I am using TaskBar methods defined within the namespace Microsoft.WindowsAPICodePack.Taskbar. Specifically, I'll focus on SetProgressState for this question.
Here is the meta-definition I get when I ask for the definition of SetProgressState:
namespace Microsoft.WindowsAPICodePack.Taskbar
{
public class TaskbarManager
{
public void SetProgressState(TaskbarProgressBarState state);
public void SetProgressState(TaskbarProgressBarState state, IntPtr windowHandle);
public void SetProgressState(TaskbarProgressBarState state, System.Windows.Window window);
}
}
Obviously, I have omitted most of that class's definition just to highlight the one method's overloads.
To this point, I have been using the single-parameter overload and have had no issues. However, today I attempted to use the two-parameter overload that accepts an IntPtr as its second parameter.
When I did that, I started getting this error during build:
The type 'System.Windows.Window' is defined in an assembly that is not
referenced. You must add a reference to assembly
'PresentationFramework, Version=3.0.0.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35'
So my question is why I did not get an error for using the single-parameter overload, but I do get an error for referencing one of the others (and for the wrong one)?
Edit (for addition sub-question):
I also tried the following, which made no difference:
SetProgressState(myState, (IntPtr) myWindowHandle);
I thought that by casting explicitly, I would avoid the compiler confusion in realizing the appropriate overload, but that was not the case.
According to the MSDN page on Overload Resolution, the compiler will start by selecting the potential candidates
Each of these contexts defines the set of candidate function members and the list of arguments in its own unique way
then, the best target is selected:
If the set contains only one function member, then that function member is the best function member.
My understanding here is that the compiler doesn't even consider the 2 arguments methods when you call it with 1 argument. However, when you use the 2 arguments version, it needs information about the argument types. In this case, it needs to know what System.Windows.Window is to be able to determine which overload you want to call.
Example
Imagine you have 2 classes in separate Class Libraries
class Foo
{
}
class Bar : Foo
{
}
and 4 methods in an other library
static void Do()
{
}
static void Do(Foo foo)
{
}
static void Do(Bar bar)
{
}
static Foo Get()
{
return new Bar();
}
You reference the Methods Library and the Library Containing Foo, but not the library containing Bar.
Then, in your application, you obtain an object of type Foo from the Methods Library (it could be a Bar too, but you don't know). How is the compiler supposed to resolve an eventual call to Do() with arguments?
It can't unless it has the type information for Bar as well.
As for your subquestion, it's a result of the above plus the fact that a cast doesn't necessarily force an overload to be chosen. Let's imagine that System.Windows.Window derives from IntPtr for a moment. Casting the argument to IntPtr doesn't help the compiler resolve the overload at all (see above example).
Since the type information is not present, the compiler emits an error because it can't know for sure. Honestly, for compilers, that's a feature.
I'll expand my comments here for clarity. Your project isn't able to find System.Windows.Window. I mispoke in my comment when I said you need to put in:
using System.Windows;
To the file.
Instead, the project needs to have a reference to System.Windows. The reference you want is given to you in the error message: PresentationFramework. You will also need to include PresentationCore(a similar error will pop up telling you to add a reference to PresentationCore).
The type 'System.Windows.Window' is defined in an assembly that is not referenced. You must add a reference to assembly 'PresentationFramework, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
Related
I'm making a RTS game with Unity. There're many types of resources in my game, such as, tree, farm. Each resource is a GameObject and has it own main script controlling it.
Ex. I want to harvest a tree, I call this.
gameObject.GetComponent<Tree>().Harvest();
If I want to harvest farm I call the same script but change "Tree" to "Farm" which is fine but code will be duplicated. So I abstract it by using generics method like this.
void Harvest<T>(){
gameObject.GetComponent<T>().Harvest();
}
But the C# compiler won't let me do that. I want to know is it possible to define generics method that use generics method inside? If not, Is there any way to abstract my code like this? Thank you.
Error message:
'T' does not contain a definition for 'Harvest' and no extension method 'Harvest' accepting a first argument of type 'T' could be found (are you missing a using directive or an assembly reference?) [Assembly-CSharp]
The problem is that in ...
void Harvest<T>(){
gameObject.GetComponent<T>().Harvest();
}
... the C# compiler does not know of which concrete type T will be. Therefore, it cannot know that there will be a method Harvest available, nor does it know its exact declaration (does it return void or bool or something else? Does it have optional arguments?). Because C# is a strongly typed language, this must be known at compile time. This gives you the certainty that everything will go well at runtime.
The solution is to give the compiler a hint by specifying a generic type constraint. To do this you must declare an interface and let the components with a Harvest method implement it.
public interface IHarvestable
{
void Harvest();
}
Specify the constraint with:
void Harvest<T>() where T : IHarvestable
{
gameObject.GetComponent<T>().Harvest();
}
In other situations where you are in control of the base class, you can also declare the required methods in the base class (possibly as abstract) and specify the base class in the generic type constraint instead of an interface.
Define an interface for all objects that use Harvest(), then define that T extends that interface:
public interface IHarvestable
{
void Harvest();
}
// In your class:
void Harvest<T>() where T: IHarvestable
{
gameObject.GetComponent<T>().Harvest();
}
BAD alternative (mentioned just as a "hacky" addition to the answer because C# supports this - do NOT use it in practice): If you want to skip -time checking you can use dynamic:
dynamic harvestable = gameObject.GetComponent<T>();
harvestable.Harvest();
Note this is a bad practice, leading to method call resolving at runtime, leading to performance drawbacks and making your code much more error prone. For instance, usage of method from a T type instance which does not implement Harvest() will be allowed by the compiler, leading to a runtime error.
I've recently encountered a dependecy resolution error that I'm hoping someone here can explain.
I have an interface defined in a 3rdparty assembly (I3rdParty), one "common" assembly that's depends on that assembly and a "client" library that depends on the "common" assembly.
Let's call them, 3rdparty.dll, common.dll and client.dll.
The client.dll should not have a dependency to the 3rdparty.dll.
in common.dll the following was defined:
public static class Factory
{
public static object Create(I3rdParty ifc) { ... }
public static object Create(string value1, string value2, long? value3 = null) { ... }
}
One of the factory methods was used from the client.dll like:
var instance = Factory.Create("SomeValue", "SomeValue2");
At this point everything worked as expected.
Then a bool parameter was introduced to the first factory method in common.dll so it became:
public static object Create(I3rdParty ifc, bool value) { ... }
Then the build of client.dll started failing due to a missing dependency to 3rdparty.dll, e.g:
The type 'I3rdParty' is defined in an assembly that is not referenced...
I'm assuming that this has something to do with that the methods now accepts the same number of parameters (since the second Create method's third parameter defaults to null).
But I thought that it would still be able to select the correct Create method based on the type of the parameters. Can anyone explain the reason for the behavior I'm seeing?
After you added a bool parameter to the first overload, the compiler has now to check for two possible method signatures to choose the one that should be used (this is the overload resolution).
You're calling Create(string, string)
With two parameters, you have the following overloads available:
Create(I3rdParty, bool)
Create(string, string)
Obviously only the second one can match (as a string cannot be implicitly converted to bool for the second parameter), but it appears the compiler is not clever enough and has to know what exactly I3rdParty is (which means it requires the reference to the assembly that defines it), before being able to determine the (I3rdParty, bool) overload wasn't an option.
I created the Class1.GetChild<T>() where T : DependencyObject extension method in lib1.dll assembly. After that, all assemblies that depends on lib1.dll failed to compile with error:
The type 'System.Windows.DependencyObject' is defined in an assemebly
that is not referenced. You must add a reference to assembly
'WindowsBase' etc...
Why dependent assemblies requires WindowsBase even if they don't use GetChild?
.
To reproduce (vs2010 .net4):
lib1.dll (references WindowsBase)
namespace lib1
{
public static class Class1
{
public static T GetChild<T>(this DependencyObject src) where T : DependencyObject
{
return default(T);
}
}
public static class Class2
{
public static int SomeExtMethod(this string src)
{
return 0;
}
}
}
lib2.dll (references lib1 but not WindowsBase)
using lib1;
class someClass
{
void someFct()
{
"foo".SomeExtMethod(); // error: The type 'System.Windows.DependencyObject'
// is defined in an assemebly that is not referenced.
// You must add a reference to assembly 'WindowsBase' etc..
}
}
.
Update:
I think there's definitly something when mixing generic methods and extension methods. I tried to demonstrate the issue in the following sample:
// lib0.dll
namespace lib0
{
public class Class0 { }
}
// lib1.dll
using lib0;
namespace lib1
{
public static class Class1
{
public static void methodA<T>() where T : Class0 { } // A
public static void methodB(Class0 e) { } // B
public static void methodC(this int src) { } // C
}
public static class Class2
{
public static void methodD(this String s) { }
}
}
// lib2.dll
using lib1;
class someClass
{
void someFct()
{
Class2.methodD(""); // always compile successfully
"".methodD(); // raise the 'must add reference to lib0' error depending on config. see details below.
}
}
A, //B, //C -> compile ok
A, B, //C -> compile ok
//A, B, C -> compile ok
A, //B, C -> raise error
A, B, C -> raise error
//A means methodA is commented. As Damien pointed out, type inference might play some role. Still curious to know the ins and outs.
Your situation has been answered by Microsoft here:
https://connect.microsoft.com/VisualStudio/feedback/details/668498/problem-with-extension-method-in-c-compiler
There are other use-cases as well independent of extension methods which produce this error wrongly.
Consider this:
Define a generic method in a type, say TP1, defined in library say LB1.
Type constrain the generic method on some type defined in some other library LB2.
Define another method in TP1.
Now in your library reference only LB1 and try to call the second method of type TP1
If you don't use TP1 but some other type defined in LB1, you do not get the error.
Also, even if one of the method of type TP1 expects a parameter of the type defined in LB2 (and you do not call this method) it does not produce this error
When one assembly depends on another assembly, the first assembly also depends on all the dependencies of the other--regardless of what is used. Assembly dependencies are effectively decoupled, another version of either assembly can be deployed after compilation, the compiler can't know that under circumstances like this one or more of the dependencies in the second assembly won't be used by the first assembly.
To solve the issue you can simply add a reference to WindowsBase.
Or, as prashanth points out, put the SomeExtMethod into a different assembly so code that uses that doesn't need to take a dependency on WindowsBase.
Update:
If you don't use anything from an assembly, you don't need any of its dependencies. But, as soon as you use one assembly, you need all the dependencies of that assembly as well. This is apparent in the way Visual Studio add references. If you add a reference to an assembly, it will copy all the dependent assemblies (not registered in the GAC) into your debug/release directories along with the assembly you added.
Update:
As to the compile error: that's the way it was written--there may be no other reason. Is it a good idea to get a compile error if you don't reference dependent assemblies? Maybe, you're likely to use something from a reference and that might use something directly from the references references--better a compile error than a deployment error.
Why not a compile error on every non-referenced secondary dependency? Again, it was written that way. Maybe an error here too would be good; but that would be a breaking change and would require really persuasive reasons.
I'm not sure this can be answered by anyone other than someone on the compiler team. I'm now thinking that it's to do with type inference - but whereas §7.6.5.1 Method Invocations talks about inference, §7.6.5.2 Extension method invocations is silent on the matter - despite the fact that inference obviously does take place when searching for applicable extension methods.
I think it's attempting some form of inference before it's performing the comparison on identifiers (which would immediately rule out the extension method since it's got the wrong name). Obviously, it can't perform any form of inference for this type if it's unable to understand the type constraints.
Hence, when you change your type constraint to just class, it now successfully passes over this method - it can infer a type parameter, but it now eliminates this extension method successfully.
When you reference another assembly, I assume the compiler needs to be able to parse any method signatures defined in that assembly, so it knows where to go to find that function if it sees a call to it.
If you replace your GetChild() function with
public static T GetChild<T>(this T src)
{
if (typeof(T) == typeof(DependencyObject)) return default(T);
else return default(T);
}
or something similar to that, it does not require you to include the reference to WindowsBase that you're running into. But if you add where T : DependencyObject to the signature, it does require it.
Effectively, you can use whatever assembly references you want in a project, so long as you don't expose them in any way. Once you expose them, then every other project which uses your library needs to be able to handle them, and thus requires those references themselves.
Maybe ILMerge would solve this problem. The idea is you create 2 dlls and merge them into one. That way you can have a single dll but reference it twice. Then way you can separate the GUI code from other code and only add the reference that you need to the particular project.
The answer is simple. It is because the method is decalre as public. This mean that it is visible to lib2.dll (in your case.) In other word you can call this method.
It also has a constrain that only classes inherited from DependencyObject can call this method. So that is the reason why you need to reference 'WindowsBase'.
Yesterday i gone through some article about EventAggregator, there some shot of code written like this,
(Message.Text as object).PublishEvent(PublishEventNames.MessageTextChanged);
public static class ExtensionServices
{
//Supplying event broking mechanizm to each object in the application.
public static void PublishEvent<TEventsubject>(this TEventsubject eventArgs, string eventTopic)
{
ServicesFactory.EventService.GetEvent<GenericEvent<TEventsubject>>()
.Publish(new EventParameters<TEventsubject> { Topic = eventTopic, Value = eventArgs });
}
}
My question is, how the object got the method "PublishEvent". Is my OOP understanding is wrong?
It was implemented as an Extension Method on the object class.
For example, this extension method (from the linked article):
public static class MyExtensions
{
public static int WordCount(this String str)
{
return str.Split(new char[] { ' ', '.', '?' },
StringSplitOptions.RemoveEmptyEntries).Length;
}
}
Is defined on the String class (by using the this String syntax and a static method on a static class) .
In the project that this is defined in String now has a WordCount method (so long as it is also in the correct namespace).
Extension methods are not actually part of the object that you appear to call the method on. Extension methods are in an additional lookup scope that the compiler looks in after looking for the method in the scope of the object itself.
So, for a method call like obj.MyExtension(), the compiler will look for "MyExtension" in the members of the type of the obj variable. It won't find any matches, because "MyExtension" isn't defined in the object's type. The compiler then looks for extension methods named "MyExtension" that are available in the current scope (because of using clauses) that have a this parameter whose type matches the type of the obj instance variable. If a match is found, then the compiler generates code to make a static method call that other method, passing obj in the this parameter.
I believe the extension methods scope is a "last chance" lookup - if the compiler can't find "MyExtension" in the available extensions, the next step is to fail with a compile error.
The tricky thing with extension methods is they're only accessible when you have added the appropriate using clause to the current source file and added a reference to the appropriate assembly that implements the extensions to bring them into scope.
Intellisense doesn't help you resolve these names by adding the appropriate using clause for you. As a user, you get used to calling a particular method on a particular type of object, and you mentally associate that method as being part of that type. When you're fleshing out a new source file it's very common to write calls to that method as you normally would and get "not found" compiler errors because you forgot to reference the namespace / assembly containing the extension method definition(s) to your source file.
The this part of this TEventsubject eventArgs determines that this is an Extension method.
It is only syntactic sugar to be able to write
TEventsubject eventArgs;
eventArgs.PublishEvent("topic");
Instead of
TEventsubject eventArgs;
ExtensionServices.PublishEvent(eventArgs, "topic");
PublishEvent is an extension method.
You can tell by the definition of the method, which includes the this keyword in the arguments list.
http://msdn.microsoft.com/en-us/library/bb383977.aspx
Extension methods are very useful syntactically; but they should be used judiciously:
1) They can clutter Intellisense if too many extensions are added for non-specific types (such as an object).
2) They should be used to augment class/interface inheritance, not replace it. IMO, If a method is shared across completely unrelated types, then it is a good candidate for an extension method. But if it is shared across related types, then it is a better candidate for a method in a base class.
I've been trying to sign an assembly and getting this error:
'Utils.Connection' does not implement interface member 'Interfaces.IConnection.BugFactory()'. 'Utils.Connection.BugFactory()' cannot implement 'Interfaces.IConnection.BugFactory()' because it does not have the matching return type of 'ThirdPartyLibrary.BugFactory'.
That error looks like a dirty, dirty lie! In Utils.Connection, I have this method:
public new BugFactory BugFactory()
I don't think the new keyword is the problem because 1) removing it doesn't stop the error and 2) I'm having the same error with another class that implements IConnection that does not use the new keyword. Update: if I use override instead of new, I get this error:
'Utils.Connection.BugFactory()': cannot override because 'ThirdPartyLibrary.ConnectionClass.BugFactory' is not a function
This is because ThirdPartyLibrary.ConnectionClass.BugFactory is a property.
There is only one BugFactory class, so it isn't a problem of the interface requiring a different BugFactory return type than what the method returns. Even if I explicitly mark my method as returning ThirdPartyLibrary.BugFactory, I still get the error when I try to strong-name the Utils DLL.
Could this be the result of ThirdPartyLibrary being an old COM library that is not CLS-compliant? I have no control over this library. When I do not try to sign the Utils assembly, I do not get the interface error.
My big question is: how can I sign this assembly?
Edit: here's what IConnection has:
using ThirdPartyLibrary; // The only using statement
namespace Interfaces
{
public interface IConnection
{
...
BugFactory BugFactory();
}
}
I'm still suspicious of the new keyword for this error.
You say "I don't think the new keyword is the problem because 1) removing it doesn't stop the error", but you must bear in mind that if your method hides a base method, the compiler will add a new, even if you don't specify it, unless you explicity specify override instead.
All the explicit new does is to prevent a compiler warning (not an error).
Is there really a method to hide or override at all?
What happens if you specify virtual instead of new on this method. Does it compile? Does it error with "no suitable method found to override?"
[Edit in response to your comment]
I get this error:
"'Utils.Connection.BugFactory()':
cannot override because
'ThirdPartyLibrary.ConnectionClass.BugFactory'
is not a function." The original
ThirdPartyLibrary.ConnectionClass.BugFactory
is a property.
I suspect this may be the issue. You are overriding a property with a method.
By using the new keyword, you are hiding the old property to anyone that has a reference to your derived class.
By contrast, anyone that has a reference cast as the superclass (the one you are inheriting from), they will see the old property, and not your new method.
Can you give some more code of the superclass (or interface) together with the derived class?
[Edit in response to your comment]
I'm trying to change the interface to
have BugFactory be a property instead
of a method
The trouble with new is that it seems like a bit of magic, that can let you change argument types and return types, but it is really pure evil.
Instead of changing the types for all consumers of the code, it only does it for consumers that are cast as the overriding new type. This gets you in the horrible position where two consumers to the same instance will see different signatures depending on how they are cast.
See if you can identify the consuming code that is complaining, and have a think around whether more of your code needs to change to support the type changes. Also, is there the possibility that you are trying to do something that is "a bit of a nasty hack"?
Namespace/version problems?
ThirdPartyLibrary.BugFactory might be a different type, if you have two different versions of the 3rd party assembly being referenced somehow: One during compile time and a different one when you sign/verify..
It sounds like you are simply referencing the COM library through the Add Reference dialog. You should probably create a Primary Interop Assembly for the COM library which can be signed. One of the caveats of signing an assembly is that all the assemblies it references must also be signed.
You would normally use the SDK program TlbImp:
TlbImp yourcomlibrary.tlb /primary /keyfile:yourkeyfile.snk /out:yourcomlibrary.dll
What does your IConnection interface look like? It seems like your ThirdPartyLibrary has a BugFactory object and you also have a BugFactory object either in your project or another reference. Did you try changing both the interface and the concrete type to explicity use ThirdPartyLibrary.BugFactory as the return type for that method?