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Great minds ... etc.
When I started looking into this sort of thing, the problems started to grow. For example, if a Message Handler throws an exception, and catches it, then stores it in the WorkResult object there are two choices - the Mediator aborts as soon as one handler throws an exception, or it continues to try any other handlers - and if they throw exceptions, do you start keeping collections of the damn things?
If the mediator itself gets an unhandled exception, then returning it to the sender might be a good idea - but then why not just leave it unhandled? it is, after all, an exception?
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.\\axxx
(That's an 'M')
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Well, I've changed my implementation and I'm busy testing it out now. The reason I've been toying around with this idea is that in some cases I've wanted to have some VMs continue processing even when one has failed due to a SQL exception because I can handle this later on. This change could be useful.
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It'll be interesting to see how it works out.
In these sort of cases are you trapping the exception in the VM and adding the info to the Mediator object, or do you leave the exception for the mediator to trap and log?
The reason I;m looking at all of this right now is that I'm writing an article (I say AN article, it's likely to be a series of about twenty the way I'm going!) about they way I'm doing MVVM
As usual with this sort of thing, as soon as I start to describe the whys and wherefores, I think of additional things I'd like to do, and the whole thing expands and expands...
The good thing is that I end up with a good, well thought out "framework" - I just will have to draw the line in the sand somewhere!
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.\\axxx
(That's an 'M')
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_Maxxx_ wrote: In these sort of cases are you trapping the exception in the VM and adding the
info to the Mediator object, or do you leave the exception for the mediator to
trap and log?
It really depends. I'm a great believer in trapping and handling errors where you can. In some cases though, I want the exception to bubble upwards - but because of the loose coupling between the VMs, I want to still allow the others to continue. In this case, the result is acting almost like a mediator message in its own right - the mediator becomes aware of the exception, but it can still continue.
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To give you an idea, this is my implementation now:
public NotificationResult NotifyColleagues<T>(T message, object args)
{
NotificationResult result = NotificationResult.Successful;
lock (SyncLock)
{
if (internalList.ContainsKey(message))
{
if (internalList[message].Count == 0)
result = NotificationResult.NoListenersForMessage;
foreach (Action<object> callback in internalList[message])
callback(args);
}
else
{
result = NotificationResult.MessageNotRegistered;
}
}
return result;
}
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Awesome!
If I keep giving you ideas will you write my whole App for me? 
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.\\axxx
(That's an 'M')
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So I have a silverlight app. The page can be referenced with arguments so when someone click on a link in another html page it starts up the silverlight app web page and works according to the arguments.
The problem is that the link on the other html page can be clicked again and it will also start up the silverlight app in *another* web page and work according to the arguments. Basically I can have two or more of my silverlight app running.
Is there a way to tell that second click that the silverlight app is already up and running and to accept these new arguments - without having to reset the entire silverlight app? I made it work where the existing app starts over again (it doesn't look good that way), but I just want the app to respond to the new arguments passed in by the link clicked on the html page. Is that even possible?
Thanks
Brent
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As there is no method for an SL app to receive data from an aspx page (except the initial parameters) then I don't think this is possible.
Caveat, I'm fairly new to SL so don't take this as a definitive answer.
Never underestimate the power of human stupidity
RAH
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Mycroft Holmes wrote: there is no method for an SL app to receive data from an aspx page
Pretty sure that's not correct. See my answer below.
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AspDotNetDev wrote: Pretty sure that's not correct
Therefore the caveat, interesting looking article, it does imply there can be an interaction between the 2 spheres after the SL app is created.
Never underestimate the power of human stupidity
RAH
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Would you want a browser plugin that could hijack the default behaviour of your browser? I wouldn't. If the app opens up in a new window, then how is this any different from having a hyperlink with a jump target on it? The SL runtime has to behave itself like any other browser component, so it has to respect the same airspace issues.
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Not sure what you mean by "hijack the default behavior". Seems to me the OP is just building a web application and would like to have the second click act differently than the first click. More specifically, the first click should open a new window and the second click should interact with that opened window. Sounds both reasonable and possible to me (see my answer below).
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So, sounds like you want the first click to open the Silverlight application in a new window, but you want the second click of that same link to cause the Silverlight app to change in some way. If that is correct, then that should be doable. I'm pretty sure you can pass variables from one window to another window opened by that first window using JavaScript. I am also fairly certain that you can interact with a Silverlight control using JavaScript, even after the Silverlight control has been created.
See here and here (note: I didn't read those fully, but they seem like what you are looking for).
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Here's what I have tried.
I created another silverlight "application" which is merely a control that looks like a hyperlink. Then I can use the LocalMessageSender to talk to my main app and also talk to the web page that my "control" app lives on.
The only problem left is that typically when a page changes, the tab in the browser flashes or goes red (at least this is the behavior in IE). This doesn't happen here. The user has no clue that anything happened until he goes to the main silverlight app page and everything shifts. It appears that the main app doesn't run the Message Received event until AFTER the tab becomes active again.
Brent
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Hello everyone,
In windows service i.e. MyWindowsService, class1.cs has the code to receive messages all the time...
Everytime a message is received, it gets added to the Queue in class1.cs.
There is class2.cs in this windows service, which does the DeQueue.
Every 10th of a second, the silverlight application calls the class2 in windows service to pull the item in the queue. Note that since the silverlight page calls class2, the item is Dequeued from the Queue and gets passed to the silverlight page.
All works fine...
So you can see that the Dequeuing happens everytime the silverlight page calls the class2. And if the silverlight page is not running, then the Queue constantly is increasing inside the windows service.
Question:
I wonder if somehow, the Dequeing should happen automatically inside the service independent of the silverlight page?
1- If so, how do you suggest this should be done
2- Should the silverlight page, call the independent call inside the service every now and then also?
Hope you see what I mean.
Thank you
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Well, the obvious way to do this I suppose would be to create a limited queue, and put the onus on the queuing mechanism to add in a number of items until it's full, at which point it starts dequeuing - if your SL app picks up stuff, great, but if not - the queue will have an effective upper limit. To do this, you should subclass the Queue class and manage it there. This is a fairly trivial piece of code to write, so I'll leave it for you to do but I will give you a couple of pointers:
1. When you dequeue your object, you'll have to lock it because you could have two threads accessing it and you want to guard against race conditions.
2. If you change the limit of your queue in code, check to see that the number of items on the queue don't exceed the new limit - if they do, then dequeue them.
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I have a string "item2" and my comboBox contains item1, item2, item3, item4 how do I set the selected item to "item2"? I.e. how do I match my string to one of the comboBox items?
I am doing this in Silverlight 4, c#
Thanks in advance.
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Set the SelectedValue property.
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I have an object with a string property called 'Path'. For arguments sake it's set to "ImageSource".
I have a class 'Item'. It has a property named <Path>. I.e., if the user has set Path to "ImageSource" then 'Item' has a property named "ImageSource", if they set Path to "ApplePie", then 'Item' has a property named "ApplePie" and so on.
Now, I have an Image control and I want to bind the Image.Source to the property that the user specified with "Path".
I know in code, I can create a Binding object and set the source and property name dynamically, but I need to do this from a data template.
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Sorry - I misread your question. The short answer is not directly. If you want to do this, you've got to use a converter.
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Did you mean to write a value converter that takes some input(s) and returns an ImageSource object? Something like:
<Image Source="{Binding ..., Converter={StaticResource ...}" ... />
Ok, well, that won't accomplish what I'm looking for. I did that yesterday and it did work, but with issues. I used reflection in the converter to obtain the value of object.<Path> and I did get the image to show up, but this is resulting in a one time binding. If the value of object.<Path> changes, it wouldn't be reflected in the UI and I need it to be. If an app changes object.ImageSource, the icon should change on the screen obviously.
I also tried setting the binding on Image.Source within the converter, but that just confused WPF and the binding engine crashed  .
Unless you had some other thought?
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Does the value of object Path raise a change notification. If it doesn't then there's not a lot you can do to updated the binding anyway. If it does, then you could use the Reactive Extensions to watch that property, and react accordingly. This could not, of course, be done in the converter - which is there purely to convert the object. You would need to do this in the VM which backs your view, and then you could react to the changes there. Thinking about it, this is the simplest way to achieve this.
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Well, this is for a custom control (an enhanced ListView control), so there is no View / ViewModel involved. It is still a lookless control of course . I'm just not tying the design of the control to MVVM. Yes, the underlying property in the test app / test object does implement INPC.
Anyways, I dumped the Converter idea and went a different route which is working how I want it.
The "ListViewEx" overrides the item container generation and creates ListViewItemEx objects instead of ListViewItem objects.
Then in ListViewItemEx.OnApplyTemplate() I find the image control in the data template and create a Binding object and call image.SetBinding(Image.Source, binding);
This way I get true data binding to the underlying property and I don't have to do any crazy voodoo magic to get stuff to refresh. Of course, there is one issue and that is if the user suddenly decides to change Path from "ImageSource" to "SomethingElse", its not going to work because OnApplyTemplate() only gets called once.
EDIT: Actually, I guess there is a work-around. ListViewItems are regenerated when they go off screen and come back on, so I guess the user could just refresh the view if they really want to change Path.
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Without knowing what effect the ListView is having, I have to wonder whether or not you could have achieved the same functionality with an attached behavior. Whenever I hear that a WPF item has had to be subclassed, I end up wondering if the wrong problem has been solved.
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