Paul Stovell

Magellan

2009-10-25T13:48:39Z

Magellan is a lightweight framework that makes it easy to build WPF navigation applications. It is inspired by the ASP.NET MVC framework. The main features are:

Model-View-Controller support
Action filters for cross-cutting concerns such as authorization and redirection
Blend behaviors to make navigation easy
Transitions between pages

Magellan was drawn from a number of samples I had put together early this year and some work done on a client project.

The source download includes an "iPhone" application for demonstrating the features.

We start with a simple project structure:

A controller implementation typically looks like this:

public class PhoneController : Controller
{
    public ActionResult Group(Group group)
    {
        var contacts = _contactRepository.GetContacts(group);

        Model = new GroupViewModel(group.Name, contacts);
        return View();
    }

Views are XAML Page objects, and can optionally have a model. Here's an example:

The idea is that upon navigation, a controller is created, the action is executed, and the view and view model are created. The view then becomes the focus of the frame. Put simply, the view and viewmodel are stateful, and the controller is stateless.

Navigation between views (with nice transitions) can be done either programatically:

Navigator.For(Frame).NavigateWithTransition("Home", "Main", "ZoomOut");

Or through Blend behaviors:

The framework supports the ASP.NET MVC concepts of Action Filters, Model Binders, View Engines and more - I'll cover them in a later post.

Enforced Strings

2009-10-09T13:02:24Z

Enterprise applications typically deal with many categories of strings. Human names, reference codes, SKU identifiers, email addresses - the list is huge. There are subtle rules that apply to many of them:

Whitespace at the start and end of many strings should probably be ignored
Human names probably shouldn't contain newlines, tab characters, the percentage symbol, or 27 dashes in a row
For some strings, casing makes no difference when deciding equality, and sometimes it does

It's common to litter our code with these assumptions, which leads to inconsistency. Sometimes we assume that the UI will handle all of these issues, and the domain layer will simply use what it's given.

Recently I have started experimenting with creating custom strings to encapsulate a lot of these subtle things. On my blog, when you browse to a URL like /enforced-strings, instead of the page name being passed around as a string, it's passed as a PageName object. PageName supports implicit conversion operators, so it can be dealt with as a regular string too. Here is part of a unit test:

PageName expected = "hello-world";

// When cast to a PageName, each of these should be converted into the above
var logicallySameAsExpected = new string[] {
    "hello-world",
    "hello-worLD",
    " hello -world ",
    " hello$-world ",
    " hello $-world ",
    " hello-$-world ",
    " hello world ",
    " -   hello   world   - ",
    " -   HeLLo  WoRLD  - ",
    " -   HeLLo  %^@#@#*()[]WoRLD  - ",
    " -   HeLLo  %^@#@#*()[]WoRLD  - $%",
    "@# -   HeLLo  %^@#@#*()[]WoRLD  - $%"
};

foreach (var match in logicallySameAsExpected)
{
    var castMatch = (PageName) match;
    Assert.AreEqual(expected, castMatch);
}

The assumption I make with PageName is that while it may be instantiated with dirty input (a malformed URL, for example), I can probably infer what was meant. PageName is used throughout my domain model and even at the data access layer - in my case, I use a custom IUserType with NHibernate to treat strings from the database as page names.

To build your own enforced strings, here are the key things to consider doing:

Create a class to wrap a real string
Make it immutable, and ideally sealed
In the constructor, massage the input string
Override all of the equality operators, GetHashCode, etc., and implement IEquatable, and IComparable
Override ToString (obviously)
Add an implicit cast operator to automatically convert from your string to real strings and back

You can see an example of this in PaulPad - first I setup a base class with most of the overloads, then I inherit from that to setup the specific string type.

jQueryPad

2009-10-08T15:19:11Z

jQueryPad is a fast JavaScript and HTML editor. Just start it, enter the HTML you want to work with, bash in your jQuery code, and hit F5 to see the results. Say goodbye to ALT+TAB.

Download

jQueryPad is xcopy deployable. It's written in WPF and uses the Web Browser Control to embed Internet Explorer for testing the script. When you press F5, the HTML and JavaScript are combined into one file and rendered. The template also references jQuery, so the jQuery functions are available.

If you want to use a different version of jQuery or reference other files, just replace the files in the Templates directory.

Hope you find it useful - feature suggestions are welcome.

Sheldon

2009-10-07T12:16:53Z

Sheldon is a WPF command line control, and code to integrate it with IronPython. It's designed as a sample that demonstrates how a WPF application might be made scriptable:

This sample was created to pitch an idea to a client about enabling a macro system in their application. Users might be able to make use of functions like OpenAccount("ACME"), ExecuteJob("SalesForecast2009"), and so on. Using the Command Pattern, commands could be written to an Output window in the application while the user uses the UI - that could be used as a learning tool for learning the command line.

The demo application shows how object models can be shared between your application and scripting environment. In C#, I set up an AutomationContext, which is made available to IronPython:

public class AutomationContext
{
    public ApplicationDefinition Application { get; set; }
    public IScriptingContext ScriptingContext { get; set; }

    public void Exit()
    {
        Environment.Exit(0);
    }
}

Then in IronPython, I create a friendly "API" that users can consume:

def GetWindow(name):
    return automation_context.Application.MainWindow
def Clear():
    automation_context.ScriptingContext.Clear()
def Exit():
    automation_context.Exit()

The ScriptingContext is an object that manages the execution and rendering of scripts, which the command line control can hook into. Multiple controls can talk to a single scripting context - here's a custom shell (I simply overrode the style and control template of the Shell control):

You can download the code here:

ZIP: Sheldon.zip
SVN: /svn/Samples/Sheldon

Editable Collection Adapter for WPF

2009-10-02T07:15:06Z

The screenshot below is of a sample WPF application that deals with editing a collection of items:

A few features:

You can make a batch of changes to the screen and hit "Save".
If you deleted items, you can click "Show deleted items" to make them visible again, then click Undo to rollback the deletion
The list on the left is bound to the same collection as the list on the right - the changes aren't written to the source until you click Save
If you change an item, it highlights in bold
If you change an item, you can undo the changes via the Undo button
If you add items to the original collection, they will appear on screen (the Remote Update button)

The object representing an individual row is just a simple POCO object with INotifyPropertyChanged support - it has no HasChanges property or similar. Likewise, the collection is just an ObservableCollection<T>.

This is all implemented with a mix of BindableLINQ and the Editable Object Adapter.

Download

Note: This sample uses the Xceed WPF DataGrid control. If you have a license, you can use your license key when running the sample (just set it in App.xaml.cs). Alternatively, you can download a 45 day trial from the Xceed website.

DelayBinding: a custom WPF Binding

2009-10-02T01:58:18Z

When you use the Outlook 2007 search, Vista's start search, or the Search bar in Explorer, there's often a short delay between when you press a key, and when the search begins.

In WPF, we could simulate this through a series of event handlers, timers and code-behind directly on controls, but we usually want to be able to use this alongside WPF's data binding capabilities. To use WPF data binding in a delayed fashion, I created a simple markup extension which creates a binding and manages the timer delay between commits.

Here's how you can use it:

<TextBox Text="{z:DelayBinding Path=SearchText}" />

You can also set an explicit delay. By default, it uses 0.5 seconds, which felt consistent with Outlook, though I didn't spend that much time working out exactly how long Outlook waits. I did look to see if there was a SystemParameters class for something like "SearchDelay", but couldn't find one. Suggestions for a better default are welcome.

<TextBox Text="{z:DelayBinding Path=SearchText, Delay='00:00:01'}" />

Instead of creating a new type of Binding, I'm using the standard WPF Binding, but setting the UpdateSourceTrigger to Explicit. As the text changes, the timer is reset, and when it ticks the value is pushed to the source.

After the short delay:

First, the code to the markup extension (XML-doc comments removed):

[MarkupExtensionReturnType(typeof(object))]
public class DelayBindingExtension : MarkupExtension
{
    public DelayBindingExtension()
    {
        Delay = TimeSpan.FromSeconds(0.5);
    }

    public DelayBindingExtension(PropertyPath path) 
        : this()
    {
        Path = path;
    }

    public IValueConverter Converter { get; set; }
    public object ConverterParamter { get; set; }
    public string ElementName { get; set; }
    public RelativeSource RelativeSource { get; set; }
    public object Source { get; set; }
    public bool ValidatesOnDataErrors { get; set; }
    public bool ValidatesOnExceptions { get; set; }
    public TimeSpan Delay { get; set; }
    [ConstructorArgument("path")]
    public PropertyPath Path { get; set; }
    [TypeConverter(typeof(CultureInfoIetfLanguageTagConverter))]
    public CultureInfo ConverterCulture { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var valueProvider = serviceProvider.GetService(typeof (IProvideValueTarget)) as IProvideValueTarget;
        if (valueProvider != null)
        {
            var bindingTarget = valueProvider.TargetObject as DependencyObject;
            var bindingProperty = valueProvider.TargetProperty as DependencyProperty;
            if (bindingProperty == null || bindingTarget == null)
            {
                throw new NotSupportedException(string.Format(
                    "The property '{0}' on target '{1}' is not valid for a DelayBinding. The DelayBinding target must be a DependencyObject, "
                    + "and the target property must be a DependencyProperty.", 
                    valueProvider.TargetProperty, 
                    valueProvider.TargetObject));
            }

            var binding = new Binding();
            binding.Path = Path;
            binding.Converter = Converter;
            binding.ConverterCulture = ConverterCulture;
            binding.ConverterParameter = ConverterParamter;
            if (ElementName != null) binding.ElementName = ElementName;
            if (RelativeSource != null) binding.RelativeSource = RelativeSource;
            if (Source != null) binding.Source = Source;
            binding.ValidatesOnDataErrors = ValidatesOnDataErrors;
            binding.ValidatesOnExceptions = ValidatesOnExceptions;

            return DelayBinding.SetBinding(bindingTarget, bindingProperty, Delay, binding);
        }
        return null;
    }
}

Now the DelayBinding class, which as you can see above is being instantiated by the DelayBindingExtension. You could also create it manually in code:

public class DelayBinding
{
    private readonly BindingExpressionBase _bindingExpression;
    private readonly DispatcherTimer _timer;

    protected DelayBinding(BindingExpressionBase bindingExpression, DependencyObject bindingTarget, DependencyProperty bindingTargetProperty, TimeSpan delay)
    {
        _bindingExpression = bindingExpression;

        // Subscribe to notifications for when the target property changes. This event handler will be 
        // invoked when the user types, clicks, or anything else which changes the target property
        var descriptor = DependencyPropertyDescriptor.FromProperty(bindingTargetProperty, bindingTarget.GetType());
        descriptor.AddValueChanged(bindingTarget, BindingTarget_TargetPropertyChanged);

        // Add support so that the Enter key causes an immediate commit
        var frameworkElement = bindingTarget as FrameworkElement;
        if (frameworkElement != null)
        {
            frameworkElement.KeyUp += BindingTarget_KeyUp;
        }

        // Setup the timer, but it won't be started until changes are detected
        _timer = new DispatcherTimer();
        _timer.Tick += Timer_Tick;
        _timer.Interval = delay;
    }

    private void BindingTarget_KeyUp(object sender, KeyEventArgs e)
    {
        _timer.Stop();
        if (e.Key == Key.Enter) _bindingExpression.UpdateSource();
    }

    private void BindingTarget_TargetPropertyChanged(object sender, EventArgs e)
    {
        _timer.Stop();
        _timer.Start();
    }

    private void Timer_Tick(object sender, EventArgs e)
    {
        _timer.Stop();
        _bindingExpression.UpdateSource();
    }

    public static object SetBinding(DependencyObject bindingTarget, DependencyProperty bindingTargetProperty, TimeSpan delay, Binding binding)
    {
        // Override some specific settings to enable the behavior of delay binding
        binding.Mode = BindingMode.TwoWay;
        binding.UpdateSourceTrigger = UpdateSourceTrigger.Explicit;

        // Apply and evaluate the binding
        var bindingExpression = BindingOperations.SetBinding(bindingTarget, bindingTargetProperty, binding);

        // Setup the delay timer around the binding. This object will live as long as the target element lives, since it subscribes to the changing event, 
        // and will be garbage collected as soon as the element isn't required (e.g., when it's Window closes) and the timer has stopped.
        new DelayBinding(bindingExpression, bindingTarget, bindingTargetProperty, delay);

        // Return the current value of the binding (since it will have been evaluated because of the binding above)
        return bindingTarget.GetValue(bindingTargetProperty);
    }
}

I imagine this would be useful for Silverlight, but since Silverlight does not support custom MarkupExtensions, and since Silverlight Binding's can't have an UpdateSourceTrigger (to set it to Explicit), I expect you would end up creating it through an attached dependency property and triggering the binding to push manually. Let me know if you write one.