如何使用MVVM模式以编程方式更改wpf中的焦点文本框？

Question

I have focused element messagetextbox like this

<DockPanel FocusManager.FocusedElement="{Binding ElementName=TextBox1}">    
    <TextBox Name="TextBox1" Text="{Binding Message}"/>
    <TextBox Name="TextBox2" Text="{Binding Message}"/>
    <TextBox Name="TextBox3" Text="{Binding Message}"/>
</DockPanel>

But later I want to change focus dynamically using elementname to "TextBox2" using code. So how to do this. Suppose I have View Model like this

private string elementToFocus;
public string ElementToFocus
{
  set{
    this.elementToFocus=value;
    OnPropertyChanged("ElementToFocus");
  }
  get{
    return this.elementToFocus;
  }
}

Anda I want maybe this kind of code but How I can do this?

<DockPanel FocusManager.FocusedElement="{Binding ElementName={Binding ElementToFocus}}">   

Because I have so many control and sometimes move focus programmatically. Thanks

Answer 1

Since setting the Focus is a View related thing, I personally prefer doing it using the Messager Class (Provided by GalaSoft-Mvvmlight), and here how:

1.register you View to receive messages from ViewModels and set the handler for those messages (inside the Constructor of the View):

Messenger.Default.Register<NotificationMessage>(this, (message) =>
        {
            switch (message.Notification)
            {
                case "TextBox1":
                   TextBox1.Focus();
                    break;
               case "TextBox2":
                   TextBox2.Focus();
                    break;
                case "TextBox3":
                   TextBox3.Focus();
                    break;
            }
        });

2.When you want to change the focus just send a message from your VM containing the Name of the Control to set the focus to :

Messenger.Default.Send(new NotificationMessage("TextBox1"))