Creating Converters and the Base View Interface

In this step you will create two converters which will be used through out your views and an interface which defines the core functionality all views will expose.

Creating converters for the views
Defining the base view interface

Creating converters for the views

In the Views folder add a Class named NullableBooleanConverter. This class must implement IValueConverter and it will be used to convert null to False for some of the bound controls in your views.

public class NullableBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType,
        object parameter, CultureInfo culture)
    {
        object result = this.NullableBooleanToFalse(value);
        return result;
    }
    public object ConvertBack(object value, Type targetType,
        object parameter, CultureInfo culture)
    {
        object result = this.NullableBooleanToFalse(value);
        return result;
    }
    private object NullableBooleanToFalse(object value)
    {
        if (value == null)
        {
            return false;
        }
        else
        {
            return value;
        }
    }
}

Public Class NullableBooleanConverter
    Implements IValueConverter
    Public Function Convert(value As Object, targetType As Type, parameter As Object,
                 culture As Globalization.CultureInfo) As Object Implements IValueConverter.Convert
        Dim result As Object = Me.NullableBooleanToFalse(value)
        Return result
    End Function
    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object,
                 culture As Globalization.CultureInfo) As Object Implements IValueConverter.ConvertBack
        Dim result As Object = Me.NullableBooleanToFalse(value)
        Return result
    End Function
    Private Function NullableBooleanToFalse(value As Object) As Object
        If IsNothing(value) Then
            Return False
        Else
            Return value
        End If
    End Function
End Class

In the Views folder add a Class named YearConverter. This class must implement IValueConverter and it will be used to convert null values to the current year for some of the bound controls in your views.

public class YearConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        object result = this.NullYearToCurrentYear(value);
        return result;
    }
    public object ConvertBack(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        object result = this.NullYearToCurrentYear(value);
        return result;
    }
    private object NullYearToCurrentYear(object value)
    {
        if (value == null)
        {
            value = DateTime.Now.Year;
        }
        return value;
    }
}

Public Class YearConverter
    Implements IValueConverter
    Public Function Convert(value As Object, targetType As Type, parameter As Object,
                 culture As Globalization.CultureInfo) As Object Implements IValueConverter.Convert
        Dim result As Object = Me.NullYearToCurrentYear(value)
        Return result
    End Function
    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object,
                 culture As Globalization.CultureInfo) As Object Implements IValueConverter.ConvertBack
        Dim result As Object = Me.NullYearToCurrentYear(value)
        Return result
    End Function
    Private Function NullYearToCurrentYear(value As Object) As Object
        If IsNothing(value) Then
            value = DateTime.Now.Year
        End If
        Return value
    End Function
End Class

In the Views folder add a Class named EmptyStringConverter. This class must implement IValueConverter and it will be used to convert empty string values to null for some of the bound controls in your views.

public class EmptyStringConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        object result = this.EmptyStringToNull(value);
        return result;
    }
    public object ConvertBack(object value, Type targetType, object parameter,
        System.Globalization.CultureInfo culture)
    {
        object result = this.EmptyStringToNull(value);
        return result;
    }
    private object EmptyStringToNull(object value)
    {
        string stringValue = (string)value;
        if (string.IsNullOrEmpty(stringValue))
        {
            return null;
        }
        return value;
    }
}

Public Class EmptyStringConverter
    Implements IValueConverter
    Public Function Convert(value As Object, targetType As Type, parameter As Object,
                 culture As Globalization.CultureInfo) As Object Implements IValueConverter.Convert
        Dim result As Object = Me.EmptyStringToNull(value)
        Return result
    End Function
    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object,
                 culture As Globalization.CultureInfo) As Object Implements IValueConverter.ConvertBack
        Dim result As Object = Me.EmptyStringToNull(value)
        Return result
    End Function
    Private Function EmptyStringToNull(value As Object) As Object
        Dim stringValue As String = CType(value, String)
        If String.IsNullOrEmpty(value) Then
            Return Nothing
        End If
        Return value
    End Function
End Class

Defining the base view interface

In the ViewInterfaces folder add a new Interface named IView. This interface will define the base functionality of all views - they can be closed through the Close() method and have a DataContext which can be set or retrieved.
```
public interface IView
{
    object DataContext { get; set; }
    void Close();
}
```
```
Public Interface IView
    Property DataContext As Object
    Sub Close()
End Interface
```

Next step: Setting up the Main View