如何在WPF MVVM中将变量绑定到列表中？

Question

I have an unknown list of variables that I wish to bind to specific controls within a WPF application. Is there a way to bind a variable out of the list with a specific name?

Here is a code example of what I am trying to do.

C#

public class Variable {
    public string Name {get;set;}
}

public class VariableViewModel : INotifyPropertyChanged {
    Variable _variable;
    public Variable Variable {
        get {
            return(_variable);
        }
        set {
            _variable = value;
            if(PropertyChanged != null) {
                PropertyChanged(this, new PropertyChangedEventArgs("Variable"));
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

public class VariableListViewModel {
    public ObservableCollection<VariableViewModel> VariableList { get; set; }

    public VariableListViewModel() {
        VariableList = new ObservableCollection<VariableViewModel>();
        var variableViewModel = new VariableViewModel { 
            Variable = new Variable { Name = "my_variable_name" } 
        };
        VariableList.Add(variableViewModel);
    }
}

WPF:

<Window>
    <Window.DataContext>
        <local:VariableListViewModel />
    </Window.DataContext>

    <StackPanel>
        <Label Content="{Binding Path=Name, ElementName=my_variable_name}" />
    </StackPanel>
</Window>

The label is clearly wrong here. My question is whether or not what I am trying to achieve is possible? I want to be able to display 'my_variable_name'.

-Stuart

Answer 1

You would normally use a ListView (or other ItemsControl ), and bind its ItemsSource to your collection ( VariableList ).

This will cause each item (a VariableViewModel ) to get displayed. You'd then use a DataTemplate to cause the VariableViewModel to display as a Label bound to Variable.Name .

Answer 2

You could use a ValueConverter and use its ConverterParameter to pass in the name of the variable:

public object ConvertTo(object value, Type targetType, object parameter, CultureInfo culture)
{
    var variableList = (IEnumerable<Variable>)value;
    var variableName = parameter != null ? parameter.ToString() : string.Empty;
    return variableList.FirstOrDefault(v=>v.Name == variableName);
}

You could then use that converter in XAML as follows:`

<Label Content="{Binding Path=ListOfVariables, 
                         Converter={StaticResource VariableConverter}, 
                         ConverterParameter='VariableName'}" />

Answer 3

Your question contradicts itself.

On the one hand you say you have an unknown list of variables, on the other hand your View knows which variables it wants to bind to.

So, either you know which variables you want to bind to or you don't know it.

Scenario 1: You know which variables you want to bind to:

Create a property per Variable in your ViewModel

Scenario 2: You don't know which variables you want to bind to:

Bind your VariableList property to an ItemsControl in the View and provide a DataTemplate that can render a VariableViewModel .

---

BTW: Having a VariableViewModel seems to be superfluous. You could use Variable directly. Especially when all VariableViewModel does is returning the Variable inside.

Answer 4

Based on Reeds solution and comments, here is my final solution. I used the same model and view model, so I will only show the View.

<Window>
    <Window.DataContext>
        <local:VariableListViewModel />
    </Window.DataContext>

    <Window.Resources>
        <DataTemplate x:Key="itemsControlDataTemplate">
            <Label x:Name="label" Content="{Binding Variable.Name}">
                <Label.Style>
                    <Style TargetType="{x:Type Label}">
                        <Setter Property="Visibility" Value="Collapsed" />
                        <Style.Triggers>
                            <Trigger Property="Content" Value="my_variable_name">
                                <Setter Property="Visibility" Value="Visible" />
                            </Trigger>
                        </Style.Triggers>
                    </Style>
                </Label.Style>
            </Label>
        </DataTemplate>
    </Window.Resources>

    <StackPanel>
        <ItemsControl ItemTemplate="{StaticResource itemsControlDataTemplate}" ItemsSource="{Binding Path=VariableList}" />
    </StackPanel>
</Window>