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The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.

Actually, as I'm self-employed, I guess that means that any views I expressed here aren't my own. That's confusing!


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Theme modified from one by Tom Watts
C#/F# code styling by Manoli (for posts pre-2016) and Google code prettify (for post from Jan 2016 and beyond)


My rambling thoughts on exploring the .NET framework and related technologies

# Tuesday, 13 January 2015

My regular reader may remember that I wrote a while ago that my computer laughs at me. Well, it lies to me as well.

Bored of the usual methods of inflicting torture upon myself, I thought I would upgrade SQL Server 2008 R2 to SQL Server 2014 (stop laughing at the back!), because, erm, well it seemed like a good idea at the time.

First problem was that in order to upgrade, I had to apply service pack 2 to my existing SQL Server 2008 R2 installation. Why? No idea. I would have thought that if I were about to upgrade, it should have all of the later goodness in the upgrade, but who am I to question the ways of the wise?

So, I downloaded SP2 and set it going. Part way through, I got an unhandled .NET exception (nice one Microsoft, very professional), and when I clicked Quit, it continued with the installation! Still, as it seemed to work, I didn’t complain, but I was a bit annoyed that it lied to me. Computers aren’t supposed to do that.

Once I had SQL Server 2014 installed, I happened to notice that SQL Server 2008 R2 was still installed. Huh, I thought we upgraded to 2014? Shouldn't it have uninstalled 2008 R2? Well, I would have thought so too, but that just shows how much we know eh? If you have Visual Studio 2013 installed, you may well have SQL Server 2012 installed as well! Good job disk space is cheap nowadays.

Having asked about this in an SQL Server forum, I was told it was safe to uninstall anything related to SQL Server 2008 R2. Whilst doing so, I came across one component that gave me a message saying that SSMS 2014 depended on it, and if I uninstalled it, that would stop working. I clicked "No" to say I didn't want to uninstall this component, but it uninstalled it anyway! Didn't seem to matter, as SQL Server worked fine afterwards, so it just shows what liars they are!

I’m very disillusioned. No wonder the world is sinking into moral decay if you can’t even rely on your computer to tell you the truth!

Tuesday, 13 January 2015 20:49:00 (GMT Standard Time, UTC+00:00)

As my regular reader will know, when Lightswitch came out, I was quickly hooked. Like many people, I saw an answer to the hassle of creating n-tier desktop applications. It was a dream. Development time was slashed, and the few annoyances that there were paled into insignificance compared to the speed of development, and the quality of the end product.

I dived in head-first, and quickly came up against some of the limitations of a first version. That’s not a criticism, it’s more a testimony to the amazing power the first version had, that we could produce real LOB applications, and were frustrated by the missing bits.

Thankfully, Microsoft did a sterling job of adding extensibility points to Lightswitch, and despite the poor documentation (an ongoing feature of Lightswitch that caused a lot of wasted hours), the potential was there to fill in the gaps.

Inspired by early experimenters, like Yann Duran’s excellent Luminous Controls (which I still use in every Lightswitch project), I had a go at producing a custom control for Lightswitch, more for the fun of tinkering than anything else. Having worked out how to get going, I added a few more controls, until the first version of the Pixata Custom Controls For Lightswitch was born. Feeling that I had something that might be of use to others, I added it to the Visual Studio Gallery, and posting about it in the (now extinct) forum. I got so excited when it had 100 downloads!

Spurred on by the great feedback, I added more controls, and the control suite hit the top three for Lightswitch extensions. It varied between the first, second and third places, but has always been in the top three. To date, it’s had over 25,000 downloads, despite that the fact that I haven’t updated the controls for over a year.

Roll on a few years, and the mobile market exploded. Smartphones and tablets gained more power, and were able to browse the web almost as well as their desktop cousins. However, probably due to political more than technical reasons, the manufacturers chose not to support Flash or Silverlight on these devices, leaving Lightswitch out in the cold.

Microsoft, fairly understandably, decided to concentrate their efforts on producing a version of Lightswitch that would support mobile devices. That's where the HTML client came in.

This was fine, except for two huge problems...

1) The HTML client was (and still is from what I can see) woefully short of being ready for the job. It's a good start, but not good enough to create LOB applications. Specifically, despite the massive growth of the mobile market, Microsoft seem to have forgotten that the desktop world still exists, and still accounts of a very significant number of users, especially in the business world. Until the HTML client supports the desktop, it can't be considered ready for serious use.

I have other misgivings about the HTML client, but they are minor in comparison to this one. I know the mobile market is important, but in business-to-business work, which is a significant part of the software development world, you just can’t afford to ignore the desktop.

2) Whilst I don't think we can criticise Microsoft for moving away from Silverlight, which must have been hard for them, having put so much effort into producing a first-class product, what is totally unforgiveable (in my opinion at least, and I know I'm not alone) is the way they just dumped the Silverlight developers without any support. Their support for the more advanced side of Lightswitch was always poor, but when the HTML client came along, Silverlight client developers were just ignored completely. The extensibility forum died a sudden death, with unanswered questions making up the sum total of all posts.

Now, before I get criticised for this, I understand that they have limited resources, and want to concentrate their efforts on the latest and greatest, but many, many developers sunk a large amount of time and energy into Silverlight-related development, and to have all support cut off in an instant was a really dirty trick. I think we can all understand why they don’t want to invest more time in active development, but at least support what’s already there.

The problem became more acute as time went on, and Microsoft were pushing the HTML client with an evangelical fervour. It got to the stage where I knew that if I had a problem, there was little point in posting in a forum, as my post would be swallowed in a sea of HTML-related questions, and wouldn’t be answered by anyone at Microsoft anyway. The only way I could get an support was peer-to-peer support from some of the Lightswitch rock stars.

It came to a head for me recently when, having invested a significant amount of time in developing a complex application, it suddenly stopped working. The only clue I had was the rather generic error message “Cannot communicate with the database” when the application started. It worked fine on my development machine, and the database connections were all correct (I could even change the connection strings in Visual Studio, and run the application against the remote production database, so I know that wasn’t the problem), but the deployed version refused to work.

After struggling to get the attention of any Microsoft support person, I eventually had to give up and rewrite the entire application in WPF and ASP.NET WebAPI2. Surprisingly, it didn’t actually take that long, and left me wondering if Lightswitch is really as RAD as I had thought, once you get away from the basic functionality.

So, I’m left with a sour taste in my mouth, and some deployed Lightswitch applications that I’m terrified to touch, in case they mysteriously stop working as well. I can’t afford to rewrite them from scratch, and know that there is no way I’ll get any support if they stop working. I’m just hoping the customers don’t want any changes.

Sad end to a promising product. I have little interest in investigating the HTML client, as ASP.NET MVC makes it so easy to produce high-quality web sites that work in both desktop and mobile environments, and I can’t see any benefits in Lightswitch for this.

As for the controls? Well, I’ve made them open source, so if anyone wants to develop them further, they can.

Sunday, 14 December 2014 15:01:00 (GMT Standard Time, UTC+00:00)

Last February, I hit a problem where I was trying to implement printing from a Lightswitch screen, and was using what has now become known as the Command Table Pattern, which allows the Lightswitch client to send a command to the server. I was encountering an error with the witty message “A new instance of the EntityObject class cannot be initialized because the ambient IDataWorkspace is not available. Please use the constructor that specifies an EntitySet” which was as clear as mud to me!

I asked about this in the Lightswitch forum, and was greatly helped by the ace Lightswitch insider Justin Anderson, who patiently explained that the problem I was facing was to do with threads, dispatchers and workspaces. This area is one of those that seems to trip up a lot of people when they start digging into Lightswitch, and is very poorly documented. The few articles I have seen are fairly difficult to understand, which only compounds the problem. Thanks to Justin’s help, I got my code working, and got a better understanding of the subject.

Well, a few weeks ago, Steve added a comment to that forum post, as he was having a very similar problem when trying to create a new entity in the Click event handler of my Pixata Static Toolbar control. As I tried to explain what the problem was, I ended up explaining threads, dispatchers and workspaces, as he had hit exactly the same lack of understanding of these that led me to make the post in the first place.

He seemed to like my explanation, so I decided to post it here, as it may help someone else. Let me say in advance that this is not a comprehensive explanation, nor is it totally accurate, because it's a complex subject and I want to try and explain it in a way you'll understand. If any Lightswitch gurus are disgusted at my explanation, please feel free to leave a comment below, or email me Smile

Let’s deal with threads first...

In order to keep the UI responsive, Lightswitch uses two threads (think of two small men inside your PC, each one doing something different, but talking to each other to keep their work in synch). The main thread, let's call him Fred, handles getting data from the server and sending it back again. The other thread, whom we'll call Jim (because Jim is a good name) handles the UI stuff, like making sure the textboxes and comboboxes are drawn on the screen, and contain the right data.

When you do things like typing, choosing from a combobox, etc, you are talking to Jim. When you hit the Save button, this sends a message to Fred. You don't talk to Fred directly like you do to Jim, as Fred is in the background, round the back of your monitor where all the dust and dead flies collect, so when you click the Save button, what really happens is that Jim sends Fred a message saying "Here Fred, this one is for you." When Fred gets the message, he sends the data to the database for you.

The tricky bit is that there are two ways that the user tells Lightswitch what to do. One is through commands, which is how you work when you add a method to the screen (Click the "Add Data Item" button and choose "Method"). This sets up a command that just tells Jim to send a message to Fred, and have Fred do the work. However, if you capture control events, such as a button's Click event, then you are asking Jim to do the work himself, and not get Fred involved at all (he's cleaning up the dead flies while he's nothing better to do).

If that hasn't confused you, then you might have a very general (and rather flippant) idea of how threads work. When you are in a method created as a data item, you are talking to Fred, and Lightswitch creates a DataWorkspace for you. When you are in a control event handler, you are talking to Jim, and there isn't a DataWorkspace around. If you want one, you have to create one.

Aside: As my regular reader will know, I’m a huge fan of Lightswitch, but I do have one big gripe with it, and I think this is the cause of a lot of confusion to new Lightswitch programmers. In the name of good software design, Microsoft used the MVVM pattern when building Lightswitch. This is a familiar pattern to WPF and Silverlight programmers, and (like MVC and MVP before it), allows a clean separation of the business layer from the UI layer.

Now, in a normal (ie WPF or Silverlight application), the view model is in a completely separate file from the view. Thus, command methods are nowhere near control event handlers, which helps keep the separation clear in the mind of the programmer.

However, in Lightswitch, the view model code is in the same file as the screen’s code, meaning that you have methods sitting right next to each other that are actually going to be executing on different threads. I think this is a very bad idea, and seems to be the source of many problems I’ve seen in the forums.

Anyway, gripe over, back to Fred and Jim...

So, if we have two threads, how do they communicate? That’s where dispatchers come in. Dispatchers are a way of having Fred pass work to Jim and vice versa.

Certain tasks need to be done by Fred, as he works with the data. However, if you are inside a control event handler, then you are talking to Jim. So, what you need to do is ask Jim very politely if he will send a message to Fred asking him to do the work. That's where dispatchers come in.

You have two dispatchers, one that passes (ie dispatches) the work to Fred (also known as Main, as he handles the main work), and one that passes the work to Jim (known as Details). Remember, when you're writing code in a control event handler, you're talking to Jim, ie to the Details thread. For example, if you are in a control’s event handler, and you want to create a new entity (as Steve was), you need to pass the job to Fred, meaning that you need to use the Main dispatcher.

In Steve’s case, he didn't actually need a dispatcher, as he could have handled the problem a different way, but if he had, he would have needed the Main dispatcher, as he was already talking to Jim (remember the code was in a control event handler), and he wanted to pass the work to Fred. In such a case, you would do something like this...

    Dispatchers.Main().BeginInvoke(Sub() 
      ' code for Fred to do goes here 
    End Sub)

(Note that Steve was working in Visual Basic.NET, which is why I departed from the norm and didn’t use C# above)

I hope this has helped. If it's any consolation, I think dispatchers are about the most complex bit of Lightswitch there is. Hopefully, if you read the above a few times, it might make some sense. If you run into exceptions to do with threads, chances are you need a dispatcher. There are two ways to work out which one you need to use. The first is good old trial and error! Try one, and if it doesn't work, try the other. This isn't really a good approach, as you don't really get to understand what you're doing. The second approach is to keep reading and trying to understand it until it goes in.

The easiest way to think about it, which will probably work for you in most cases, is that if you are coding in an event control handler, then if you need to dispatch, you use Dispatchers.Main().BeginInvoke. If you are in a data item method, then you will need to dispatch using Me.Details.Dispatcher.BeginInvoke.

Although the DataWorkspace side of this issue is less commonly encountered, I might as well add on a quick overview of that, as it was relevant to the forum post. In simple terms, the DataWorkspace is what you use when dealing with data in Lightswitch, and one is created for you in the view model. However, when working in the screen’s code-behind, you don't have one, which is why the error message shown at the top appears. If you need to access data from an event handler, you’ll probably need to grab your own DataWorkspace.

In my original case (which is the same as Steve’s), I was trying to create a new entity. The entities that Lightswitch creates from your database have a parameterless constructor that uses the ambient DataWorkspace, meaning the one that Lightswitch creates for you (ambient = hanging around counting dead flies, waiting for you to do something that it knows about). If you are in a view model, then this works fine, which is why you generally don’t have to worry about DataWorkspaces, as most of your code should be written in the view model.

However, sometimes you need to do this stuff in event handlers, and you don’t have an ambient DataWorkspace hanging around. In this case, you need to use another entity constructor that takes a DataWorkspace as a parameter. In my case, this meant doing this...

  new InvoiceAction(this.DataWorkspace.MyAppData.InvoiceActions);

All this does is grab hold of a DataWorkspace explicitly, and pass it to the entity’s constructor. Once you know about this, the error message at the start of this article makes more sense, but when you first encounter it, your eyes start to glaze over, and you wonder why there are so many dead flies behind your monitor (Fred has been too busy dealing with your errors to clean them out).

I hope this has been helpful to someone! If you have any comments, or would like to hear how Fred and Jim are getting on, please click the “Comments” link below and let me know.

Thursday, 29 November 2012 15:51:00 (GMT Standard Time, UTC+00:00)
# Tuesday, 30 October 2012

This one amused me...

protected void On_DayLoad(object sender, EventArgs e) {
  Beverage coffee = new Beverage("coffee");
  coffee.Add(Beverage.Sweetener.Sugar);
  coffee.Cream = false;
  Cup mug = new Cup();
  mug.Add(coffee);
  Me.Consume(mug);
  mug.Dispose();
}

Of course, you could argue that the hard-coded string in the Beverage class constructor is bad design, but it’s only a joke eh?

This one is an old one, but I liked the variation of answer...

Question: How many programmers does it take to change a light bulb?

Answer 1: None, it's a hardware issue

Answer 2: A properly designed light bulb object would inherit a Change() method from a generic base Lighting class, so all you'd have to do is send a light bulb change message

Tuesday, 30 October 2012 14:00:00 (GMT Standard Time, UTC+00:00)

Why a toolbar control?

A month ago, I posted an article showing how to create a custom toolbar for a Lightswitch application. At the time, I thought that this was so easy that there was little point in creating a control extension for it. However, the more I thought about it, the more I realised that whilst it’s very easy for an experienced programmer, it wouldn’t be quite so easy for someone with less experience. Furthermore, easy as it was, it still requires you to build the toolbar yourself and write the code.

This niggled me enough to have a go at creating a control extension to implement the toolbar. Along the way I learned some new Lightswitch tricks, and ended up with a control that’s even easier to use than writing your own!

You’ll need the latest version (1.15, published today on the Visual Studio Gallery) of the control extension to follow along. Imagine we have a Lightswitch application that maintains contact details for ferrets (as you do!). We have a list and details screen that displays the ferrets’ information, and want to add a toolbar above the details side to allow the user to change the selected ferret’s name. This is a contrived example, but was the best I could think up on the spur of the moment and with little sleep! For a more realistic example of why you might want a toolbar, see my previous blog post.

Here’s a screen shot of what we’re aiming for...

A static toolbar in action

Regular readers will recognise the dear elephant that has graced this blog several times. The other icons come from my usual source, www.findicons.com, although I recently discovered some great free icons at www.proicons.com. One of the good things about that site is that the icons are organised into themes, rather than being a random collection of individual icons like www.findicons.com. Anyway, you can see that the toolbar above has five buttons, three with just an image, one with an image and text, and one with just text. The Pixata Static Toolbar control allows you to choose how your button will look (including completely restyling it if you want, see later).

Using the toolbar control

To use the control, click the “Add A Data Item” button on the Lightswitch designer window, and add a new Local Property. As with all the static controls, this is merely to get around the Lightswitch limitation of requiring all controls to be bound to something, so you can leave it as a string (uncheck the “Is Required” checkbox) and name it anything you like. I tend to call mine StaticProperty, as it helps me remember what it is when looking at the designer, but you can call it anything you like.

Drag this property onto the designer wherever you want the toolbar to appear, and change the control type to Pixata Static Toolbar control...

Choosing the Pixata Static Toolbar control

Setting the button properties

Have a look in the Properties panel. The first three properties apply to all buttons in the toolbar. The “Image width” and “Image height” properties set the size of the images to be displayed on the buttons. For simplicity (and to make the toolbar look nicer), you have to set the one width and one height, and this will be used for every button. Next you can set the margin for the button. The default is “0,0,5,0” which gives 5 pixels space to the right of each button, so they don’t squash right up next to each other. You change this to whatever you like, but the default setting is probably all you’ll ever need.

After that, you’ll see five groups of properties that look like this...

The properties for a button

Unfortunately, I don’t think there is any way to group these visually, but you’ll see that there are five sets of identical properties. The checkbox specifies if the button is displayed or not. The toolbar allows you up to five buttons, but also allows you less by clearing the checkboxes. If you want more than five buttons in a toolbar, just add two of them.

The link below the checkbox allows you to select the image that will be used for the button. The text for the button is shown next. If you just want an image on the button (like in the 1st, 3rd and 5th buttons in the screen shot at the top of this post), then leave this property blank. If you choose an image and enter text, you’ll end up with both, like the 2nd button in the screen shot earlier. If you just enter text and don’t choose an image, then you’ll end up with a text-only button, like the 4th button above. This last option isn’t that exciting, as you can do this in Lightswitch alone.

The tooltip is the text that will be displayed when your mouse hovers over the button. In the screen shot earlier, my mouse (which you can’t see) was hovering over the 2nd button, and the tooltip text is displayed.

The “Tag text” property allows you to set the tag of the button to a string. The purpose of this will be explained below.

Handling the button click event

The only other thing you need to do is to handle the event when a button is clicked. This is the only place you need to write code to use this control. Click the “Write code” button in the screen designer, and choose the ScreenName_InitializeDataWorkspace event. The first thing you need to do is add the following line at the top of the file...

using PixataCustomControls.Presentation.Controls;

Then add the following lines inside the event handler that was created for you...

partial void FerretsListDetail_InitializeDataWorkspace(List<IDataService> saveChangesTo) {
  var toolbar1 = this.FindControl("FerretToolbar");
  toolbar1.ControlAvailable += (S, E) => {
    StaticToolbar stb = ((StaticToolbar)E.Control);
    stb.ButtonClick += new System.EventHandler<StaticToolbarEventArgs>(FerretToolbar_BtnClick);
  };
}

My toolbar is called FerretToolbar, so unless you’ve chosen the same name (welcome fellow ferret fan!), you’ll need to change that to match what you chose. By default, Lightswitch will name it after your static property, but you can change this to something more meaningful.

When the ControlAvailable event fires, the code above grabs the toolbar control (which I’ve stored in a local variable called stb), and then subscribes to the ButtonClick event, which will be fired whenever someone clicks one of the toolbar buttons. To make life easier, I only added one event instead of five.

All you need now is the event handler. Here is a sample...

void FerretToolbar_BtnClick(object sender, StaticToolbarEventArgs e) {
  FerretsSet.SelectedItem.Name = e.TagText;
}

This simple example simply updates the selected ferret’s name to the tag text of the button that was clicked. If your application requires similar behaviour for each button, then using the tag text is a great way to simplify the code. This is similar to the way I inserted standard text in the previous blog post. If you don’t set the tag text, then this will set the name to the empty string.

If you want to have your buttons do distinct things, then this isn’t necessarily the best way to go, as the tag text doesn’t give enough flexibility. In this case, you can just check which button was clicked, and branch appropriately. The ButtonClick event takes a StaticToolbarEventArgs object, that contains the tag text (as shown above), as well as the number of the button. Note that the buttons are numbered one to five and NOT zero to four, as I thought that was too confusing for the general user.

Here is a sample of how to handle this case...

void FerretToolbar_BtnClick(object sender, StaticToolbarEventArgs e) {
  switch (e.ButtonNumber) {
    case 1:
      DoButtonOneStuff();
      break;
    case 2:
      DoButtonTwoStuff();
      break;
  }
}

I’ve only shown two cases here to save some space, but it would work the same if you use more buttons.

Modifying the buttons as much as you like

I know that there are people out there who will immediately ask me if they can get hold of the individual buttons, so they can customise them like crazy! Well, I’m one step ahead of you! The control exposes an indexer, which allows you to get the actual buttons on the toolbar. Once you have the toolbar itself (as I did in the FerretsListDetail_InitializeDataWorkspace event handler earlier), you can just do this...

stb[1].Content = "New Text For Button #1";

This rather pointless example shows you how to set the Content for the button to a plain string. As mentioned above, you can do this from the Properties panel without needing code, or you can use a regular Lightswitch button (generated when you drag a method onto the designer surface). However, the point here is that stb[1] is the actual button, so you can do anything to it that you could do to a normal button, including replacing the Content with something of your own invention. I can’t think of any suitably weird example, so I’ll leave that to you dear reader!

Note again that the buttons are numbered from one to five, so if you attempt to access button zero, you will get an IndexOutOfRangeException exception.

One small niggle

One thing I found was that if you want a toolbar with more than five buttons, and you use two of my static toolbar controls next to each other, Lightswitch helpfully adds three pixels of blank space between them. It does this to all controls, so they don’t get all squashed up, but in this case, it is not desirable. I contemplated hacking around to try and remove these three pixels, but decided it wasn’t worth the effort, especially as most toolbars will not have more than five buttons that need to be together. You generally find that toolbars have their buttons in smaller groups, with a vertical divider between the groups. You can do this easily by using several static toolbar controls, and separating them with the Pixata Vertical Divider control. You’ll need to add something between the divider and the next toolbar, so that Lightswitch adds its three pixels. The easiest way to do this is use a Pixata Spacer Control, with the width set to zero.. .

The 1st and 4th controls in that Columns Layout are two static toolbars. The second control is the vertical divider (width set to 1), and the 3rd control is a spacer whose width is zero.

The result of this looks like this...

I hope you find this new control useful. As usual, if you have any comments or questions, please leave them on the Visual Studio Gallery page.

Update 24th Sept ‘12

For those using VB.NET, here is a sample of an entire screen code that does pretty much the same as the code above.

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Imports PixataCustomControls.Presentation.Controls

Namespace LightSwitchApplication

Public Class Customers

Private Sub Customers_InitializeDataWorkspace(saveChangesTo As System.Collections.Generic.List(Of Microsoft.LightSwitch.IDataService))
  AddHandler Me.FindControl("FerretToolbar").ControlAvailable, AddressOf FerretToolbar_ControlAvailable
End Sub

Private Sub FerretToolbar_ControlAvailable(sender As Object, e As ControlAvailableEventArgs)
  Dim FerretToolbar As StaticToolbar = TryCast(e.Control, StaticToolbar)
  AddHandler FerretToolbar.ButtonClick, AddressOf FerretToolbar_ButtonClick
  ' Set properties here if you like
End Sub

Private Sub FerretToolbar_ButtonClick(sender As Object, e As StaticToolbarEventArgs)
  Customers1.SelectedItem.Name = e.TagText
End Sub

End Class

End Namespace
Sunday, 03 June 2012 14:48:00 (GMT Daylight Time, UTC+01:00)