Developing web parts

  Previous topic Next topic JavaScript is required for the print function Mail us feedback on this topic! Mail us feedback on this topic!  

This chapter will guide you through the process of creating a very simple "Hello world" web part that displays a label and a button. When the button is clicked, it updates the current time displayed by the label.


1. Open the web project in Visual Studio (or Visual Web Developer) using the WebProject.sln file or using File -> Open -> Web site... in Visual Studio.

2. Right-click the CMSWebParts folder in the Solution Explorer window and choose New Folder. Rename the folder to MyWebParts.

3. Right-click the MyWebParts folder and choose Add New Item. Choose to create a new Web User Control and call it HelloWorld.ascx.

4. Display the HelloWorld control on the Design tab. Drag and drop a new Button control and a new Label control onto the form:

5. Double-click the Button control and add the following code to the Button1_Click method:



Label1.Text = DateTime.Now.ToString();




Label1.Text = DateTime.Now.ToString()


6. Add the following line to the beginning of the code:



using CMS.PortalControls;




Imports CMS.PortalControls


7. Change the following line:



public partial class CMSWebParts_MyWebParts_HelloWorld : System.Web.UI.UserControl
public partial class CMSWebParts_MyWebParts_HelloWorld : CMSAbstractWebPart




Partial Class CMSWebParts_MyWebParts_HelloWorld

  Inherits System.Web.UI.UserControl




Partial Class CMSWebParts_MyWebParts_HelloWorld

  Inherits CMSAbstractWebPart


This ensures that the user control behaves as a web part.

8. Add the following code to the Page_Load method:



Button1.Text = (string)this.GetValue("ButtonText");




(Visual Basic.NET doesn't create the Page_Load method automatically, so you need to add the whole method:)


Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

   Button1.Text = CType(My.GetValue("ButtonText"), String)

End Sub


It sets the button text to the value configured in Kentico CMS Desk.

9. Save all changes.

10. Open Site Manager -> Development -> Web parts, click the root and click WidgetNewCategory New category. Enter My web parts into the Category display name field, MyWebParts into the Category name field and click OK.

11. Click the new category and click NewWebPart New web part. Choose to create a new web part and enter the following values:


Display name: Hello world
Code name: HelloWorld
File name: ~/CMSWebParts/MyWebParts/HelloWorld.ascx


Click OK.

12. Switch to the Properties tab and add (AddWebPart) the following property:


Attribute name: ButtonText
Attribute type: Text
Attribute size: 100
Field caption: Button text
Field type: Text box


Click OK.


13. Switch to CMS Desk.

14. Create a new blank page using the Simple layout (or any other layout) under the root and switch to the Design tab.

15. Click Add web part in the upper right corner of the web part zone and choose to add the Hello world web part:

16. The Web part properties dialog of the HelloWorld web part appears, set the value of the Button text field to Hello world!

17. Now switch to the Live site mode using the button in the main toolbar. You will see the button with text Hello world! When you click it, the label displays the current date and time:

You have learned how to create a simple web part.



Tip: Displaying content on the web part


You can also use Kentico CMS Controls in the web part (in the ASCX control) to display content from Kentico CMS in a customized form.





Error message "The control collection cannot be modified during DataBind, Init, Load, PreRender or Unload phases."


If you get this error message you may need to modify the code of your web part, so that it doesn't display any content on the Design tab - for example:


using CMS.PortalEngine;


public override void OnContentLoaded()



if ((this.PagePlaceholder.ViewMode == ViewModeEnum.Design)

    || (this  .HideOnCurrentPage) || (!this.IsVisible))


        this.Repeater1.DataSourceID = "";

        this.CMSRepeater1.StopProcessing = true;






Initializing Kentico CMS controls in your custom web parts


If you are using Kentico CMS controls in your web parts, it is recommended to initialize the controls' properties using a combination of the OnContentLoaded and SetupControl methods. This is the way it is handled in all Kentico CMS web parts. You can view the code of any of the web parts located in <project folder>/CMSWebParts and use it as an example.


If you are using classic .NET controls or third party controls, this can be handled in the PageLoad method.


If a problem occurs (e.g. on postback), try loading the control dynamically. This can be achieved by making a control from the web part and loading it dynamically (e.g. using the General -> User control web part).


Page url: