WPF Input and Commands Patterns

Handling user input and implementing command patterns in WPF applications.

1. Command System Overview

ICommand (Interface)
├── RoutedCommand (WPF built-in)
│   ├── ApplicationCommands (Copy, Paste, Cut, etc.)
│   ├── NavigationCommands (BrowseBack, BrowseForward, etc.)
│   ├── MediaCommands (Play, Pause, Stop, etc.)
│   └── EditingCommands (ToggleBold, ToggleItalic, etc.)
└── RelayCommand / DelegateCommand (MVVM)

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2. Built-in Commands

2.1 ApplicationCommands

<Window.CommandBindings>
    <CommandBinding Command="ApplicationCommands.Copy"
                    Executed="CopyCommand_Executed"
                    CanExecute="CopyCommand_CanExecute"/>
    <CommandBinding Command="ApplicationCommands.Paste"
                    Executed="PasteCommand_Executed"/>
</Window.CommandBindings>

<StackPanel>
    <Button Command="ApplicationCommands.Copy" Content="Copy (Ctrl+C)"/>
    <Button Command="ApplicationCommands.Paste" Content="Paste (Ctrl+V)"/>
    <Button Command="ApplicationCommands.Undo" Content="Undo (Ctrl+Z)"/>
    <Button Command="ApplicationCommands.Redo" Content="Redo (Ctrl+Y)"/>
</StackPanel>

private void CopyCommand_Executed(object sender, ExecutedRoutedEventArgs e)
{
    // Copy logic
    Clipboard.SetText(SelectedText);
}

private void CopyCommand_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    // Enable condition
    e.CanExecute = !string.IsNullOrEmpty(SelectedText);
}

2.2 Common Built-in Commands

Category	Commands
ApplicationCommands	New, Open, Save, SaveAs, Close, Print, Copy, Cut, Paste, Undo, Redo, Find, Replace, SelectAll, Delete, Properties, Help
NavigationCommands	BrowseBack, BrowseForward, BrowseHome, BrowseStop, Refresh, Favorites, Search, GoToPage, NextPage, PreviousPage, FirstPage, LastPage
MediaCommands	Play, Pause, Stop, Record, NextTrack, PreviousTrack, FastForward, Rewind, ChannelUp, ChannelDown, TogglePlayPause, IncreaseVolume, DecreaseVolume, MuteVolume
EditingCommands	ToggleBold, ToggleItalic, ToggleUnderline, IncreaseFontSize, DecreaseFontSize, AlignLeft, AlignCenter, AlignRight, AlignJustify

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3. Custom RoutedCommand

3.1 Define Custom Command

namespace MyApp.Commands;

using System.Windows.Input;

public static class CustomCommands
{
    // Define custom command
    public static readonly RoutedCommand RefreshData = new(
        nameof(RefreshData),
        typeof(CustomCommands),
        new InputGestureCollection
        {
            new KeyGesture(Key.F5),
            new KeyGesture(Key.R, ModifierKeys.Control)
        });

    public static readonly RoutedCommand ExportToPdf = new(
        nameof(ExportToPdf),
        typeof(CustomCommands),
        new InputGestureCollection
        {
            new KeyGesture(Key.E, ModifierKeys.Control | ModifierKeys.Shift)
        });

    public static readonly RoutedCommand ToggleFullScreen = new(
        nameof(ToggleFullScreen),
        typeof(CustomCommands),
        new InputGestureCollection
        {
            new KeyGesture(Key.F11)
        });
}

3.2 Use Custom Command in XAML

<Window xmlns:cmd="clr-namespace:MyApp.Commands">
    <Window.CommandBindings>
        <CommandBinding Command="{x:Static cmd:CustomCommands.RefreshData}"
                        Executed="RefreshData_Executed"
                        CanExecute="RefreshData_CanExecute"/>
        <CommandBinding Command="{x:Static cmd:CustomCommands.ExportToPdf}"
                        Executed="ExportToPdf_Executed"/>
    </Window.CommandBindings>

    <Menu>
        <MenuItem Header="_File">
            <MenuItem Header="_Refresh"
                      Command="{x:Static cmd:CustomCommands.RefreshData}"
                      InputGestureText="F5"/>
            <MenuItem Header="_Export to PDF"
                      Command="{x:Static cmd:CustomCommands.ExportToPdf}"
                      InputGestureText="Ctrl+Shift+E"/>
        </MenuItem>
    </Menu>
</Window>

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4. InputBinding (Keyboard/Mouse Shortcuts)

4.1 KeyBinding

<Window.InputBindings>
    <!-- Keyboard shortcut -->
    <KeyBinding Key="N" Modifiers="Control" Command="ApplicationCommands.New"/>
    <KeyBinding Key="S" Modifiers="Control" Command="ApplicationCommands.Save"/>
    <KeyBinding Key="S" Modifiers="Control+Shift" Command="ApplicationCommands.SaveAs"/>
    <KeyBinding Key="F4" Modifiers="Alt" Command="ApplicationCommands.Close"/>

    <!-- Function keys -->
    <KeyBinding Key="F1" Command="ApplicationCommands.Help"/>
    <KeyBinding Key="F5" Command="{x:Static cmd:CustomCommands.RefreshData}"/>

    <!-- MVVM Command binding -->
    <KeyBinding Key="Delete" Command="{Binding DeleteCommand}"/>
</Window.InputBindings>

4.2 MouseBinding

<Border.InputBindings>
    <!-- Double-click -->
    <MouseBinding MouseAction="LeftDoubleClick"
                  Command="{Binding OpenDetailCommand}"/>

    <!-- Middle click -->
    <MouseBinding MouseAction="MiddleClick"
                  Command="{Binding CloseTabCommand}"/>

    <!-- Ctrl + Left click -->
    <MouseBinding MouseAction="LeftClick"
                  Modifiers="Control"
                  Command="{Binding MultiSelectCommand}"/>
</Border.InputBindings>

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5. CommandParameter

5.1 Static Parameter

<Button Command="{Binding NavigateCommand}"
        CommandParameter="Home"
        Content="Go to Home"/>

<Button Command="{Binding SetZoomCommand}"
        CommandParameter="100"
        Content="Zoom 100%"/>

5.2 Binding Parameter

<ListBox x:Name="ItemList" ItemsSource="{Binding Items}"/>
<Button Command="{Binding DeleteCommand}"
        CommandParameter="{Binding SelectedItem, ElementName=ItemList}"
        Content="Delete Selected"/>

<!-- Self-reference -->
<Button Command="{Binding ProcessCommand}"
        CommandParameter="{Binding RelativeSource={RelativeSource Self}}"
        Content="Process This Button"/>

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6. CommandTarget

6.1 Redirecting Command Target

<StackPanel>
    <TextBox x:Name="TargetTextBox"/>

    <!-- Commands target the TextBox even when button is focused -->
    <Button Command="ApplicationCommands.Copy"
            CommandTarget="{Binding ElementName=TargetTextBox}"
            Content="Copy from TextBox"/>

    <Button Command="ApplicationCommands.Paste"
            CommandTarget="{Binding ElementName=TargetTextBox}"
            Content="Paste to TextBox"/>
</StackPanel>

---

7. Handling Keyboard Input

7.1 Key Events

namespace MyApp.Views;

using System.Windows;
using System.Windows.Input;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        // Preview events (Tunneling - captured before child elements)
        PreviewKeyDown += OnPreviewKeyDown;

        // Normal events (Bubbling - captured after child elements)
        KeyDown += OnKeyDown;
    }

    private void OnPreviewKeyDown(object sender, KeyEventArgs e)
    {
        // Global shortcut handling
        if (e.Key == Key.Escape)
        {
            // Close popup or cancel operation
            e.Handled = true;
        }

        // Modifier key combinations
        if (Keyboard.Modifiers == ModifierKeys.Control && e.Key == Key.G)
        {
            // Ctrl+G: Go to line
            ShowGoToLineDialog();
            e.Handled = true;
        }
    }

    private void OnKeyDown(object sender, KeyEventArgs e)
    {
        // Handle if not processed by child elements
    }
}

7.2 TextInput Event

private void TextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    // Allow only numeric input
    if (!char.IsDigit(e.Text, 0))
    {
        e.Handled = true;
    }
}

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8. Handling Mouse Input

8.1 Mouse Events

namespace MyApp.Controls;

using System.Windows;
using System.Windows.Input;

public partial class DrawingCanvas : FrameworkElement
{
    private Point _startPoint;
    private bool _isDragging;

    public DrawingCanvas()
    {
        MouseLeftButtonDown += OnMouseLeftButtonDown;
        MouseMove += OnMouseMove;
        MouseLeftButtonUp += OnMouseLeftButtonUp;
        MouseWheel += OnMouseWheel;
    }

    private void OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        _startPoint = e.GetPosition(this);
        _isDragging = true;

        // Capture mouse to receive events outside the element
        CaptureMouse();

        // Click count detection
        if (e.ClickCount == 2)
        {
            // Double click
        }
    }

    private void OnMouseMove(object sender, MouseEventArgs e)
    {
        if (!_isDragging) return;

        var currentPoint = e.GetPosition(this);
        var delta = currentPoint - _startPoint;

        // Draw or drag logic
    }

    private void OnMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        if (_isDragging)
        {
            _isDragging = false;
            ReleaseMouseCapture();
        }
    }

    private void OnMouseWheel(object sender, MouseWheelEventArgs e)
    {
        // e.Delta: positive = scroll up, negative = scroll down
        var zoomFactor = e.Delta > 0 ? 1.1 : 0.9;
        ApplyZoom(zoomFactor);
    }
}

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9. Focus Management

9.1 Programmatic Focus Control

// Set focus
myTextBox.Focus();

// Set keyboard focus specifically
Keyboard.Focus(myTextBox);

// Check focus
if (myTextBox.IsFocused)
{
    // Has focus
}

if (myTextBox.IsKeyboardFocused)
{
    // Has keyboard focus
}

9.2 FocusManager

<!-- Set default focused element -->
<Window FocusManager.FocusedElement="{Binding ElementName=FirstTextBox}">
    <StackPanel>
        <TextBox x:Name="FirstTextBox"/>
        <TextBox x:Name="SecondTextBox"/>
    </StackPanel>
</Window>

<!-- Define focus scope -->
<ToolBar FocusManager.IsFocusScope="True">
    <Button Content="Button 1"/>
    <Button Content="Button 2"/>
</ToolBar>

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10. References

• Commanding Overview - Microsoft Docs
• Input Overview - Microsoft Docs
• Focus Overview - Microsoft Docs