Implementing INotifyPropertyChanged in C# WPF

Question

I am pretty new to C# and WPF framework,my question might sound silly. I am using the two-way binding feature. So I implement INotifyPropertyChanged interface. I have a property named DisplayFormat, so whenever the format changes from Binary to Hex, my text should convert accordingly. My question is where should I include the code/logic for the conversion between Binary and decimal?

[DefaultValue(displayFormat.Binary)]
public displayFormat DisplayFormat
{
    get { return this.format; }
    set { this.format = value; OnPropertyChanged("DisplayFormat"); }
}

public event PropertyChangedEventHandler PropertyChanged;

protected void OnPropertyChanged(string name)
{
    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler != null)
    {
        handler(this, new PropertyChangedEventArgs(name));
    }
}

Answer 1

Whenever you need to convert something to something else, you use a converter. A converter is just a class that implements IValueConverter.

public class NumberToSpecialStringConverter : IValueConverter
{
   ...
}

Converters take two inputs, the value (whatever is actually displayed or bound to) and a parameter. The parameter can be whatever you want, but cannot be bound. Since you want a bound parameter, we need to inherit from DependencyObject as well and declare a DependencyProperty to bind to:

public class NumberToSpecialStringConverter : DependencyObject, IValueConverter
{
    public displayFormat CurrentFormat
    { //Dependency property stuff }

    //Other DP stuff, use the 'propdp' snippet to get it all, or look on MSDN

    public Convert(...)
    {
       //This is going to the UI, from the Model
       return displayFormat.Convert(value); //Or whatever you have
    }

    public ConvertBack(...)
    {
       //This is going to the Model, from the UI
       return displayFormat.ConvertBack(value); //Or whatever you have
    }
}

Now that you have that, you just need to declare and use it:

<Window.Resources>
   <local:NumberToSpecialStringConverter x:Key="FormatConverter" CurrentFormat="{Binding DisplayFormat}"/>
</Window.Resources>
...
<TextBlock Text="{Binding Path=MyValue, Converter={StaticResource FormatConverter}"/>

There is one more catch. Changing "DisplayFormat" will cause NotifyPropertyChanged to fire, which will update the value inside the converter. However, the UI isn't running the convert function because it doesn't think anything has changed. Thus, you need to "pretend" that the value changed by invoking its NotifyPropertyChanged as well:

[DefaultValue(displayFormat.Binary)]
public displayFormat DisplayFormat
{
    get { return this.format; }
    set
    { 
        this.format = value; 
        OnPropertyChanged("DisplayFormat"); 
        OnPropertyChanged("MyValue");
    }
}

Now the UI will perform a fresh "get" and conversion and display what you wanted!