DynamicValueConverter.cs source code in C# .NET

                        Code:
                         / DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Framework / MS / Internal / Data / DynamicValueConverter.cs / 3 / DynamicValueConverter.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved.
//  
//
// 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; 
    }
 
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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DynamicValueConverter.cs source code in C# .NET

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