Conditional Binding Issue-CodePudding

I am currently trying to bind a textbox conditionally based on 3 different objects depending on a Level enum value. In the code sample below, what I hoping to achieve is to display values depending on the following condition:

Person Level0, bind/display ViewModel.Person.Level0.Name
Person Level1, bind/display ViewModel.Person.Level1.Name
Person Level2, bind/display ViewModel.Person.Level2.Name

With all that, the problem i have is that not of the objects are displaying as i am hoping. The textbox remains empty, with no values on display. What am i doing wrong?

<TextBox Margin="0,0,0,5">
    <interactivity:Interaction.Behaviors>
        <core:DataTriggerBehavior Binding="{x:Bind ViewModel.Person.Level, FallbackValue='', Mode=OneWay}" ComparisonCondition="Equal" Value="Level0">
            <core:ChangePropertyAction PropertyName="Text" Value="{x:Bind ViewModel.Person.Level0.Name, FallbackValue=''}" />
        </core:DataTriggerBehavior>
        <core:DataTriggerBehavior Binding="{x:Bind ViewModel.Person.Level, FallbackValue='', Mode=OneWay}" ComparisonCondition="Equal" Value="Level1">
            <core:ChangePropertyAction PropertyName="Text" Value="{x:Bind ViewModel.Person.Level1.Name, FallbackValue='', Mode=OneWay}" />
        </core:DataTriggerBehavior>
        <core:DataTriggerBehavior Binding="{x:Bind ViewModel.Person.Level, FallbackValue='', Mode=OneWay}" ComparisonCondition="Equal" Value="Level2">
            <core:ChangePropertyAction PropertyName="Text" Value="{x:Bind ViewModel.Person.Level2.Name, FallbackValue='', Mode=OneWay}" />
        </core:DataTriggerBehavior>
    </interactivity:Interaction.Behaviors>
</TextBox>

CodePudding user response：

This should work.

Notes:

This code uses a string instead of Level in the Person class because enum binding seems not to work (I'm not sure) with ChangePropertyAction.
The MainPage is named as "ThisPage" so we can bind the ViewModel inside the ChangePropertyAction.

MainPage.xaml

<Page
    x:Class="ConditionalBindingTest.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:core="using:Microsoft.Xaml.Interactions.Core"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:interactivity="using:Microsoft.Xaml.Interactivity"
    xmlns:local="using:ConditionalBindingTest"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    x:Name="ThisPage"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
    mc:Ignorable="d">
    <Grid>
        <TextBox>
            <interactivity:Interaction.Behaviors>
                <core:DataTriggerBehavior
                    Binding="{x:Bind ViewModel.Person.Level, Mode=OneWay}"
                    ComparisonCondition="Equal"
                    Value="Level0">
                    <core:ChangePropertyAction
                        PropertyName="Text"
                        Value="{Binding ElementName=ThisPage, Path=ViewModel.Person.Level0.Name, Mode=OneWay}" />
                </core:DataTriggerBehavior>
                <core:DataTriggerBehavior
                    Binding="{x:Bind ViewModel.Person.Level, Mode=OneWay}"
                    ComparisonCondition="Equal"
                    Value="Level1">
                    <core:ChangePropertyAction
                        PropertyName="Text"
                        Value="{Binding ElementName=ThisPage, Path=ViewModel.Person.Level1.Name, Mode=OneWay}" />
                </core:DataTriggerBehavior>
            </interactivity:Interaction.Behaviors>
        </TextBox>
    </Grid>
</Page>

MainPage.xaml.cs

using Microsoft.UI.Xaml.Controls;

namespace ConditionalBindingTest;

public sealed partial class MainPage : Page
{
    public MainPage()
    {
        this.InitializeComponent();
    }

    public MainPageViewModel ViewModel { get; } = new();
}

MainPageViewModel.cs

using CommunityToolkit.Mvvm.ComponentModel;

namespace ConditionalBindingTest;

public enum Level
{
    Level0,
    Level1,
}

public class LevelName
{
    public LevelName(Level level)
    {
        Name = $"{level} Name";
    }

    public string Name { get; }
}

public class Person
{
    public string Level { get; } = ConditionalBindingTest.Level.Level0.ToString();

    public LevelName Level0 { get; } = new(ConditionalBindingTest.Level.Level0);

    public LevelName Level1 { get; } = new(ConditionalBindingTest.Level.Level1);
}

public partial class MainPageViewModel : ObservableObject
{
    [ObservableProperty]
    private Person person = new();
}

CodePudding user response：

What am i doing wrong?

You use x:Bind where it's not supported
You implement logic in the XAML markup of the view

x:Bind directly to another read-only property of the view model that is defined something like this:

public string DisplayValue
{
    get
    {
        switch (Person.Level)
        {
            case "Level0":
                return Person.Level0.Name;
            case "Level1":
                return Person.Level1.Name;
            case "Level2":
                return Person.Level2.Name;
        }

        return string.Empty;
    }
}

C# is a much more expressive, more concise language than XAML, and while it may be possible to create an entire fairly complex view in markup only, it doesn't mean that it's always a good idea doing so. In this case, you should move the logic to the view model or the Person class itself.