Set Command property of CommandBinding using internal namespace with custom commands? - wpf

Question

I'm exploring WPF and seeing if I can work my way to using a full MVVM approach. For now, I think I need to learn how to reference my own custom objects/commands that I've defined in a nearby namespace.
This is my folder structure:
This is my XAML
<Window x:Class="WpfApp1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
xmlns:commands="clr-namespace:WpfApp1.Commands"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Window.CommandBindings>
<CommandBinding
Command="commands:WordSearchCommand"
CanExecute="CanExecuteChanged"/>
</Window.CommandBindings>
<Grid>
<StackPanel Orientation="Horizontal">
<Label Target="{Binding ElementName=wordSearchBox}">Word _Search:</Label>
<TextBox
Name="wordSearchBox"
Height="25"
Width="600"
VerticalAlignment="Top"
SpellCheck.IsEnabled="True"
Text="{Binding Path=SearchWord}">
</TextBox>
<Button Height="25" Width="100" VerticalAlignment="Top" Command="{Binding Path=WordSearchCommand}" CommandParameter="{Binding Path=SearchWord}">Search</Button>
</StackPanel>
</Grid>
</Window>
This is my MainWindow code-behind:
using AppLogicCommandsAndQueries;
using System.Windows;
using WpfApp1.ViewModels;
namespace WpfApp1
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
Bootstrapper.Bootstrap();
InitializeComponent();
DataContext = new WordSearchViewModel();
}
}
}
This is my WordSearchCommand definition:
using System;
using System.Windows;
using System.Windows.Input;
namespace WpfApp1.Commands
{
public class WordSearchCommand : ICommand
{
private string previousSearch;
public event EventHandler CanExecuteChanged = delegate (object s, EventArgs e)
{
MessageBox.Show("word search can execute changed");
};
public bool CanExecute(object parameter)
{
return previousSearch != (string)parameter;
}
public void Execute(object parameter)
{
// if online check online db else check offline db
MessageBox.Show("word search command");
previousSearch = (string)parameter;
}
}
}
I've tried rebuilding, switching CPU targets, switching to Release mode and back, etc. There's got to be a coding error, right?
This is the error displayed in my build output:
WpfApp1\MainWindow.xaml(14,134,14,151): error CS1061: 'MainWindow' does not contain a definition for 'CanExecuteChanged' and no accessible extension method 'CanExecuteChanged' accepting a first argument of type 'MainWindow' could be found (are you missing a using directive or an assembly reference?)

Answer 1

It seems like I don't understand C# events or WPF event routing very well. I was able to get the desired behavior by changing the CanExecuteChanged event handler on my WordSearchCommand.
Before I had:
public event EventHandler CanExecuteChanged = delegate (object s, EventArgs e)
{
MessageBox.Show("word search can execute changed");
};
Which would never execute (I never saw the message box). Also, the CanExecute method would only get called once.
Now, I have:
public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
}
and now my CanExecute method gets called a ton (a bunch at the beginning, and basically anytime I interact with the Window?).
I tried adding event accessors before but didn't realize I needed to remove the delegate signature for the accessor definitions to become syntactically valid. I definitely took inspiration from a RelayCommand definition as well as other posts on StackOverflow. I'm still not exactly sure what's going on here, but I've stumbled upon a solution that I can use for now.