, is responsible for creating a structured array of tab items based on the data parsed from a JSON string. This JSON contains the metadata of the tabs, including their titles and the names of the templates they reference. The method `JSON.parse()` converts the string into an object that the function can iterate over, dynamically building each tab with its corresponding template. This dynamic approach ensures flexibility, allowing templates to be defined once in Razor and reused across multiple tabs without duplication.

The method `$().dxTabPanel("instance")` retrieves the instance of the TabPanel widget, giving direct access to its properties and methods. This is critical for injecting new content into the TabPanel at runtime. After mapping the templates from the parsed JSON into the required structure, the `option("items", items)` method updates the TabPanel’s content with the new tab definitions. This step ensures that the correct templates are assigned to their respective tabs, solving the issue of tabs appearing empty despite being created successfully.

A vital component in this setup is ensuring that the HTML content of the templates is fetched correctly using the jQuery selector with the `.html()` method. This guarantees that the content is transferred from the Razor-defined templates to the dynamically generated tabs. Additionally, the use of modular functions like `parseTemplates` and `updateTabPanel` improves code readability and reusability, making the script easier to maintain and extend. To validate the functionality, unit tests using Jest are implemented, verifying that the TabPanel contains the expected number of tabs and that the titles match the predefined values.

// Front-end solution using JavaScript for dynamic template handling
function populateTabPanel() {
    let jsonString = '{
        "ParentID": 1,
        "ParentName": "Administration",
        "ID": 1,
        "Text": "Employee",
        "Templates": [
            {"ID": 1, "TemplateName": "employeeListTemplate", "Title": "Current Employees"},
            {"ID": 2, "TemplateName": "addEditEmployeeTemplate", "Title": "Add/Update Employee"}
        ]
    }';
    let templateObj = JSON.parse(jsonString);
    let items = templateObj.Templates.map(t => ({
        template: $(`#${t.TemplateName}`).html(),
        title: t.Title
    }));
    $("#contentTabPanel").dxTabPanel("instance").option("items", items);
}

// Function to parse template JSON
function parseTemplates(json) {
    return JSON.parse(json).Templates.map(template => ({
        template: $(`#${template.TemplateName}`).html(),
        title: template.Title
    }));
}
// Function to update TabPanel with new items
function updateTabPanel(items) {
    const tabPanel = $("#contentTabPanel").dxTabPanel("instance");
    tabPanel.option("items", items);
}
// Main function to populate TabPanel
function populateTabPanel() {
    const jsonString = '{"Templates": [
        {"TemplateName": "employeeListTemplate", "Title": "Current Employees"},
        {"TemplateName": "addEditEmployeeTemplate", "Title": "Add/Update Employee"}
    ]}';
    const items = parseTemplates(jsonString);
    updateTabPanel(items);
}

@(Html.DevExtreme().Button()
    .ID("addTabsButton")
    .OnClick("populateTabPanel")
    .Text("Add Tabs")
    .Type(ButtonType.Default)
    .Width(100)
)
@(Html.DevExtreme().TabPanel()
    .ID("contentTabPanel")
    .Loop(false)
    .AnimationEnabled(false)
    .DeferRendering(false)
    .RepaintChangesOnly(false)
)
@using (Html.DevExtreme().NamedTemplate("employeeListTemplate")) {
    @(Html.DevExtreme().DataGrid()
        .Columns(c => {
            c.Add().DataField("FirstName").AllowEditing(true);
            c.Add().DataField("LastName").AllowEditing(true);
        })
    )
}
@using (Html.DevExtreme().NamedTemplate("addEditEmployeeTemplate")) {
    <div>This is Admin -> Add/Edit Employee</div>
}

describe('TabPanel Population', () => {
    it('should correctly populate TabPanel with templates', () => {
        populateTabPanel();
        const tabPanelInstance = $("#contentTabPanel").dxTabPanel("instance");
        const items = tabPanelInstance.option('items');
        expect(items.length).toBe(2);
        expect(items[0].title).toBe('Current Employees');
        expect(items[1].title).toBe('Add/Update Employee');
    });
});

Improving Dynamic Content Management in DevExpress TabPanel

When working with the DevExpress TabPanel, another critical aspect developers must address is ensuring that content updates dynamically without requiring full page reloads. This is essential when building modern web applications where user interaction needs to be fast and responsive. Using JavaScript to update templates dynamically provides an efficient way to inject content into the ASP.NET Core application. However, developers must carefully manage how the templates are rendered and refreshed within the TabPanel to prevent delays or rendering issues.

One common challenge is ensuring that the TabPanel accurately reflects any backend changes, especially when templates or data grids rely on live data. To solve this, using the option() method to update TabPanel content ensures that new data is seamlessly injected. Additionally, DeferRendering should be set to false to avoid the default lazy-loading behavior, which can cause templates to remain invisible until manually refreshed. These optimizations allow content to appear instantly, maintaining smooth user interaction.

Another aspect to consider is handling errors when injecting content dynamically. Using proper error handling with JavaScript ensures that missing or malformed templates don’t break the TabPanel’s functionality. Developers should implement fallback logic to display a default message if a template fails to load. Moreover, to improve performance, ensuring that templates are properly cached and reused is essential. This reduces unnecessary processing and improves load times for the user interface.