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Learn how to manage multiple dropdown lists in Flutter by preventing users from selecting the same item twice. Improve your app's user experience with effective dropdown management!
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This video is based on the question https://stackoverflow.com/q/69412131/ asked by the user 'Vincent Agbo' ( https://stackoverflow.com/u/10870664/ ) and on the answer https://stackoverflow.com/a/69415927/ provided by the user 'Peter Koltai' ( https://stackoverflow.com/u/14726230/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Prevent Duplicate Selections in Dropdown Lists in Flutter

When developing Flutter applications, there may be scenarios where you're required to implement dropdown lists that should not allow duplicate selections. For example, you might want to prevent users from selecting the same security question twice. This can be important for ensuring a smooth user experience and maintaining data integrity.

In this post, we will explore one effective way to achieve that by dynamically filtering the dropdown items based on the selected values of other dropdown lists.

Problem Overview

Suppose you have two dropdowns, both populated from the same set of security questions. The challenge arises when a user makes a selection in one dropdown— how do you ensure that this selection is no longer available in the other dropdown? This scenario is common in applications that require users to select unique items from a list.

Example Scenario:

User selects a security question in the first dropdown.

The same question should not appear in the second dropdown.

Both dropdowns should update dynamically as selections are made.

Solution Breakdown

To resolve this, we will utilize Flutter's DropdownButton widget and a state management technique using setState(). Here’s how you can implement this solution step-by-step:

Step 1: Set Up Your Environment

First, be sure to have your Flutter environment set up correctly. Import the necessary material package with the following code:

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Step 2: Create a Stateful Widget

We’ll start by creating a simple Stateful Widget to manage dropdown selections.

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Step 3: Define Your Data

Define a list of options that will populate the dropdowns. You can update this list to pull data from APIs or other sources as needed.

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Step 4: Create Your Dropdowns

In your build method, add two DropdownButton widgets inside a Column. You'll need to use the setState() method to manage the selections:

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

Repeat this for the second dropdown, changing _selected1 to _selected2:

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

Step 5: Complete the Flutter App Structure

Ensure you've wrapped your dropdowns within a Scaffold and provided a proper entry point to your Flutter app.

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

Efficiency Consideration

It’s essential to note that the outlined method is efficient for a small set of items but may not scale well with larger datasets. If efficiency becomes a concern, consider maintaining separate lists for the available options and dynamically updating them based on selections without creating new lists each time.

Conclusion

By following this approach, you can effectively manage multiple dropdowns in Flutter while preventing duplicate selections from being made. This not only enhances the user experience but also ensures that your applications maintain data accuracy. Implement this technique in your applications and improve the interactivity and usability of your forms!