I am designing a WPF app and using MVVM pattern. Let's say I have one view called View1, and it's DataContext is set to ViewModel1 in it's contractor. The VM has one Commandcalled RefreshCommand whose job is to calculate the data to be displayed on the view. Now I'd like to call this RefreshCommand right after my view is shown, but I don't know how to do that.
I tried to call it in the code-behind where I handle the Loadedevent for the usercontrol, something like this:
Private Sub AfterLoad(sender As Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
RefreshButton.Command.Execute(sender)
End Sub
However, that's when I noticed that at this moment the RefreshButton.Command is still set as Nothing. Note that in the UI interaction the invoke of this button/command is fine. So when should I call the command to perform such operation? Thanks!
That looks like it should work. Show your XAML and viewmodel?
Normally I would just have my VM get its data immediately and show the data in the View via bindings. Try executing the Refresh command in your VM constructor
Related
So I've started looking at the Catel MVVM framework and it looks like it will solve a couple of problems I have encountered, but I have one really silly issue. I think I'm just missing something small.
I took one of my smaller WPF projects to switch over the Catel as a way for me to learn it. I have a simple 'Player Registration' form, with fields like name and surname. I recreated my original view model by using the vm codesnippet and all is good, all the properties and attributes I've set up as I've read in the documentation.
I then changed the UserControl I used for 'Player Registration' (PlayerRegistrationView) to a catel:UserControl. I placed PlayerRegistrationView on a standard WPF Window (nothing else, just a xmlns for the View and the view as the only content on the window, no attributes)
But here is my problem:
I have a MainWindow with a button on to open the Window for the player registration. The on-click event simply is this:
private void ButtonPlayerClick(object sender, RoutedEventArgs e)
{
var playerRegistration = new PlayerRegistrationDialog
{
Owner = this,
DataContext = new PlayerRegistrationViewModel(),
};
playerRegistration.Show();
}
Running my program and then clicking on the button results in an NotSupportedException on my PlayerRegistrationView: The view model of the view could not be resolved. Use either the GetViewModelType() method or IViewModelLocator
I tried making the ViewModel a static resource on the window and setting the datacontext there, but it produces the same error.
I am at a loss. What have I missed?
Thanks
The whole point of Catel is that it automatically wires up all the views and view models. The "complex" thing that you are trying to achieve is that you have a view which is placed on a window. You want the window to have the same data context as the view in order to do some stuff in the window as well.
In Catel, it is possible to place any view with datacontext management on a DataWindow (window in Catel). Then it will work like this:
DataWindow
|=> View
If the DataWindow and the View share the same view model type, then they share the same view model. For example:
PlayerRegistrationWindow => derives from catel:DataWindow
PlayerRegistrationView => derives from catel:UserControl
Since both start with PlayerRegistration, they will both be resolved to PlayerRegistrationViewModel automatically.
To show the window, the only thing you have to do is this:
var viewModel = new PlayerRegistrationViewModel();
var uiVisualizerService = ServiceLocator.Default.ResolveType<IUIVisualizerService>();
uiVisualizerService.Show(viewModel);
All will work automatically and you don't have to worry about setting any datacontext yourself.
I have a menu in MainViewModel, now on selection of a particular menuItem I wanted to update data of a view which is already loaded.
i.e. although there's an instance of that viewModel in MainViewModel, when I try to invoke the method thru that instance and change the data property, it doesnt show the changes in the view. Whereas same changes occur when I invoke that method through relay command using a button on that viewModel's view.
Now its like I need to invoke relay command of that viewModel from MainViewModel, I guess that will fix the problem, but how to do that? what's easiest way. Will i need to use messaging?
I tried MVVM Light messenger class, its quite straightforward and elegant (keeps ViewModels loosely coupled)!! and most importantly it works
code:
Send:
Messenger.Default.Send(stringParameter, "key_anything");
Register:
Messenger.Default.Register<string>(this, "key_anything", invokeFunction);
private void invokeFunction(string stringParamter)
{
//code goes here!
}
I'm in a situation where I need to fire some IResults from within a viewmodel, without an action from the view triggering it. If I use Coroutine.Execute(MyActions().GetEnumerator()) then the ActionExecutionContext does not contain information about my view. Is there a way I can work around this?
If your ViewModel inherits from Screen or implements IViewAware, then you have access to the instance of the View from your ViewModel. So, in the case of subclassing Screen, you would override OnViewLoaded, grab the instance of the View and use that to build up an ActionExecutionContext.
I have a WPF application with form that has a textbox named "txtStatusWindow". I also have a vb.net class handed to me by a co-worker that needs to be called and executed by the code in my application code-behind. My co-worker insists that I will need to use common .net events to update the textbox on my form.
The separate vb.net class:
Public Class globalclass
Public Event txtStatusWindow(ByVal Text As String)
Public Sub InitializeProgram()
RaiseEvent txtStatusWindow("Updating something.")
System.Threading.Thread.Sleep(2000)
RaiseEvent txtStatusWindow("Updating something else.")
System.Threading.Thread.Sleep(2000)
RaiseEvent txtStatusWindow("Updating something other than else.")
System.Threading.Thread.Sleep(2000)
RaiseEvent txtStatusWindow("Updating something other than the else stuff.")
System.Threading.Thread.Sleep(2000)
End Sub
End Class
I need to be able to call the sub "InitializeProgram()" from my code-behind, and it needs to be able to update "txtStatusWindow.text" as it runs.
I told him that the updating of the text box can be done with data-binding, but I don't know how to integrate a separate class like this into my project, how to call methods in it, or how to cause it to update my text blocks through data binding.
I also suggested that the methods in this class aren't optimal for connecting to the WPF project anyway, but he just wrote it as an example to discover how to connect the two projects.
Eventually, I will need to integrate classes like these that will be running separate threads to update their data from a dynamic source, and cause many controls to update in my application.
So far, the only way we have been able to get this to work from my code-behind is this:
Partial Public Class SplashScreen
Dim NewText as String
Public WithEvents Globals As globalclass = New globalclass
Public Delegate Sub StringDelegate(ByVal Text As String)
Public SplashText As String
Public Sub New()
MyBase.New()
Me.InitializeComponent()
Me.Show()
Globals.InitializeProgram()
End Sub
Public Sub UpdateSplashscreenHandler(ByVal Text As String) Handles Globals.UpdateSplashScreen
StatusWindowText.Text = Text
End Sub
Notwithstanding the fact that the WPF screen "freezes" until the "globalclass InitializeProgram" method completes (txtStatusWindow.Text does not update while sub without using the esoteric "refresh" extension...), I fully believe we are going about this the wrong way.
There are precious few examples out there concerning the integration and then binding to objects in existing code. Thanks for examining our little quandary.
If this status window is in XAML and the status window is a UserControl, then add a StatusText dependency property to the status window. Then, in the XAML you can bind to the value of that property with something like:
<UserControl x:Name="MyStatusWindow" ...>
<TextBlock Text="{Binding Path=StatusText, ElementName=MyStatusWindow}" />
</UserControl>
Then, from your event, just update the value of that StatusText property.
(Is that even close to what you were asking?)
Also, about that freezing: Instead of doing that updating in the constructor of that class, you might want to do it from the Loaded event of that control. It will still be freezing, though, unless you move it to a separate thread. Right now, that's happening on the same thread that the UI message pump is running on. This is the Dispatcher for that UI.
I have legacy windows forms user control that exposses several public methods. I wrapped this control on a wpf user control and encapsulated the Methods with a relaycommand on the new wpf usercontrol.
Now my problem is how to use the mvvm pattern to execute the commands on my user control form the viewmodel that is used with the view hosting the new wpf usercontrol.
In viewmodel you have to add a field say
Public ICommand CommandOne
Now this command will create a new RelayCommand object depending upon your requirements/conditions.
Now, you can bind this 'CommandOne' command with any object say button on your control form.
So, whenever the button is clicked then the RelayCommand object will be created and it will execute the action given to it as a parameter.
Hope it works for you.
I Fond out how to get this to work with bindings. Need to set the mode to OneWayToSource to get the command from the user control. The tricky part is that the initialization of the command has to be done inside the loaded event of the usercontrol. If you try to do it inside of the constructor, you will end up with the default initialization from the binding which could be null.
Use PRISM EventAggregator? You can fireoff an event from ViewModel, from your Usercontrol subscribe to it.
http://www.codeproject.com/Articles/355473/Prism-EventAggregator-Sample
https://msdn.microsoft.com/en-us/library/ff921122.aspx