C#C
C#•4y ago•
27 replies
p. frost

Passing a string property to a command via a button CommandParameter in .NET 6

Hello

So I'm trying to pass a string (that's bound to a text field via a data context 
<TextBox [...] Text="{Binding SearchString}"/>
 which I made sure already works) using a button's 
CommandParameter
. The relevant button code is as follows (I've hidden layout arguments) 

<Button [...] Command="{Binding PerformSearch}" CommandParameter="{Binding SearchString}" />


PerformSearch
 is a property of the class 
MainViewModel
 that I have defined as a custom class
    internal class SearchCommand : ICommand
    {
        public event EventHandler? CanExecuteChanged;

        public bool CanExecute(object? parameter)
        {
            System.Diagnostics.Debug.WriteLine("CanExecute(parameter) : parameter=" + parameter);
            return true;
        }

        public void Execute(object? parameter)
        {
            System.Diagnostics.Debug.WriteLine("Execute(parameter) : parameter=" + parameter);
        }
    }
    //...
    internal class MainViewModel : INotifyPropertyChanged
    {
        // ...
        public ICommand? PerformSearch { get; } = new SearchCommand();
        // ...
    }


This does however not work, pressing the button does call the command and I do see
CanExecute(parameter) : parameter=
Execute(parameter) : parameter=

in the program's output, however after testing 
parameter
 is null. If I pass a string directly instead of using a binding, I do get the string as an output
<Button [...] Command="{Binding PerformSearch}" CommandParameter="Hello" />

which produces
CanExecute(parameter) : parameter=Hello
Execute(parameter) : parameter=Hello


What am I doing wrong with my previous binding? Maybe this is the wrong way of handling button presses? I've seen people just use 
CommandParameter="Binding"
 and pass the whole ViewModel, and it does indeed pass the whole viewmodel, but I feel like it defeats the purpose of having a separate class handle the command.
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