Скачать или смотреть Solving the Bindings Not Updating Issue in Xamarin.Forms

Discover how to fix the frustrating issue of bindings not updating in your Xamarin.Forms application, with clear explanations and solutions to common problems when using INotifyPropertyChanged.
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This video is based on the question https://stackoverflow.com/q/64300134/ asked by the user 'DaddyProphet' ( https://stackoverflow.com/u/13771925/ ) and on the answer https://stackoverflow.com/a/64309953/ provided by the user 'DaddyProphet' ( https://stackoverflow.com/u/13771925/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving the Bindings Not Updating Issue in Xamarin.Forms: A Step-by-Step Guide

If you've ever worked with Xamarin.Forms and encountered a situation where your bindings stop updating despite correctly implemented PropertyChanged events, you’re not alone. This problem can surface even when you believe everything is set up correctly. Let’s unravel the issue and explore a comprehensive solution.

The Problem

You have a page called SubjectsPage that utilizes INotifyPropertyChanged to update UI elements based on changes in your data models. You've set a binding context, and you've confirmed that property notifications are indeed being triggered. Despite this, the UI doesn’t reflect these changes visually.

To illustrate:

Your Subjects property is bound to an ObservableCollection<Subject>.

You have a test label binding to an integer value in your ViewModel, but it doesn't update in the UI.

You’ve checked that all initial values display correctly.

It seems that while the property notifications are being fired, binding updates aren’t being seen on the interface.

Investigating the Binding Context

Initially, your binding context for SubjectsPage is set in the OnAppearing method. This is where you suspected the problem might originate. Here’s how you set it:

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

The async initialization of the ViewModel might complicate binding if executed incorrectly, but the core issue lies in the implementation of your BaseViewModel and BaseModel.

The Root of the Problem: SetProperty Method

Upon digging deeper, you discovered that the actual challenge was with the SetProperty method in your BaseViewModel.

Originally, you implemented it like this:

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

Why This Fails

The problem with the SetProperty method is tied to how nameof() works in this context. By using nameof(publicProperty), it returns the name of the local variable "publicProperty," not the name of the property passed to it. Therefore, when the PropertyChanged event is fired, it’s using the wrong name. This means that any UI elements looking to subscribe to changes aren’t notified correctly.

Solution: Refactoring SetProperty

To resolve this, you need to modify your SetProperty method to require a string for the property name. This way, you explicitly define the property name using nameof() when calling this method. Here’s how to adjust it:

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

How to Implement This Change

Update BaseViewModel: Change the method as illustrated above, so that it takes a string for the property name.

Call SetProperty Correctly: When setting properties in your ViewModel, be sure to use nameof() to pass the property name correctly.

For instance:

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

This way, each time you set a property, the correct property name is published with the PropertyChanged event, ensuring that any UI elements listening for updates can receive them appropriately.

Conclusion

With the above changes, the bindings in your SubjectsPage should now update correctly in response to property changes. By ensuring that the correct property names are passed during the property change notifications, you can eliminate those frustrating issues of bindings appearing broken in Xamarin.Forms.

Now, you can enjoy a seamless experience as your UI reflects the data model changes correctly and consistently. Remember, when working with binding contexts and property notifications, always double-check that your events are being fired with the correct property names!



Implementing this small yet crucial modificatio