Develop Reference

Akavache and collectionChanged event

(1) I am having trouble getting the CollectionChanged event of an ObservableCollection to fire whilst using Akavache, here is the code I have (simplified)
GraphCollection = new ObservableCollection<UserData>();
_cache.GetOrFetchObject(TabType.Graph.ToString(),
async () => await _dataStore.GetAllDocuments(TabType.Graph))
.Subscribe(
GraphList =>
{
GraphCollection = new ObservableCollection<UserData>(GraphList);
//GraphCollection.Shuffle();
NoGraphItems = GraphCollection.Count == 0;
});
GraphCollection.CollectionChanged += (sender, args) =>
{
NoGraphItems = GraphCollection.Count == 0;
};
Ideally, when I Add/Delete data I want to trigger the event to check to see if the collection is empty and then assign a bool property that it is or isn't empty.
I am making simple Add/Delete like so, and then calling a RefreshCache method to invalidate the data and recreate the data, not sure if this is the most efficient way to do it as well.
var graphRecord = GraphCollection.FirstOrDefault(x => x.Id == data.Id);
GraphCollection.Remove(dreamRecord);
RefreshCache(TabType.Graphs, DreamsCollection);
private void RefreshCache(TabType tabType, ObservableCollection<UserData> collection)
{
_cache.InvalidateObject<UserData>(tabType.ToString());
_cache.InsertObject(tabType.ToString(), collection);
}
(2) I am not currently setting the DateTime offset, do I need this? Can someone give me an example of how to write it out, the docs don't clearly state this.
DateTimeOffset? absoluteExpiration

your Subscribe creates a new instance of GraphCollection so the event handler that was assigned to the original instance no longer works with the new instance
try this instead
GraphList =>
{
GraphCollection = new ObservableCollection<UserData>(GraphList);
NoGraphItems = GraphCollection.Count == 0;
GraphCollection.CollectionChanged += // handler goes here
});

C# MVVM pattern update UI in Infinite loop thread? [duplicate]

This question already has an answer here:
Lifeupdate DataGrid from TextFile with good performance
(1 answer)
Closed 5 years ago.
I have a background thread to listen data, so this infinite loop to output data.
And, I using a ObservableCollection to bind a ListBox and show log.
I try to use Dispather.BeginInvoke, but no use, it not realtime. I have no idea for update UI in MVVM.
xaml
<ListBox x:Name="lsb_log" Width="auto" ItemsSource="{Binding DisplayLogs}"/>
code
private ObservableCollection<string> _displayLogs;
public ObservableCollection<string> DisplayLogs
{
get
{
return _displayLogs;
}
}
public Testpro()
{
_displayLogs = new ObservableCollection<string>();
Task.Run(new Action(outputData));
}
private void outputData()
{
string str = "";
while (true)
{
string newString = GetInfoString();
if (string.IsNullOrWhiteSpace(newString) || str == newString)
continue;
str = newString;
Debug.WriteLine(str);
Application.Current.Dispatcher.BeginInvoke((Action)delegate ()
{
DisplayLogs.Add(str);
});
}
}
*Edit:
GetInfoString will call by a dll file.

You should really use something designed for this kind of update. I'm going to suggest Microsoft's Reactive Framework (NuGet "System.Reactive" & "System.Reacive.Windows.Threading").
Then you can do this after the _displayLogs = new ObservableCollection<string>(); line:
IDisposable subscription =
Observable
.Interval(TimeSpan.FromSeconds(1.0))
.Select(_ => GetInfoString())
.Where(newString => !string.IsNullOrWhiteSpace(newString))
.DistinctUntilChanged()
.ObserveOnDispatcher()
.Subscribe(newString =>
{
Debug.WriteLine(newString);
DisplayLogs.Add(newString);
});
That should call GetInfoString() every second and update your UI. It handles all of the threading and marshalling issues.
If you keep a reference to subscription you can stop it at any stage by calling subscription.Dispose().

You can use async-await therefore. Your OutputData-Method can look something like:
private async void OutputData(IProgress<string> onProgress)
{
await Task.Factory.StartNew(() =>
{
string str = string.Empty;
while (true)
{
string newString = GetInfoString();
if(string.IsNullOrWhiteSpace(newString) || str == newString)
continue;
str = newString;
// call the UI to update your bound collection
onProgress.Report(str);
// give the ui some time to respond before continue with your endless-loop
Thread.Sleep(200);
}
});
}
And you can call this method with:
OutputData(new Progress<string>((str) =>
{
DisplayLogs.Add(str);
}));
That's it

wpf dispatcher error in tag property

I have an error accessing a WPF element in code behind (see indicated error line):
Thumb sThumb = new Thumb();
...
TextBox Thumbtxt = (TextBox)sThumb.Template.FindName("TextThumb", sThumb);
if (Thumbtxt.Tag != null) <-- Unhandled Exception: The calling thread cannot access this object because a different thread owns it.
{
if (Thumbtxt.Tag.ToString() == "Disabled")
IsDisabled = true;
}
I then tried to execute the code in the dispatcher, as follows:
System.Windows.Application.Current.Dispatcher.Invoke(DispatcherPriority.Normal, new Action(() =>
{
Thumb sThumb = new Thumb();
...
TextBox Thumbtxt = (TextBox)sThumb.Template.FindName("TextThumb", sThumb);
if (Thumbtxt.Tag != null)
{
if (Thumbtxt.Tag.ToString() == "Disabled")
IsDisabled = true;
}));
Still, I get the same error in the very same line. I use this dispatcher invoke in other parts and it works fine, but apparently it doesn't like the "Tag" property, for some reason.
Can someone please shed some light?
Thanks in advance

Try to use TaskScheduler.FromCurrentSynchronizationContext
await Task.Run(() => { TextBox Thumbtxt = (TextBox)sThumb.Template.FindName("TextThumb", sThumb); })
.ContinueWith(
res =>
{
you code here
},
TaskScheduler.FromCurrentSynchronizationContext());

Try to use the dispatcher that is associated with the Thumbtxt control:
Thumbtxt.Dispatcher.Invoke(new Action(()=>
{
if (Thumbtxt.Tag != null)
{
if (Thumbtxt.Tag.ToString() == "Disabled")
IsDisabled = true;
};
}));

Update treeview from another thread

I'm quite new to threads in c# (WPF) and since I've implemented some label and progressbar update successfully, I do not understand Why when I try to add items to the treeView of my GUI from another class called in a separate thread I get an exception:
An unhandled exception of type 'System.InvalidOperationException'
occurred in WindowsBase.dll
Additional information: The calling thread cannot access this object
because a different thread owns it.
My update treeview code is this:
private void updateTreeView(TreeView tree, List<TreeViewItem> items, Boolean clear) {
tree.Dispatcher.Invoke(new Action(() => {
if (clear) {
tree.Items.Clear();
}
ItemCollection treeitems = tree.Items;
foreach (TreeViewItem item in items) {
treeitems.Dispatcher.Invoke(new Action(() => {
treeitems.Add(item);
}));
}
tree.ItemsSource = treeitems;
}));
}
And the exception points at the line:
treeitems.Add(item);
Thanks in advance.

you can use the following :
delegate void DUpdateTreeView(TreeView tree, List<TreeViewItem> items, Boolean clear);
private void UpdataTreeView(TreeView tree, List<TreeViewItem> items, Boolean clear)
{
if (tree.InvokeRequired)
{
DUpdateTreeView d = new DUpdateTreeView(UpdataTreeView);
// replace this by the main form object if the function doesn't in the main form class
this.Invoke(d, new object[] { tree, items, clear });
}
else
{
if (clear)
{
tree.Items.Clear();
}
else
{
// Here you can add the items to the treeView
/***
ItemCollection treeitems = tree.Items;
foreach (TreeViewItem item in items)
{
treeitems.Dispatcher.Invoke(new Action(() =>
{
treeitems.Add(item);
}));
}
tree.ItemsSource = treeitems;
***/
}
}
}

This is a really old question but I figured I would answer it. You have two dispatchers in your sample. You have a treeview that you are getting its thread and a list that seems to be created in a different thread.
But the code should look more like this. Sorry about the VB in this case I'm using a delegate inside the invoke.
tree.Dispatcher.BeginInvoke(Sub()
Dim node = new TreeViewItem() With {.Header = "Header"}
tree.items.add(node)
End Sub)
I am not jumping out of the UI thread to add the node like in the original question.

Equivalent to InvokeRequired in WPF

Is there an equivalent to Form.InvokeRequired in WPF, e.g. Dispatcher.InvokeRequired?

This is slightly odd as it doesn't appear in intellisense, but you can use:
var dispatcher = myDispatcherObject.Dispatcher;
if (dispatcher.CheckAccess()) { /* ... */ }
As all UI components inherit from DispatcherObject this should solve your specific problem, but it is not specific to the UI thread - it can be used for any dispatcher.

The equivalent is Dispatcher.CheckAccess.

A possible solution that came to mind is:
if ( Dispatcher.Thread.Equals( Thread.CurrentThread ) )
{
Action( );
}
else
{
Dispatcher.Invoke( Action );
}

If you're building a Windows Store app, the above example won't work. Here's an example that does work. Modify as needed, of course :)
/// <summary>
/// Updates the UI after the albums have been retrieved. This prevents the annoying delay when receiving the albums list.
/// </summary>
/// <param name="albums"></param>
public void UpdateUiAfterAlbumsRetrieved(System.Collections.ObjectModel.ObservableCollection<PhotoAlbum> albums)
{
if (!Dispatcher.HasThreadAccess)
{
Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
ddlAlbums.DataContext = albums;
ddlAlbums.IsEnabled = true;
tbxProgress.Text = String.Empty;
ProgressBar.IsIndeterminate = false;
ProgressBar.Visibility = Windows.UI.Xaml.Visibility.Collapsed;
});
}
else
{
ddlAlbums.DataContext = albums;
ddlAlbums.IsEnabled = true;
tbxProgress.Text = String.Empty;
ProgressBar.IsIndeterminate = false;
}
}