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New Post: Binding RelativeSource

throb — Tue, 22 Sep 2009 02:00:15 GMT

Hi Vinay,

the Path in Bindings in WPF and Silverlight are searched from a sertain source. This source can be:

Given explicitly using the Source attribute in the binding.
Given explicitly using the ElementName attribute in the binding. This refers then to the object in the same namingscope as the element you set the binding on, with the specified name.
Given relatively to the object you define the binding on using RelativeSource. (a bit limited in silverlight)
Using the default which is the 'DataContext' of the element you set the binding on. This DataContext is passed from parent to child unless overriden on a given element.

In the example the DataContext was overriden on the top-level element (UserControl), after which it was passed on to all it's children. The TextBox was a child of this UserControl and therefore inherited this DataContext. As you noticed this DataContext was set to the UserControl itself. This makes sense because the properties we wanted to bind to are on the UserControl (code behind). The Path in the binding then simply needed to refer to the Sum property of the UserControl and then the Value.

Different way would have been to set a name on the UserControl and use ElementName in the binding.

<UserControl x:Class="Poc.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    mc:Ignorable="d" d:DesignWidth="640" d:DesignHeight="480"
    Name="TopDog"
    >
  <Grid x:Name="LayoutRoot">
        <TextBox Text="{Binding ElementName=TopDog, Path=Sum.Value}" />
    </Grid>
</UserControl>

There are also some special things you can do in the path of a binding that has to do with the currently selected item in a view source. What way is best in your situation I don't know. Sometimes it can be quite tedious to get right. I do know that WPF/Silverlight programming is a lot about data binding. So my best advice is still to get a good book and study all the options and details.

Hope this helps and Regs,

Thomas.

New Post: Binding RelativeSource

vkapoorjefco — Mon, 21 Sep 2009 13:20:33 GMT

In the sample you sent, if the DataContext is not set to RelativeSource Binding the information is not even displayed. I was nt sure if that was how it was intended. I was trying to implement the same on a Textblock included in a template (A Header template within a datagrid). However, in that case the binding does nt seem to pick up.

Thanks

New Post: Binding RelativeSource

throb — Sat, 19 Sep 2009 05:29:05 GMT

Hi Vinay,

No, there is no special need for the DataContext to be set like that. It is just a way to bind to the desired values. Any valid binding will work. The obtics properties are just normal properties.

But that is all standard WPF / Silverlight stuff. I'd suggest grab a good WPF / Silverlight book because there are may options.

Regards,

Thomas.

New Post: Binding RelativeSource

vkapoorjefco — Fri, 18 Sep 2009 15:36:07 GMT

Thomas,

Is there a specific reason why the Binding to an element needs to be

DataContext="{Binding RelativeSource={RelativeSource Self}}

This works if I have a textblock within the main grid. However, if i have a textblock within a Template of a datagrid, it does not seem to bind.

On a similar note, is there also a way to Bind the ExpressionObserver over a PagedViewCollection or the DataContext of a control e.g. a Datagrid. I am trying to bind a datagrid to a PagedCollectionView which inturn is binded to an ObservableCollection. However, I need to track the current view shown by the PagedCollectionView (after a filter is applied / a different page is being viewed).

Thanks again for the help.

Vinay

New Post: Notifications for simple queries are not fired

throb — Tue, 15 Sep 2009 12:50:28 GMT

Hi,

That can be explained as follows:

Obtics is a concurrent system and it assumes that when you get the enumerator before you register for change events that you "missed all the events in between" and therefore do not have a valid base collection to apply all subsequent incremental changes to. It can also be interpreted as "You were temporarily not interested in changes to this result". So kicking the observable linq query to send change events is only valid when you have at least one listener attached.

Btw. in the list in my previous posting containing all the 'Will not send' points; It should actually be read as 'May not send'.

Regs,

Thomas.

New Post: Notifications for simple queries are not fired

arconaut — Tue, 15 Sep 2009 07:24:53 GMT

Thanks Thomas,

It's clear now why enumerator has to be called, but I still don't understand why I have to subscribe at least once before calling the enumerator.

Maybe the answer is in your explanation, but apparently i didn't find it :)

New Post: Notifications for simple queries are not fired

throb — Mon, 14 Sep 2009 22:09:42 GMT

Hi,

This may surprise you but it is actually by design.

The idea is that most of those CollectionChanged events (except the Reset event) are incremental changes on a given base collection. This base collection can be aquired using the enumerator. Without first getting this base collection the incremental change events wouldn't make sense. The Observable linq queries will hold back change events untill at least some client has read (aquired the enumerator) the base collection.

Observable sequences that are (temporarily) not used do not send change events. This may seem silly but leads to some very nice optimizations.

Naturaly this has NOT been documented (I sooo badly need a user guide; just too much to do).

Observable Linq queries will not send change events untill some client aquires its enumerator
Observable Linq queries will STOP sending change events after sending a RESET event, untill some client aquires its enumerator again
Observable Values will not send change events untill some client reads its value and then only one until some client reads it again.

When manually registering for CollectionChanged events make sure that:

you read the contents from the same object instance as the one where your registered for change events.
make sure you unregister from the same object instance when your are done listening and DO unregister.

Obtics will try it's hardest to return the same object instance at each call to 'c.Orders' but it is not a quarantee. Better store an instance in a field and use that.

For those, I suspect rare cases where you want to know when the results of an observable linq query changes without actually being interested in the query contents itself; I'd suggest you create a nice extension method that would return an object with a 'Changed' event and that does all the 'not so pretty' stuff under the hood. That shouldn't be to hard and when you have it, with your permission, I would like to refer to it in the wiki.

Hope this clarifies it a bit and any sugestions are very welcome.

Regs,

Thomas

New Post: Notifications for simple queries are not fired

arconaut — Mon, 14 Sep 2009 16:09:54 GMT

Hi!

We've been trying to use the Obtics framework but got stuck with some problems. The problem seems to be quite strange.

I can email the complete 'dummy' project which is buildable and shows the problem very clearly.

It's a simple WPF project, with one window, which does nothing and holds only one listbox. ListBox is only there to check how Obtics works with WPF - and just as declared, it works fine.

ListBox is supposed to show all Orders (exposed by a property, which getter returns an Obtics query) of one Customer created on Window_Loaded. The p roblem is when I try to catch notifications in code myself. Somehow notifications are fired only when I enumerate the property after the subscription.

Here's the code:

public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            Loaded += new RoutedEventHandler(Window1_Loaded);
        }

        void Window1_Loaded(object sender, RoutedEventArgs e)
        {
            Customer c = new Customer { CustomerId = 1 };
            //lstOrders.DataContext = c;                    // When uncommented, binding works fine

            ((INotifyCollectionChanged)c.Orders).CollectionChanged += CustomerOrders_CollectionChanged;
            c.Orders.GetEnumerator().MoveNext();            // If you comment this, or move it before the subscription - notifications are not received

            Order.AllOrders.Add(new Order { OrderId = 1, DueDate = DateTime.Now, CustomerId = 1 });
            Order.AllOrders.Add(new Order { OrderId = 2, DueDate = DateTime.Now, CustomerId = 1 });
            Order.AllOrders.Add(new Order { OrderId = 3, DueDate = DateTime.Now, CustomerId = 2 });
            Order.AllOrders.Add(new Order { OrderId = 4, DueDate = DateTime.Now, CustomerId = 1 });
        }

        void CustomerOrders_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            MessageBox.Show("Orders collection modified");
        }
    }

public class Order : INotifyPropertyChanged
    {
        protected int _OrderId;
        public int OrderId
        {
            get { return _OrderId; }
            set
            {
                if (_OrderId != value)
                {
                    _OrderId = value;
                    RaisePropertyChanged("OrderId");
                }
            }
        }

        protected DateTime _DueDate;
        public DateTime DueDate
        {
            get { return _DueDate; }
            set
            {
                if (_DueDate != value)
                {
                    _DueDate = value;
                    RaisePropertyChanged("DueDate");
                }
            }
        }

        protected int _CustomerId;
        public int CustomerId
        {
            get { return _CustomerId; }
            set
            {
                if (_CustomerId != value)
                {
                    _CustomerId = value;
                    RaisePropertyChanged("CustomerId");
                }
            }
        }


        protected static ObservableCollection<Order> _AllOrders = new ObservableCollection<Order>();
        public static ObservableCollection<Order> AllOrders
        {
            get
            {
                return _AllOrders;
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void RaisePropertyChanged(string name)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(name));
        }

    }

public class Customer : INotifyPropertyChanged
    {
        protected int _CustomerId;
        public int CustomerId
        {
            get { return _CustomerId; }
            set
            {
                if (_CustomerId != value)
                {
                    _CustomerId = value;
                    RaisePropertyChanged("CustomerId");
                }
            }
        }

        public IEnumerable<Order> Orders
        {
            get 
            {
                return from o in Order.AllOrders
                       where o.CustomerId == this.CustomerId
                       select o;
            }
        }


        public event PropertyChangedEventHandler PropertyChanged;
        protected void RaisePropertyChanged(string name)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(name));
        }


    }

So, as a workaround we can create an empty subscription and then enumerate each such property in the constructor. But it definitely seems not pretty.

Any comments?

New Post: Use with Silverlight project

throb — Sun, 13 Sep 2009 12:42:05 GMT

Hi Vinay,

Unfortunately I'm not much of a WCF expert (yet).

Bottom line is that Obtics needs to be informed when something of interest has changed value. The most common route (for properties) is to implement INotifyPropertyChanged(*). If and how this can be done with (runtime generated?) WCF objects I'm not sure. Most classes generated by tools in VisualStudio are partial classes, so you might be able to insert the logic in a partial class?

If you have more details about your challenge I might be able to give some hints but no guarantees.

*It is possible to notify Obtics in different ways but these are more complex. If you are interested you can check out the 'CustomMapping and ObticsToXml' projects. I'm sorry that the documentation is still too rudimentary.

Regs,

Thomas.

New Post: Use with Silverlight project

vkapoorjefco — Fri, 11 Sep 2009 19:12:48 GMT

Thomas, that was correct, I had to raise OnPropertyChanged to reflect the changes. That made it work. But if I export an object from a WCF service, and then implement updates, how do I raise the event there. The stub does implement a Notifychanged but how do we further add a OnPropertyChanged for some properties.

Thanks

Vinay

New Post: Use with Silverlight project

throb — Thu, 10 Sep 2009 21:00:41 GMT

Hi Vinay,

Though I have not been able to verify it yet; I think the problem with your code is that the Person class is not public.

Due to CAS restrictions (reflection) when running with Silverlight, Obtics is not allowed to compile expressions with references to members that are not public. Though Income is public it is still hidden because the owning class is not.

If you would like the result to respond to changes in Income you will need to make Income a property, implement INotifyPropertyChanged on Person and raise PropertyChanged events whenever you change the value of income.

Hope this helps.

Thomas.

New Post: Tracking Expressions

vkapoorjefco — Thu, 10 Sep 2009 17:49:33 GMT

Thomas,

Thanks for the quick response. I would love to be helpful whereever I could.

Vinay

New Post: Use with Silverlight project

vkapoorjefco — Thu, 10 Sep 2009 17:07:19 GMT

Thomas

Thanks for the quick response.

In a similar exercise, the following seems to give a runtime error. It worked well if i have native type in observablecollection.

MainPage.xaml

public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();

            for (int i = 0; i < 10; ++i)
                _Integers.Add(new Person(_Rnd.Next(100)));

            _Timer.Interval = new TimeSpan(0, 0, 2);
            _Timer.Tick += new EventHandler(_Timer_Tick);
            _Timer.Start();
        }

        void _Timer_Tick(object sender, EventArgs e)
        {
            _Integers[_Rnd.Next(10)].AddIncome(_Rnd.Next(100)); 
        }

        Random _Rnd = new Random();
        System.Windows.Threading.DispatcherTimer _Timer = new System.Windows.Threading.DispatcherTimer();

        ObservableCollection<Person> _Integers = new ObservableCollection<Person>();

        public IValueProvider<int> Sum
        { get { return ExpressionObserver.Execute(_Integers, c => c.Sum(p=>p.Income)).Concrete(); } }
    }

    class Person
    {
        public int Income;
        public Person(int income)
        {
            this.Income = income;
        }
        public void AddIncome (int inc)
        {
            this.Income += inc;
        }
    }

MainPage.xaml

<TextBox Text="{Binding Path=Sum.Value}" />

New Post: Tracking Expressions

throb — Wed, 09 Sep 2009 15:10:31 GMT

Hi Vinay,

Yes, both are very possible:

For the first you can use the standard Enumerable.Distinct method like:

ExpressionObserver.Execute(
    Persons,
    persons => persons.Select( p => p.Name ).Distinct()
).Cascade();

The Cascade method will return an IEnumerable<string> provided Name is of type string.

For the second just use the expression you want:

ExpressionObserver.Execute(
    Person,
    person => person.Income * 0.3 - person.Expense
);

And bind to the Value property of the returned IValueProvider. Income and Expense properties naturaly need to be observable if you want the resulting Value to react to changes. (The owning class needs to implement INotifyPropertyChanged (Silverlight))

If you have a collection of persons:

ExpressionObserver.Execute(
    Persons,
    persons => 
        from p in persons
        select p.Income * 0.3 - p.Expense
).Cascade();

If you feel like donating an Obtics users guide, I would be very interested. :-)

Regs,

Thomas

New Post: Tracking Expressions

vkapoorjefco — Wed, 09 Sep 2009 14:21:32 GMT

I have another question wrt to the implementation though.

Is it possible to track Distincts on a particular property within observablecollection<T>. Say I need to bind distincts of Person.Name within the the collection and bind to a dropdownlist.
Is it possible to track Expressions based out of a calculation on properties. E.g. Savings = (Person.Income * 30%) - Person.Expense and bind it to a control or a column in a datagrid.

I am sure this is what you intended with this api, but a guidance in the implementation approach will be very helpful.

Thanks for your help

Vinay

New Post: Use with Silverlight project

vkapoorjefco — Wed, 09 Sep 2009 14:18:59 GMT

Thomas thanks a lot for the sample. I was incorrectly binding from the XAML.

New Post: Use with Silverlight project

throb — Fri, 28 Aug 2009 23:59:12 GMT

Hi Vinay,

Find an example project here: http://obtics.codeplex.com/Wiki/View.aspx?title=Poc

It is almost the same. For simplicity it takes the sum over an ObservableCollection of int and uses a timer to randomly change elements in the collection.

Regs,

Thomas.

New Post: Use with Silverlight project

vkapoorjefco — Fri, 28 Aug 2009 15:39:44 GMT

Thomas, I tried your suggested approach again. I have a simple Page with just a textblock with an observablecollection which updates every second based on a timer. I am not using using an MVVM model. Its a very simple bind to control approach.

TextBlock Text="Status" Foreground="#FF14517B" Margin="5,0,0,0"></TextBlock>

TextBlock x:Name="total" Text="{Binding Path=Total.Value}"/>

public IValueProvider<int> Total
        {
            get
            {
                return ExpressionObserver.Execute(custOrdersList, c => c.Sum(p => p.ExecSharesCum)).Concrete();
            }
        }

However I dont see the textblock display any data. Should i be doing something else. I will appreciate if you could forward me a quick sample displaying the same.

Thanks again for all the help

New Post: Use with Silverlight project

vkapoorjefco — Fri, 28 Aug 2009 14:26:36 GMT

Thomas, Thanks a lot for the response. Since I needed the option urgently, I created another object implementing INotifychanged. The helpfile being broken, I meant that I am not able to see the details of the indeces. It may be some settings on my PC. I will try this in detail because it may turn out to be very useful in circumstances where one wants to bind multiple controls out of a single observable collection. E.g. I need to implement filter options on an observablecollection which is binded to a datagrid, by using distinct feature for each property (or column) in the grid. Also the observable collection implements a real time listening and binding, so I believe obtics supports that. Thanks for the help on this

New Post: Use with Silverlight project

throb — Thu, 27 Aug 2009 17:26:51 GMT

Hi Vinay,

The snipped provided here is just the code behind. You should be able to bind to it in silverlight using code like:

Explicit property reference doesn't seem to work in Silverlight. (The Text="{Binding Path=Total.(ov:IValueProvider.Value)" version). What is needed is the Concrete() extension method. It creates an adapter for the IValueProvider interface that is of a concrete and public type. The Concrete() method is used in the example snipped.

The bit: ()=> _vals.Sum(p=>p.somefield) in the snipped is a lambda expression. Just one that doesn't take any arguments. The snipped could also be written as (and would actually be better but slightly more code) :

using System.Linq;
using Obtics;
using Obtics.Values;
//using Obtics.Collections; Not!

public partial class Test : UserControl
{
    ObservableCollection<TElement> _vals;

    public IValueProvider<TSomefield> Total 
    {
        get
        {
            return ExpressionObserver.Execute( _vals, c => c.Sum(p=>p.somefield) ).Concrete();
        }
    }
}

The project ObticsUnitTestRunner_SilverLight in the solution (source files) builds a silverlight application. In the ViewModel class (in ViewModel.cs) is a property 'PassedCount' and 'FailedCount'. These properties do not use in-place compilation but pre-compile the lambda expressions. The principle is the same though. The last method executed to yield the result is Concrete() and the Xaml (MainPage.Xaml) binds to the properties.

So for the PassedCount property (pre-compiled):

#region PassedCount ; total number of visible test methods that have passed during their last run.
        public IValueProvider<int> PassedCount
        { get { return _PassedCountF(this).Async().Concrete(); } }

        static Func<ViewModel, IValueProvider<int>> _PassedCountF =
            ExpressionObserver.Compile(
                (ViewModel t) =>
                    t.VisibleMethods
                        .Where(m => t.Context.GetTestMethodResult(m.TestMethod).Value.Type == TestResultType.Success)
                        .Count()
            );
#endregion

Xaml (ViewModel is the DataContext):

<ContentControl Margin="0,12,12,12"  Content="{Binding Path=PassedCount.Value}" />

What do you mean by the help file seems broken? Undoubtedly many things are still missing but it does work. You need a viewer for it (an HTML help 1x viewer) and it may be possible that windows blocks the helpfile (because you downloaded it from the internet). You may need to right-mouse-click on it, select properties and click 'Unblock' on the 'General' tab.

Hope this helps.

Regs,

THomas.