Скачать или смотреть Setting the Initial Value for a Picker in Xamarin: A Clear Solution

Discover how to effectively set the initial value of a Picker control in Xamarin to improve user experience in your app.
---
This video is based on the question https://stackoverflow.com/q/67370345/ asked by the user 'Vivendi' ( https://stackoverflow.com/u/1175327/ ) and on the answer https://stackoverflow.com/a/67370498/ provided by the user 'Jason' ( https://stackoverflow.com/u/1338/ ) 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: Set initial value for Picker in ViewModel in Xamarin

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.
---
Setting the Initial Value for a Picker in Xamarin

Creating intuitive and responsive applications in Xamarin is essential for a seamless user experience. One common challenge developers face is setting the initial value for Picker controls. If you've encountered a scenario where your Picker does not show the expected initial value, you're not alone. This guide will address this issue and provide you with a straightforward solution.

The Problem

In your Xamarin.Forms application, you may have set up a Picker control to allow users to select their gender. However, when you try to set an initial value in your ViewModel's constructor, the Picker does not reflect this value. This can be frustrating, especially when you see other controls, like DateTime, working correctly. The core of the issue lies in how objects for the Picker are being managed in the ViewModel.

Code Example of the Issue

Let’s take a look at the relevant code that demonstrates the trouble you're facing with setting the initial value for the Picker:

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

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

Despite setting the gender to "Female" in the constructor, the Picker does not display it correctly.

The Solution

The reason your Picker is not showing the initially set value is that you are creating a new instance of GenderItem, which does not match any of the existing instances in the GenderItems list. The Picker relies on object reference equality rather than just value equality. Essentially, the Picker does not recognize your new GenderItem as being the same as the existing ones, even if they have the same name.

Correct Approach to Set Initial Value

To ensure that the Picker recognizes the initially selected gender, follow these steps:

Assign Existing Object from GenderItems:
Instead of creating a new GenderItem instance, you should directly assign an existing item from your GenderItems list to the Gender property.

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

This effectively assigns the reference of the existing "Female" GenderItem to Gender, which allows the Picker to recognize it properly.

Summary of Adjustments

Identify Object Reference: Always assign an object reference from the collection that is bound to the Picker.

Utilize Collection Methods: Use methods like FirstOrDefault to retrieve an existing object by its properties, ensuring a proper match.

Conclusion

Setting the initial value of a Picker in Xamarin can seem tricky, but understanding the importance of object references clears the confusion. By ensuring that the Picker's SelectedItem property refers to an existing object rather than a newly created one, you enhance the user experience by providing an appropriate initial state for your application’s users.

Feel free to reach out with further questions or examples you'd like to explore in Xamarin or similar frameworks!