TypeConverter Class (System.ComponentModel)

The most common type of converter is one that converts to and from a text representation. The type converter for a class is bound to the class with a TypeConverterAttribute. Unless this attribute is overridden, all classes that inherit from this class use the same type converter as the base class.

Note
For general type system purposes, do not access a type converter directly. Instead, access the appropriate converter by using TypeDescriptor. For more information, see the code examples provided.

Note   For XAML purposes, a XAML processor searches for the TypeConverterAttribute directly, instead of going through TypeDescriptor. For cases where you do want a TypeDescriptor instance from code, or where you create a shared instance in WPF resources, it is acceptable to construct it directly without referencing TypeDescriptor or other reflection and type system support.

Classes derived from TypeConverter are often referenced as part of how a XAML processor converts an attribute or initialization text value from markup (which is inherently a string) and generates an object for a run-time representation. Custom type authors that intend to support a type conversion behavior for XAML typically implement a TypeConverter class that supports their own unique ConvertFrom behavior from a string. This behavior enables type conversion from the string provided as a XAML attribute value and provides a XAML processor with the support needed to create an object from the string, so that the object can be produced in a parsed object graph. Custom types or members of custom types are indicated by applying TypeConverterAttribute to the definitions, with the attribute referencing the custom TypeConverter implementation. For more information, see Type Converters for XAML Overview.

Note

The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: SharedState. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

Inherit from TypeConverter to implement your own conversion requirements. When you inherit from this class, you can override the following methods:

• To support custom type conversion, override the CanConvertFrom, CanConvertTo, ConvertFrom, and ConvertTo methods.

• To convert types that must re-create the object to change its value, override the CreateInstance and GetCreateInstanceSupported methods.

• To convert types that support properties, override the GetProperties and GetPropertiesSupported methods. If the class you are converting does not have properties, and you need to implement properties, you can use the TypeConverter.SimplePropertyDescriptor class as a base for implementing the property descriptors. When you inherit from TypeConverter.SimplePropertyDescriptor, you must override the GetValue and SetValue methods.

• To convert types that support standard values, override the GetStandardValues, GetStandardValuesExclusive, GetStandardValuesSupported and IsValid methods.

Note
Your derived type might be marked as internal or private, but an instance of your type can be created with the TypeDescriptor class. Do not write insecure code by assuming the caller is trusted. Assume instead that callers might create instances of your type in partial trust.

For more information about type converters for general (non-XAML) purposes, see How to: Implement a Type Converter or Generalized Type Conversion.

The following code example shows how to create an instance of a type converter and bind it to a class. The class implementing the converter, MyClassConverter, must inherit from the TypeConverter class.

<TypeConverter(GetType(MyClassConverter))> _
Public Class Class1
    ' Insert code here.
End Class 'MyClass

[TypeConverter(typeof(MyClassConverter))]
 public class MyClass {
    // Insert code here.
}

public:
   [TypeConverter(Sample::MyClassConverter::typeid)]
   ref class MyClass
   {
      // Insert code here.
   };

When you have a property that has an enumeration, check to see whether an enumeration value is valid before setting the property. The next code example requires that an enumeration called MyPropertyEnum has been declared.

Public WriteOnly Property MyProperty() As MyPropertyEnum
    Set
        ' Checks to see if the value passed is valid.
        If Not TypeDescriptor.GetConverter(GetType(MyPropertyEnum)).IsValid(value) Then
            Throw New ArgumentException()
        End If
        ' The value is valid. Insert code to set the property.
    End Set 
End Property

public MyPropertyEnum MyProperty {
    set {
       // Checks to see if the value passed is valid.
       if (!TypeDescriptor.GetConverter(typeof(MyPropertyEnum)).IsValid(value)) {
          throw new ArgumentException();
       }
       // The value is valid. Insert code to set the property.
    }
 }

public:
   property MyPropertyEnum MyProperty 
   {
      void set( MyPropertyEnum value )
      {
         // Checks to see if the value passed is valid.
         if ( !TypeDescriptor::GetConverter( MyPropertyEnum::typeid )->IsValid( value ) )
         {
            throw gcnew ArgumentException;
         }
         // The value is valid. Insert code to set the property.
      }
   }

Another common type converter usage is to convert an object to a string. The following code example prints out the name of the Color stored in the variable c.

Dim c As Color = Color.Red
Console.WriteLine(TypeDescriptor.GetConverter(c).ConvertToString(c))

Color c = Color.Red;
    Console.WriteLine(TypeDescriptor.GetConverter(c).ConvertToString(c));

Color c = Color::Red;
Console::WriteLine( TypeDescriptor::GetConverter( c )->ConvertToString( c ) );

You can also use a type converter to convert a value from its name, as shown in the next code example.

Dim c As Color = CType(TypeDescriptor.GetConverter(GetType(Color)).ConvertFromString("Red"), Color)

Color c = (Color)TypeDescriptor.GetConverter(typeof(Color)).ConvertFromString("Red");

Color c =  (Color)(TypeDescriptor::GetConverter( Color::typeid )->ConvertFromString( "Red" ));

In the following code example, you can use a type converter to print out the set of standard values that the object supports.

Dim c As Color
For Each c In  TypeDescriptor.GetConverter(GetType(Color)).GetStandardValues()
    Console.WriteLine(TypeDescriptor.GetConverter(c).ConvertToString(c))
Next c

foreach(Color c in TypeDescriptor.GetConverter(typeof(Color)).GetStandardValues()) {
    Console.WriteLine(TypeDescriptor.GetConverter(c).ConvertToString(c));
 }

for each ( Color c in TypeDescriptor::GetConverter( Color::typeid )->GetStandardValues() )
{
   Console::WriteLine( TypeDescriptor::GetConverter( c )->ConvertToString( c ) );
}

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

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