How works IViewFor Bind extension method? - wpf

Question

Simple question, but I dons see solution. Or may be dont understand how Bind method works.
The goal is two way binding between ViewModel and DataContext properties.
public MainWindow()
{
InitializeComponent();
this.Bind(this, v => v.DataContext, v => v.ViewModel);
}
public static readonly DependencyProperty ViewModelProperty = DependencyProperty.Register(
"ViewModel", typeof (string), typeof (MainWindow));
public string ViewModel
{
get { return (string) GetValue(ViewModelProperty); }
set { SetValue(ViewModelProperty, value); }
}
when I set ViewModel property, I get InvalidCastException "System.String" to "WpfApplication1.MainWindow".
But xaml binding works perfectly.
<MainWindow
DataContext="{Binding RelativeSource={RelativeSource Self}, Path=ViewModel, Mode=TwoWay}" ...
full xaml.cs/xaml code is here http://pastebin.com/iCKeNS7R
Where I wrong ?
update:
this code:
this.WhenAnyValue(v => v.ViewModel).BindTo(this, v => v.DataContext);
this.WhenAnyValue(v => v.DataContext).BindTo(this, v => v.ViewModel);
also works as expected
update 2
Question: Does this.Bind(viewModelParam, ...) ignore viewModelParam argument ??
example^ http://pastebin.com/e2aPaGNc
I bind to _otherViewModel, but when type text into textBox, ViewModel.StrProp changed, not _otherViewModel.
Does anybody know, how this.Bind work ??

Answer 1

Bind doesn't work between ViewModel and DataContext because the types don't match (i.e. I could set DataContext to '4' and now it can't assign that to ViewModel).
However, if you are using ReactiveUI bindings, you don't need DataContext at all, you should just use RxUI bindings everywhere. Please ignore the other answers on this thread that tell you how to do things the wrong way.

Answer 2

you can just bind the ViewModel via XAML:
<Window x:Class="YourNameSpace.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:ViewModel="clr-namespace:YourNameSpace"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<ViewModel:MainViewModel x:Key="MainViewModel"/>
</Window.Resources>
<Grid>
<TextBox Text="{Binding YourProperty, Mode=TwoWay, Source={StaticResource MainViewModel}, UpdateSourceTrigger=PropertyChanged}"/>
</Grid>
</Window>
your viewmodel should implement INotifyPropertyChanged.
public class MainViewModel : INotifyPropertyChanged
{
private string _yourProperty;
public string YourProperty
{
get { return _yourProperty; }
set { _yourProperty = value; OnPropertyChanged("YourProperty"); }
}
public MainViewModel()
{
_yourProperty = "Some string";
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged = delegate { };
protected void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}