Passing constructor parameters in xaml file

Question

Passing constructor parameters in xaml file

Michell 45

I would like to know how to pass constructor parameters in a xaml file?

Example:

NewChart.cs

public partial class NewChart : UserControl
{
    public MainWindowViewModel mainWindowViewModel { get; set; }
    public NewChart(MainWindowViewModel _instance)
    {
        InitializeComponent();
        mainWindowViewModel = _instance;

    }
}

In the XAML file, how can I pass the argument {Binding _instance} inside views:NewChart

I tried that but it didn't work

<views:NewChart MainWindowViewModel="{Binding _instance}">

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Answer 1

Hui Liu-MSFT 48,676 Microsoft External Staff

Hi,@Michell .Welcome Microsoft Q&A.

In XAML, you could not directly pass constructor parameters when creating an instance of a UserControl. Constructor parameters are typically used to initialize the object and are not directly accessible from XAML.

Instead, you can use Data Binding to pass data to the UserControl from its parent view (e.g., MainWindow).

Here's how you could do it using Data Binding:

NewChart.xaml:

 <Grid>
        <TextBlock Text="{Binding ChartName}" Width="200" Height="50" FontSize="20" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>       
    </Grid>

MainWindowViewModel.cs:

  public class MainWindowViewModel
    {
        public string ChartName { get; set; }
        public MainWindowViewModel()
        {
            ChartName = "Child";
        }
    }

MainWindow.xaml:

<Window x:Class="WpfApp1.MainWindow"
      ...
        xmlns:local="clr-namespace:WpfApp1"
        xmlns:views="clr-namespace:WpfApp1.Views"
        
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
     
        <views:MainWindowViewModel x:Key="_instance" />
    </Window.Resources>

    <StackPanel>
        <views:NewChart DataContext="{StaticResource _instance}" />
      
    </StackPanel>

 
</Window>

MainWindow.xaml.cs:

 public partial class MainWindow : Window
    {
        public MainWindowViewModel _instance { get; set; }

        public MainWindow()
        {
            InitializeComponent();

            
            _instance = new MainWindowViewModel();
            DataContext = _instance;
        }

    }

The result:

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Michell 45 Reputation points

2023-08-03T12:45:11.44+00:00
Hui Liu-MSFT,

Thank you so much for replay.

Let me give more details.

The CS file has a contructor called NewChart and the arguments/parameters of this constructor is of the type MainWindowViewModel:

NewChart.cs

public partial class NewChart : UserControl { public MainWindowViewModel mainWindowViewModel { get; set; } public NewChart(MainWindowViewModel _instance) { InitializeComponent(); mainWindowViewModel = _instance; } }

I would like to call the constructor NewChart on XAML file inside views:NewChart, however I don't know how can I pass the arguments/parameters of the type MainWindowViewModel inside views:NewChart.

I tried that but it didn't work

<views:NewChart MainWindowViewModel="{Binding _instance}">
Michell 45 Reputation points

2023-08-03T12:55:58.6166667+00:00
Hui Liu-MSFT, Thank you for reply.

Unfortunately it didn't work. My mistake.

Instead of instantiating a new MainWindowViewModel inside MainWindow.xaml.cs: (e.g. _instance = new MainWindowViewModel(); ), how can I use the MainWindowViewModel that is already instantiated, in the NewChart.axaml.cs (UserControl) file ?

Example:

In the clickCancel method of the file NewChart.axaml.cs (UserControl) I would like to call a method CloseMenu that is inside the MainWindowViewModel.cs that has already been instantiated:

The code below did not work.

NewChart.axaml.cs public partial class NewChart : UserControl { public MainWindowViewModel instance { get; set; } public NewChart() { InitializeComponent(); instance = new MainWindowViewModel(); DataContext = instance; } public void clickCancel(object sender, RoutedEventArgs args) { instance.CloseMenu(); } }

Hui Liu-MSFT 48,676 Microsoft External Staff

Hi,@Michell .You could check the code below to see if it is what you want. If you still have problems, please show me the complete code that can reproduce your problem so I can analyze it.

 <StackPanel >
        <CheckBox IsChecked="{Binding IsMenuOpen}" Width="200" Height="50" FontSize="20" FontWeight="Bold" HorizontalAlignment="Center" VerticalAlignment="Center"/>
        <Button Content="Cancel" Click="clickCancel" Width="100" Height="50" />
    </StackPanel>

 public partial class NewChart : UserControl
    {
        public MainWindowViewModel instance { get; set; }
        public NewChart()
        {
            InitializeComponent();
            instance = new MainWindowViewModel();
            DataContext = instance;
        }
        public void clickCancel(object sender, RoutedEventArgs args)
        {
            instance.CloseMenu();
        }
    }

MainWindowViewModel :

 public class MainWindowViewModel : INotifyPropertyChanged
    {
        public string Name { get; set; } = "init";
       
        private bool isMenuOpenar;

        public bool IsMenuOpen
        {
            get { return isMenuOpenar; }
            set { isMenuOpenar = value; OnPropertyChanged("IsMenuOpen"); }
        }


        internal void CloseMenu()
        {
            IsMenuOpen = true;
        }
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

    }

MainWindow:

<StackPanel>
      
        <views:NewChart x:Name="c"  />

    </StackPanel>

The result:

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Passing constructor parameters in xaml file

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