I'm trying to create an event aggregator in C++/CLI, I know that the valid syntax in C# would be as follows:
//C# code
public partial class Foo : UserControl, IView, IDisposable
{
private IEventAggregator _aggregator;
public Foo(IEventAggregator aggregator)
{
InitializeComponent();
this._aggregator = aggregator;
if (this._aggregator == null)
throw new Exception("null pointer");
_subToken =_aggregator.GetEvent<fooEvent>().Subscribe(Handler, ThreadOption.UIThread, false);
}
private SubscriptionToken _subToken = null;
private void Handler(fooEventPayload args)
{
//this gets run on the event
}
}
However directly converting this to C++/CLI gives the error "a pointer-to-member is not valid for a managed class" on the indicated line. Is there a workaround? I think it has something to do with how C# generates "Action".
//C++/CLI code
ref class Foo
{
public:
Foo(IEventAggregator^ aggregator)
{
void InitializeComponent();
this->_aggregator = aggregator;
if (this->_aggregator == nullptr)
throw gcnew Exception("null pointer");
//error in the following line on Hander, a pointer-to-member is not valid for a managed class
_subToken = _aggregator->GetEvent<fooEvent^>()->Subscribe(Handler, ThreadOption::UIThread, false);
private:
IEventAggregator ^ _aggregator;
SubscriptionToken ^ _addActorPipelineToken = nullptr;
void Handler(fooEventPayload^ args)
{
//this gets run on the event
}
}
You need to explicitly instantiate the delegate object, rather than allowing C# to do this for you.
_subToken = _aggregator->GetEvent<fooEvent^>()->Subscribe(
gcnew Action<fooEventPayload^>(this, &Foo::Handler), ThreadOption::UIThread, false);
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Explicitly instantiate the delegate.
// ^^^^ Object to call the delegate on.
// ^^^^^^^^^^^^^ C++-style reference to the method.
Related
I'm trying to add a mutator for an existing private final field. I can transform the field modifiers to remove the final specification and add an accessor method:
// accessor interface
public interface UniqueIdAccessor {
Serializable getUniqueId();
}
// mutator interface
public interface UniqueIdMutator {
void setUniqueId(Serializable uniqueId);
}
...
// fragment of Java agent implementation
return new AgentBuilder.Default()
.type(hasSuperType(named("org.junit.runner.Description")))
.transform(new Transformer() {
#Override
public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription,
ClassLoader classLoader, JavaModule module) {
return builder.field(named("fUniqueId")).transform(ForField.withModifiers(FieldManifestation.PLAIN))
.implement(UniqueIdAccessor.class).intercept(FieldAccessor.ofField("fUniqueId"))
// .implement(UniqueIdMutator.class).intercept(FieldAccessor.ofField("fUniqueId"))
.implement(Hooked.class);
}
})
.installOn(instrumentation);
...
Here's a method that uses reflection to check the modifiers of the target field and calls the accessor to get the value of the field.
private static void injectProxy(Description description) {
try {
Field bar = Description.class.getDeclaredField("fUniqueId");
System.out.println("isFinal: " + ((bar.getModifiers() & Modifier.FINAL) != 0));
} catch (NoSuchFieldException | SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Serializable uniqueId = ((UniqueIdAccessor) description).getUniqueId();
System.out.println("uniqueId: " + uniqueId);
}
// isFinal: false
// uniqueId: <description-unique-id>
... but if I uncomment the second "implement" expression to add the mutator, the transform blows up:
// isFinal: true
// java.lang.ClassCastException:
// class org.junit.runner.Description cannot be cast to class com.nordstrom.automation.junit.UniqueIdAccessor
// (org.junit.runner.Description and com.nordstrom.automation.junit.UniqueIdAccessor
// are in unnamed module of loader 'app')
I could set the field value with reflection, but that defeats the purpose of using Byte Buddy in the first place!
The problem with this approach is that the field accessor considers the input type prior to the modification. Byte Buddy prohibits this as it does not consider the mutation to be legal, not knowing about the removed modifier. As a result, the transformation fails in its entirety and you get the error you are seeing. (Register a listener to see this error.)
To avoid this, you can implement a custom Implementation using FieldAccess (without or). You can have a look at the more convenient FieldAccessor to see how this is implemented, only that you need to drop the validity checks.
Thanks for pointing me in the right direction! I assemble the StackManipulation object that defines the mutator method with this:
final TypeDescription description = TypePool.Default.ofSystemLoader().describe("org.junit.runner.Description").resolve();
final Generic _void_ = TypeDescription.VOID.asGenericType();
final Generic serializable = TypePool.Default.ofSystemLoader().describe("java.io.Serializable").resolve().asGenericType();
final MethodDescription.Token setUniqueIdToken = new MethodDescription.Token("setUniqueId", Modifier.PUBLIC, _void_, Arrays.asList(serializable));
final MethodDescription setUniqueId = new MethodDescription.Latent(description, setUniqueIdToken);
final Token fUniqueIdToken = new FieldDescription.Token("fUniqueId", Modifier.PRIVATE, serializable);
final FieldDescription fUniqueId = new FieldDescription.Latent(description, fUniqueIdToken);
final StackManipulation setUniqueIdImpl = new StackManipulation.Compound(
MethodVariableAccess.loadThis(),
MethodVariableAccess.load(setUniqueId.getParameters().get(0)),
Assigner.DEFAULT.assign(serializable, serializable, Typing.STATIC),
FieldAccess.forField(fUniqueId).write(),
MethodReturn.VOID
);
... and I transform the target class with this:
return new AgentBuilder.Default()
.type(hasSuperType(named("org.junit.runner.Description")))
.transform(new Transformer() {
#Override
public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription,
ClassLoader classLoader, JavaModule module) {
return builder.field(named("fUniqueId")).transform(ForField.withModifiers(FieldManifestation.PLAIN))
.implement(AnnotationsAccessor.class).intercept(FieldAccessor.ofField("fAnnotations"))
.implement(UniqueIdAccessor.class).intercept(FieldAccessor.ofField("fUniqueId"))
.implement(UniqueIdMutator.class).intercept(new Implementation.Simple(setUniqueIdImpl));
}
})
.installOn(instrumentation);
Here are the definitions of the three interfaces used in the transform:
// annotations accessor interface
public interface AnnotationsAccessor {
Annotation[] annotations();
}
// unique ID accessor interface
public interface UniqueIdAccessor {
Serializable getUniqueId();
}
// unique ID mutator interface
public interface UniqueIdMutator {
void setUniqueId(Serializable uniqueId);
}
I have the following Xamarin.Mac code:
[Register("Swizzler")]
public class Swizzler : NSObject
{
[DllImport("/usr/lib/libobjc.dylib")] public static extern IntPtr class_getInstanceMethod(IntPtr classHandle, IntPtr Selector);
[DllImport("/usr/lib/libobjc.dylib")] public static extern bool method_exchangeImplementations(IntPtr m1, IntPtr m2);
public void AttemptSwizzle()
{
var swizzledClassPtr = Class.GetHandle("Swizzled");
var swizzlerClassPtr = Class.GetHandle("Swizzler");
SwizzleInstanceMethod(swizzledClassPtr, new Selector("originalMethod"), swizzlerClassPtr, new Selector("newMethod"));
var swizzled = new Swizzled();
swizzled.PerformSelector(new Selector("originalMethod"));
}
internal void SwizzleInstanceMethod(IntPtr originalClassPtr, Selector originalSelector, IntPtr newClassPtr, Selector newSelector)
{
var originalMethod = class_getInstanceMethod(originalClassPtr, originalSelector.Handle);
var swizzledMethod = class_getInstanceMethod(newClassPtr, newSelector.Handle);
method_exchangeImplementations(originalMethod, swizzledMethod);
}
[Export("newMethod")]
public void NewMethod()
{
Console.WriteLine("New method called");
}
}
[Register("Swizzled")]
internal class Swizzled : NSObject
{
[Export("originalMethod")]
public void OriginalMethod()
{
Console.WriteLine("Original method called");
}
}
Code sample at https://github.com/alataffective/XamarinSwizzler.
When calling new Swizzler().AttemptSwizzle() I get the following output:
SomeMethod called
That is, the swizzling isn't happening. Why not?
The problem is that you exchange implementations of exported C# methods. Exports share a single implementation, that performs it's own mapping from selectors to C# methods. Therefore, switching them has no effect. You can check it yourself when you call method_getImplementation() for both exported methods and compare returned values.
Just try swizzling original Objective-C methods of original Objective-C classes and you'll see that it works:
public void AttemptSwizzle()
{
var swizzledClassPtr = Class.GetHandle("NSWindow");
var swizzlerClassPtr = Class.GetHandle("NSWindow");
SwizzleInstanceMethod(swizzledClassPtr, new Selector("title"), swizzlerClassPtr, new Selector("tabbingIdentifier"));
var swizzled = new NSWindow();
swizzled.TabbingIdentifier = "TabbingIdentifier";
var result = swizzled.Title;
Console.WriteLine($"title:{result}");
}
If you want to swizzle original Objective-C method with a plain, not exported C# one, you still can, making use of the following methods:
Marshal.GetFunctionPointerForDelegate()
method_setImplementation()
method_getImplementation()
So i have a class that makes an array list for me and i need to access it in another class through a constructor but i don't know what to put into the constructor because all my methods in that class are just for manipulating that list. im either getting a null pointer exception or a out of bounds exception. ive tried just leaving the constructor empty but that dosent seem to help. thanks in advance. i would show you code but my professor is very strict on academic dishonesty so i cant sorry if that makes it hard.
You are confusing the main question, with a potential solution.
Main Question:
I have a class ArrayListOwnerClass with an enclosed arraylist property or field.
How should another class ArrayListFriendClass access that property.
Potential Solution:
Should I pass the arraylist from ArrayListOwnerClass to ArrayListFriendClass,
in the ArrayListFriendClass constructor ?
It depends on what the second class does with the arraylist.
Instead of passing the list thru the constructor, you may add functions to read or change, as public, the elements of the hidden internal arraylist.
Note: You did not specify a programming language. I'll use C#, altought Java, C++, or similar O.O.P. could be used, instead.
public class ArrayListOwnerClass
{
protected int F_Length;
protected ArrayList F_List;
public ArrayListOwnerClass(int ALength)
{
this.F_Length = ALength;
this.F_List = new ArrayList(ALength);
// ...
} // ArrayListOwnerClass(...)
public int Length()
{
return this.F_Length;
} // int Length(...)
public object getAt(int AIndex)
{
return this.F_List[AIndex];
} // object getAt(...)
public void setAt(int AIndex, object AValue)
{
this.F_List[AIndex] = AValue;
} // void setAt(...)
public void DoOtherStuff()
{
// ...
} // void DoOtherStuff(...)
// ...
} // class ArrayListOwnerClass
public class ArrayListFriendClass
{
public void UseArrayList(ArrayListOwnerClass AListOwner)
{
bool CanContinue =
(AListOwner != null) && (AListOwner.Length() > 0);
if (CanContinue)
{
int AItem = AListOwner.getAt(5);
DoSomethingWith(Item);
} // if (CanContinue)
} // void UseArrayList(...)
public void AlsoDoesOtherStuff()
{
// ...
} // void AlsoDoesOtherStuff(...)
// ...
} // class ArrayListFriendClass
Note, that I could use an indexed property.
I have this code for the C# in Visual Studio 2012.
public Task SwitchLaserAsync(bool on)
{
return Task.Run(new Action(() => SwitchLaser(on)));
}
This will execute SwitchLaser method (public nonstatic member of a class MyClass) as a task with argument bool on.
I would like to do something similar in managed C++/CLI. But I am not able to find out any way how to run a task, which will execute a member method taking one parameter.
Current solution is like this:
Task^ MyClass::SwitchLaserAsync( bool on )
{
laserOn = on; //member bool
return Task::Run(gcnew Action(this, &MyClass::SwitchLaserHelper));
}
Implementation of SwitchLaserHelper function:
void MyClass::SwitchLaserHelper()
{
SwitchLaser(laserOn);
}
There must be some solution like in C# and not to create helper functions and members (this is not threadsafe).
There isn't yet any way to do this.
In C# you have a closure. When your C++/CLI compiler was written, the standardized syntax for closures in C++ was still being discussed. Thankfully, Microsoft chose to wait and use the standard lambda syntax instead of introducing yet another unique syntax. Unfortunately, it means the feature isn't yet available. When it is, it will look something like:
gcnew Action([this, on](){ SwitchLaser(on) });
The current threadsafe solution is to do what the C# compiler does -- put the helper function and data members not into the current class, but into a nested subtype. Of course you'll need to save the this pointer in addition to your local variable.
ref class MyClass::SwitchLaserHelper
{
bool laserOn;
MyClass^ owner;
public:
SwitchLaserHelper(MyClass^ realThis, bool on) : owner(realThis), laserOn(on) {}
void DoIt() { owner->SwitchLaser(laserOn); }
};
Task^ MyClass::SwitchLaserAsync( bool on )
{
return Task::Run(gcnew Action(gcnew SwitchLaserHelper(this, on), &MyClass::SwitchLaserHelper::DoIt));
}
The C++ lamdba syntax will simply create that helper class for you (currently it works for native lambdas, but not yet for managed ones).
Here's generic code I wrote this afternoon which might help (although it's not an exact match for this question). Maybe this will help the next person who stumbles onto this question.
generic<typename T, typename TResult>
ref class Bind1
{
initonly T arg;
Func<T, TResult>^ const f;
TResult _() { return f(arg); }
public:
initonly Func<TResult>^ binder;
Bind1(Func<T, TResult>^ f, T arg) : f(f), arg(arg) {
binder = gcnew Func<TResult>(this, &Bind1::_);
}
};
ref class Binder abstract sealed // static
{
public:
generic<typename T, typename TResult>
static Func<TResult>^ Create(Func<T, TResult>^ f, T arg) {
return (gcnew Bind1<T, TResult>(f, arg))->binder;
}
};
Usage is
const auto f = gcnew Func<T, TResult>(this, &MyClass::MyMethod);
return Task::Run(Binder::Create(f, arg));
Here's the working answer.. Have tested it.. Passing an argument (int) to the action sampleFunction.
#include "stdafx.h"
#include "CLRSamples.h"
using namespace System;
using namespace System::Threading;
using namespace System::Threading::Tasks;
using namespace System::Collections;
using namespace System::Collections::Generic;
void CLRSamples::sampleFunction(Object^ number)
{
Console::WriteLine(number->ToString());
Thread::Sleep((int)number * 100);
}
void CLRSamples::testTasks()
{
List<Task^>^ tasks = gcnew List<Task^>();
for (int i = 0; i < 10; i++)
{
tasks->Add(Task::Factory->StartNew((Action<Object^>^)(gcnew Action<Object^>(this, &CLRSamples::sampleFunction)), i));
}
Task::WaitAll(tasks->ToArray());
Console::WriteLine("Completed...");
}
int main(array<System::String ^> ^args)
{
CLRSamples^ samples = gcnew CLRSamples();
samples->testTasks();
Console::Read();
return 0;
}
I had a similar problem when I wanted to provide a parameter to a task executing a method which does not return a value (retuns void). Because of that Func<T, TResult> was not an option I could use. For more information, please check the page Using void return types with new Func.
So I ended up with a solution where I created a helper class
template <typename T>
ref class ActionArguments
{
public:
ActionArguments(Action<T>^ func, T args) : m_func(func), m_args(args) {};
void operator()() { m_func(m_args); };
private:
Action<T>^ m_func;
T m_args;
};
which is using Action<T> delegate to encapsulate a method that has a single parameter and does not return a value.
I would then use this helper class in a following way
ref class DisplayActivationController
{
public:
DisplayActivationController();
void StatusChanged(EventArgs^ args) { };
}
Action<EventArgs^>^ action =
gcnew Action<EventArgs^>(this, &DisplayActivationController::StatusChanged);
ActionArguments<EventArgs^>^ action_args =
gcnew ActionArguments<EventArgs^>(action, args);
Threading::Tasks::Task::Factory->
StartNew(gcnew Action(action_args, &ActionArguments<EventArgs^>::operator()));
Approach using the helper class is probably not the most elegant solution, but is the best one I could find to be used in C++/CLI which does not support lambda expressions.
If you are using c++/ CLR, then make a C# dll and add reference to it
namespace TaskClrHelper
{
public static class TaskHelper
{
public static Task<TResult> StartNew<T1, TResult>(
Func<T1, TResult> func,
T1 arg)
=> Task.Factory.StartNew(() => func(arg));
public static Task<TResult> StartNew<T1, T2, TResult>(
Func<T1, T2, TResult> func,
T1 arg1, T2 arg2)
=> Task.Factory.StartNew(() => func(arg1, arg2));
}
}
bool Device::Stop(int timeout)
{
_ResetEvent_Running->Set();
return _ResetEvent_Disconnect->WaitOne(timeout);
}
Task<bool>^ Device::StopAsync(int timeout)
{
auto func = gcnew Func<int, bool>(this, &Device::Stop);
return TaskClrHelper::TaskHelper::StartNew<int,bool>(func,timeout);
}
I'm wanting to have a simple duck typing example in C# using dynamic objects. It would seem to me, that a dynamic object should have HasValue/HasProperty/HasMethod methods with a single string parameter for the name of the value, property, or method you are looking for before trying to run against it. I'm trying to avoid try/catch blocks, and deeper reflection if possible. It just seems to be a common practice for duck typing in dynamic languages (JS, Ruby, Python etc.) that is to test for a property/method before trying to use it, then falling back to a default, or throwing a controlled exception. The example below is basically what I want to accomplish.
If the methods described above don't exist, does anyone have premade extension methods for dynamic that will do this?
Example: In JavaScript I can test for a method on an object fairly easily.
//JavaScript
function quack(duck) {
if (duck && typeof duck.quack === "function") {
return duck.quack();
}
return null; //nothing to return, not a duck
}
How would I do the same in C#?
//C# 4
dynamic Quack(dynamic duck)
{
//how do I test that the duck is not null,
//and has a quack method?
//if it doesn't quack, return null
}
If you have control over all of the object types that you will be using dynamically, another option would be to force them to inherit from a subclass of the DynamicObject class that is tailored to not fail when a method that does not exist is invoked:
A quick and dirty version would look like this:
public class DynamicAnimal : DynamicObject
{
public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result)
{
bool success = base.TryInvokeMember(binder, args, out result);
// If the method didn't exist, ensure the result is null
if (!success) result = null;
// Always return true to avoid Exceptions being raised
return true;
}
}
You could then do the following:
public class Duck : DynamicAnimal
{
public string Quack()
{
return "QUACK!";
}
}
public class Cow : DynamicAnimal
{
public string Moo()
{
return "Mooooo!";
}
}
class Program
{
static void Main(string[] args)
{
var duck = new Duck();
var cow = new Cow();
Console.WriteLine("Can a duck quack?");
Console.WriteLine(DoQuack(duck));
Console.WriteLine("Can a cow quack?");
Console.WriteLine(DoQuack(cow));
Console.ReadKey();
}
public static string DoQuack(dynamic animal)
{
string result = animal.Quack();
return result ?? "... silence ...";
}
}
And your output would be:
Can a duck quack?
QUACK!
Can a cow quack?
... silence ...
Edit: I should note that this is the tip of the iceberg if you are able to use this approach and build on DynamicObject. You could write methods like bool HasMember(string memberName) if you so desired.
Try this:
using System.Linq;
using System.Reflection;
//...
public dynamic Quack(dynamic duck, int i)
{
Object obj = duck as Object;
if (duck != null)
{
//check if object has method Quack()
MethodInfo method = obj.GetType().GetMethods().
FirstOrDefault(x => x.Name == "Quack");
//if yes
if (method != null)
{
//invoke and return value
return method.Invoke((object)duck, null);
}
}
return null;
}
Or this (uses only dynamic):
public static dynamic Quack(dynamic duck)
{
try
{
//invoke and return value
return duck.Quack();
}
//thrown if method call failed
catch (RuntimeBinderException)
{
return null;
}
}
Implementation of the HasProperty method for every IDynamicMetaObjectProvider WITHOUT throwing RuntimeBinderException.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Dynamic;
using Microsoft.CSharp.RuntimeBinder;
using System.Linq.Expressions;
using System.Runtime.CompilerServices;
namespace DynamicCheckPropertyExistence
{
class Program
{
static void Main(string[] args)
{
dynamic testDynamicObject = new ExpandoObject();
testDynamicObject.Name = "Testovaci vlastnost";
Console.WriteLine(HasProperty(testDynamicObject, "Name"));
Console.WriteLine(HasProperty(testDynamicObject, "Id"));
Console.ReadLine();
}
private static bool HasProperty(IDynamicMetaObjectProvider dynamicProvider, string name)
{
var defaultBinder = Binder.GetMember(CSharpBinderFlags.None, name, typeof(Program),
new[]
{
CSharpArgumentInfo.Create(
CSharpArgumentInfoFlags.None, null)
}) as GetMemberBinder;
var callSite = CallSite<Func<CallSite, object, object>>.Create(new NoThrowGetBinderMember(name, false, defaultBinder));
var result = callSite.Target(callSite, dynamicProvider);
if (Object.ReferenceEquals(result, NoThrowExpressionVisitor.DUMMY_RESULT))
{
return false;
}
return true;
}
}
class NoThrowGetBinderMember : GetMemberBinder
{
private GetMemberBinder m_innerBinder;
public NoThrowGetBinderMember(string name, bool ignoreCase, GetMemberBinder innerBinder) : base(name, ignoreCase)
{
m_innerBinder = innerBinder;
}
public override DynamicMetaObject FallbackGetMember(DynamicMetaObject target, DynamicMetaObject errorSuggestion)
{
var retMetaObject = m_innerBinder.Bind(target, new DynamicMetaObject[] {});
var noThrowVisitor = new NoThrowExpressionVisitor();
var resultExpression = noThrowVisitor.Visit(retMetaObject.Expression);
var finalMetaObject = new DynamicMetaObject(resultExpression, retMetaObject.Restrictions);
return finalMetaObject;
}
}
class NoThrowExpressionVisitor : ExpressionVisitor
{
public static readonly object DUMMY_RESULT = new DummyBindingResult();
public NoThrowExpressionVisitor()
{
}
protected override Expression VisitConditional(ConditionalExpression node)
{
if (node.IfFalse.NodeType != ExpressionType.Throw)
{
return base.VisitConditional(node);
}
Expression<Func<Object>> dummyFalseResult = () => DUMMY_RESULT;
var invokeDummyFalseResult = Expression.Invoke(dummyFalseResult, null);
return Expression.Condition(node.Test, node.IfTrue, invokeDummyFalseResult);
}
private class DummyBindingResult {}
}
}
impromptu-interface seems to be a nice Interface mapper for dynamic objects... It's a bit more work than I was hoping for, but seems to be the cleanest implementation of the examples presented... Keeping Simon's answer as correct, since it is still the closest to what I wanted, but the Impromptu interface methods are really nice.
The shortest path would be to invoke it, and handle the exception if the method does not exist. I come from Python where such method is common in duck-typing, but I don't know if it is widely used in C#4...
I haven't tested myself since I don't have VC 2010 on my machine
dynamic Quack(dynamic duck)
{
try
{
return duck.Quack();
}
catch (RuntimeBinderException)
{ return null; }
}
Have not see a correct answer here, MS provides an example now with casting to a dictionary
dynamic employee = new ExpandoObject();
employee.Name = "John Smith";
employee.Age = 33;
foreach (var property in (IDictionary<String, Object>)employee)
{
Console.WriteLine(property.Key + ": " + property.Value);
}
// This code example produces the following output:
// Name: John Smith
// Age: 33