MvvmHelper | rapid development framework , Kotlin language development | Model View Controller library

You could change the item color to gray when you click the item to triger the SelectionChanged event of CollectionView.

Xaml:

Yes, you can create a model and create different properties for different controls. I created a simple demo based on your code(take the PriceDifLabel 's text and text color for example).

You can refer to the following code:

1.create a model MyViewModel.cs and implement interface INotifyPropertyChanged.

And when we change the value of UpdatedCost(bind for Entry UpdatedCost),we can also change the PriceDif accordingly.

MyViewModel.cs

You need a as the child node of your :

There is a typo mistake in your Register.xaml, that results in different namespace between the xaml and the cs partial definition of your Register class.

You have

You could achieve this in XAML only, by using a multi-binding on the IsEnabled property on the Sign In Button to the user name and the password TextBoxes along with a custom value converter that converts the bound strings to a bool that indicates whether they are empty or not.

However, in this case that is not possible, since you should avoid using Command and IsEnabled at the same time, as it can lead to strange behavior. Commands offer a mechanism to determine, if an action is possible or not and will in turn set the IsEnabled state.

A command can indicate whether an action is possible by implementing the CanExecute method. A button can subscribe to the CanExecuteChanged event and be disabled if CanExecute returns false or be enabled if CanExecute returns true.

As you can see, setting both a Command and IsEnabled will interfere with each other. Although it might work, if you specify IsEnabled before Command in XAML, this is a brittle solution, so choose one, in this case favor Command with its built in mechanism.

The good news is that instead of doing this in XAML, you can achieve the same in your view model and save yourself some code by passing a CanExecute delegate to your LoginCommand as follows.

There are two reasons why Apple reject this submitted version.

ITMS-90338: Non-public API usage - The app references non-public selectors in [project name]: applicationWillTerminate, fontWeight, newSocketQueueForConnectionFromAddress:onSocket:, setOrientation:animated:, socket:didConnectToHost:port:, socket:didReadPartialDataOfLength:tag:, socket:didReceiveTrust:completionHandler:, socket:didWritePartialDataOfLength:tag:, socket:shouldTimeoutReadWithTag:elapsed:bytesDone:, socket:shouldTimeoutWriteWithTag:elapsed:bytesDone:, socketDidCloseReadStream:, socketDidSecure:, terminateWithSuccess.

This means that you need to modify the list names of methods with another name, because these names will conflict with the private method names of Apple's system. You need to find them and replace them with other names.

ITMS-90809: Deprecated API Usage - New apps that use UIWebView are no longer accepted. Instead, use WKWebView for improved security and reliability.

Starting in April 2020, Apple will reject apps that still use the deprecated UIWebView API. While Xamarin.Forms has switched to WKWebView as the default, there is still a reference to the older SDK in the Xamarin.Forms binaries. Current iOS linker behavior does not remove this, and as a result the deprecated UIWebView API will still appear to be referenced from your app when you submit to the App Store.

A preview version of the linker is available to fix this issue. To enable the preview, you will need to supply an additional argument --optimize=experimental-xforms-product-type to the linker.

Detailed steps can refer to UIWebView Deprecation and Xamarin.Forms.

There are two problems with shared code.

First is the GestureRecognizers used for Lable(background color for testing) need to modify as follows:

Change the constructor of HomeTabPage to

You have several good options here.
Since the last solution, which uses a DataTrigger, is the most flexible, as it allows to trigger on certain states of the ComboBox.SelectedItem, I recommend to implement it to solve your problem. It's also a XAML only solution and doesn't require an extra property like LanguageChanged.

In order to animate a property like LanguageChanged, the property must be a DependencyProperty. The first example therefore implements LanguageChanged as a DependencyProperty of MainWindow:

MainWindow.xaml.cs