Friday, June 29, 2012

Simple Extension Methods (part 2)

In the previous post I presented an extension method used mostly for overriding the edit and delete commands of a collection. One may ask “why do I want to do this?”. Apart from any other requirements/business logic dependent reason one might want to implement, for me there is one simple yet important reason: I don’t like at all (to be kind) the default add/edit modal windows when adding or editing an entry. It’s not a coincidence that the FIRST sample I wrote for LightSwitch and posted in the Samples of was a set of extension methods and contracts to easily replace standard modal windows with custom ones.
Most of the times when I have an editable grid screen, selecting Add or Edit I DON’T want the modal window to pop-up, I just want to edit in the grid. Or in list and details screen I want to edit the new or existing entry in the detail part of the screen.
This is the main reason I most of the times override the default Add/Edit command behavior. And for this reason I created and use the next two extension methods:
public static void AddFocus<T>(this VisualCollection<T> collection, string focusControl, bool inCollection)
      where T : class, IEntityObject {
      collection.EditFocus(focusControl, inCollection);

    public static void EditFocus<T>(this VisualCollection<T> collection, string focusControl, bool inCollection)
      where T : class, IEntityObject {
      if (focusControl != null) {
        try {
          IContentItemProxy control = null;
          if (inCollection)
            control = collection.Screen.FindControlInCollection(focusControl, collection.SelectedItem);
            control = collection.Screen.FindControl(focusControl);
          Microsoft.LightSwitch.Threading.Dispatchers.Main.BeginInvoke(() => {
            try {
            catch {
        catch {
          if (collection.HasSelection())

So what you have to do in your MyCollectionAddAndEditNew_Execute partial method is write something like:
MyCollection.AddFocus("TheNameOfTheControlYouWantToFocus", true);

or for MyCollectionEdit_Execute partial method:
MyCollection.EditFocus("TheNameOfTheControlYouWantToFocus", true);

if you have a list detail screen the same code applies but with inCollection = false.

One could implement one method for collections and one for details. Also notice where constraints applied to T generic parameter. The class constraint is required for declaring VisualCollection<T>. The IEntityObject constraint is required so that we avoid the arbitrary casting of collection.SelectedItem to IEntityObject so as to be passed to FindControlInCollection as second parameter.

Notice that in the extension methods I don’t check if the control name exists. I just use try catch. On error (if the control name is not valid) I choose to fall-back to the default behavior. You can change this without any intellectual rights being violated Smile.

Tuesday, June 26, 2012

Simple Extension Methods (part 1)

As soon as I started writing LightSwitch applications I noticed that many times I was repeating the same code over and over for trivial tasks. So after all this time I have collected a number of extension methods that I widely use in my apps.
For me reusing code is a must and although the implementation of LS (IMHO) does not provide for this out of the box the underlying framework is ideal for writing extension classes and methods that are a major step towards code reusability. If you have downloaded any of my samples from msdn or have seen my Application Logo post, you already suspect I am an “extension method fanatic”.
So I will present a small series (I don’t know how small) of posts with extension methods from my Base.LightSwitch.Client library.
The first method is one of the first (if not the first one) extension methods I wrote. As soon as you want to override the code for default commands like Edit and Delete for a collection (let’s name it MyCollection) you have to write something like that:
partial  void MyCollectionDelete_CanExecute(ref bool result){
  if (this.MyCollection is null || this.MyCollection.SelectedItem == null)
    result = false;
    result = true;

This is the minimum code (it can be written more elegantly I know but this is the concept) you need to write. I don’t take into account the permissions issue.

A similar chunk of code has to be written for Edit.

Isn’t the code listed below easier to read:
partial  void MyCollectionDelete_CanExecute(ref bool result){
  result = this.HasSelection("MyCollection");
It’s not only easier to read but is less error prone than the original. Plus you can inject any security logic in this HasSelection method.
And this is the code:
public static bool HasSelection(this IScreenObject screen, string collectionName) {
  if (!screen.Details.Properties.Contains(collectionName))
    return false;
  IVisualCollection collection =
    screen.Details.Properties[collectionName].Value as IVisualCollection;
  return collection != null &&
         collection.SelectedItem != null &&

         (collection.SelectedItem as IEntityObject).Details.EntityState != EntityState.Deleted;
For the ones that dislike using string property names I can suggest this version :
public static bool HasSelection<T>(this VisualCollection<T> collection) where T : class, IEntityObject {
  return collection != null &&
         collection.SelectedItem != nul &&
         collection.SelectedItem.Details.EntityState != EntityState.Deleted;

This version is more concrete is generic and also does not have to do the (out of thin air) conversion of SelectedItem to IEntityObject. If you use this version though you have to change your partial method as you cannot extend null:
partial void MyCollectionDelete_CanExecute(ref bool result){
  result = MyCollection!= null && MyCollection.HasSelection();
The choice is yours…Smile

Friday, June 22, 2012

RIAlity Issues

Recently I had to face a very frustrating issue regarding the integration of a RIA Service as a LightSwitch Datasource. I tried to find references for it in the web. I did. But none of them (at least the ones I managed to find) didn’t seem to match my case. So after solving my issue I thought sharing was a good idea…
After having implemented and tested my RIA service using a small Silverlight application I decided to add a datasource and use it. Which I did. Focusing at the part of the RIA service that caused the problem, I had a class called ImageAttachment and 2 queries exposing it. Below you can see the initial code:
   1:      [Query(IsDefault = true)]
   2:      public IQueryable<ImageAttachment> GetImageAttachments() {
   3:        return new List<ImageAttachment>().AsQueryable();
   4:      }
   6:      public IQueryable<ImageAttachment> GetFolderItemImageAttachments(Guid? providerId, string folderId, string mailItemId) {
   7:        if (!providerId.HasValue || folderId == null || mailItemId == null)
   8:          return GetImageAttachments();
   9:        return GetAttachments(providerId.Value, folderId, mailItemId);
  10:      }

Importing the RIA Service GetFolderItemImageAttachments was properly imported as an optional query for ImageAttachment.


I added an ImageAttachment visual collection in a screen fetching results from GetFolderItemImageAttachments query. Everything worked smoothly. But when the time came to load the visual collection (i.e. run the query) I got an exception I hadn’t come across before neither as a LS developer nor as a Silverlight one:

Load operation failed for query ‘GetFolderItemImageAttachments’.  The remote server returned an error: NotFound.

The behavior was very strange. Although the query was recognized and imported from LS for some reason at runtime it looked like the method was not found. I placed a breakpoint at the method and it didn’t hit. The method was never called. Before doing this I was sure it was some bug of mine in the implementation that caused the RIA service to throw this generic exception. But no! The execution never reached the web method. It was then that I decided to “google” it. Looked like it was a RIA Services+LightSwitch(?) issue. All references where either not appropriate in my case or had no effect. Then I did what I usually do when I have problem I cannot solve: I scrolled to the part of code listed above and started to just stare at the code waiting for an answer. And I came to me! Why not make sure the query method IS a query? So what I did was just add the QueryAttribute to my method with no parameters:

   1:      [Query(IsDefault = true)]
   2:      public IQueryable<ImageAttachment> GetImageAttachments() {
   3:        return new List<ImageAttachment>().AsQueryable();
   4:      }
   6:      [Query]
   7:      public IQueryable<ImageAttachment> GetFolderItemImageAttachments(Guid? providerId, string folderId, string mailItemId) {
   8:        if (!providerId.HasValue || folderId == null || mailItemId == null)
   9:          return GetImageAttachments();
  10:        return GetAttachments(providerId.Value, folderId, mailItemId);
  11:      }

I thought that if it didn’t solve the problem I surely would not cause a new one. It IS a query method after all. Why let LS infer it? And it worked.

I am quite sure I was lucky. I mean, the query was recognized either way. I cannot explain what exactly was the bug the QueryAttribute fixed. To stress my point more, I have to admit that went back to the RIA Service and I removed the attribute. Still worked! Like a deadlock resolved. Maybe only LightSwitch Team can explain. Anyhow I thought of sharing in case anyone else runs into something like this.Smile

Monday, June 11, 2012

You Are I.

Finding my application’s URI address either in deployment or development/debugging environment has been an issue I had to face in my early LightSwitch days. Although not a LightSwitch issue, but rather a Siverlight/ASP.NET one, I thought that sharing the 2 lines of code I have ended up using to discover the URI (along with the port, most important for debugging and/or standalone deployments) might be useful.
First the client. The first and easy approach was extracting the URI and port from System.Windows.Browser.HtmlPage.Document.DocumentUri. Nice! Not really. This only works for web and NOT OOB (Out of Browser) or Desktop according to LS naming, applications. System.Windows.Browser namespace is in general not available in ΟΟΒ applications.
The way I ended up adopting is accessing System.Windows.Application.Current.Host.Source.AbsoluteUri. Ok, I know it’s WPF/Silverlight way (System.Windows… I mean) but my experience says that a similar approach will be available even if HTML 5 is the next (not too soon I expect) output of LS.
Then the server. Here things are simpler and for as long as the server part of a LS application remains a Web Service the path will always be the same: HttpContext.Current.Request.Headers["HOST"].
That’s it! Short but juicy (I hope Smile).

Monday, June 4, 2012

CLASS Extensions Version 2 Fixes and Promises

Although it's been some time since my last post, I didn't quit on CLASS Extensions. On the contrary, I have been very busy working for a corporate project that uses CLASS Extensions and in the process I have made additions and fixes in CLASS Extensions. The most important fix is about Drawing business type and control so as to support standalone deployment.
As you might know, when running standalone a new host is launched every time, listening to a different port. As the drawing business type uses uris to set the drawing's background, the port active when the image was selected from the server, is included in the drawing serialization string. This means that next time the application is launched (standalone or debugging) and the port is changed the drawing's background is lost. This is fixed. Although the port is still serialized along with the drawing the port is automatically replaced with the current port of the hosting process.
There are also other small fixes regarding functionality.
Additions are to be announced officially but a (not all inclusive) sample list would include:

  • an expander group control allowing you to expand/collapse regions of your screen (both horizontal and vertical).
  • an ImageContainer group control that adds standard functionality to image editors and drawing controls to import automatically from camera and scanner (yes Del Sole's code is at the background, so before publishing I will definetly ask for permissions)
  • a printable area group control which allows to both save a snapshot of the contained screen region and/or print it.
  • a new color picker control that allows you to define a color by selecting it directly from an image using a sampler tool.
The additional features will not be released before the end of August. The price will be adjusted accordingly. Anyone that has already purchased the original version until then, they will get the new features for free earlier than official release for beta testing.