Implement custom Copy and Paste in WPF DataGrid which works when there are no rows in it

too picture too · Apr 14, 2015 · Viewed 16.8k times · Source

I need to implement a custom copy + cut + paste for data (not text or CSV) to be copied between grids in a WPF application. Using standard ApplicationCommands and defining CommandBinding works really well but only if the DataGrid contains at least 1 row of data and when it's selected. When there are no rows or focus is not on any of them, all commands are disabled.

To fix the problem I tried calling CommandManager.InvalidateRequerySuggested() and setting Focusable=true and/or FocusManager.IsFocusScope=true on the DataGrid but it seems internally DataGrid as a whole is "not interested" in handling Copy/Paste operations, only it's rows are re-querying commands CanExecute state and calling Execute accordingly. It also ignores KeyBindings.

How to make DataGrid handle requerying ApplicationCommands?

Please find the example on which I tested the problem below:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <DataGrid x:Name="TheGrid">
        <DataGrid.Columns>
            <DataGridTextColumn Header="Number" Binding="{Binding}"/>
        </DataGrid.Columns>
        <DataGrid.InputBindings>
            <KeyBinding Key="A" Command="{x:Static ApplicationCommands.New}"/>
        </DataGrid.InputBindings>
        <DataGrid.CommandBindings>
            <CommandBinding Command="{x:Static ApplicationCommands.Paste}" CanExecute="CanPaste" Executed="Paste"/>
            <CommandBinding Command="{x:Static ApplicationCommands.Copy}" CanExecute="CanCopy" Executed="Copy"/>
            <CommandBinding Command="{x:Static ApplicationCommands.New}" CanExecute="CanAddNew" Executed="AddNew"/>
        </DataGrid.CommandBindings>
        <DataGrid.ContextMenu>
            <ContextMenu>
                <MenuItem Command="{x:Static ApplicationCommands.Copy}" Header="Copy"/>
                <MenuItem Command="{x:Static ApplicationCommands.Paste}" Header="Paste"/>
                <MenuItem Command="{x:Static ApplicationCommands.New}" Header="New row"/>
            </ContextMenu>
        </DataGrid.ContextMenu>
    </DataGrid>
</Window>

And the code behind:

using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Windows;
using System.Windows.Input;

namespace WpfApplication1
{
    public partial class MainWindow
    {
        public MainWindow()
        {
            InitializeComponent();
            TheGrid.ItemsSource = numbers;
            // Following line enables commands when row is selected
            numbers.Add(0);
        }

        private void Copy(object sender, ExecutedRoutedEventArgs e)
        {
            Clipboard.SetData(DataFormats.Text, string.Join(",", numbers));
        }

        private void CanCopy(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = numbers.Count > 0;
        }

        private void CanPaste(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = numbers.Count > 0;
            e.Handled = true;
        }

        private void Paste(object sender, ExecutedRoutedEventArgs e)
        {
            Close();
        }

        private void CanAddNew(object sender, CanExecuteRoutedEventArgs e)
        {
            e.CanExecute = true;
            e.Handled = true;
        }

        private void AddNew(object sender, ExecutedRoutedEventArgs e)
        {
            numbers.Add(numbers.Count);
        }

        private readonly ICollection<int> numbers = new ObservableCollection<int>();
    }
}

Edit

The code only solution by Ayyappan Subramanian is the closest match to the application it will be used in. Eventually as I already inherit the grid because it has custom copy+paste format to work on, I added some code which ensures that focus is within a grid in 3 cases:

  1. Context menu is shown
  2. User clicks in the grid (empty) area when it's child visuals have no focus
  3. (Our app specific case) User clicks on a grid navigation TreeView which then brings focus to the grid so shortcuts will work straight away.

Relevant code:

public class MyDataGrid: DataGrid
{
        protected override void OnContextMenuOpening(ContextMenuEventArgs e)
        {
            base.OnContextMenuOpening(e);
            Focus();
        }

        protected override void OnMouseUp(MouseButtonEventArgs e)
        {
            base.OnMouseUp(e);
            if(e.ChangedButton == MouseButton.Left && !IsKeyboardFocusWithin)
            {
                Focus();
            }
        }
}

Answer

Ayyappan Subramanian picture Ayyappan Subramanian · Apr 17, 2015

When the ContextMenu is openning then you can set the focus to the grid which will enable all the menu items. Good explanation is given in here http://www.wpftutorial.net/RoutedCommandsInContextMenu.html

Also for implementing the paste refer the SO post WPF datagrid pasting

WPF:

<DataGrid x:Name="TheGrid" CanUserAddRows="True" 
          ContextMenuOpening="TheGrid_ContextMenuOpening">
    <DataGrid.Columns>
        <DataGridTextColumn Header="Number" Binding="{Binding}"/>
    </DataGrid.Columns>
    <DataGrid.InputBindings>
        <KeyBinding Key="A" Command="{x:Static ApplicationCommands.New}"/>
    </DataGrid.InputBindings>
    <DataGrid.CommandBindings>                
        <CommandBinding Command="{x:Static ApplicationCommands.Paste}" 
                        CanExecute="CanPaste" Executed="Paste"/>
        <CommandBinding Command="{x:Static ApplicationCommands.Copy}" 
                        CanExecute="CanCopy" Executed="Copy"/>
        <CommandBinding Command="{x:Static ApplicationCommands.New}" 
                        CanExecute="CanAddNew" Executed="AddNew"/>
    </DataGrid.CommandBindings>
    <DataGrid.ContextMenu>
        <ContextMenu>                   
            <MenuItem Command="{x:Static ApplicationCommands.Copy}" Header="Copy"/>
            <MenuItem Command="{x:Static ApplicationCommands.Paste}" Header="Paste"/>
            <MenuItem Command="{x:Static ApplicationCommands.New}" Header="New row"/>
        </ContextMenu>
    </DataGrid.ContextMenu>
</DataGrid>

C# code:

public partial class Window1 : Window
{
    public Window1()
    {
        InitializeComponent(); 
        TheGrid.ItemsSource = numbers;
    }

    private void Copy(object sender, ExecutedRoutedEventArgs e)
    {
        Clipboard.SetData(DataFormats.Text, string.Join(",", numbers));
    }

    private void CanCopy(object sender, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
    }

    private void CanPaste(object sender, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
        e.Handled = true;
    }

    private void Paste(object sender, ExecutedRoutedEventArgs e)
    {
        Close();
    }

    private void CanAddNew(object sender, CanExecuteRoutedEventArgs e)
    {
        e.CanExecute = true;
        e.Handled = true;
    }

    private void AddNew(object sender, ExecutedRoutedEventArgs e)
    {
        numbers.Add(numbers.Count);
    }

    private readonly ICollection<int> numbers = new ObservableCollection<int>();

    private void TheGrid_ContextMenuOpening(object sender, ContextMenuEventArgs e)
    {
        TheGrid.Focus();
    }

}