Binding to ViewModel.SubClass.Property (sub-property)

Question

let's say i have a section on my screen where "current record" is edited.. so my view model has a class with all currently edited properties such as:

class Record { public string Notes { get { return "Foo"; } set { _notes = value; Notify("Notes"); } }

and we add this class to the view model:

class AdjustsmentViewModel { public Record CurrentRecord { get { return new Record(); }} }

How can i bind to Notes property of CurrentRecord in my view? I tried this:

<TextBox Text="{Binding CurrentRecord.Notes, Mode=TwoWay}" VerticalScrollBarVisibility="Auto" TextWrapping="WrapWithOverflow" AcceptsReturn="True" />

This is not working however. I also tried setting DataContext of surrounding StackPanel:

<StackPanel DataContext="{Binding CurrentRecord}">

After that, i tried in my TextBox {Binding Notes} and {Binding Path=Notes}, but none of these seem to work.

Perhaps above really should work and i am messing something elsewhere?

Update

This is happening in a user control. This user control has a separate view model, from it's parent window.

this.DataContext = UnityUtil.Resolve<AdjustmentsViewModel>();

Also i am seeing a binding error: 'Notes' property not found on 'object' ''MainViewModel'

that view model is set on the main window.

to verify that i have the right ViewModel bound, i just added this property directly on the viewmodel:

public string Notes2 { get { return "Bar"; } }

and corresponding textblock in the view:

<TextBlock Text="{Binding Path=Notes2}" />

this works as expected.

Great Success

Thanks to Ryan, i was able to find the problem. It was not in the property itself, but the way CurrentRecord was being set. In my setter, i make a call to INotifyPropertyChange handler, but that had the old name of the property in it. So the view was not getting a CurrentRecord notification, so i guess Notes notification was not enough ..

in conclusion, this notation is correct: {Binding Path=CurrentRecord.Notes}

no errors. i just don't see the value (my default Foo string) in the textbox — Sonic Soul
– Sonic Soul, Commented Jul 23, 2012 at 20:19
What is your view...a window, a user control, a data template? How are you setting the datacontext of your view to your view model object? — Thelonias
– Thelonias, Commented Jul 23, 2012 at 20:30
One thing you're going to want to fix is that you need a "setter" for your Notes property if you want TwoWay binding. — Thelonias
– Thelonias, Commented Jul 23, 2012 at 20:37
Yeah, that's a drawback of using strings as the mechanism to notify a property has changed. I think some of the MVVM frameworks, e.g. PRISM, let you notify via the property itself (which in turn just uses some reflection I think). Glad you're all set. — Thelonias
– Thelonias, Commented Jul 23, 2012 at 21:05

cguedel · Accepted Answer · 2012-07-23 20:16:54Z

8

The above should work, {Binding Path=CurrentRecord.Notes} is right. Can you check that your datacontext is set to your viewmodel?

Also check if your viewmodel implements INotifyPropertyChanged.

edit: I just created a sample project to recreate this. No need to implement INotifyPropertyChanged, it just works when the datacontext is set to the VM.

edited Jul 23, 2012 at 20:16

answered Jul 23, 2012 at 20:11

cguedel

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10 Comments

Sonic Soul Over a year ago

i have not tried this particular binding before actually.. but it still doesn't seem to work..

Thelonias Over a year ago

@SonicSoul what exactly does work...Your notes inside a record aren't showing up in your textbox or when you type in the textbox, they aren't going to your record's notes...or both? Are there any errors in your Output window...like a binding error?

Sonic Soul Over a year ago

both do not work. i default my string to Foo. that doesn't show up. if i type in some other value in the textbox and press a button to look at the debugger.. the property still has "Foo" in it, so it was not affected, or showed.. not seeing any relevant errors in the Output

cguedel Over a year ago

Does the output window show a System.Windows.Data binding error?

Sonic Soul Over a year ago

yes. "'Notes' property not found on 'object' ''MainViewModel' " Not sure why it is looking there.. that is the view model for the window.. where as i am in a user control with a different viewmodel set (and working, as my other properties bind fine)

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Thelonias · Accepted Answer · 2012-07-23 23:01:04Z

Make sure that your CurrentRecord property is 1) being set and 2) notifying the UI layer that a change has occurred.

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