Скачать или смотреть How to Update InputSelect Source in Blazor

Learn how to effectively repopulate an `InputSelect` control in Blazor to update dropdown options dynamically based on user selections.
---
This video is based on the question https://stackoverflow.com/q/67094072/ asked by the user 'David Shochet' ( https://stackoverflow.com/u/1029771/ ) and on the answer https://stackoverflow.com/a/67166212/ provided by the user 'David Shochet' ( https://stackoverflow.com/u/1029771/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to update InputSelect source

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Update InputSelect Source in Blazor: A Simple Guide

When working with web applications using Blazor, one common requirement is to dynamically update the options in a dropdown list based on user actions. For example, if a user selects a country, you might want to change the list of states or provinces available for that selection. This can enhance the user experience by making forms more interactive.

In this guide, we will address a specific issue related to updating an InputSelect control in Blazor and provide a step-by-step solution to ensure your dropdown options refresh appropriately.

The Challenge

You have an InputSelect control on your component intended to display a list of states or provinces. The problem arises when you need to repopulate the dropdown dynamically based on the selected country. Despite attempting to update the list of states, the dropdown does not display the updated values. Here’s the relevant part of your existing code:

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

In the code-behind, you instantiate your states and have an event callback setup to capture state changes. However, after retrieving the updated list of states, nothing appears to update in your dropdown.

The Solution

After some exploration, the solution became clear: you need to manually invoke a method to notify Blazor that the component state has changed. The missing piece was the StateHasChanged() method. Here are the steps to correctly implement the solution.

Step 1: Fetch Updated States

Ensure that you are correctly fetching the updated state or province list based on the selected country. For instance, your code might look like this:

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

Step 2: Notify the Component of State Change

After you've set your States property with the new list of state or province items, you need to call StateHasChanged() to force the component to re-render with the latest data:

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

Why StateHasChanged() is Important

Re-renders the Component: Calling StateHasChanged() tells Blazor that the component’s state has changed and it should re-render. This is crucial in ensuring your UI reflects the latest data.

Immediate UI Update: It will ensure that any change in your data model is promptly reflected in the UI, keeping the user experience seamless.

Conclusion

Updating an InputSelect source in Blazor is straightforward once you know the importance of notifying Blazor about state changes. By integrating the StateHasChanged() method after you update your data source, your dropdown will correctly display the updated list of states or provinces as users make their selections.

Feel free to implement these steps in your Blazor application and enhance the interactivity of your forms. Happy coding!