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//---------------------------------------------------------------------------
//
// <copyright file="DynamicValueConverter.cs" company="Microsoft">
// Copyright (C) Microsoft Corporation. All rights reserved.
// </copyright>
//
// Description: wrapper around default converter to dynamcially pick
// and change value converters depending on changing source and target types
//
//---------------------------------------------------------------------------
using System;
using System.Globalization;
using System.Collections;
using System.ComponentModel;
using System.Reflection;
using System.Windows;
using System.Windows.Data;
using MS.Internal; // Invariant.Assert
using System.Diagnostics;
namespace MS.Internal.Data
{
// dynamically pick and switch a default value converter to convert between source and target type
internal class DynamicValueConverter : IValueConverter
{
internal DynamicValueConverter(bool targetToSourceNeeded)
{
_targetToSourceNeeded = targetToSourceNeeded;
}
internal DynamicValueConverter(bool targetToSourceNeeded, Type sourceType, Type targetType)
{
_targetToSourceNeeded = targetToSourceNeeded;
EnsureConverter(sourceType, targetType);
}
internal object Convert(object value, Type targetType)
{
return Convert(value, targetType, null, CultureInfo.InvariantCulture);
}
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
object result = DependencyProperty.UnsetValue; // meaning: failure to convert
if (value != null)
{
Type sourceType = value.GetType();
EnsureConverter(sourceType, targetType);
if (_converter != null)
{
result = _converter.Convert(value, targetType, parameter, culture);
}
}
else
{
if (!targetType.IsValueType)
{
result = null;
}
}
return result;
}
public object ConvertBack(object value, Type sourceType, object parameter, CultureInfo culture)
{
object result = DependencyProperty.UnsetValue; // meaning: failure to convert
if (value != null)
{
Type targetType = value.GetType();
EnsureConverter(sourceType, targetType);
if (_converter != null)
{
result = _converter.ConvertBack(value, sourceType, parameter, culture);
}
}
else
{
if (!sourceType.IsValueType)
{
result = null;
}
}
return result;
}
private void EnsureConverter(Type sourceType, Type targetType)
{
if ((_sourceType != sourceType) || (_targetType != targetType))
{
// types have changed - get a new converter
if (sourceType != null && targetType != null)
{
// DefaultValueConverter.Create() is more sophisticated to find correct type converters,
// e.g. if source/targetType is object or well-known system types.
// if there is any change in types, give that code to come up with the correct converter
if (_engine == null)
{
_engine = DataBindEngine.CurrentDataBindEngine;
}
Invariant.Assert(_engine != null);
_converter = _engine.GetDefaultValueConverter(sourceType, targetType, _targetToSourceNeeded);
}
else
{
// if either type is null, no conversion is possible.
// Don't ask GetDefaultValueConverter - it will use null as a
// hashtable key, and crash (bug 110859).
_converter = null;
}
_sourceType = sourceType;
_targetType = targetType;
}
}
private Type _sourceType;
private Type _targetType;
private IValueConverter _converter;
private bool _targetToSourceNeeded;
private DataBindEngine _engine;
}
}
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