ASP.NET Cookbook

12.1. Drawing Button Images on the Fly

Problem

You need to create a button image on the fly using text generated during the running of your application.

Solution

Create a web form that is responsible for creating the button image using the System.Drawing classes and then streaming the image to the Response object.

In the .aspx file, enter an @Page directive, but omit any head or body tags. The @ Page directive links the ASP.NET page to the code-behind class that draws the image.

In the code-behind class for the page, use the .NET language of your choice to:

1. Import the System.Drawing and System.Drawing.Imaging namespaces.

2. Create a makeButton (or similarly named) method that creates a bitmap for a button using text generated during the running of the application—for example, text passed in on the URL.

3. Create a MemoryStream object and save the bitmap in JPEG format (or other format) to the memory stream.

4. Write the resulting binary stream to Response object.

Example 12-1 through Example 12-3 show the .aspx file and VB and C# code-behind files for an application that creates a button image whose label is provided by the application user.

To use a dynamically generated image in your application, you need to set the Src attribute of the image tags for your button bitmaps to the URL of the ASP.NET page that creates the images, passing the image text in the URL.

In the .aspx file for the page, add an img tag for displaying the dynamically created image.

In the code-behind class for the page that uses ...