Description
Description
The dispatcher hook OperationPriorityChanged is called when the priority has not changed yet on the DispatcherOperation. It is already changed in the PriorityQueue of the dispatcher, but a subscriber of the event has no way of knowing this new priority.
Reproduction Steps
Create a new WPF application
exchange contents of App.xaml.cs with
using System.Diagnostics;
using System.Windows;
using System.Windows.Threading;
namespace WpfApp
{
public partial class App : Application
{
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
Dispatcher.Hooks.OperationPriorityChanged += (sender, args) =>
{
// Note that args.Operation.Priority is still Inactive here
Debugger.Break();
};
Action action = () => { };
var operation = Dispatcher.BeginInvoke(action, DispatcherPriority.Inactive);
operation.Priority = DispatcherPriority.Send;
}
}
}Expected behavior
I would expect the OperationPriorityChanged event to be called, when the priority change was completely finished.
Actual behavior
The OperationPriorityChanged is called when the DispatcherOperation does not reflect the change.
Regression?
I don't think so. This was probably designed this way.
Known Workarounds
No workarounds.
Impact
This is probably an edge case.
I am writing diagnostics for some dispatcher queue issues I am seeing in an application.
This makes it harder to debug. I probably will ignore dispatcher priority changes and just show diagnostics for the original Inactive state.
Configuration
- .NET 8.0.5 (but I think this is not version dependent. Probably all versions since introduction of WPF)
- Windows 11
- x64
- It is not specific to this configuration
Other information
When changing priority on DispatcherOperation, the operation tells it's dispatcher to move it to the new priority chain. The dispatcher will raise the event, and DispatcherOperation will change it's _priority field after the fact.
Activity