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Discover why your Nativescript `@ Input` strings result in `undefined` and learn how to resolve it for a smoother Angular experience.
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This video is based on the question https://stackoverflow.com/q/63837258/ asked by the user 'hamdalaye' ( https://stackoverflow.com/u/4410375/ ) and on the answer https://stackoverflow.com/a/63837767/ provided by the user 'Phix' ( https://stackoverflow.com/u/978005/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the undefined Issue with Nativescript @ Input String Parameters

When working with Nativescript and Angular, developers sometimes encounter unexpected behavior with data binding, especially when using @ Input properties. One common issue is when string inputs result in an undefined value, while numeric inputs work perfectly. In this guide, we will discuss this issue, provide clarity on why it occurs, and present practical solutions so you can get back to building great applications.

Understanding the Issue

A developer faced a peculiar problem: the @ Input property for a string was returning undefined, whereas a number was passed without issues. Here’s a simplified version of the situation reported:

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This developer was puzzled. Why could step accept a number but stepstring did not yield the expected result?

Analyzing the Code

Key Sections of the Code

Component Definition:

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Using the Component:

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The Fundamental Mistake

When you use brackets (i.e., [stepstring]), you are indicating to Angular that you want to bind to a variable. However, Angular requires an explicit string if you choose to bind a string value. Although numbers can be passed directly and will be treated appropriately, strings require explicit syntax.

The Solution

Fortunately, there are a couple of straightforward solutions to fix this issue.

1. Using Attribute Binding Without Brackets

One way to resolve the issue is to omit the brackets for string values:

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Why This Works: By removing the brackets from stepstring, you are telling Angular that you are passing a simple string literal rather than trying to bind a variable.

2. Explicitly Binding the String with Quotes

If you prefer to keep the brackets for consistency or if there's a need to ensure that you are using binding throughout, you can wrap the string in single quotes as follows:

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Why This Works: Here, the explicit quote tells Angular that toto is a string that needs to be evaluated as a constant value.

Conclusion

Understanding the differences in data binding between numbers and strings in Nativescript with Angular can save a lot of debugging time and frustration. By correctly configuring your inputs — either by dropping the brackets for string literals or by explicitly quoting string values — you can ensure that your components receive the data they need.

If you face other related challenges or have questions regarding the use of @ Input, feel free to reach out or leave a comment below!