Скачать или смотреть Resolving Null Reference Exception in Telerik Blazor DropDownList

Learn how to fix the persistent `null reference exception` in the Telerik Blazor DropDownList component with this easy-to-follow guide.
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This video is based on the question https://stackoverflow.com/q/68286796/ asked by the user 'Hans Kilian' ( https://stackoverflow.com/u/3924803/ ) and on the answer https://stackoverflow.com/a/68287290/ provided by the user 'A A' ( https://stackoverflow.com/u/1409661/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Null Reference Exception in Telerik Blazor DropDownList: A Step-by-Step Guide

When developing with Telerik's Blazor components, developers sometimes encounter frustrating issues that can drive them to distraction. One common problem is facing a null reference exception deep within the Telerik DropDownList component. If you’ve found yourself in this situation, you are not alone! This guide will help you understand what might be causing this issue and how to troubleshoot it effectively.

The Problem: Null Reference Exception

In the specific case discussed here, a developer was trying to implement a TelerikDropDownList component bound to a datasource called UserDataSource. However, they encountered a null reference exception when running the application, and the error messages led into complex internal workings of Telerik's libraries, making it difficult to debug.

Example Code

Here is the original code that triggered the error:

[[See Video to Reveal this Text or Code Snippet]]

The line of code leading to the exception is inside the Telerik component handling the selected item mapping, but the source of the fault lies in how the User class is defined.

The Solution: Proper Model Definition

The solution to this problem is relatively straightforward: you need to ensure that your model's properties are properly defined. In this case, the User class was using public fields instead of properties, which is incompatible with Blazor's data binding system and caused the null reference exception.

Recommended Change

Here's the modified version of the User class that will fix the issue:

[[See Video to Reveal this Text or Code Snippet]]

Summary of Changes

Define Properties Instead of Fields: Change public long UserNumber; to public long UserNumber { get; set; } and likewise for Name. This allows Blazor’s data binding to work correctly, preventing errors like null reference exceptions.

Final Thoughts

By simply modifying your class to use properties instead of fields, you can resolve the null reference exception in the TelerikDropDownList. This not only improves the binding experience but also adheres to the design principles of Blazor components.

If you’ve ever faced similar challenges while working with Telerik components or Blazor in general, this guide should serve as a helpful reference. Happy coding!