c# - MVVM- How can I select text in a textbox?

Question

Is there a MVVM way to select text in a textbox? The MVVM framework that I am using is Laurent Bugnion's MVVM Light Toolkit.

Answer 1

Whenever I am trying to directly affect the the View in a "pure" MVVM application (no code-behind in View), I will use Attached Properties to encapsulate whatever effect I am trying to achieve. I will create an interface that defines the actions I wish to take using custom events. I then implement this interface in each ViewModel that will be "running" these commands on the View. Finally, I bind my ViewModel to the attached property in my View definition. The following code shows how to this for SelectAll and a TextBox. This code can be easily expanded to perform just about any action on any component in the View.

My Attached Property and interface definition:

using System.Windows;
using System.Windows.Controls;
using System;
using System.Collections.Generic;

namespace SelectAllSample
{
    public static class TextBoxAttach
    {
        public static readonly DependencyProperty TextBoxControllerProperty = DependencyProperty.RegisterAttached(
            "TextBoxController", typeof(ITextBoxController), typeof(TextBoxAttach),
            new FrameworkPropertyMetadata(null, OnTextBoxControllerChanged));
        public static void SetTextBoxController(UIElement element, ITextBoxController value)
        {
            element.SetValue(TextBoxControllerProperty, value);
        }
        public static ITextBoxController GetTextBoxController(UIElement element)
        {
            return (ITextBoxController)element.GetValue(TextBoxControllerProperty);
        }

        private static readonly Dictionary<ITextBoxController, TextBox> elements = new Dictionary<ITextBoxController, TextBox>();
        private static void OnTextBoxControllerChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var element = d as TextBox;
            if (element == null)
                throw new ArgumentNullException("d");

            var oldController = e.OldValue as ITextBoxController;
            if (oldController != null)
            {
                elements.Remove(oldController);
                oldController.SelectAll -= SelectAll;
            }

            var newController = e.NewValue as ITextBoxController;
            if (newController != null)
            {
                elements.Add(newController, element);
                newController.SelectAll += SelectAll;
            }
        }
        private static void SelectAll(ITextBoxController sender)
        {
            TextBox element;
            if (!elements.TryGetValue(sender, out element))
                throw new ArgumentException("sender");
            element.Focus();
            element.SelectAll();
        }
    }

    public interface ITextBoxController
    {
        event SelectAllEventHandler SelectAll;
    }

    public delegate void SelectAllEventHandler(ITextBoxController sender);
}

My ViewModel definition:

public class MyViewModel : ITextBoxController
{
    public MyViewModel()
    {
        Value = "My Text";
        SelectAllCommand = new RelayCommand(p =>
        {
            if (SelectAll != null)
                SelectAll(this);
        });
    }

    public string Value { get; set; }
    public RelayCommand SelectAllCommand { get; private set; }

    public event SelectAllEventHandler SelectAll;
}

My View definition:

<Window x:Class="SelectAllSample.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:loc="clr-namespace:SelectAllSample"
    Title="Window1" Height="150" Width="150">
    <x:Code><![CDATA[
        public Window1()
        {
            InitializeComponent();
            DataContext = new MyViewModel();
        }
    ]]></x:Code>
    <StackPanel>
        <TextBox Text="{Binding Value}" loc:TextBoxAttach.TextBoxController="{Binding}" />
        <Button Content="Select All" Command="{Binding SelectAllCommand}" />
    </StackPanel>
</Window>

Note: Thanks to Josh Smith for RelayCommand (see code in Figure 3 on this page). It is used in MyViewModel in this example (and just about all my MVVM code).