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Discover how to validate user input in Flutter when comparing two values in a single TextFormField. Learn step-by-step methods to implement effective validation!
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Mastering Input Validation in Flutter: Comparing Two Variables in One TextFormField

When building a user-friendly application with Flutter, data validation becomes crucial. A common scenario might involve comparing two different inputs—like ensuring a sale price does not exceed a given original price. However, when using TextFormField, developers face a unique challenge: the validator function typically only handles a single value. In this blog, we will explore how to implement a solution that allows you to validate user input by comparing two variables.

The Problem: Validating User Input

In this example, we want to ensure that the sale price entered by the user cannot be greater than the original price. To illustrate, we will compare two variables representing prices: couponSalePriceCtrlr for the sale price and couponOrigPriceCtrlr for the original price. The usual constraint is that the validator only accepts one input parameter (the current value of the form field), complicating our task of comparing the two price inputs.

The Solution: Step-by-Step Validation

Step 1: Parse Input Values

Both the sale price and original price inputs come as String types from the text fields. To make comparisons, we need to convert these values into double. Here's how to achieve that:

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

Step 2: Implementing TextFormField for Original Price

First, implement the TextFormField for the original price. It will accept numeric input from the user:

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

Step 3: Implementing TextFormField for Sale Price with Validator Function

Next, we need to create another TextFormField for the sale price. This is where we add our custom validator function to enforce the restriction:

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

Step 4: Putting It All Together

Below is a concise implementation of the widget that encompasses both the original and sale prices with appropriate validation:

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

Conclusion

By using the outlined approach, we can effectively validate inputs in Flutter where two variables are compared within a single TextFormField. Ensuring the sale price does not exceed the original price maximizes user experience and prevents invalid data submissions. Keep experimenting with Flutter's rich widget library to enhance your applications further!

With this guide, you'll be well on your way to mastering validation any time you need to compare multiple inputs in your Flutter applications.