What are ASP.NET Custom controls?

1. What are ASP.NET Custom controls?

Custom controls extend the tools available to Web developers. Using custom controls, you can encapsulate key aspects of the visual interface and program logic that you want to reuse throughout your application, or throughout your organization.

2. What are the 3 types of custom controls in ASP.NET?

Microsoft Visual Studio .NET provides three types of custom control for use on Web forms.

1. Web user controls

These combine existing server and HTML controls by using the Visual Studio .NET Designer to create functional units that encapsulate some aspect of the user interface. User controls reside in content files, which must be included in the project in which the controls are used.

2. Composite custom controls

These create new controls from existing server and HTML controls. Although similar to user controls, composite controls are created in code rather than visually, and therefore they can be compiled into an assembly (.dll), which can be shared between multiple applications and used from the Toolbox in Visual Studio .NET.

3. Rendered custom controls

These create entirely new controls by rendering HTML directly rather than using composition. These controls are compiled and can be used from the Toolbox, just like composite controls, but you must write extra code to handle tasks that are performed automatically in composite controls.

3. What are the limitations of user controls in ASP.NET?

As the user controls are not compiled into assemblies, they have the following limitations:

1. A copy of the control must exist in each Web application project in which the control is used.

2. User controls can’t be loaded in the Visual Studio .NET Toolbox; instead, you must create them by dragging the control from Solution Explorer to the Web form.

3. User control code is initialized after the Web form loads, which means that user control property values are not updated until after the Web form’s Load event.

4. What are the steps to follow for creating and using a user control in a Web application?

1. Add a Web user control page (.ascx) to your project.

2. Draw the visual interface of the control in the designer.

3. Write code to create the control’s properties, methods, and events.

4. Use the control on a Web form by dragging it from Solution Explorer to the Web form on which you want to include it.

5. Use the control from a Web form’s code by declaring the control at the module level and then using the control’s methods, properties, and events as needed within the Web form.

5. How do you identify user controls?

User controls are identified by their .ascx file extensions.

6. What is the base class from which user controls derive?

User controls derive from System.Web.UI.UserControl base class. This base class provides the base set of properties and methods you use to create the control.

7. What are the steps to follow to create properties and methods for the user control that you can use from a Web form?

To create properties and methods for the user control that you can use from a Web form, follow these steps:

1. Create the public property or method that you want to make available on the containing Web form.

2. Write code to respond to events that occur for the controls contained within the user control. These event procedures do the bulk of the work for the user control.

3. If the property or method needs to retain a setting between page displays, write code to save and restore settings from the control’s ViewState.

8. What happens when you drag a user control from solution explorer and drop it on a web form?

When you drag a user control from solution explorer and drop it on a web form, Visual Studio .NET generates a @Register directive and HTML tags to create the control on the Web form.

9. What are composite custom controls?

Composite custom controls combine one or more server or HTML controls within a single control class, which can be compiled along with other control classes to create an assembly (.dll) that contains a custom control library. Once created, the custom control library can be loaded into Visual Studio .NET and used in the same way as the standard server and HTML controls.

Composite custom controls are functionally similar to user controls, but they reside in their own assemblies, so you can share the same control among multiple projects without having to copy the control to each project, as you must do with user controls. However, composite controls are somewhat more difficult to create because you can’t draw them visually using the Visual Studio .NET Designer.

10. What are the steps to follow create and use a custom control in a Web application?

1. Create a solution containing a custom control project.

2. Add a Web application project to the solution, and set it as the startup project. You will use the Web application project to test the custom control during development.

3. Add a project reference from the Web application to the custom control project, and add an HTML @Register directive and control element to use the custom control on a Web form.

4. Create the custom control’s visual interface by adding existing controls to it through the custom control’s CreateChildControls method.

5. Add the properties, methods, and events that the custom control provides.

6. Build and test the custom control.

11. In general what is the base class for every composite custom control?

System.Web.UI.WebControls.WebControl

12. Which directive is used to add a custom control to a Web form?

Register directive.

13. What are the 3 Register directives’ attributes?

TagPrefix: - This name identifies the group that the user control belongs to. For example, the tag prefix for ASP.NET server controls is “asp”. You use this prefix to create a naming convention to organize your custom controls.

Namespace:-This is the project name and namespace within the custom control assembly that contains the controls to register. Microsoft Visual Basic .NET uses the project name as an implicit namespace, so for controls written in Visual Basic .NET, use the project name.

Assembly:-This is the name of the assembly (.dll) containing the custom controls. The control assembly must be referenced by the Web application. Referencing the assembly maintains a copy of it in the Web application’s /bin directory.

14. What are the differences between User Controls and Custom Controls?

1. User Controls are easy to create where as Custom Controls are difficult to create.

2. User Controls cannot be compiled into an assembly; where as Custom Controls can be compiled into an assembly.

3. User Controls cannot be added to tool box, where as Custom controls can be added to the toolbox.

4. You need to have a copy of user control in every project where you want to use it, where as this is not the case with custom controls. You can install a single copy of the Web custom control in the global assembly cache and share it between applications, which make maintenance easier.

5. User controls are used for reusing existing user interface elements and code, but are not useful for developing reusable components for multiple web applications.

15. What are the 2 ways provided by ASP.NET to format output in a Web application?

1. Use cascading style sheets (CSS) to control the appearance of elements on a Web form. These styles can set the color, size, font, and behavior of the HTML elements on a Web page.

2. Use Extensible Stylesheet Language Transformations (XSLT) to convert information from an Extensible Markup Language (XML) file to HTML output and position that information on a Web form. XSLT puts data from the XML file into HTML elements and applies styles to those elements.

16. What are Cascading style sheets?

Cascading style sheets (CSS) collect and organize all of the formatting information applied to HTML elements on a Web form. Because they keep this information in a single location, style sheets make it easy to adjust the appearance of Web applications.

17. What are the 3 levels at which formatting can be applied with in a web application?

1. Styles can be defined in a style sheet file. Styles in a style sheet can be applied to all webforms referencing the style sheet.

2. You can also define styles in the page’s head element. These styles can be applied to all elements on the current page.

3. You can also define styles inline, in the HTML tag itself. Inline styles are applicable only to the HTML element in which these styles are defined.

Inline formatting takes precedence over local formatting, which, in turn, takes precedence over global formatting. These precedence rules are the reason style sheets are referred to as cascading.

18. What are the advantages of storing style definitions in a style sheet file (.css) rather than locally in each Web form or inline with each HTML element?

1. Formatting can be maintained in one location so that you make changes only once for an entire application.

2. Several sets of parallel formatting rules can be maintained in separate style sheets for formatting output on different devices or for different user needs. For example, an application might provide standard, enlarged-type, and printer-friendly style sheets that the user can select at run time.

3. In general, you should use page and inline styles only when you have a really good reason to override the global styles. Relying heavily on page and inline styles can make it difficult to maintain the formatting in a Web application.

19. What HTML element is used to reference a style sheet on webform?

To reference a style sheet on webform you must add a link element to the page’s head element, as shown below.

<link href="Styles.css" type="text/css" rel="stylesheet">

20. What is the use of Style Builder?

Style Builder is used to change the appearance of any of the styles in a style sheet. Changes to the style sheet change the appearance of all Web forms that reference that style sheet.

21. How do you modify a style sheet using style builder?

To modify a style sheet using style builder, follow these steps:

1. Open the style sheet in Visual Studio. Visual Studio .NET displays the style definitions in the Document window and an outline of the style sheet in the Tool window

2. Select the style to modify from the Tool window. Visual Studio .NET displays the definition for that style in the Document window.

3. Right-click in the style definition or right-click the style in the Tool window, and select Build Style from the shortcut menu. Visual Studio .NET displays the Style Builder Wizard.

4. Use the Style Builder to compose the formatting that you want to add or modify in the selected style, and then click OK.

5. When you have finished, you’ll see that the Style Builder adds the new or modified style attributes to the style definition.

22. Can you apply styles using class names or element IDs?

Yes, using class names allows you to apply a single style to a number of different elements or to style the same element differently, depending on how the element is used. Using element IDs allows you to apply a style to a unique element on one or more Web forms.

When you create a style rule for a class, Visual Studio .NET adds a style definition to the style sheet using a .class name identifier.

You apply the style class to HTML elements by using the class attribute. You apply the style to server controls by using the CSS Class attribute.

23. Can you change style sheets at run time?

Yes.

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