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Can you pass generic delegate without the type parameter?

I have three projects
MVC Web application
Service application which is kind of two layers business/repository
Entity framework (all EF configuration lives here)
MVC references > service
Service references > EF
I have these three methods currently that do some work.
public bool StoreUpload<T>(UploadInformation information)
where T : class, IUploadEntity { }
public bool RemoveUpload<T>(UploadInformation information)
where T : class, IUploadEntity { }
public bool CommitUpload<T>(UploadInformation information)
where T : class, IUploadEntity { }
I call these three methods from my controller using these interfaces which delegate to the work methods above:
Boolean StoreUpload(UploadInformation information);
Boolean RemoveUpload(UploadInformation information);
Boolean CommitStoredDocuments(UploadInformation information);
Based on a condition from UploadTypes enumeration in a switch I call the correct work method. I do this because I don't want my mvc project to have access to the EF database types otherwise I know someone is going to start querying data from all over the application. I use these switch statements for all interfaced methods:
public bool StoreUpload(UploadInformation information)
{
switch (information.Type)
{
case UploadTypes.AutoIncident:
return RemoveUpload<AutoIncident>(information);
case UploadTypes.Incident:
return RemoveUpload<IncidentInjury>(information);
case UploadTypes.Inspection:
return RemoveUpload<Inspection>(information);
case UploadTypes.OtherIncident:
return RemoveUpload<OtherIncident>(information);
default:
return false;
}
}
public bool RemoveUpload(UploadInformation information) { ... }
public bool CommitStoredUpload(UploadInformation information) { ... }
This method might shed a little light on what the types parameters are being used for. I am updating tables in a generic way using EF.
private bool CommitStoredDocuments<T>(UploadInformation information) where T : class, IUploadEntity
{
var uploads = GetStoredUploads(information.UniqueId);
var entity = db.Set<T>().Include(e => e.Uploads)
.Single(e => e.UniqueId == information.UniqueId);
entity.Uploads.AddRange(uploads);
...
}
It would be nice to be able to pass the work method which requires a type parameter as a delegate to the switch work method calls.
public bool DoSomeWork(delegateMethod, information) {
switch(information.Type) {
case UploadTypes.AutoInciden:
return delegateMethod<AutoIncident>(information);
...
}
}
Can this be done?
Also, I had trouble constructing a good title for this question so please comment if these is a better way to describe the challenge.

It cannot be done directly due to several reasons.
First of all, as you probably noticed, delegateMethod<FooBar>(information) simply does not compile. This is because in your example the delegateMethod is a local variable (method parameter actually, but still a variable), and you cannot apply "type arguments" <FooBar> to a variable - you can apply them only on an identifier that indicates a (generic) type or a (generic) method.
Second reason is more interesting. When you pass a method as a delegate, the delegate actually catches the whole method signature, including all parameter types.
void Blah<T>(UploadInformation information){ ... }
var one = new Action<int>(Blah); // -> Blah<int>
var two = new Action<float>(Blah); // -> Blah<float>
var thr = new Action<andsoon>(Blah); // -> Blah<andsoon>
MagicDoSomeWork(one, ...); // these all
MagicDoSomeWork(two, ...); // delegates are already bound
MagicDoSomeWork(thr, ...); // and remember their concrete T
You need to actually specify the type for the Action so a proper version of generic method will be picked from a general description called Blah. These delegates are bound to concrete versions of the method and will accept only that types. These delegates are 'closed' in terms of their type arguments. Using normal ways, the MagicDoSomeWork will simply have no way of altering the T which these delegates already have remembered.
That two things are a kind of show stoppers, since by normal code only, you cannot write things like
var nope1 = new Action(Blah); // ctor for Action NEEDS type parameter
since Action constructor simply requires a type parameter. And once you pass any, it will lock the Blah type arguments
Also you cannot use open delegates:
var nope1 = new Action<>(Blah); // can't use empty <> in this context :(
since new operator requires a full type to create an object.
However, with a bit of reflection voodoo, it is possible to analyze and build a generic type or a generic method dynamically.
// first, build the delegate in a normal way
// and pick anything as the type parameters
// we will later replace them
var delegateWithNoType = new Action<object>(Blah);
// delegate has captured the methodinfo,
// but uses a stub type parameter - it's useless to call it
// but it REMEMBERS the method!
// .... pass the delegate around
// later, elsewhere, determine the type you want to use
Type myRealArgument;
switch(..oversomething..)
{
default: throw new NotImplemented("Ooops");
case ...: myRealArgument = typeof(UploadTypes.AutoIncident); break;
...
}
// look at the delegate definition
var minfo = delegateWithNoType.Method;
var target = delegateWithNoType.Target; // probably NULL since you cross layers
var gdef = minfo.GetGenericDefinition();
var newinfo = gdef.MakeGenericMethod( myRealArgument );
// now you have a new MethodInfo object that is bound to Blah method
// using the 'real argument' type as first generic parameter
// By using the new methodinfo and original target, you could now build
// an updated delegate object and use it instead the original "untyped" one
// That would be a NEW delegate object. You can't modify the original one.
// ...but since you want to call the method, why don't use the methodinfo
UploadInformation upinfo = ... ;
newinfo.Invoke(target, new object[] { upinfo });
// -> will call Blah<UploadTypes.AutoInciden>(upinfo)
word of warning: this is a sketch to show you how the delegate.Method/Target and methodinfo and getgenericdefinition and makegenericmethod work. I wrote it from memory, never compiled, never ran. It can contain minor typos, overlooked things and invisible rainbow unicorns. I didn't noticed any. Probably because they were invisible.

You can do it like this
public bool Invoke(EntityType entityType, ActionType action, Object[] arguments)
{
var actionType = Enum.GetName(typeof(ActionType), action);
var type = GetType();
var method = type.GetMethods().Single(m => m.IsGenericMethod && m.Name == actionType);
switch (entityType)
{
case EntityType.IncidentInjury:
var genericMethod = method.MakeGenericMethod(typeof(IncidentInjury));
return (bool)genericMethod.Invoke(this, arguments);
default:
return false;
}
}
The enum will just be a list of methods that I want to invoke this way and I create a base class for my services so I don't have to pass the instance to the Invoke method.

Instead of using delegates, consider using an interface (or abstract class). This way, your methods can retain their generic nature.
For example, if you create an interface like:
interface IUploadAction
{
bool Perform<T>(UploadInformation information)
where T : class, IUploadEntity;
}
Note that the T is not exposed in the type, it's only on the method. This is the key part.
Now you can implement this for your database methods:
class CommitStoredDocuments : IUploadAction
{
public bool Perform<T>(UploadInformation information)
where T : class, IUploadEntity
{
var uploads = GetStoredUploads(information.UniqueId);
var entity = db.Set<T>().Include(e => e.Uploads)
.Single(e => e.UniqueId == information.UniqueId);
entity.Uploads.AddRange(uploads);
//...
}
}
Your switching/dispatching method can look like this:
public bool DoAction(IUploadAction action, UploadInformation information)
{
switch (information.Type)
{
case UploadTypes.AutoIncident:
return action.Perform<AutoIncident>(information);
case UploadTypes.Incident:
return action.Perform<IncidentInjury>(information);
case UploadTypes.Inspection:
return action.Perform<Inspection>(information);
case UploadTypes.OtherIncident:
return action.Perform<OtherIncident>(information);
default:
return false;
}
}
And then you can write something like:
IUploadAction storeUpload;
public bool StoreUpload(UploadInformation information) => DoAction(storeUpload, information);

Using Reflection to create automatically a List of Delegates

I have a Class called Operations.cs with some method. I want to create a List of Delegates to pick a method randomly. Right now I have the following working solution:
public delegate void Delmethod(ExampleClass supervisor);
public static Operations op = new Operations();
public List<Delmethod> opList = new List<Delmethod>();
opList.Add(op.OpOne);
opList.Add(op.OpTwo);
opList.Add(op.OpThree);
opList.Add(op.OpFour);
opList.Add(op.OpFive);
opList.Add(op.OpSix);
opList.Add(op.OpSeven);
But what I really want is generate the List opList automatically in the case I add a new method in the Operations.cs. I was trying to use reflection in an atempt to solve my problem as follows:
List<MethodInfo> listMethods = new List<MethodInfo>(op.GetType().GetMethods().ToList());
foreach (MethodInfo meth in listMethods)
{
opList.Add(meth);
}
I believe that this doesn't work because I'm making a confusion about the meaning of delegate, but I'm out of ideas.

You have to make a delegate from particular method info.
Assuming, that Operations has only public instance methds with the same signature, the code will look like this:
public static Operations op = new Operations();
public List<Action<ExampleClass>> opList = new List<Action<ExampleClass>>();
oplist.AddRange(op
.GetType()
.GetMethods()
.Select(methodInfo => (Action<ExampleClass>)Delegate.CreateDelegate(typeof(Action<ExampleClass>), op, methodInfo)));
Note, that you don't need to declare Delmethod, since there is Action<T>.

What is the alternate of javascript object in c# without using class?

ok, so in javascript, we can declare an object like this,
var obj={name:"Irshu",age:22};
console.log(obj);
How do we do the same in c#? the reason i ask because my function need to return a string and a bool together. I dont want to create a class for it, and i dont want to use the dictionary. Are there any alternatives?
public void Message(){
var obj=GetObject(val);
Messagebox.Show(Convert.ToString(obj.ind));
}
public object GetObject(string val){
return new {ind=val,flag=true};
}
This is not valid, is it?

.Net supports ExpandoObject since .NET 4.
http://msdn.microsoft.com/en-us/library/system.dynamic.expandoobject%28v=vs.110%29.aspx
It lets you declare the object and add properties as your would in javascript.
Traditionally it is for JS interop and I can't recommend it for production work. Tuple<T> is more appropriate as you get strong typing for free. Ultimately you will write less code and see less runtime errors.
What you have in your code is an anonymous type. Anonymous types cannot exist outside the scope in which they are declared. Generally, we use these for transforming LINQ results to temporary objects.

You can't return anonymous types from a method. You can do however something like this:
public void Message(){
var obj = new { ind = "oaiwejf", flag = true };
Messagebox.Show(obj.ind);
}
EDIT
Check this MSDN article

turns out, its posible, one genius on the internet posted this:
public void Message()
{
var obj=GetObject("Irshu");
var y= Cast(obj, new { ind= "", flag= true });
Messagebox.Show(y.ind); //alerts Irshu
}
public object GetObject(string val){
return new {ind=val,flag=true};
}
T Cast<T>(object obj, T type)
{
return (T)obj;
}

Is there a way to get an array of the arguments passed to a method?

Say I have a method:
public void SomeMethod(String p1, String p2, int p3)
{
#if DEBUG
object[] args = GetArguments();
LogParamaters(args);
#endif
// Do Normal stuff in the method
}
Is there a way to retrieve an array of the arguments passed into the method, so that they can be logged?
I have a large number of methods and want to avoid manually passing the arguments by name to the logger, as human error will inevitably creep in.
I'm guessing it will involve reflection in some form - which is fine, as it will only be used for debugging purposes.
Update
A little more information:
I can't change the method signature of SomeMethod, as it is exposed as a WebMethod and has to replicate the legacy system it is impersonating.
The legacy system already logs the arguments that are passed in. To start with the new implementation will wrap the legacy system, so I'm looking to log the parameters coming into the C# version, so that I can verify the right parameters are passed in in the right order.
I'm just looking to log the argument values and order, not their names.

If you use Postsharp you can simply add an attribute to the method you want to log. Within this attribute you can write the logging code and also will provide the arguments you need. This is known as cross cutting concerns and AOP (Aspect orientated programming)

I am unsure if the API to access the call stack provides a means to get the argument list.
However there are ways to inject IL to intercept method calls and execute custom code.
The Library I use frequently is PostSharp by Gael Fraiteur, it includes an application that runs postbuild and injects IL in your output assemblies depending on the Aspects that you are using. There are attributes with which you can decorate assemblies, types, or individual methods. For instance:
[Serializable]
public sealed class LoggingAttribute : OnMethodBoundaryAspect
{
public override void OnEntry(MethodExecutionArgs eventArgs)
{
Console.WriteLine("Entering {0} {1} {2}",
eventArgs.Method.ReflectedType.Name,
eventArgs.Method,
string.Join(", ", eventArgs.Arguments.ToArray()));
eventArgs.MethodExecutionTag = DateTime.Now.Ticks;
}
public override void OnExit(MethodExecutionArgs eventArgs)
{
long elapsedTicks = DateTime.Now.Ticks - (long) eventArgs.MethodExecutionTag;
TimeSpan ts = TimeSpan.FromTicks(elapsedTicks);
Console.WriteLine("Leaving {0} {1} after {2}ms",
eventArgs.Method.ReflectedType.Name,
eventArgs.Method,
ts.TotalMilliseconds);
}
}
After this you can just decorate the method you want with this Attribute:
[Logging]
public void SomeMethod(String p1, String p2, int p3)
{
//..
}

Well, if you just want to pass the values, you can cheat and define an object array:
public static void LogParameters(params object[] vals)
{
}
This will incur boxing on value types and also not give you any parameter names, however.
Say I have a method:
public void SomeMethod(String p1, String p2, int p3)
{
#if DEBUG
LogParamaters(p1, p2, p3);
#endif
// Do Normal stuff in the method
}
Update: unfortunately reflection will not do it all automatically for you. You will need to provide the values, but you can use reflection to provide the param names/types:
How can you get the names of method parameters?
So the method sig would change to something like:
public static void LogParameters(string[] methodNames, params object[] vals)
{ }
Then you can enforce/assume that each index in each collection tallies, such that methodNames[0] has the value vals[0].

Well params help with the log call, but won't help the existing method signatures. Logging using an AOP framework might be a more productive approach?

Sure can ...check out this post, it gets the actual values of the params.
how to enumerate passed method parameters

There's some functionality with the dynamic type system that can do it, but then your class needs to inherit from the dynamic base classes

might not work in some scenarios but should get you started :)
class Program
{
static void Main(string[] args)
{
M1("test");
M2("test", "test2");
M3("test", "test2", 1);
Console.ReadKey();
}
static void M1(string p1)
{
Log(MethodBase.GetCurrentMethod());
}
static void M2(string p1, string p2)
{
Log(MethodBase.GetCurrentMethod());
}
static void M3(string p1, string p2, int p3)
{
Log(MethodBase.GetCurrentMethod());
}
static void Log(MethodBase method)
{
Console.WriteLine("Method: {0}", method.Name);
foreach (ParameterInfo param in method.GetParameters())
{
Console.WriteLine("ParameterName: {0}, ParameterType: {1}", param.Name, param.ParameterType.Name);
}
}
}

As long as you know what types to expect you could log them in an SQL database. Write a method that does a type check, and then fills the appropriate DB column with the parameter (argument) value. If you have a custom type then you can use the type name and save that as string in it's own special column.
-Edit
Also, using the MethodBase.Name extension method, you could associate your parameters with the method that took them as arguments as mentioned in another post below. Be a handy way of keeping track of all methods used, and with which arguments, and of which type.
Is this even vaguely a good idea? :)

Here's what I came up with as a solution:
PostSharp or another AOP solution wasn't really practical in this situation, so unfortunately I had to abandon that idea.
It appears that while it is possible to parameter names and types using reflection, the only way to access the runtime values is with a debugger attached.
See here for more info:
StackOverflow
microsoft.public.dotnet.framework
So that still left me with the problem of ~50 methods that needed this logging adding by hand.
Reflection to the rescue...
public String GetMethodParameterArray()
{
var output = new StringBuilder();
output.AppendLine();
Type t = typeof(API);
foreach (var mi in t.GetMethods())
{
var argsLine = new StringBuilder();
bool isFirst = true;
argsLine.Append("object[] args = {");
var args = mi.GetParameters();
foreach (var pi in args)
{
if (isFirst)
{
isFirst = false;
}
else
{
argsLine.Append(", ");
}
argsLine.AppendFormat("{0}", pi.Name);
}
argsLine.AppendLine("};"); //close object[] initialiser
output.AppendLine(argsLine.ToString());
output.AppendFormat("Log(\"{0}\",args);", mi.Name);
output.AppendLine();
output.AppendLine();
}
return output.ToString();
}
This code snippet loops through the methods on a class and outputs an object[] array initialised with the arguments passed into the method and a Log call containing the arguments and the method name.
Example output:
object[] args = {username, password, name, startDate, endDate, cost};
Log("GetAwesomeData",args);
This block can then be pasted into the top of the method to achieve the required effect.
It is more manual than I would have liked, but it is a lot better than having to type the parameters by hand and far less error prone.

Calling MethodBase's Invoke on a constructor (reflection)

First of all, sorry if this has been asked before. I've done a pretty comprehensive search and found nothing quite like it, but I may have missed something.
And now to the question: I'm trying to invoke a constructor through reflection, with no luck. Basically, I have an object that I want to clone, so I look up the copy constructor for its type and then want to invoke it. Here's what I have:
public Object clone(Object toClone) {
MethodBase copyConstructor = type.GetConstructor(
new Type[] { toClone.GetType() });
return method.Invoke(toClone, new object[] { toClone }); //<-- doesn't work
}
I call the above method like so:
List<int> list = new List<int>(new int[] { 0, 1, 2 });
List<int> clone = (List<int>) clone(list);
Now, notice the invoke method I'm using is MethodBase's invoke. ConstructorInfo provides an invoke method that does work if invoked like this:
return ((ConstructorInfo) method).Invoke(new object[] { toClone });
However, I want to use MethodBase's method, because in reality instead of looking up the copy constructor every time I will store it in a dictionary, and the dictionary contains both methods and constructors, so it's a Dictionary<MethodBase>, not Dictionary<ConstructorInfo>.
I could of course cast to ConstructorInfo as I do above, but I'd rather avoid the casting and use the MethodBase method directly. I just can't figure out the right parameters.
Any help? Thanks so much.
EDIT
Benjamin,
Thanks so much for your suggestions. I was actually doing exactly what you suggest in your second edit, except (and that's a big "except") my dictionary was where
class ClonerMethod {
public MethodBase method;
public bool isConstructor;
...
public Object invoke(Object toClone) {
return isConstructor ?
((ConstructorInfo) method).Invoke(new object[] { toClone }) : //<-- I wanted to avoid this cast
method.Invoke(toClone, null);
}
}
And then I called ClonerMethod's invoke on what I found in the dictionary. I didn't add the code the deals with all that because the answer I was looking for was just how to call Invoke on a ConstructorInfo using MethodBase's Invoke method, so I didn't want to add unnecessary info and too much code for you guys to read through. However, I like your use of Func<,> much MUCH better, so I'm switching to that. Also making the Clone method generic is a nice addition, but in my case the caller doesn't know the type of the object, so I'll keep it non-generic instead.
I didn't know about Func<,>, and if I knew about the lambda operator I had forgotten (I hadn't really needed something like this before), so I've actually learnt a lot from your answer. I always love to learn new things, and this will come in very handy in the future, so thanks a lot! :)

If you know that the object is having a constructor like that, did you think about using this overload of Activator.CreateInstance instead?
Update: So you have a cascading search for MethodInfo/MethodBase already and store them -> You don't want/cannot use Activator.
In that case I don't see a way to do what you want without a cast. But - maybe you could change the architecture to store a Dictionary<Type, Func<object, object>> and add those Func<> instances instead. Makes the calling code nicer (I assume) and would allow you to do this cast once:
// Constructor
dictionary.Add(type,
source => ((ConstructorInfo) method).Invoke(new object[] {source})
);
// Clone
dictionary.Add(type,
source => method.Invoke(source, new object[]{})
);
In fact, since you only care about the difference between constructor and normal method at the very site where you grab them, you wouldn't need a cast at all, would you?
// Constructor 2
dictionary.Add(type,
source => yourConstructorInfo.Invoke(new object[] {source})
);
Unless I'm missing something (quite possible, of course) this could resolve the problem by doing this once on the defining side of the fence and the caller wouldn't need to mind if this is constructor or not?
One last time, then I'm going to stop the edit spam. I was bored and came up with the following code. Is that what you are trying to accomplish?
public class Cloner {
private readonly IDictionary<Type, Func<object, object>> _cloneMap =
new Dictionary<Type, Func<object, object>>();
public T Clone<T>(T source) {
Type sourceType = source.GetType();
Func<object, object> cloneFunc;
if (_cloneMap.TryGetValue(sourceType, out cloneFunc)) {
return (T)cloneFunc(source);
}
if (TryGetCopyConstructorCloneFunc(sourceType, out cloneFunc)) {
_cloneMap.Add(sourceType, cloneFunc);
return (T)cloneFunc(source);
}
if (TryGetICloneableCloneFunc(sourceType, out cloneFunc)) {
_cloneMap.Add(sourceType, cloneFunc);
return (T)cloneFunc(source);
}
return default(T);
}
private bool TryGetCopyConstructorCloneFunc(Type type,
out Func<object, object> cloneFunc) {
var constructor = type.GetConstructor(new[] { type });
if (constructor == null) {
cloneFunc = source => null;
return false;
}
cloneFunc = source => constructor.Invoke(new[] { source });
return true;
}
private bool TryGetICloneableCloneFunc(Type type,
out Func<object, object> cloneFunc) {
bool isICloneable = typeof(ICloneable).IsAssignableFrom(type);
var cloneMethod = type.GetMethod("Clone", new Type[] { });
if (!isICloneable || (cloneMethod == null)) {
cloneFunc = source => null;
return false;
}
cloneFunc = source => cloneMethod.Invoke(source, new object[] {});
return true;
}
}