C-Sharp Asp.net Asp.net Ajax

Understanding AJAX Autocomplete and Webservice Calls

When developing web applications, a common requirement is to provide users with an interactive way of searching and selecting items. One popular feature for this functionality is AJAX Autocomplete. However, developers often run into roadblocks, particularly when calling web service methods associated with Autocomplete controls. This blog post addresses a common question: How should you correctly use the ServiceMethod property in the AutoCompleteExtender?

The Dilemma: Using Generics in AJAX Web Services

The Setup

In a typical implementation, you may have a method that requires a type to be passed for fetching data for the autocomplete functionality. Consider the following setup:

ServiceMethod="DropDownLoad&lt;&lt;%=(typeof)subCategory%&gt;&gt;"

In this case, subCategory is a property that retrieves data from a database. Below is a simplified representation of how this property may look:

protected SubCategory subCategory
{
    get
    {
        var subCategory = NHibernateObjectHelper.LoadDataObject&lt;SubCategory&gt;(Convert.ToInt32(Request.QueryString["SCID"]));
        return subCategory;
    }
}

The Confusion

The concern arises when trying to call a generic method for the web service. Specifically, the question becomes whether you can successfully use a generic type in conjunction with a web service call.

The Solution: Understanding Web Method Limitations

Generic vs Non-Generic Methods

In ASP.NET, two web methods are often created to handle similar tasks:

[WebMethod]
public string[] GetSearchList(string prefixText, int count)
{
}

[WebMethod]
public string[] GetSearchList2&lt;T&gt;(string prefixText, int count)
{
}

While both methods seem to serve the same purpose, there is a significant difference in functionality:

Non-Generic Method: GetSearchList can be readily exposed and called from web services.
Generic Method: GetSearchList2<T> is not adequately supported for web service calls due to restrictions imposed by SOAP 1.x and HTTP POST protocols. This means you cannot call a generic method when interacting with a web service.

Conclusion: Best Practices

To avoid confusion and errors in your AJAX autocomplete implementation:

Stick to Non-Generic Methods: Use simple and straightforward web methods without generic parameters to ensure compatibility with AJAX calls.
Validate Service Methods: Ensure you test and validate your web methods using tools like Postman or Fiddler to confirm they are accessible and behave as expected.

By following these best practices, you can streamline your interactions with web services and ensure a smoother user experience for your applications.

Remember, clear understanding and careful implementation of these service calls can save you a lot of headaches down the road!