Simon Ransom's space: Silverlight

Silverlight expiry August/November 2007

Wed, 09 Jan 2008 17:29:17 GMT

According to the current Terms and Conditions for the September 1.1 Alpha refresh, they will expire on 1st August (Mac) and 1st November (PC) 2007. This is not true, I posted this question (via my psuedonym LittleClive :-)) to http://silverlight.net/forums/p/8248/25757.aspx#25757

See http://www.microsoft.com/silverlight/license-mac-dev.aspx and http://www.microsoft.com/silverlight/license-win-dev.aspx

This operation can only occur on the UI Thread

Thu, 04 Oct 2007 11:27:31 GMT

So to avoid the JSON serialization length limit mentioned in a previous post, I have created a separate LoadMenuPage method that takes a menu file and a page number. The total number of pages is returned in the first LoadMenu call. At the moment, my client application loads all of the menus and merges them together into a single menu so the result is the same but this can take some time. The menus have to be limited to 10 menu items per web-service call and since there are 84 items in one of the menus, this requires 9 calls plus merge time.

I wanted to give some feedback to the user about this long running application so I tried starting an animation before the long call and then hiding it afterwards. This didn't work because the long running call was executing on the UI thread so I moved the web-service invocation and merging logic to another thread. When it completes, it needs to populate a UI control which it can't do if it's not on the UI thread and there's no Dispatcher in Silverlight yet. So I created a custom dispatcher using the HtmlTimer (which is marked obsolete but from research seems to be the only choice at the moment):

    public class CustomDispatcher
    {
        private Queue<Delegate> uiWork = new Queue<Delegate>();
        private HtmlTimer timer = new HtmlTimer();

        public void Start()
        {
            timer.Start();
        }

        public void InvokeOnUIThread(Delegate d)
        {
            uiWork.Enqueue(d);
        }

        private void OnTick(object sender, EventArgs args)        
        {
            if (uiWork.Count > 0)
            {
                Delegate d = uiWork.Dequeue();
                d.Method.Invoke(d.Target, null);
            }
        }

        public CustomDispatcher()        
        {
            timer.Interval = 100; 
            timer.Tick += new EventHandler(OnTick);
        }
    }

So all is looking good-ish, but then I hit another wall when I ran it up because I got the error I had been trying to avoid "This operation can only occur on the UI Thread":

It seems the web-service proxy code requires an internal call to System.Windows.Browser.HtmlPage.get_DocumentUri() which needs to be executed on the UI thread. I haven't tried the asynchronous BeginLoad in the proxy yet...

Fixing the Silverlight 1.1 SDK Alpha controls

Thu, 04 Oct 2007 06:57:43 GMT

It's great that the source code is provided for these controls. I've had to fix the ListBox so that it scrolls back to the top when UpdateItems is called, otherwise the canvas can appear empty when drilling down through menus:

        //Updates the content children with the current items in the list
        public void UpdateItems()
        {
            //remove all the children and start from empty
            content.Children.Clear();

            content.SetValue(Canvas.TopProperty, 0);

I've also had to fix the list box so that after scrolling it doesn't select content if you release the mouse button inside the content area which has greatly reduced the number of mis-selections:

        /// <summary>
        /// Keep track of where mouse was originally pressed
        /// </summary>
        private bool mouseDownInsideContentArea;

        // CaptureMouse
        protected void OnMouseLeftButtonDown(object sender, MouseEventArgs args)
        {
            if (CheckMousePosition(args))
            {
                ActualControl.CaptureMouse();
                mouseDownInsideContentArea = true;
            }
            else
            {
                mouseDownInsideContentArea = false;
            }
        }

        // If the mouse is on the ListBox find on which item and select it.
        protected void OnMouseLeftButtonUp(object sender, MouseEventArgs args)
        {
            ActualControl.ReleaseMouseCapture();

            //do thing only if we are outside the ScrollBar [Simon Ransom: and the mouse was originally pressed when not on scroll bar]
            if (CheckMousePosition(args) && mouseDownInsideContentArea) {
                Point pt = args.GetPosition(this);
                if ((items.Count > 0) &&
                    (pt.X < Width) && (pt.Y < Height)) {
                    double contentY = pt.Y - (double)(content.GetValue(Canvas.TopProperty));
                    int itemNumber = (int)(contentY / itemHeight);
                    FrameworkElement newSelection = itemNumber < items.Count ? items[itemNumber] : null;
                    if (selectedItem != newSelection) {
                        Select(newSelection);
                        if (SelectionChanged != null) {
                            SelectionChanged(this, null);
                        }
                    }
                }
            }
        }

JSON serialization and "Error invoking service."

Tue, 02 Oct 2007 19:17:43 GMT

To serve up my menu XML files which I already have .NET serialization classes for, I've created a webservice:

[WebService(Namespace = "http://www.simonransom.com/menuservice/3.0")]

[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

[ToolboxItem(false)]

[System.Web.Script.Services.ScriptService]

public class MenuService : System.Web.Services.WebService

{

[WebMethod]

[ScriptMethod(ResponseFormat = ResponseFormat.Json)]

public SegmentedMenu Load(string menu)

{

string path = Server.MapPath("~/menufiles/" + menu);

return new SegmentedMenu(MenuManager.GetInstance().Load(path));

}

From this I learnt a few things:

If I went to the webservice page menuService.asmx in Internet Explorer or Firefox, the browser would only return the XML version of the results which looked fine (as long as you were expecting XML - which given that I'd specified Json serialization I wasn't)

Using TCPTrace from Simon Fell & Matt Humphrey, the message requests from Silverlight were of the more expected form and have a MIME Content-Type of application/json

{"menu":"publicphotos.xml"}

So it looks like .NET is supporting both serialization forms depending on the client request type. The response back to Silverlight from my webservice is in the form:

{"d":{"__type":"PBL.App.Menus.WebService.SegmentedMenu","Header":{"MenuLargeImage":null,"Filename":"publicphotos.xml","AudioPlaylist":null,"A... etc.

For some of the menus I get a System.Net.WebException with a message stating "Error invoking service." (not particularly helpful and no inner exception). However in TCPTrace I get a more helpful:

{"Message":"Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.","StackTrace":" at System.Web.Script.Services.RestHandler.InvokeMethod(HttpContext context, WebServiceMethodData methodData, IDictionary`2 rawParams)\r\n at System.Web.Script.Services.RestHandler.ExecuteWebServiceCall(HttpContext context, WebServiceMethodData methodData)","ExceptionType":"System.InvalidOperationException"}

My original menu serialization used inheritance and System.Xml.Serialization.XmlInclude to have a base MenuItem and subclasses of MenuItemPhoto, MenuItemMovie, etc. however although the XML looked ok, the JSON serialization format does not support OO inheritance so all the classes on the client end were stripped down to the base class MenuItem. To work around this, I created a SegmentedMenu class which could be created based on the original Menu class but separated each of the MenuItems into different lists (e.g. List<MenuItemPhoto> photos) depending on class type. This could then be passed back but loses the benefit of interleaving different types and increases a mapping overhead but overall not a bad solution for what I need.

So now I need to work out how make the larger menus smaller or increase the maxJasonLength property.

Week 1-ish

Fri, 28 Sep 2007 13:51:03 GMT

Downloaded:

Visual Studio 2008 Beta 2
Microsoft Silverlight Tools Alpha for Visual Studio 2008 Beta 2
Silverlight 1.1 Alpha SDK (includes some basic controls like button, listbox etc.)
Blend 2 September Preview

The beginnings of my photo/video browser

Fri, 28 Sep 2007 13:40:49 GMT

I'm learning Silverlight and for my "hello world" app I've chosen to reimplement my family photo, video and music site. So I keep track of what I'm learning I'll blog it here.

Firstly the "legacy" system I have already built in .NET 2.0 at a high-level creates xml menu files for driving the navigation on the website.

It has a number of plugins to

extract Exif information
create thumbnails, playlists, web preview images
create movie files in Divx, Wmv (standard and VC-1) and Quicktime formats
render 3d artwork using Povray (e.g. piles of photos that are bigger depending on the size of the category)
extract stills from movies to create animated thumbnails
uses Amazon webservice to search for album art and then screenscrape the images to produce a 3d view of the CD case

This system is separate from the website itself so that I could easily move away from ASP.NET to an alternative interface and that's exactly what I'm doing now....