too too - 2 months ago 64
C# Question

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

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

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

 <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>
 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();
    }

}