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Cheap generic overnight viagra I'm not going to delve into the definition of static reflection here, cheap generic overnight viagra but you'll see how it's implemented, cheap generic overnight viagra and how I found it can help me with implementing INotifyPropertyChanged.

Cheap generic overnight viagra Now, cheap generic overnight viagra I've never been a fan of INotifyPropertyChanged myself, cheap generic overnight viagra mostly because it feels wet (read: not DRY).  I'm working on a WPF app at the moment, cheap generic overnight viagra and have come to realize, cheap generic overnight viagra if I embrace INotifyPropertyChanged, cheap generic overnight viagra I get to take full advantage of the excellent WPF databinding story.

Cheap generic overnight viagra Here is what a normal use of INotifyPropertyChanged looks like:

    public class Person : INotifyPropertyChanged
    {
        private string _firstName;
        private string _lastName;

        public event PropertyChangedEventHandler PropertyChanged;

        public string FirstName
        {
            get { return _firstName; }
            set
            {
                if (_firstName != value)
                {
                    _firstName = value;
                    FirePropertyChanged("FirstName");
                }
            }
        }

        public string LastName
        {
            get { return _lastName; }
            set
            {
                if (_lastName != value)
                {
                    _lastName = value;
                    FirePropertyChanged("LastName");
                }
            }
        }

        private void FirePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, cheap generic overnight viagra new PropertyChangedEventArgs(propertyName));
            }
        }
    }

Cheap generic overnight viagra Here is what the static reflection use of INotifyPropertyChanged looks like:

    public class PersonStaticReflection : NotifyPropertyChanged
    {
        private string _firstName;
        private string _lastName;

        public string FirstName
        {
            get { return _firstName; }
            set { SetProperty(()=> FirstName, cheap generic overnight viagra ()=> _firstName, cheap generic overnight viagra value); }
        }

        public string LastName
        {
            get { return _lastName; }
            set
            {
                SetProperty( () => LastName, cheap generic overnight viagra () => _lastName, cheap generic overnight viagra value, cheap generic overnight viagra () =>
                   {
                       // do something useful here
                   });
            }
        }
    }

Cheap generic overnight viagra Doesn't that just feel DRYer?  It does to me!

Cheap generic overnight viagra There are several important pieces to note:

  • Inheriting from NotifyPropertyChanged, cheap generic overnight viagra this is the class that holds the SetProperty method, cheap generic overnight viagra and hides the static reflection magic.
  • We're calling SetProperty with three arguments in the FirstName property
    • first: a LINQ Expression pointing to the property we're changing
    • second: a LINQ Expression pointing to the field to backing the property
    • third: the new, cheap generic overnight viagra incoming value
  • We're calling SetProperty with a fourth argument in the LastName property
    • fourth: an action that will get executed only if the values were different
  • Cheap generic overnight viagra The SetProperty method, cheap generic overnight viagra is going to look at the current value of the field, cheap generic overnight viagra and the incoming value.  If the two are different, cheap generic overnight viagra it will assign the new value to the field, cheap generic overnight viagra and then fire the NotifyPropertyChanged event, cheap generic overnight viagra with the name of the property given via the first argument.  I ended up pulling this into its own class so I could use it as the layer supertype in my View Model layer. Cheap generic overnight viagra Here is the implementation:

    public class NotifyPropertyChanged : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected void SetProperty < T>( Expression < Func> propExpr, cheap generic overnight viagra Expression> fieldExpr, cheap generic overnight viagra T value )
        {
            SetProperty(propExpr, cheap generic overnight viagra fieldExpr, cheap generic overnight viagra value, cheap generic overnight viagra ()=> { });
        }

        protected void SetProperty < T>( Expression < Func> propExpr, cheap generic overnight viagra Expression < Func < T>> fieldExpr, cheap generic overnight viagra T value, cheap generic overnight viagra Action doIfChanged )
        {
            var prop = (PropertyInfo)((MemberExpression)propExpr.Body).Member;
            var field = (FieldInfo)((MemberExpression)fieldExpr.Body).Member;

            var currVal = prop.GetValue( this, cheap generic overnight viagra null );

            if( currVal == null && value == null )
                return;
            if( currVal == null || !currVal.Equals( value ) )
            {
                field.SetValue( this, cheap generic overnight viagra value );
                doIfChanged();

                if( PropertyChanged != null )
                    PropertyChanged( this, cheap generic overnight viagra new PropertyChangedEventArgs( prop.Name ) );
            }
        }
    }

Cheap generic overnight viagra Questions/comments/likes/dislikes? Let me know.

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Comments (7) Trackbacks (4)
  1. I was always annoyed by implementing INotifyPropertyChanged. I’ll definitely being using this in the future

  2. It seems like you want a decent (i.e. not C preprocessor) macro system. On .Net the best language for this is probably Nemerle or Boo. You can just write (in Nemerle, I don’t remember Boo syntax)

    [NotifiableProperty]
    public string _firstName;

    and it will be converted to

    public string FirstName
    {
    get { return _firstName; }
    set
    {
    if (_firstName != value)
    {
    _firstName = value;
    FirePropertyChanged(“FirstName”);
    }
    }
    }

    at compile time, no run time overhead! See here: http://nemerle.org/Macros

  3. It seems like you really want a decent macro system. In .Net that means, at the moment, either Nemerle or Boo.

    I don’t remember Boo syntax, but in Nemerle you can just write

    [Accessor(flags = WantSetter)]
    mutable _someField : int;

    and it will be converted at compile time to

    mutable _someField : int;
    public SomeField : int {
    get { some_field }
    set { some_field = value }
    }

    Writing a macro which would insert FirePropertyChange calls as well is pretty easy.

  4. Sorry for the double comment

  5. Great work. Helped me very much.

  6. Err, what about the situation where you cannot really subclass from NotifyPropertyChanged because you’re already inheriting from something else? This whole approach hinges on inheritance which prevents it being used anywhere. At this point, I’d typically suggest a mixin, except that mixins cannot contain state (without a lot of pain), and you have an event whose value must be accessible.

    I think, for the time being, it makes sense to just use PostSharp for the INotifyPropertyChanged problem.


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