Passing two command parameters using a WPF binding

Question

I have a command which I am executing from my XAML file using the following standard syntax    lt Button Content  Zoom  Command   Binding MyViewModel ZoomCommand    gt    This worked fine until I realized that I needed TWO pieces of information from the view in order to make this operation complete the way users expect  the width and height of the canvas specfically    It seems like it s possible to pass an array as an argument to my command  but I don t see there being a way to specify the binding to my two canvas properties in the CommandParameter    lt Button Content  Zoom           Command   Binding MyViewModel ZoomCommand           CommandParameter   Binding ElementName MyCanvas  Path Width    gt    How do I pass both Width and Height to my command   It doesn t seem like this is possible using commands from XAML and I need to wire up a click handler in my codebehind to get this information to pass to my zoom method

User · Answer

This task can also be solved with a different approach. Instead of programming a converter and enlarging the code in the XAML, you can also aggregate the various parameters in the ViewModel. As a result, the ViewModel then has one more property that contains all parameters.

An example of my current application, which also let me deal with the topic. A generic RelayCommand is required: https://stackoverflow.com/a/22286816/7678085

The ViewModelBase is extended here by a command SaveAndClose. The generic type is a named tuple that represents the various parameters.

public ICommand SaveAndCloseCommand => saveAndCloseCommand ??= new RelayCommand<(IBaseModel Item, Window Window)>
    (execute =>
    {
        execute.Item.Save();
        execute.Window?.Close(); // if NULL it isn't closed.
    },
    canExecute =>
    {
        return canExecute.Item?.IsItemValide ?? false;
    });
private ICommand saveAndCloseCommand;

Then it contains a property according to the generic type:

public (IBaseModel Item, Window Window) SaveAndCloseParameter 
{ 
    get => saveAndCloseParameter ; 
    set 
    {
        SetProperty(ref saveAndCloseParameter, value);
    }
}
private (IBaseModel Item, Window Window) saveAndCloseParameter;

The XAML code of the view then looks like this: (Pay attention to the classic click event)

<Button 
    Command="{Binding SaveAndCloseCommand}" 
    CommandParameter="{Binding SaveAndCloseParameter}" 
    Click="ButtonApply_Click" 
    Content="Apply"
    Height="25" Width="100" />
<Button 
    Command="{Binding SaveAndCloseCommand}" 
    CommandParameter="{Binding SaveAndCloseParameter}" 
    Click="ButtonSave_Click" 
    Content="Save"
    Height="25" Width="100" />

and in the code behind of the view, then evaluating the click events, which then set the parameter property.

private void ButtonApply_Click(object sender, RoutedEventArgs e)
{
    computerViewModel.SaveAndCloseParameter = (computerViewModel.Computer, null);
}

private void ButtonSave_Click(object sender, RoutedEventArgs e)
{
    computerViewModel.SaveAndCloseParameter = (computerViewModel.Computer, this);
}

Personally, I think that using the click events is not a break with the MVVM pattern. The program flow control is still located in the area of ??the ViewModel.

User · Answer

About using Tuple in Converter  it would be better to use  object  instead of  string   so that it works for all types of objects without limitation of  string  object   public class YourConverter   IMultiValueConverter              public object Convert object   values                             Tuple lt object  object gt  tuple   new Tuple lt object  object gt  values 0   values 1            return tuple                   Then execution logic in Command could be like this   public void OnExecute object parameter         var param    Tuple lt object  object gt   parameter          e g  for two TextBox object     var txtZip    System Windows Controls TextBox param Item1      var txtCity    System Windows Controls TextBox param Item2      and multi-bind with converter to create the parameters  with two TextBox objects    lt Button Content  Zip City paste  Command   Binding PasteClick    gt       lt Button CommandParameter gt           lt MultiBinding Converter   StaticResource YourConvert   gt               lt Binding ElementName  txtZip   gt               lt Binding ElementName  txtCity   gt           lt  MultiBinding gt       lt  Button CommandParameter gt   lt  Button gt

User · Answer

Use Tuple in Converter  and in OnExecute  cast the parameter object back to Tuple   public class YourConverter   IMultiValueConverter              public object Convert object   values                             Tuple lt string  string gt  tuple   new Tuple lt string  string gt                string values 0    string values 1            return  object tuple                          public void OnExecute object parameter         var param    Tuple lt string  string gt   parameter

User · Answer

Firstly  if you re doing MVVM you would typically have this information available to your VM via separate properties bound from the view  That saves you having to pass any parameters at all to your commands   However  you could also multi-bind and use a converter to create the parameters    lt Button Content  Zoom  Command   Binding MyViewModel ZoomCommand  gt       lt Button CommandParameter gt           lt MultiBinding Converter   StaticResource YourConverter   gt                lt Binding Path  Width  ElementName  MyCanvas   gt                lt Binding Path  Height  ElementName  MyCanvas   gt           lt  MultiBinding gt       lt  Button CommandParameter gt   lt  Button gt    In your converter   public class YourConverter   IMultiValueConverter       public object Convert object   values                     return values Clone                       Then  in your command execution logic   public void OnExecute object parameter        var values    object   parameter      var width    double values 0       var height    double values 1

User · Answer

In the converter of the chosen solution  you should add values Clone   otherwise the parameters in the command end null  public class YourConverter   IMultiValueConverter       public object Convert object   values                     return values Clone

User · Answer

If your values are static  you can use x Array    lt Button Command   Binding MyCommand   gt 10    lt Button CommandParameter gt       lt x Array Type  system Object  gt          lt system String gt Y lt  system String gt          lt system Double gt 10 lt  system Double gt       lt  x Array gt     lt  Button CommandParameter gt   lt  Button gt

[wpf] Passing two command parameters using a WPF binding

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