MVVM Light Toolkit

Commented Issue: NullRefBug in RelayCommand when changing Window Language [7561]

Gentlehag — Wed, 22 Feb 2012 09:30:03 GMT

A Button in a Listbox binds to a RelayCommand<int>, as Parameter it binds a int property of an entity.

When the listbox clears everything works fine as long as the WindowLanguage isn't changed manually. (So en-us)

But i have to change the window language to the current Culture. (s. http://stackoverflow.com/questions/9382696/showing-culture-aware-short-date-and-time-string-from-datetimeoffset-in-xaml)

Then the relaycommand raises a Nullreference Exception. (s. Stacktrace)
when I change the RelayCommand<int> to RelayCommand<object> I can see the reason.

When the language isn't change, the Action for CanExecuteChanged isn't raised when the entity doesn't exists.
But when the language is changed to de-de than the Action is raised with null as value. So I assume that in this case a convert to int is tried inside the Command.

Stacktrace

Server stack trace:
at GalaSoft.MvvmLight.Command.RelayCommand`1.CanExecute﴾Object
parameter﴿
at
MS.Internal.Commands.CommandHelpers.CanExecuteCommandSource﴾IComma
ndSource commandSource﴿
at System.Windows.Controls.Primitives.ButtonBase.UpdateCanExecute﴾﴿
at
System.Windows.Controls.Primitives.ButtonBase.OnCanExecuteChanged﴾Object
sender, EventArgs e﴿
at System.EventHandler.Invoke﴾Object sender, EventArgs e﴿
at
GalaSoft.MvvmLight.Command.RelayCommand`1.RaiseCanExecuteChanged﴾﴿
at BE.FogBugz.Tracker.ViewModel.WorkingOnTasksViewModel.refresh﴾﴿ in

Comments: Here screenshot of the exception

Created Issue: NullRefBug in RelayCommand when changing Window Language [7561]

Gentlehag — Wed, 22 Feb 2012 09:29:44 GMT

New Post: SL5 assemblies missing XmlnsDefinition

lbugnion — Mon, 20 Feb 2012 21:29:27 GMT

Hi Mike,

Please download the new DLLs from https://skydrive.live.com/redir.aspx?cid=40cffde85f1ab56a&resid=40CFFDE85F1AB56A!1110&parid=40CFFDE85F1AB56A!129&authkey=!AJ738Uba7ZhZZ1c

Download the MVVMLight_V3.0.20 package.

Extract this locally and copy the DLLs (either from Debug or Release) into your C:\Program Files (x86)\Laurent Bugnion (GalaSoft)\Mvvm Light Toolkit\Binaries folder. Then please test it out and let me know if that fixes your issue.

If the test works fine, I will create a new installer.

Cheers,

Laurent

New Post: bind in code behind

lbugnion — Mon, 20 Feb 2012 21:04:21 GMT

namespace MvvmLight4
{
    public partial class MainPage : UserControl
    {
        public MainViewModel Vm
        {
            get
            {
                return (MainViewModel)DataContext;
            }
        }

        public MainPage()
        {
            InitializeComponent();

            Vm.PropertyChanged += (s, e) =>
            {
                if (e.PropertyName == MainViewModel.WelcomeTitlePropertyName)
                {
                    // Do something
                }
            };
        }
    }
}

Commented Issue: DirectoryNotFoundException on ViewModelLocator [7560]

tkowalczyk — Mon, 20 Feb 2012 10:04:50 GMT

Hi,
I`m not sure that this is a bug of framework or it`s problem on my side but when I want to read data from for example *xml files in ViewModel, I have a DirectoryNotFoundException when I open a *xaml View, but the directory and files are there?

So how about that? or what is the good way to read data from files and pass them to the view model?
Comments: ok thx for your answer, my fault, design time data wasn`t provided

New Post: bind in code behind

genvej — Sun, 19 Feb 2012 18:51:09 GMT

Thx. I follow you all the way to the eventhandler. Could you show me in example.

If this is my viewModel object

public string

WelcomeTitle

{

get

{

return

_welcomeTitle;

}

set

{

if (_welcomeTitle == value

)

{

return

;

}

_welcomeTitle =

value

;

RaisePropertyChanged(WelcomeTitlePropertyName);

}

How do attach that as an eventhandler in my View?

Commented Issue: DirectoryNotFoundException on ViewModelLocator [7560]

lbugnion — Sun, 19 Feb 2012 18:02:52 GMT

Hi,
I`m not sure that this is a bug of framework or it`s problem on my side but when I want to read data from for example *xml files in ViewModel, I have a DirectoryNotFoundException when I open a *xaml View, but the directory and files are there?

So how about that? or what is the good way to read data from files and pass them to the view model?
Comments: Hi, Can you explain more? When do you get the exception exactly? If you get it in Blend, it is to be expected, you will need to provide design time data to satisfy Blend. Cheers, Laurent

New Post: bind in code behind

lbugnion — Sun, 19 Feb 2012 18:01:40 GMT

Hi,

This is very simple. Get a reference to your VM in the code behind:

public MyViewModel Vm
{
get
{
return (MyViewModel)DataContext;
}
}

then, in the Page's constructor, after the call to InitializeComponent, add an event handler to Vm.PropertyChanged.

Hope this helps,

Laurent

New Post: bind in code behind

genvej — Sun, 19 Feb 2012 17:38:34 GMT

Hi. I have a project that uses the galasoft mvvm light toolkit. I have a problem.

I need to catch changes to a property in my viewmodel from my codebehind. I already did bind in my xaml and that works fine. However I need to do other things from the codebehind when the propery in the viewmodel changes. Im using the observableobject. Could someone provide an example how to catch those events in the View codebehind plz? I assume its quite simple, however Googling has brought me nowhere :-)

New Post: SL5 assemblies missing XmlnsDefinition

lbugnion — Sun, 19 Feb 2012 16:17:47 GMT

Something does not compute here. V3 never had XmlnsDefinition. It is a feature I added in V4. You must have used V4 at some point.

That said, I can add XmlnsDefinition to V3 in order to solve your issues. I must finish something else first but I should be able to do that either tonight or tomorrow.

Cheers,

Laurent

New Post: SL5 assemblies missing XmlnsDefinition

mikepost — Sun, 19 Feb 2012 15:05:36 GMT

I used the SL5 binaries from this installer: http://mvvmlight.codeplex.com/releases/view/71278

It's definitely V3. V4 is not an option for us because it's still in beta.

New Post: SL5 assemblies missing XmlnsDefinition

lbugnion — Sun, 19 Feb 2012 10:41:40 GMT

Hi Mike,

I tried to repro your issue, and I cannot. Here is what I did:

- Checked the code in the Silverlight 5 version of MVVM Light on Codeplex: The XmlnsDefinition attribute is defined correctly.

- Installed MVVM Light V4.0.2.19 from http://mvvmlight.codeplex.com/releases/view/73208

- Created a new MVVM Light (SL5) application in Visual Studio.

- Opened the solution in Blend 4 preview for Silverlight 5

- Added an EventToCommand to the TextBlock on the main page

- Checked the XAML: The XmlnsDefinition was found and recognized by Blend. The prefix added is: xmlns:Custom="http://www.galasoft.ch/mvvmlight" (which is what I expected).

I am wondering what went wrong in your case. Could it be that, by mistake, you installed V3 instead of V4?

Let me know and let's solve this issue.

Thanks,
Laurent

Created Issue: DirectoryNotFoundException on ViewModelLocator [7560]

tkowalczyk — Fri, 17 Feb 2012 13:42:53 GMT

Commented Issue: RelayCommand and Memory Leak caused by CanExecuteChanged event [7532]

nico008 — Fri, 17 Feb 2012 08:47:18 GMT

Hi Laurent,

CanExecuteChanged event keeps strong reference to Button which Command is bound to an instance of RelayCommand and it may leads to memory leak if we use long living view models with short living views. Maybe it would be better to use some kind of weak event listener. I made a fast try to use Silverlight Toolkit's WeakEventListener:

private EventHandler _canExecuteChanged;
public event EventHandler CanExecuteChanged {
add {
WeakEventListener<EventHandler, object, EventArgs> weakEventListener = new WeakEventListener<EventHandler, object, EventArgs>(value);
weakEventListener.OnEventAction = (h, s, e) => {
h(s, e);
};
weakEventListener.OnDetachAction = (w) => {
CanExecuteChanged -= w.OnEvent;
};
}
remove {
this._canExecuteChanged -= value;
}
}

and despite the fact that it might be not the perfect implementation, the problem with memory leak seems go away.
Comments: Hi there! Any fully working fix for this memory leak? I'm currently using a converter for using WeakEvent in RelayCommand. Unfortunatly, I still have memory leaks : WeakReference, <GCHandle>, EventHandler, WeakEventListener<CanExecuteChangedWeakEventSource, ICommand, EventArgs> and more When will it be included in official MvvmLight? @Laurent : thanks for you great work! Greetings from Belgium

New Post: SL5 assemblies missing XmlnsDefinition

mikepost — Wed, 15 Feb 2012 14:38:32 GMT

Laurent, thanks for replying. I appreciate your situation. Unfortunately my situation is that I work under some onerous rules regarding open source and modifying the source and rebuilding is simply not an option for me. (Crazy, I know. But that's what happens when the CMMI yahoos meet up with the security yahoos and they start jointly running the asylum.) So I'm stuck waiting for an official build. :/

Hope your conferences went off well.

New Post: SL5 assemblies missing XmlnsDefinition

lbugnion — Wed, 15 Feb 2012 08:00:41 GMT

Update: I was just notified that the donation button is broken. Damn, noone reported THAT bug ;)

New Post: SL5 assemblies missing XmlnsDefinition

lbugnion — Wed, 15 Feb 2012 06:55:33 GMT

Hey Mike,

I am sorry for the lack of response. The past few weeks have shown an increase activity in my firm with a huge project I am involved with. I am also out conferencing this week and had to find a little time to prepare. But I don't mean to complain :)

Yes you are right about the XmlnsDefinition, it is a regrettable omission. Making the fix will take a very short time, making a new installer and testing will take an evening, and I didn't have one until now (hopefully it will clear a bit soon, hoping to have a fix this weekend).

I wouldn't wait for the fix though. Open source is a great concept that means that you can download the source and fix it yourself. That's really awesome. In this case, compare the AssemblyInfo to the one in SL4. Let me know if you have any issue and I will do my best to answer faster :)

Cheers,
Laurent

PS: I would leave my day job and work only on MVVM Light if I could. However people keep sending me bills and insist that I pay them on time. That sucks, I know. Unfortunately the Donation page is very idle, won't be able to leave any time soon (http://www.galasoft.ch/mvvm/donate/) ;)

New Post: SL5 assemblies missing XmlnsDefinition

mikepost — Wed, 15 Feb 2012 00:17:13 GMT

No reply in almost 2 weeks? Really? So the PRISM team is going to beat MVVM Light to SL5?

New Post: UpdateCommandParameterBeforeExecuting

AlexIdsa — Thu, 09 Feb 2012 05:25:31 GMT

To solve a problem a problem described in this question: http://stackoverflow.com/questions/9173936/eventtocommand-update-commandparameter, I have made changes to MVVM Light codebase (see an answer in that question). Don't you find it valuable to integrate to MVVM codebase?

New Post: SL5 assemblies missing XmlnsDefinition

mikepost — Thu, 02 Feb 2012 23:23:26 GMT

We recently upgraded to SL5, but missed our MVVM Light dependencies. So I tried to upgrade to the SL5 version of MVVM Light (v3 because we can't ship beta level software) and it looks like SL5 assemblies are both missing the XmlnsDefinition attribute. Our code doesn't compile (we're cross compiling SL5 to WPF4 so we require an XmlnsDefinition; referencing by assembly name will break the cross compile) so we're stuck with the SL4 assemblies for now.