Hi,I have to admit it took me a little while and a fair amount of Googling to figure this out - but the solution seems to be to set the SynchronizationContext of the main thread to a new DispatcherSynchronizationContext e.g.
var syncCtx = new DispatcherSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(syncCtx);
The issue is that the Initialized event is firing on a different thread from the one on which the FeatureLayer is created, hence the exception you're seeing about the calling thread. As far as I know, this shouldn't happen. Working with your code in a console application I added additional code in each event (Initialized and UpdateCompleted) to get the Dispatcher of the FeatureLayer then call CheckAccess on that Dispatcher which confirms whether an Invoke is required to post back onto the calling thread. I also added code to write out the current thread id, just so I could easily check what was going on. This confirmed that the Initialized event was always firing on a different thread but I do not know why and even when I did call Dispatcher.Invoke (or .BeginInvoke) to post back on to the original thread it still failed with the same exception. A colleague suggested I should check the SynchronizationContext of the main thread and of the thread on which the event was firing. However, the SynchronizationContext of the main thread was always null and unfortunately I still do not know the reason for this - but it seems to be the reason why the event was firing on a different thread. Fortunately I found a blog post which, although addressing a different use case, showed me how to make sure there is a SynchronizationContext (http://blogs.msdn.com/b/pfxteam/archive/2012/01/21/10259307.aspx) - see code snippet above and full code below. Once I had added this code it worked perfectly. The code may not even need all the Dispatcher checks/invokes once the Sync Context is now set but I think it's good practice in this scenario.Here's the full code:
using System;
using System.Threading;
using System.Windows.Threading;
using ESRI.ArcGIS.Client;
namespace UpdateGraphicsConsole
{
class Program
{
static string _url = "http://sampleserver6.arcgisonline.com/arcgis/rest/services/Wildfire/FeatureServer/0";
// Make sure the main thread is an STA thread
[STAThread]
static void Main(string[] args)
{
// For some reason the SynchronizationContext of the main thread is null.
// Create and set a new DispatcherSynchronizationContext.
var syncCtx = new DispatcherSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(syncCtx);
// Get the current dispatcher to check thread access.
Dispatcher d = Dispatcher.CurrentDispatcher;
// Create a FeatureLayer
FeatureLayer fl1 = new FeatureLayer
{
Url = _url,
ID = "23",
Mode = FeatureLayer.QueryMode.Snapshot,
AutoSave = false,
};
// Report which thread the FeatureLayer was created on
Console.WriteLine("FeatureLayer created on Thread " + d.Thread.ManagedThreadId.ToString());
// Register a handler for the Initialized event
fl1.Initialized += (sender, eventArgs) =>
{
// Report which thread the event fired on (this was always a different thread until the DispatcherSynchronizationContext was set
Console.WriteLine("Initialized event handled on Thread " + Dispatcher.CurrentDispatcher.Thread.ManagedThreadId.ToString());
// Get the FeatureLayer
FeatureLayer fl2 = sender as FeatureLayer;
// Get the FeatureLayer dispatcher
Dispatcher d1 = fl2.Dispatcher;
// Report the thread we're invoking the Update call on (this was always the original thread)
Console.WriteLine("Invoking Update on Thread " + d1.Thread.ManagedThreadId.ToString());
// CheckAccess always returned false because this code was running on a different thread until the DispatcherSynchronizationContext was set
if (fl2.Dispatcher.CheckAccess())
{
fl2.Update();
}
else
d1.BeginInvoke(
DispatcherPriority.Normal,
new Action(delegate()
{
fl2.Update();
}));
};
// Register a handler for the UpdateCompleted event and call SaveEdits()
fl1.UpdateCompleted += (sender, e) =>
{
// Get the FeatureLayer
FeatureLayer fl3 = sender as FeatureLayer;
// Get the FeatureLayer Dispatcher
Dispatcher d2 = fl3.Dispatcher;
// Update the graphic attribute (or perform any other edits)
fl3.Graphics[0].Attributes["description"] = Guid.NewGuid().ToString();
// Write out the new value
Console.WriteLine(
"Updated Graphic ObjectID "
+ fl3.Graphics[0].Attributes["objectid"]
+ " with Description: "
+ fl3.Graphics[0].Attributes["description"]);
// Call CheckAccess to confirm whether we need to post back to the original thread
// Then call SaveEdits
if (fl3.Dispatcher.CheckAccess())
{
fl3.SaveEdits();
}
else
d2.BeginInvoke(
DispatcherPriority.Normal,
new Action(() => fl3.SaveEdits()));
};
// Register a handler for the EndSaveEdits event and write out the status
fl1.EndSaveEdits += (sender, e) =>
{
Console.WriteLine(e.Success ? "Success" : "Fail");
// Can check results online at query endpoint (by description value, objectid, etc)
// http://sampleserver6.arcgisonline.com/arcgis/rest/services/Wildfire/FeatureServer/0/query
};
// Register a handler for the InitializationFailed event
fl1.InitializationFailed += (sender, e) =>
{
// Report error
FeatureLayer fl4 = sender as FeatureLayer;
Console.WriteLine(fl4.InitializationFailure.Message);
};
// Register a handler for the UpdateFailed event
fl1.UpdateFailed += (sender, e) =>
{
// Report failure to update layer
Console.WriteLine(e.Error);
};
// Register a handler for the SaveEditsFailed event
fl1.SaveEditsFailed += (sender, e) =>
{
// Report failure
Console.WriteLine(e.Error);
};
Console.WriteLine("Calling Initialize on Thread " + d.Thread.ManagedThreadId.ToString());
// Call Initialize method (in a map/UI scenario this call would be handled by the Map).
fl1.Initialize();
// Need to call Dispatcher.Run
Dispatcher.Run();
}
}
}
CheersMike
