input binding is not firing command wpf wvvm - wpf

Question

i have this in MainWindow.xaml
<Window.InputBindings>
<KeyBinding Modifiers="Ctrl" Key="Delete" Command="{Binding DelAllMessages}"/>
</Window.InputBindings>
and in MainViewModel
public void DelAllMessages()
{
MessageBoxResult result = MessageBox.Show(
"Are you sure you want to delete?",
"Confirmation",
MessageBoxButton.YesNo,
MessageBoxImage.Question);
if (result == MessageBoxResult.Yes)
{
// todo
}
}
}
when i press ctrl+del in keyboard in window then this method does not hit.what is missing?

Answer 1

You need to use Commands instead of directly binding the method. One think to keep in mind is in order to have a communication between View model and View is via Properties.
Step 1:-
Create a Command Handler class and Implement ICommand as shown in the below code.
public class CommandHandler : ICommand
{
private Action<object> _action;
private bool _canExeute;
public event EventHandler CanExecuteChanged;
private bool canExeute
{
set
{
_canExeute = value;
CanExecuteChanged(this, new EventArgs());
}
}
public CommandHandler(Action<object> action, bool canExecute)
{
_action = action;
_canExeute = canExecute;
}
public bool CanExecute(object parameter)
{
return _canExeute;
}
public void Execute(object parameter)
{
_action(parameter);
}
}
Step 2:-
Use the newly created class of Command in your Window's code behind.
Create a property of ICommand and provide your DelAllMessages() as your action to that Command, so when there is Clt + Del Pressed, it calls your method.
private ICommand _KeyCommand;
public ICommand KeyCommand
{
get { return _KeyCommand ?? (_KeyCommand = new CommandHandler(obj => DelAllMessages(), true)); }
}
Step 3:-
Assign your your window class as DataContext to the windows' Xaml.
this.DataContext = this;
Check out whole class Code.
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = this;
}
private ICommand _KeyCommand;
public ICommand KeyCommand
{
get { return _KeyCommand ?? (_KeyCommand = new CommandHandler(obj => DelAllMessages(), true)); }
}
public void DelAllMessages()
{
MessageBoxResult result = MessageBox.Show(
"Are you sure you want to delete?",
"Confirmation",
MessageBoxButton.YesNo,
MessageBoxImage.Question);
if (result == MessageBoxResult.Yes)
{
// todo
}
}
}
Step 4:-
Bind the newly created Command property in Xaml.
<Window.InputBindings>
<KeyBinding Modifiers="Ctrl" Key="Delete" Command="{Binding KeyCommand}"/>
</Window.InputBindings>
Whole Xaml Code:-
<Window x:Class="WpfApp4.TriggerTest"
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:WpfApp4"
mc:Ignorable="d"
Title="Window1" Height="450" Width="800">
<Window.InputBindings>
<KeyBinding Modifiers="Ctrl" Key="Delete" Command="{Binding KeyCommand}"/>
</Window.InputBindings>
<Grid>
</Grid>
</Window>