Asp net designer xx generates already contains a definition for control error

ASP.NET is a widely used programming language for web applications. It provides a powerful framework that allows developers to build dynamic and interactive websites. However, like any programming language, ASP.NET can sometimes present challenges and errors that need to be resolved. One error that developers may encounter is the “Asp net designer xx generates already a definition for control error.” In this article, we will explore this error and provide solutions to resolve it.

The “Asp net designer xx generates already contains a definition for control error” typically occurs when there is a duplicate definition for a control in the ASP.NET designer-generated code. This error can be frustrating as it prevents the application from compiling and running properly. However, with a few simple steps, you can resolve this error and get your application back on track.

To understand the error better, let's consider an example. Suppose you have a web form with a control named “btnSubmit”. You have defined this control in the designer file (e.g., Default.aspx.designer.cs) as follows:

protected global::System.Web.UI.WebControls.Button btnSubmit;

Now, let's say you accidentally add another button control with the same name in the markup file (e.g., Default.aspx):

When you try to compile the application, you will encounter the “Asp net designer xx generates already contains a definition for control error.” This error occurs because the designer-generated code already contains a definition for the “btnSubmit” control, and adding another control with the same name causes a conflict.

To resolve this error, you need to remove the duplicate control from the markup file. In our example, you can simply remove the duplicate button control from the Default.aspx file:

Once you have removed the duplicate control, save the file and recompile the application. The error now be resolved, and your application should compile and run without any issues.

In some cases, the error may not be as obvious as a duplicate control in the markup file. It could be caused by other factors such as conflicting namespaces or control references. In such cases, it is important to carefully review your code and identify any potential conflicts or errors.


The “Asp net designer xx generates already contains a definition for control error” can be frustrating, but with a systematic approach, it can be easily resolved. By identifying and removing any duplicate control definitions or other conflicts, you can ensure that your ASP.NET application compiles and runs smoothly.

Remember to always review your code carefully and pay attention to any error messages or warnings provided by the . messages can often provide valuable into the root cause of the error and guide you towards the appropriate solution.

By following these steps and maintaining good coding practices, you can minimize the occurrence of such errors and build robust and error-free ASP.NET applications.

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