Re: Two-way binding problem - WPF Discussion Boards

17-Jul-09 9:42

Hi,
Recently I'm trying to learn WPF, and I've stumbled across a problem, I can solve it, but I'm not happy with the result code, so maybe someone could help me to polish it a bit.

Let's say, I have class XManager, that manages classes X, also, it has reference to currently active X instance, each class X has it's own Text property, I want to do a two way binding between textbox and this text property.

It looks like this:

class XManager
{
  private X activeX;

  public X ActiveX
  {
    get { return activeX; }
  }
}

class X : INotifyPropertyChanged
{
  public string Text { get; set; }

  public void PutSomeTextProgramatically(string someText)
  {
    Text += someText;
    if (PropertyChanged != null)
      PropertyChanged(this, new PropertyChangedEventArgs("Text"));
  }
}

Now, I do have a manager accessible from XAML:

<Windows.Resources>
  <local:XManager x:Key="xManager"/>
</Windows.Resources>

My binding to it looks like this:

<TextBox Name="someBox">
  <TextBox.Text>
    <Binding Mode="TwoWay" Source="{StaticResource xManager}" Path="ActiveX.Text" />
  </TextBox.Text>
</TextBox>

Such code won't work properly, because we've binded to XManager's "ActiveX.Text", but we never change it, so workaroun I did was to add do my manager such code:

//This one is invoked when activeSession signals PropChange
void XSession_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
  if (e.PropertyName == "Text")
  {
    if (PropertyChanged != null)
      PropertyChanged(this, new PropertyChangedEventArgs("ActiveSession.Text"));
  }
}

Now it will work, but I find such code a bit ugly, I'd like to bind "directly" to PropertyChange event inside XSession, not to some sort of a wrapper. Is this possible, or maybe I don't see something obvious?

User 27100918-Jul-09 5:21

18-Jul-09 5:21

The Path "ActiveX.Text" should be "Text"

Change to: <Binding Mode="TwoWay" Source="{StaticResource xManager}" Path=".Text" />

BTW: Any reason you're not setting the DataContext on the TextBoxes Parent container to an instance of the xManager class? Then you don't need a resource. Your application may need to follow the pattern you've described, just want me sure you knew there are other ways.

Also, xManager is not public. I've run into problems when the classes exposed on the UI are not public. Not all cases, just mentioning I've hit issues.

Cheers, Karl

» CodeProject 2008 MVP, CodeProject 2009 MVP

My Blog | Mole's Home Page |
XAML Power Toys Home Page

Just a grain of sand on the worlds beaches.

modified 27-Feb-21 21:01pm.

Ravadre18-Jul-09 5:56

18-Jul-09 5:56

Karl Shifflett wrote:
The Path "ActiveX.Text" should be "Text"

Change to: <Binding Mode="TwoWay" Source="{StaticResource xManager}" Path=".Text" />

I've actually did, just forgot to include this change in my post Smile | :)

, actually, I've manage to make it work without this wrapper thing on XManager. If I would set Path="Text", I'd have to include this wrapper, so XManager would have to catch it's activeX text change and repost it, but now for some reason I am able to set two way binding without this wrapper, just binding to Path="ActiveX.Text" (it did not work earlier heh).

Karl Shifflett wrote:
BTW: Any reason you're not setting the DataContext on the TextBoxes Parent container to an instance of the xManager class? Then you don't need a resource. Your application may need to follow the pattern you've described, just want me sure you knew there are other ways.

This may be a newbie question, but how I do that? If I won't add the XManager to window resources, but only create it's instance in the code part, I don't see any of binding to it, I was actually thinking is it possible to bind to an instance of a class that was created in code, but I gave up and just used resources.

User 27100918-Jul-09 6:04

18-Jul-09 6:04

DataContext is KEY to programming in WPF. Without a full understand of this property you will struggle with WPF when infact it's super powerful and simple (once you grasp how it works.)

Strongly recommend you read, print, study, this post: http://msdn.microsoft.com/en-us/library/ms752347.aspx[^]

It's some VERY good Microsoft documentation on Data Binding.

Another fantasic WPF Data Binding resource is: http://bea.stollnitz.com/blog/[^]

Cheers, Karl

» CodeProject 2008 MVP, CodeProject 2009 MVP

My Blog | Mole's Home Page |
XAML Power Toys Home Page

Just a grain of sand on the worlds beaches.

modified 27-Feb-21 21:01pm.

Ravadre18-Jul-09 6:10

18-Jul-09 6:10

I do get your point, I just don't see why I can't use XManager as a resource, and how else I can refer to it's instance, if I won't declare it this way? I'm using Data contexts with success while referring to resources, using
DataContext="{Binding Source={StaticResource resourceKeyName}}"

User 27100918-Jul-09 6:14

18-Jul-09 6:14

Not sure I understand the question or what is not working as expected.

I do have another consideration.

When you create xManager as a resource, it is actually instantiating an instance of the xManager. So... that instance will be available to your UI but not the code-behind unless you reference the instance using resource lookup.

Hope this helps.

Cheers, Karl

» CodeProject 2008 MVP, CodeProject 2009 MVP

My Blog | Mole's Home Page |
XAML Power Toys Home Page

Just a grain of sand on the worlds beaches.

modified 27-Feb-21 21:01pm.

Ravadre18-Jul-09 6:27

18-Jul-09 6:27

I think we need a 'reset', cause I'm a bit lost in our discussion as well Smile | :)

.

So:
1. Not, I do not have any problems with code not working, I'm just referring to your statement, that I could throw out XManager from resources.
2. Let's consider such code (pseudo-xaml):

<Window>
  <Window.Resources>
    &lt;local:XManager x:Key="xManager"/&gt;
  </Window.Resources>
  <Grid DataContext="{Binding Source={StaticResource xManager}}">
    ...
    <TextBox Text="{Binding Mode=TwoWay, Path=ActiveSession.InputText}" />
  </Grid>
</Window>

This is a simplified situation of what I have right now in my code. Referring to your post, I could throw out xManager from resources -> this implies that I create instance of the XManager in the code, fe. in the Window ctor; my question is then, how I could refer to such an instance in XAML in DataContext, and if it's not easy / possible, what's the advantage of throwing out xManager from resources.

Also, inside a code I did something like this:

XManager xMgr;
public MainWindow()
{
  InitializeComponent();
  xMgr = (XManager)FindResource("xManager");

So basically, I do have a straightforward access to this instance from a code.

User 27100918-Jul-09 6:34

18-Jul-09 6:34

Loose the resource and all references to it.
Loose the Grid DataContext XAML.

In code (ctor or Loaded Event) set Window DataContext.

this.DataContext = new xManager;

Cheers, Karl

» CodeProject 2008 MVP, CodeProject 2009 MVP

My Blog | Mole's Home Page |
XAML Power Toys Home Page

Just a grain of sand on the worlds beaches.

modified 27-Feb-21 21:01pm.

Ravadre18-Jul-09 7:15

Re: Visibiltiy Collapse issues

18-Jul-09 7:15

Working great, I think I've tried to over-Xaml heh Smile | :)

. I can see how this can be useful, altough not in every situation, but still, works fine.

Thank you very much for the support.

Message Removed

16-Jul-09 9:27

N_tro_P

16-Jul-09 9:27

Message Removed

User 27100918-Jul-09 5:29

Re: Visibiltiy Collapse issues

18-Jul-09 5:29

Make sure that the chart data source implements change notification. (INotifyCollectionChanged)

That way when you make the chart visible and the collection its bound gets new data it will notify the Chart and it will display.

In WPF or Silverlight you can use the System.Collections.ObjectModel.ObservableCollection(Of T)

Cheers, Karl

» CodeProject 2008 MVP, CodeProject 2009 MVP

My Blog | Mole's Home Page |
XAML Power Toys Home Page

Just a grain of sand on the worlds beaches.

modified 27-Feb-21 21:01pm.

Message Removed

20-Jul-09 6:15

N_tro_P

20-Jul-09 6:15

Message Removed

User 27100920-Jul-09 16:51