Getting Started with the ExpansionPanel

This tutorial explains how to set up a basic Telerik UI for ASP.NET Core ExpansionPanel and highlights the major steps in the configuration of the component.

You will initialize an ExpansionPanel component in expanded mode and integrate a Card component into its content. Next, you will handle the ExpansionPanel events to change dynamically the header background color. Finally, you can run the sample code in Telerik REPL and continue exploring the components.

Prerequisites

To successfully complete the tutorial, you need a project that is already configured to use the Telerik UI for ASP.NET Core components:

• To create a new pre-configured project for the Telerik UI for ASP.NET Core components, you can use a project template.

• To manually configure an existing project, follow the First Steps on Windows or First Steps on Mac articles.

1. Prepare the CSHTML File

The first step is to add the required directives at the top of the .cshtml document:

• To use the Telerik UI for ASP.NET Core HtmlHelpers:

  @using Kendo.Mvc.UI
  

• To use the Telerik UI for ASP.NET Core TagHelpers:

  @addTagHelper *, Kendo.Mvc
  

Optionally, you can structure the View content by adding the desired HTML elements like headings, divs, paragraphs, and others.

    @using Kendo.Mvc.UI

    <h4>Review content by expanding the panel</h4>
    <div>

    </div>

    @addTagHelper *, Kendo.Mvc

    <h4>Review content by expanding the panel</h4>
    <div>

    </div>

2. Initialize the ExpansionPanel

Use the ExpansionPanel HtmlHelper or TagHelper to add the component to a page:

• The Name() configuration method is mandatory as its value is used for the id and the name attributes of the ExpansionPanel element.
• The Title() option specifies the title that will be displayed in the panel header.
• The SubTitle() option sets a subtitle next to the expand/collapse icon in the header.
• The Content() method defines the component content. It can be added as a string or as an HTML.

    @using Kendo.Mvc.UI

    <h4>Review content by expanding the panel</h4>
    <div>
        @(Html.Kendo().ExpansionPanel()
            .Name("expPanel")
            .Title("Summer vacation")
            .SubTitle("Greece")
            .Content("Include the desired content here")
        )
    </div>

    @addTagHelper *, Kendo.Mvc

    <h4>Review content by expanding the panel</h4>
    <div>
        <kendo-expansionpanel name="expPanel" title="Summer vacation" sub-title="Greece">
            <content>
                Include the desired content here
            </content>
        </kendo-expansionpanel>
    </div>

3. Configure the Card into the ExpansionPanel

The next step is to add a Card as content of the ExpansionPanel. Attach the onclick event to the Card action and change the icon class to mark the Card as liked.

    @using Kendo.Mvc.UI

    <h4>Review content by expanding the panel</h4>
    <div>
        @(Html.Kendo().ExpansionPanel()
            .Name("expPanel")
            .Title("Summer vacation")
            .SubTitle("Greece")
            .Expanded(true)
            .Content(@"
                <div class='k-card k-card-vertical'>
                    <div class='k-card-header k-hbox k-align-items-center'>
                        <div>
                            <h4 class='k-card-title'>Seaview Apartments</h4>
                            <h5 class='k-card-subtitle'>Greece, Santorini</h5>
                        </div>
                    </div>
                    <img class='k-card-media' alt='seaview' src=' " + @Url.Content("~/shared/web/cards/seaview-appartments.png")  + @" ' />
                    <div class='k-card-body'><p>A luxurious two-bedroom apartment with the best views over Santorini</p></div>
                    <span class='k-card-separator'></span>
                    <div class='k-actions k-card-actions'>
                        <span class='k-button k-button-flat-base k-button-flat k-button-md k-rounded-md k-icon-button' onclick='favoritesClick(event)'><span class='k-icon k-i-heart-outline'></span></span>
                    </div>
                </div>")
        )
    </div>

    @addTagHelper *, Kendo.Mvc

    <h4>Review content by expanding the panel</h4>
    <div>
        <kendo-expansionpanel name="expPanel" title="Summer vacation" sub-title="Greece" expanded="true">
            <content>
                <div class='k-card k-card-vertical'>
                    <div class='k-card-header k-hbox k-align-items-center'>
                        <div>
                            <h4 class='k-card-title'>Seaview Apartments</h4>
                            <h5 class='k-card-subtitle'>Greece, Santorini</h5>
                        </div>
                    </div>
                    <img class='k-card-media' alt='seaview' src='~/shared/web/cards/seaview-appartments.png' />
                    <div class='k-card-body'><p>A luxurious two-bedroom apartment with the best views over Santorini</p></div>
                    <span class='k-card-separator'></span>
                    <div class='k-actions k-card-actions'>
                        <span class='k-button k-button-flat-base k-button-flat k-button-md k-rounded-md k-icon-button' onclick='favoritesClick(event)'><span class='k-icon k-i-heart-outline'></span></span>
                    </div>
                </div>
            </content>
        </kendo-expansionpanel>
    </div>

    <script>
        function favoritesClick(event){
            if($(event.target).hasClass("k-i-heart-outline")) {
                $(event.target).removeClass("k-i-heart-outline");
                $(event.target).addClass("k-i-heart");
            } else {
                $(event.target).addClass("k-i-heart-outline");
                $(event.target).removeClass("k-i-heart");
            }
        }
    </script>

4. Handle the ExpansionPanel Events

The ExpansionPanel exposes events that you can handle and further customize the functionality of the component. In this tutorial, you will use the Expand and Collapse events to alter the component's header background color when in an expanded state.

    @(Html.Kendo().ExpansionPanel()
        .Name("brazil")
        .Title("Brazil")
        .SubTitle("South America")
        .Events(ev => ev.Expand("onExpand").Collapse("onCollapse"))
        .Content("")
     )

     <script>
        function onExpand() {
            $(".k-expander-header").css("background-color","#c1e2eb");
        }

        function onCollapse() {
            $(".k-expander-header").css("background-color","inherit");
        }
    </script>

    <kendo-expansionpanel name="expPanel" on-expand="onExpand" on-collapse="onCollapse">
        <content>

        </content>
    </kendo-expansionpanel>

     <script>
        function onExpand() {
            $(".k-expander-header").css("background-color","#c1e2eb");
        }

        function onCollapse() {
            $(".k-expander-header").css("background-color","inherit");
        }
    </script>

5. (Optional) Reference Existing ExpansionPanel Instances

You can reference the ExpansionPanel instances that you have created and build on top of their existing configuration:

1. Use the id attribute of the component instance to establish a reference.

       <script>
           $(document).ready(function() {
               var expansionPanelReference = $("#expPanel").data("kendoExpansionPanel"); // expansionPanelReference is a reference to the existing ExpansionPanel instance of the helper.
           });
       </script>
   

2. Use the ExpansionPanel client-side API to control the behavior of the component. In this example, you will use the toggle method to toggle the state of the control dynamically (for example, when a button is clicked).

       @(Html.Kendo().Button()
           .Name("btn")
           .Content("Toggle ExpansionPanel")
           .Events(ev => ev.Click("onBtnClick"))
       )
   

       @addTagHelper *, Kendo.Mvc
       <kendo-button name="btn" on-click="onBtnClick">
           Toggle ExpansionPanel
       </kendo-button>
   

       <script>
           function onBtnClick() {
               var expansionPanelReference = $("#expPanel").data("kendoExpansionPanel");
               expansionPanelReference.toggle();
           }
       </script>
   

For more information on referencing specific helper instances, see the Methods and Events article.

Explore this Tutorial in REPL

You can continue experimenting with the code sample above by running it in the Telerik REPL server playground:

• Sample code with the ExpansionPanel HtmlHelper
• Sample code with the ExpansionPanel TagHelper

Next Steps

• Setting the ExpansionPanel Default State
• Using the Keyboard Navigation of the ExpansionPanel for ASP.NET Core (Demo)
• Using the Right-To-Left-Feature of the ExpansionPanel for ASP.NET Core (Demo)

See Also

• Using the API of the ExpansionPanel for ASP.NET Core (Demo)
• Client-Side API of the ExpansionPanel
• Server-Side API of the ExpansionPanel
• Knowledge Base Section