private static Func <object> GetCommandExecutionProviderConstructor(CommandExecutionProviderKey key)
{
Func <object> constructor;
if (!CompiledConstructors.TryGetValue(key, out constructor))
{
var executionProviderType = typeof(CommandExecutionProvider <>).MakeGenericType(key.TargetType);
var executionProviderCtor =
executionProviderType.GetConstructor(new[] { typeof(Type), typeof(string), typeof(string) });
var executionProviderCtorParamaters = new Expression[]
{
Expression.Constant(key.TargetType),
Expression.Constant(key.CanExecuteMethodName, typeof(string)),
Expression.Constant(key.ExecutedMethodName, typeof(string))
};
Debug.Assert(executionProviderCtor != null, "executionProviderCtor != null");
var executionProviderCtorExpression = Expression.New(
executionProviderCtor,
executionProviderCtorParamaters);
constructor = Expression.Lambda <Func <object> >(executionProviderCtorExpression).Compile();
}
return(constructor);
}
private static ICommandExecutionProvider GetCommandExecutionProvider(
object target,
string canExecuteMethodName,
string executedMethodName)
{
if (target == _disconnectedItemSentinelValue)
{
return(null);
}
var key = new CommandExecutionProviderKey(target.GetType(), canExecuteMethodName, executedMethodName);
ICommandExecutionProvider executionProvider;
if (!ExecutionProviders.TryGetValue(key, out executionProvider))
{
try
{
executionProvider = (ICommandExecutionProvider)GetCommandExecutionProviderConstructor(key)();
}
catch (TargetInvocationException)
{
// Thanks to Mark Bergan for finding this issue!
// Unfortunately we have some nastiness around a performance optimization in C# 4.0.
// Because we are listening to DataContext events we may end up being provided a DataContext
// value that is an internal place holder for the DataContext of disconnected containers WPF.
// There is no easy way to detect this object, hence the reflection. Basically we just want to
// ignore any disconnected DataContext items. The best documentation I have found is located in
// Answer 10 on the forum located here:
// http://www.go4answers.com/Example/disconnecteditem-causing-it-115624.aspx
if (_disconnectedItemSentinelValue == null)
{
if (IsDisconnected(target))
{
_disconnectedItemSentinelValue = target;
}
////var targetType = target.GetType();
////if (targetType.FullName == "MS.Internal.NamedObject")
////{
//// var nameField = targetType.GetField("_name", BindingFlags.Instance | BindingFlags.NonPublic);
//// if (nameField != null)
//// if ((string)nameField.GetValue(target) == "DisconnectedItem")
//// {
//// _DisconnectedItemSentinelValue = target;
//// }
////}
}
if (target != _disconnectedItemSentinelValue)
{
throw;
}
}
ExecutionProviders.TryAdd(key, executionProvider);
}
return(executionProvider);
}
private static ICommandExecutionProvider GetCommandExecutionProvider(object target, string canExecuteMethodName, string executedMethodName)
{
if (target == _DisconnectedItemSentinelValue)
{
return(null);
}
var key = new CommandExecutionProviderKey(target.GetType(), canExecuteMethodName, executedMethodName);
ICommandExecutionProvider executionProvider = null;
_Lock.EnterUpgradeableReadLock();
try
{
if (!_ExecutionProviders.TryGetValue(key, out executionProvider))
{
_Lock.EnterWriteLock();
try
{
if (!_ExecutionProviders.TryGetValue(key, out executionProvider))
{
var executionProviderType = typeof(CommandExecutionProvider <>).MakeGenericType(key.TargetType);
var executionProviderCtor = executionProviderType.GetConstructor(new Type[] { typeof(Type), typeof(string), typeof(string) });
try
{
executionProvider = (ICommandExecutionProvider)executionProviderCtor.Invoke(new object[] { key.TargetType, key.CanExecuteMethodName, key.ExecutedMethodName });
}
catch (TargetInvocationException)
{
//
// Thanks to Mark Bergan for finding this issue!
// Unfortunately we have some nastiness around a performance optimization in C# 4.0.
// Because we are listening to DataContext events we may end up being provided a DataContext
// value that is an internal place holder for the DataContext of disconnected containers WPF.
// There is no easy way to detect this object, hence the reflection. Basically we just want to
// ignore any disconnected DataContext items. The best documentation I have found is located in
// Answer 10 on the forum located here:
// http://www.go4answers.com/Example/disconnecteditem-causing-it-115624.aspx
if (_DisconnectedItemSentinelValue == null)
{
var targetType = target.GetType();
if (targetType.FullName == "MS.Internal.NamedObject")
{
var nameField = targetType.GetField("_name", BindingFlags.Instance | BindingFlags.NonPublic);
if (nameField != null)
{
if ((string)nameField.GetValue(target) == "DisconnectedItem")
{
_DisconnectedItemSentinelValue = target;
}
}
}
}
if (target != _DisconnectedItemSentinelValue)
{
throw;
}
}
_ExecutionProviders.Add(key, executionProvider);
}
}
finally
{
_Lock.ExitWriteLock();
}
}
}
finally
{
_Lock.ExitUpgradeableReadLock();
}
return(executionProvider);
}
