Develop Reference

Passing shared parameter to blazorcomponents

I'm building a Blazor server app that has a side navigation component as well as a top navigation component.
I want the side nav's "selected" status to get cleared if the user selects an item from the top nav menu.
In my MainLayout.blazor.cs I have a variable called ResetSelection:
protected bool ResetSelection { get; set; } = false;
I'm passing this from the MainLayout.blazor file into both top and side nav components:
<SideNav AuthUser="#navAuth.User.GetAuthUserModel()" ResetSelection="#ResetSelection" />
<TopNav AuthUser="#Auth.User.GetAuthUserModel()" ResetSelection="#ResetSelection" />
In TopNav.razor.cs I check if a nav item has been selected, and if it has, I set the variable to true:
private void itemSelected(MenuEventArgs<CategoryModel> args)
{
// if item selected set the main nav selected item to null
// breakpoint gets hit-- this method gets fired as expected
ResetSelection = true;
}
In the SideNav.razor.cs component I use an OnParameterSet to check if the param is true, and if so I clear the current selected nav item and reset the variable to false:
protected override void OnParametersSet()
{
base.OnParametersSet();
if (ResetSelection == true)
{
// we never get here!
NavMenu.UnselectAll();
ResetSelection = false;
}
}
I don't ever get the OnParametersSet triggered with a ResetSelection == true condition-- and I don't understand why. I can't seem to make this interaction work between two child components.
Is the parameter passed in being scoped to the local component when it has its value changed in TopNav.razor.cs?

You can apply the Blazor Notification Pattern to your problem.
This approach gets away from the fragile spaghetti plumbing inevitable when you try and create more than simple Parameter/Callback relationships between parent/child components.
Create a simple State object and then cascade it. readonly and IsFixed prevents RenderTree cascades: renders are driven by events.
State Object:
public class MenuState
{
public event EventHandler<EventArgs>? StateChanged;
public void NotifyStateCahnged(object? sender)
=> this.StateChanged?.Invoke(sender, EventArgs.Empty);
}
Your layout.
<CascadingValue Value="_state" IsFixed>
//... layout markup
</CascadingValue>
#code {
private readonly MenuState _state = new();
}
Then wherever you use it:
#implements IDisposable
<h3>TopMenu</h3>
#code {
[CascadingParameter] private MenuState State { get; set; } = new();
protected override void OnInitialized()
=> this.State.StateChanged += this.OnStateChanged;
protected async Task MenuClicked()
{
// do whatever maybe async
// emulate an async action
await Task.Delay(10);
this.State.NotifyStateCahnged(this);
}
private void OnStateChanged(object? sender, EventArgs e)
{
// only need to render if it wasn't me who triggered the event
if (sender != this)
{
// Do whatever
this.StateHasChanged();
}
}
public void Dispose()
=> this.State.StateChanged -= this.OnStateChanged;
}
An alternative to the cascade is to register MenuState as a Scoped Service and then inject it where you need it.

Updating a databound value in the parent component?

Assuming that there some event that will call the showEditPage function. Which will update the value of isEditPageVisible.
Index Base class
public abstract class IndexBase : ComponentBase
{
protected bool isEditPageVisble = false;
public void showEditPage(){
isEditPageVisble != isEditPageVisble;
}
}
How would I get it right to update the value of isEditPageVisble in the Index component as well
when someEditPageEvent is called?
Edit component
#page "/Edit/{isEditPageVisble}"
#inherits Project.IndexBase
#using Project.Model;
#if (isEditPageVisble)
{
<EditPage #bind-isVisible="isEditPageVisble"></EditPage>
}
Edit base class
public abstract class EditBase : IndexBase
{
[Parameter]
public bool isEditPageVisble { get; set; }
[Parameter]
public EventCallback<bool> isEditPageVisbleChanged { get; set; }
protected async Task ChangeValueAsync()
{
await isEditPageVisbleChanged .InvokeAsync(isEditPageVisble );
}
public void someEditPageEvent(){
isEditPageVisble = false;
}
}
Edit component
EditPage.razor
<SomeComponent Visible="isEditPageVisble"></SomeComponent>

Use a State/Notification Service. Here's a simple example for your question.
using System;
namespace StackOverflow.Answers.Data
{
public class PageStateService
{
public bool IsEditPageVisible
{
get => _isEditPageVisible;
set
{
if (value != _isEditPageVisible)
{
IsEditPageVisible = value;
EditPageVisibilityChanged?.Invoke(this, EventArgs.Empty);
}
}
}
private bool _isEditPageVisible;
public event EventHandler EditPageVisibilityChanged;
}
}
Register as a scoped service, and inject it into the components that need to use it. If you want to update a component when IsEditPageVisible gets change, wire up an event handler to the EditPageVisibilityChanged.
It should look like this:
private void OnEditPageVisibilityChanged(object sender, EventArgs e)
=> StateHasChanged();

How to prevent Xamarin forms, a custom menu and WebView renderer with EvaluateJavascript from freezing?

I have created a custom menu item which appears in the default menu which pops up when selecting text on my custom WebView.
On clicking on the menu item it calls EvaluateJavascript to get the selected WebView text, and then passes the text to another page.
However after performing this action once or twice, some text on certain areas of the screen start to become unresponsive to clicks eg. text on the parts of the WebView become unselectable, clicks on that part of the screen on other pages becomes unresponsive and even the soft keyboard becomes unclickable in some spots. If this continues for a while sometimes my app will then suddenly freeze the entire operating system and I have to soft reset my phone. It appears that there maybe some serious memory leakage going on.
I create my custom menu item in the MainActivity class:
public override void OnActionModeStarted(ActionMode mode)
{
if (Root.IsCurrentPageType<DictPage>() && DictP.IsWebViewFocused())
{
IMenu menu = mode.Menu;
menu.Add("To Notes");
menu.GetItem(0).SetOnMenuItemClickListener(new MyMenuItemOnMenuItemClickListener(this, mode));
}
base.OnActionModeStarted(mode);
}
It is then handled in the Listener class...
public class MyMenuItemOnMenuItemClickListener : Java.Lang.Object, IMenuItemOnMenuItemClickListener
{
private MainActivity mContext;
ActionMode _mode;
public MyMenuItemOnMenuItemClickListener(MainActivity activity, ActionMode mode)
{
this.mContext = activity;
_mode = mode;
}
public bool OnMenuItemClick(IMenuItem item)
{
WEB.CopyToMainNotes();
Device.BeginInvokeOnMainThread(() =>
{
//close menu if clicked
_mode?.Finish();
});
return true;
}
}
...which calls CopyToMainNotes on my derived WebView class and its associated Renderer and EventHandler classes:
public class WebViewEx : Xamarin.Forms.WebView
{
public static WebViewEx WEB;
//Namespace
//YourClass
public event WebViewExEventHandler CallNativeMethodEvent;
public void CallNativeMethod(WebViewExEventType type)
{
WebViewExEventArgs e = new WebViewExEventArgs();
e.EventType = type;
CallNativeMethodEvent?.Invoke(this, e);
}
public WebViewEx()
{
WEB = this;
}
public void CopyToMainNotes()
{
Device.BeginInvokeOnMainThread(() =>
{
CallNativeMethod(WebViewExEventType.copyToMainNotes);
});
}
}
public delegate void WebViewExEventHandler(object sender, WebViewExEventArgs e);
public class WebViewExEventArgs : EventArgs
{
public enum WebViewExEventType { copyToMainNotes };
public WebViewExEventType EventType = WebViewExEventType.copyToMainNotes;
public WebViewExEventArgs() : base()
{
}
}
public class WebViewExRenderer : WebViewRenderer
{
public WebViewExRenderer(Android.Content.Context context) : base(context)
{
}
protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.WebView> e)
{
base.OnElementChanged(e);
if (Control != null)
{
WebViewEx ex = e.NewElement as WebViewEx;
ex.CallNativeMethodEvent += WebViewEx_CallNativeMethodEvent;
}
}
internal class JavascriptCallback : Java.Lang.Object, IValueCallback
{
public JavascriptCallback(Action<string> callback)
{
_callback = callback;
}
private Action<string> _callback;
public void OnReceiveValue(Java.Lang.Object value)
{
_callback?.Invoke(Convert.ToString(value));
}
}
private void WebViewEx_CallNativeMethodEvent(object sender, WebViewExEventArgs e)
{
switch (e.EventType)
{
case WebViewExEventType.copyToMainNotes:
{
CopyToMainNotes();
break;
}
}
}
public void CopyToMainNotes()
{
string script = "(function(){ return window.getSelection().toString()})()";
var response = string.Empty;
Control?.EvaluateJavascript(script, new JavascriptCallback((r) =>
{
response = r;
Device.BeginInvokeOnMainThread(() =>
{
DPage.CopyThisTextToAnotherPage(response.ToString().Trim('\"'));
});
}));
}
}
The CopyToMainNotes method above is where the EvaluateJavascript takes place and the selected text finally gets sent to another page.
Any ideas where I might be going wrong here? Thanks in advance!

Conditional settings in WPF application

I'm making user changeable settings for my media player and I'm struggling to find an elegant solution to the problem.
One of my settings for example - pauses the video at it's last frame, if not checked it will either continue through the playlist or if it's only 1 file, reset it and pause it at the start.
This is how I've implemented it:
private void OnMediaEndedCommand()
{
if (GeneralSettings.PauseOnLastFrame)
{
MediaPlayer.SetMediaState(MediaPlayerStates.Pause);
return;
}
if (PlayListViewModel.FilesCollection.Last().Equals(PlayListViewModel.FilesCollection.Current) && !Repeat)
{
ChangeMediaPlayerSource(PlayListViewModel.ChangeCurrent(() => PlayListViewModel.FilesCollection.MoveNext()));
MediaPlayer.SetMediaState(MediaPlayerStates.Stop);
return;
}
ChangeMediaPlayerSource(PlayListViewModel.ChangeCurrent(() => PlayListViewModel.FilesCollection.MoveNext()));
}
This is contained inside the ViewModel of the main window, where the media element is and GeneralSettings.PauseOnLastFrame is a boolean property.
This command is binded as follows:
<MediaElement ....>
<ia:Interaction.Triggers>
<ia:EventTrigger EventName="MediaEnded">
<ia:InvokeCommandAction Command="{Binding MediaEndedCommand}"/>
</ia:EventTrigger>
</ia:Interaction.Triggers>
</MediaElement>
It works but it's awful, how should I go about implementing such setting system in an elegant way? Some settings might not be boolean, they might have multiple options, some might be applied only on startup and others, as the one illustrated above, event based.

Based on the information and sample code you provided, I would suggest
Approach - 1
A tightly couple ViewModel with System.Configuration.ApplicationSettingsBase and you can mention all you properties in ViewModel and map single of them with a separate application setting property. You can use your settings directly in biding afterwards e.g. : {x:Static Settings.Default.Whatevs}. Othe "Save" button click event or main window close event, you can save all you settings e.g. : Settings.Default.Save();
Approach - 2
A better approach, I would suggest / prefer (if I am developing this app) is to develop a wrapper class (e.g.: SettingProvider) that implement an inheritance (e.g: ISettingProvider) which uncovers all you settings as separate properties and also have a save method which saves all setting values. You can use this wrapper class into your ViewModel to handle all the commands and setting values in better way.
The benefit of this approach is the if you decide to change you setting to database , you need not to make change to you ViewModel as all job is done in SettingProvider class.
I am not sure but based on viewing your code, I assume that you used Approach-1. Please put you comments and any feedback to this answer. I would like to know what you think and may be you have got more simple and interesting way of achieving this.
UPDATE-1
Example
Enum for showing you demo
public enum MediaStatus
{
Playing = 0,
Stopped = 1,
Paused = 2
}
Interface
public interface ISettingProvider
{
double Volumne { get; set; }
string LastMediaUrl { get; set; }
MediaStatus PlayingMediaStatus;
void SaveSettings();
}
Wrapper Class
public class SettingProvider : ISettingProvider
{
private double volumne;
public double Volumne // read-write instance property
{
get
{
return volumne;
}
set
{
volumne = value;
Settings.Default.Volumne = volumne;
}
}
private string lastMediaUrl;
public string LastMediaUrl // read-write instance property
{
get
{
return lastMediaUrl;
}
set
{
lastMediaUrl = value;
Settings.Default.LastMediaUrl = lastMediaUrl;
}
}
private MediaStatus playingMediaStatus;
public MediaStatus PlayingMediaStatus // read-write instance property
{
get
{
return playingMediaStatus;
}
set
{
playingMediaStatus = value;
Settings.Default.PlayingMediaStatus = (int)playingMediaStatus;
}
}
public void SaveSettings()
{
Settings.Default.Save();
}
//Constructor
public SettingProvider()
{
this.Volumne = Settings.Default.Volumne;
this.LastMediaUrl = Settings.Default.LastMediaUrl;
this.PlayingMediaStatus = (MediaStatus)Settings.Default.PlayingMediaStatus;
}
}
ViewModelBase Class
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
}
CommandHandler Class
public class CommandHandler : ICommand
{
public event EventHandler CanExecuteChanged { add { } remove { } }
private Action<object> action;
private bool canExecute;
public CommandHandler(Action<object> action, bool canExecute)
{
this.action = action;
this.canExecute = canExecute;
}
public bool CanExecute(object parameter)
{
return canExecute;
}
public void Execute(object parameter)
{
action(parameter);
}
}
ViewModel
public class SettingsViewModel : ViewModelBase
{
SettingProvider objSettingProvider = new SettingProvider();
public double Volumne
{
get
{
return objSettingProvider.Volumne;
}
set
{
objSettingProvider.Volumne = value;
OnPropertyChanged("Volumne");
}
}
// Implementaion of other properties of SettingProvider with your ViewModel properties;
private ICommand saveSettingButtonCommand;
public ICommand SaveSettingButtonCommand
{
get
{
return saveSettingButtonCommand ?? (saveSettingButtonCommand = new CommandHandler(param => saveSettings(param), true));
}
}
private void saveSettings()
{
objSettingProvider.SaveSettings();
}
}
UPDATE-2
public interface ISettingProvider
{
bool PauseOnLastFrame;
bool IsAutoPlay;
MediaStatus PlayingMediaStatus;
void SaveSettings();
}
public class SettingProvider : ISettingProvider
{
private bool pauseOnLastFrame;
public bool PauseOnLastFrame // read-write instance property
{
get
{
return pauseOnLastFrame;
}
set
{
pauseOnLastFrame = value;
Settings.Default.PauseOnLastFrame = volumne;
}
}
private bool isAutoPlay;
public bool IsAutoPlay // read-write instance property
{
get
{
return isAutoPlay;
}
set
{
isAutoPlay = value;
Settings.Default.IsAutoPlay = volumne;
}
}
}
public class SettingsViewModel : ViewModelBase
{
SettingProvider objSettingProvider = new SettingProvider();
MediaStatus PlayingMediaStatus
{
get
{
return objSettingProvider.PlayingMediaStatus;
}
set
{
if(value == MediaStatus.Paused)
MediaPlayer.Pause();
if(value == MediaStatus.Playing)
MediaPlayer.Play();
if(value == MediaStatus.Stopped)
MediaPlayer.Stop();
objSettingProvider.PlayingMediaStatus = (int)value;
OnPropertyChanged("PlayingMediaStatus");
}
}
private string currentMediaFile;
public string CurrentMediaFile
{
get
{
return currentMediaFile;
}
set
{
currentMediaFile = value;
MediaPlayer.Stop();
MediaPlayer.Current = currentMediaFile;
if(objSettingProvider.IsAutoPlay)
MediaPlayer.Play();
OnPropertyChanged("CurrentMediaFile");
}
}
// Implementaion of other properties of SettingProvider with your ViewModel properties;
private ICommand onMediaEndedCommand;
public ICommand OnMediaEndedCommand
{
get
{
return onMediaEndedCommand ?? (onMediaEndedCommand = new CommandHandler(param => onMediaEnded(param), true));
}
}
private void onMediaEnded()
{
if(objSettingProvider.PauseOnLastFrame)
{
PlayingMediaStatus = MediaStatus.Paused;
}
else if(PlayListViewModel.FilesCollection.Last().Equals(PlayListViewModel.FilesCollection.Current) && !Repeat)
{
PlayingMediaStatus = MediaStatus.Stopped;
}
else
{
CurrentMediaFile = PlayListViewModel.FilesCollection.MoveNext();
}
}
}
NOTE: This is the detailed example I put here and also avoid some syntax error or naming error if I missed somewhere. Please correct it.
I am not aware which media player settings you are using. I took some sample properties. This is just an example of structure you can implement for you application. You may need to alter more code to implement this structure.

An elegant way to implement this IMHO would be to use a dependency injection container, this will provide great flexibility while allowing you to completely separate concerns (i.e. the settings implementation from your view models and custom controls).
There are many DI frameworks out there, for my example I will use simple injector because it is free (open source), simple and fast but you can apply the same principle to other frameworks (Unity, Ninject, etc..).
Start by creating an interface for your settings service, for example:
public interface ISettingsService
{
double Volumne { get; set; }
string LastMediaUrl { get; set; }
MediaStatus PlayingMediaStatus;
void SaveSettings();
}
Then add your implementation for the service, the beauty of using DI is that you can change the implementation at anytime or completely replace it and your application will continue to work as usual.
Let's say you want to use application settings, here is your service:
public class SettingsServiceFromApplication : ISettingsService
{
public double Volume
{
get
{
return Properties.Settings.Volume;
}
}
[...]
}
Or let's say you want to use a database to store your settings:
public class SettingsServiceFromDb : ISettingsService
{
public double Volume
{
get
{
return MyDb.Volumen;
}
}
[...]
}
Then you can use a DI container to specify which implementation to use:
Start by installing the library using NuGet:
Install-Package SimpleInjector -Version 4.0.12
You need a way to share your container throughout the application, I usually just go with a static class that I initialize when starting the app:
using Container = SimpleInjector.Container;
namespace YourNamespace
{
public class Bootstrapper
{
internal static Container Container;
public static void Setup()
{
//Create container and register services
Container = new Container();
//Let's specify that we want to use SettingsServiceFromApplication
Container.Register<ISettingsService, SettingsServiceFromApplication>();
//You can use your bootstrapper class to initialize other stuff
}
}
You need to call Setup when starting the App, the best place is in the App constructor:
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
Bootstrapper.Setup();
}
}
So now you have an app wide depedency injection container that you can use to request "services" (specific implementations of an interface).
To get the settings implementation in your view models you could simply call the container as follows:
// This will return an instance of SettingsServiceFromApplication
ISettingsService settingsService = Bootstrapper.Container.GetInstance<ISettingsService>();
double volumen = settingsService.Volume;
To make it easier to work with, I usually create a base view model that will allow to get services more easyly, for example:
public abstract BaseViewModel
{
private ISettingsService _settings;
protected ISettingsService GeneralSettings
{
get
{
if (_settings == null)
_settings = Bootstrapper.Container.GetInstance<ISettingsService>();
return _settings;
}
}
}
Every view model inheriting from this class will have access to the settings:
public class YourViewModel : BaseViewModel
{
private void OnMediaEndedCommand()
{
if (GeneralSettings.PauseOnLastFrame)
{
MediaPlayer.SetMediaState(MediaPlayerStates.Pause);
return;
}
if (PlayListViewModel.FilesCollection.Last().Equals(PlayListViewModel.FilesCollection.Current) && !Repeat)
{
ChangeMediaPlayerSource(PlayListViewModel.ChangeCurrent(() => PlayListViewModel.FilesCollection.MoveNext()));
MediaPlayer.SetMediaState(MediaPlayerStates.Stop);
return;
}
ChangeMediaPlayerSource(PlayListViewModel.ChangeCurrent(() => PlayListViewModel.FilesCollection.MoveNext()));
}
}
As you can see the code is the same as your code! But now the settings are coming from your container. Where is the elegance? Well, let's say that one year from now someone decides that you will store your settings in a database, what do you need to change in your code?
Container.Register<ISettingsService, SettingsServiceFromDb>();
A single line. Everything else should work as usual.
As well as view models, you could use this mechanism in your own controls:
public class MyMediaElement : UserControl //Or MediaElement and instead of commands you can override real events in the control code behind, this does not break the MVVM pattern at all, just make sure you use depedency properties if you need to exchange data with your view models
{
private void OnMediaEndedCommand()
{
//Get your settings from your container, do whatever you want to do depending on the settings
[...]
}
}
Then just use your control in your Views / ViewModels:
<local:MyMediaElement />
Yep, that's all you need because you handle everything in your User / Custom control, your view models doesn't need to care about how you handle settings in the control.
There are many options you can use to register containers, I recommend you take a look at the docs:
https://simpleinjector.org/index.html
https://simpleinjector.readthedocs.io/en/latest/index.html

I think maybe you are looking for an interface approach?
public interface IMediaEndedHandler
{
bool AlternateHandling(MediaPlayer player);
}
public class NullMediaEndedHandler : IMediaEndedHandler
{
public bool AlternateHandling(MediaPlayer player)
{
return false;
}
}
public class PauseOnLastFrameHandler : IMediaEndedHandler
{
public bool AlternateHandling(MediaPlayer player)
{
player.SetMediaState(MediaPlayerStates.Pause);
return true;
}
}
public class GeneralSettings
{
private bool pauseOnLastFrame;
private bool PauseOnLastFrame
{
get
{
return pauseOnLastFrame;
}
set
{
pauseOnLastFrame = value;
MediaEndedHandler = value
? new PauseOnLastFrameHandler()
: new NullMediaEndedHandler();
}
}
public IMediaEndedHandler MediaEndedHandler = new NullMediaEndedHandler();
}
Then:
private void OnMediaEndedCommand()
{
if (GeneralSettings.MediaEndedHandler.AlternateHandling(MediaPlayer))
return;
if (PlayListViewModel.FilesCollection.Last().Equals(PlayListViewModel.FilesCollection.Current) && !Repeat)
{
ChangeMediaPlayerSource(PlayListViewModel.ChangeCurrent(() => PlayListViewModel.FilesCollection.MoveNext()));
MediaPlayer.SetMediaState(MediaPlayerStates.Stop);
return;
}
ChangeMediaPlayerSource(PlayListViewModel.ChangeCurrent(() => PlayListViewModel.FilesCollection.MoveNext()));
}
This way, if your setting is, for example. an enum instead of a bool, you can specify a different implementation of the interface for each possible value.

caliburn.micro Condutor not working

We are using caliburn.micro for one of our projects and I'm currently having a puzzling problem:
we have the following classes:
ToolViewerViewModel : Conductor<Screen>.Collection.OneActive
DocViewerViewModel : Conductor<DocumentViewModel>
and various document-views, all with this base class:
DocumentViewModel : Screen
The ToolViewerViewModel is to manage multiple dock-able tool views which allow the user to control different aspects of the program.
The DocViewerViewModel is to show the user the data he's working on/with. It is here to present one of the many DocumentViewModel to the user. and is implemented as a special dock-able view which can not be closed or detached from the ToolViewerView. For every aspect of the data a specific DocumentViewModel is generated by the DocViewerViewModel and presented to the user.
The DocumentViewModel is the base class for all presentation aspects of the data. One may present the data as a table an other may present it as a chart, and so on...
We now encounter problems in terms of OnActivate() and OnDeactivate() which are not called when we expect them to be called.
First Problem:
The system is up and running; The DocumentViewModel is displayed in the DocViewerViewModel which is embedded in the ToolViewerViewModel along with one or two other dock-able views. The currently selected dock-able view is the DocViewerViewModel. When the user now selects one of the other dock-able views the OnDeactivate() method from the DocumentViewModel is being called. Which makes absolutely no sense to me. I'd expect the DocViewerViewModel.OnDeactivate() to be called.
Second Problem:
The system is up and running; The DocumentViewModel is displayed in the DocViewerViewModel which is embedded in the ToolViewerViewModel along with one or two other dock-able views. The currently selected dock-able view is the view that enables the user to change the DocumentViewModel presented by the DocViewerViewModel. When the user now selects an other DocumentViewModel the following code is being executed within the DocViewerViewModel:
DocViewerViewModel.DeactivateItem(oldDocumentViewModel, true);
DocViewerViewModel.ActivateItem(new DocumentViewModel());
I'd expect the DocumentViewModel.OnDeactivate() to be called upon the DocViewerViewModel.DeactivateItem(oldDocumentViewModel, true) call. but that never happens.
Conclusion:
The only proper working Conductor is the ToolViewerViewModel which is managing everything. But this behavior is not what we want or expect to happen: We'd like to have the ToolViewerViewModel only Conduct the dock-able views and the DocViewerViewModel to conduct the DocumentViewModel. This is important because there are two different use cases in place: One to manage multiple instances at the same time and the other where only one instance is active and used, the old instance shall be thrown away.
Hopefully anyone here can help me to get the behavior I'm looking for.
I Now have an example code for you:
public class ToolViewerViewModel : Conductor<Screen>.Collection.OneActive
{
private readonly IDockManager _dockManager;
private readonly DocViewerViewModel _docViewerViewModel;
private readonly IList<DockableViewModel> _toolViews = new List<DockableViewModel>();
public ToolViewerViewModel(IViewModelFactory viewModelFactory, DocViewerViewModel docViewerViewModel, IDockManager dockManager)
{
_dockManager = dockManager;
_viewModelFactory = viewModelFactory;
_docViewerViewModel = docViewerViewModel;
}
protected override void OnViewLoaded(object view)
{
_dockManager.Link(this);
_dockManager.CreateSpecialPaneFor(_docViewerViewModel);
ActivateItem(_docViewerViewModel);
ShowToolView<ProjectExplorerViewModel>();
base.OnViewLoaded(view);
}
public void ShowToolView<T>() where T : DockableViewModel
{
if (!IsToolViewOpen<T>())
{
var viewModel = _viewModelFactory.Create<T>();
ActivateItem(viewModel);
RefreshMenu(typeof(T));
}
}
}
Next class:
public class DocViewerViewModel : Conductor<DocumentViewModel>
{
private readonly IViewModelFactory _viewModelFactory;
public DocViewerViewModel(IViewModelFactory viewModelFactory)
{
_viewModelFactory = viewModelFactory;
}
public bool ShowInMainView<T>() where T : DocumentViewModel
{
return ShowInMainView(typeof(T));
}
private bool ShowInMainView(Type viewModelType)
{
var ret = false;
// close the current view
if (ActiveItem != null)
{
DeactivateItem(ActiveItem, true); //The close flag is on true since we want to remove the current instance from the memory
}
// check whether the current viewModel has been closed successfully
if (ActiveItem == null)
{
try
{
var viewModel = _viewModelFactory.Create(viewModelType) as DocumentViewModel;
if (viewModel != null)
{
ActivateItem(viewModel);
ret = true;
}
else
{
ActivateItem(_viewModelFactory.Create<NoDataViewModel>());
}
}
catch (Exception ex)
{
ActivateItem(_viewModelFactory.Create<NoDataViewModel>());
}
}
return ret;
}
}
and the last one:
public abstract class DocumentViewModel : Screen
{
private bool _isDirty;
protected IViewModelFactory ViewModelFactory { get; private set; }
protected IEventAggregator EventAggregator { get; private set; }
public bool IsDirty
{
get
{
return _isDirty;
}
protected set
{
if (value.Equals(_isDirty))
{
return;
}
_isDirty = value;
NotifyOfPropertyChange(() => IsDirty);
}
}
protected DocumentViewModel(IViewModelFactory viewModelFactory, IEventAggregator eventAggregator)
{
ViewModelFactory = viewModelFactory;
EventAggregator = eventAggregator;
}
protected override void OnDeactivate(bool close)
{
if (close)
{
if (EventAggregator != null)
{
EventAggregator.Unsubscribe(this);
}
}
base.OnDeactivate(close);
}
protected override void OnActivate()
{
if (EventAggregator != null)
{
EventAggregator.Subscribe(this);
}
base.OnActivate();
}
public override void CanClose(Action<bool> callback)
{
var ret = true;
if (IsDirty && (ViewModelFactory != null))
{
var saveDialog = ViewModelFactory.Create<SaveDialogViewModel>();
saveDialog.Show();
if (saveDialog.DialogResult == DialogResult.Cancel)
{
ret = false;
}
else
{
if (saveDialog.DialogResult == DialogResult.Yes)
{
Save();
}
else
{
Discard();
}
IsDirty = false;
}
}
callback(ret);
}
public abstract void Save();
public virtual void Discard()
{
}
}
With this code the only time the DocumentViewModel.OnDeactivate() is being called when the user brings an other dock-able view into focus while the DocViewerViewModel was having the focus. This should not happen!
When the user is changing the focus between the dock-able views the DocumentViewModel.OnDeactivate() should not get call. But it must get called when ever the Method DocViewerViewModel.ShowInMainView<SomeDocumentViewModel>() is being called. Which isn't the case currently.

As far as I can tell, there is nothing wrong with the way your code is written. Since you are using MVVM, I suggest you design a test case like I've provided here.
And here's a snippet of the test case
// TestHarness.cs
[TestMethod]
public void CheckDeactivation()
{
// We'd like to have the ToolViewerViewModel only Conduct the dock-able views
// and the DocViewerViewModel to conduct the DocumentViewModel.
IViewModelFactory factory = new ViewModelFactory();
DocViewerViewModel docViewer = new DocViewerViewModel(factory);
IDockManager dockManager = null;
var toolViewer = new ToolViewerViewModel(factory, docViewer, dockManager);
var mockToolView = new UserControl();
(toolViewer as IViewAware).AttachView(mockToolView);
DocumentViewModel docView1 = new NoDataViewModel();
DocumentViewModel docView2 = new NoDataViewModel();
docViewer.ActivateItem(docView1);
docViewer.ActivateItem(docView2);
Assert.AreEqual(0, docViewer.CountDeactivated());
}

I have had the exact same problem as you, and ended up using PropertyChangedBase instead of Screen and got the problem to disappear.
Later, after reading the docs on Screens and Conductors here, I realized that I wasn't activating the conductor itself further up in the view hierarchy!
So have a look at wherever you use your ToolViewerViewModel, and make sure you activate that instance!

Thank you very much for your Test. Even thought it is really nice code it tests the wrong code part. Your code simply tests whether the Method ActivateItem() or DeactivateItem() is being called:
public override void ActivateItem(DocumentViewModel item)
{
_countActivated++;
base.ActivateItem(item);
}
public override void DeactivateItem(DocumentViewModel item, bool close)
{
_countDeactivated++;
base.DeactivateItem(item, close);
}
But since these Methods are being called explicitly we don't need to test for that...
The real Problem is that the Conductor is not calling the OnActivate() or OnDeactivate() on the DocumentViewModel class. To enhance your test I used the following code:
public class DummyViewModelFactory : IViewModelFactory
{
private readonly Dictionary<Type, Func<object>> _registredCreators = new Dictionary<Type, Func<object>>();
public T Create<T>() where T : PropertyChangedBase
{
return Create(typeof(T)) as T;
}
public object Create(Type type)
{
if (type == null)
{
return null;
}
if (_registredCreators.ContainsKey(type))
{
return _registredCreators[type]();
}
return null;
}
public void Release(object instance)
{
}
public void RegisterCreatorFor<T>(Func<T> creatorFunction)
{
_registredCreators.Add(typeof(T), () => creatorFunction());
}
}
As concrete DocumentViewModel implementation I made:
public class NoDataViewModel : DocumentViewModel
{
public NoDataViewModel(IEventAggregator eventAggregator,
IViewModelFactory viewModelFactory)
: base(viewModelFactory, eventAggregator, )
{
}
public override void Save()
{
// nothing to do
}
public override void Reload()
{
// nothing to do
}
}
public class NoDataViewModelMock : NoDataViewModel
{
private static int activationCounterForTesting = 0;
private static int deactivationCounterForTesting = 0;
public static int ActivationCounterForTesting
{
get
{
return activationCounterForTesting;
}
}
public static int DeactivationCounterForTesting
{
get
{
return deactivationCounterForTesting;
}
}
public NoDataViewModelMock()
: base(null, null)
{
}
protected override void OnActivate()
{
activationCounterForTesting++;
base.OnActivate();
}
protected override void OnDeactivate(bool close)
{
deactivationCounterForTesting++;
base.OnDeactivate(close);
}
}
And I changed your Testmethod to this:
[TestMethod]
public void CheckDeactivation()
{
var viewModelFactory = new DummyViewModelFactory();
viewModelFactory.RegisterCreatorFor<NoDataViewModel>(() => new NoDataViewModelMock());
var docViewer = new DocViewerViewModel(viewModelFactory);
IDockManager dockManager = null;
var toolViewer = new ToolViewerViewModel(viewModelFactory, docViewer, dockManager);
var mockToolView = new UserControl();
(toolViewer as IViewAware).AttachView(mockToolView);
docViewerViewModel.ShowInMainView<NoDataViewModel>();
docViewerViewModel.ShowInMainView<NoDataViewModel>();
docViewerViewModel.ShowInMainView<NoDataViewModel>();
Assert.AreEqual(3, NoDataViewModelMock.ActivationCounterForTesting);
Assert.AreEqual(2, NoDataViewModelMock.DeactivationCounterForTesting);
}
Then you'll see that the OnActivate() and OnDeactivate() methods are never been called.
With a little more advanced test you'd also see that they are being called but from the ToolViewerViewModel directly. I'd like to know why and how I can change this behavior to fit my needs:
The DocumentViewModel.OnActivate() method should get called when the DocViewerViewModel.ShowInMainView<T>() method gets called.
The DocumentViewModel.OnDeactivate() method should get called on the old DocumentViewModel when a new one is being shown by calling the DocViewerViewModel.ShowInMainView<T>()

Our Solution for that Problem is to remove the use Screen as BaseClass for DocViewerViewModel an implement the Conductor Logic our self.