How come "var" works without specifying the namespace? - c#

I have the following code:
var dataExistsResult = await _service.CheckifExists(RequestDto);
if (dataExistsResult != null && dataExistsResult.CountProperties() > 0)
//do something
But if i specify "var" PropertiesWithData dataExistsResult = await _service.CheckifExists(RequestDto); it doesn't work since the namespace is not included in the file:
namespace Core.Common
{
public class PropertiesWithData
{
I need to set using Core.Common; for that to work. How come "var" is working when running the program? And how come it possible to access properties of "var" if it knows the type but using Core.Common; is not in the file? eg: dataExistsResult.CountProperties() Is Core.Common.PropertiesWithData added at runtime? eg Core.Common.PropertiesWithData dataExistsResult = await _service.CheckifExists(RequestDto);


Namespaces are part of the type name. So when your code refers to a type (by name), it must specify the namespace one way or another.
When using var, the type is not referred to by name, so no namespace is necessary. The compiler knows what type it is because the method declaration includes the type name (including namespace).

Related

Why does Type.GetType not return a Type when given an input the exact same as typof(X).GetFullName? [duplicate]

This code:
Type.GetType("namespace.a.b.ClassName")
returns null.
I have in the usings:
using namespace.a.b;
The type exists, it's in a different class library, and I need to get it by it's name given as string.

Type.GetType("namespace.qualified.TypeName") only works when the type is found in either mscorlib.dll or the currently executing assembly.
If neither of those things are true, you'll need an assembly-qualified name:
Type.GetType("namespace.qualified.TypeName, Assembly.Name")

You can also get the type without assembly qualified name but with the dll name also, for example:
Type myClassType = Type.GetType("TypeName,DllName");
I had the same situation and it worked for me. I needed an object of type "DataModel.QueueObject" and had a reference to "DataModel" so I got the type as follows:
Type type = Type.GetType("DataModel.QueueObject,DataModel");
The second string after the comma is the reference name (dll name).

Try this method.
public static Type GetType(string typeName)
{
var type = Type.GetType(typeName);
if (type != null) return type;
foreach (var a in AppDomain.CurrentDomain.GetAssemblies())
{
type = a.GetType(typeName);
if (type != null)
return type;
}
return null;
}

If the assembly is part of the build of an ASP.NET application, you can use the BuildManager class:
using System.Web.Compilation
...
BuildManager.GetType(typeName, false);

Dictionary<string, Type> typeCache;
...
public static bool TryFindType(string typeName, out Type t) {
lock (typeCache) {
if (!typeCache.TryGetValue(typeName, out t)) {
foreach (Assembly a in AppDomain.CurrentDomain.GetAssemblies()) {
t = a.GetType(typeName);
if (t != null)
break;
}
typeCache[typeName] = t; // perhaps null
}
}
return t != null;
}

if your class is not in current assambly you must give qualifiedName and this code shows how to get qualifiedname of class
string qualifiedName = typeof(YourClass).AssemblyQualifiedName;
and then you can get type with qualifiedName
Type elementType = Type.GetType(qualifiedName);

As Type.GetType(String) need the Type.AssemblyQualifiedName you should use Assembly.CreateQualifiedName(String, String).
string typeName = "MyNamespace.MyClass"; // Type.FullName
string assemblyName = "MyAssemblyName"; // MyAssembly.FullName or MyAssembly.GetName().Name
string assemblyQualifiedName = Assembly.CreateQualifiedName(assemblyName , typeName);
Type myClassType = Type.GetType(assemblyQualifiedName);
The Version, Culture and PublicKeyToken are not required for assemblyName that's why you can use MyAssembly.GetName().Name.
About Type.GetType(String) :
If the type is in the currently executing
assembly or in Mscorlib.dll, it is sufficient to supply the type name
qualified by its namespace.

When I have only the class name I use this:
Type obj = AppDomain.CurrentDomain.GetAssemblies().SelectMany(t => t.GetTypes()).Where(t => String.Equals(t.Name, _viewModelName, StringComparison.Ordinal)).First();

If it's a nested Type, you might be forgetting to transform a . to a +
Regardless, typeof( T).FullName will tell you what you should be saying
EDIT: BTW the usings (as I'm sure you know) are only directives to the compiler at compile time and cannot thus have any impact on the API call's success. (If you had project or assembly references, that could potentially have had influence - hence the information isnt useless, it just takes some filtering...)

I am opening user controls depending on what user controls the user have access to specified in a database. So I used this method to get the TypeName...
Dim strType As String = GetType(Namespace.ClassName).AssemblyQualifiedName.ToString
Dim obj As UserControl = Activator.CreateInstance(Type.GetType(strType))
So now one can use the value returned in strType to create an instance of that object.

If the assembly is referenced and the Class visible :
typeof(namespace.a.b.ClassName)
GetType returns null because the type is not found, with typeof, the compiler may help you to find out the error.

Try using the full type name that includes the assembly info, for example:
string typeName = #"MyCompany.MyApp.MyDomain.MyClass, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null";
Type myClassType = Type.GetType(typeName);
I had the same situation when I was using only the the namesspace.classname to get the type of a class in a different assembly and it would not work. Only worked when I included the assembly info in my type string as shown above.

Make sure that the comma is directly after the fully qualified name
typeof(namespace.a.b.ClassName, AssemblyName)
As this wont work
typeof(namespace.a.b.ClassName ,AssemblyName)
I was stumped for a few days on this one

For me, a "+" was the key!
This is my class(it is a nested one) :
namespace PortalServices
{
public class PortalManagement : WebService
{
public class Merchant
{}
}
}
and this line of code worked:
Type type = Type.GetType("PortalServices.PortalManagement+Merchant");

This solution above seems to be the best to me, but it didn't work for me, so I did it as follows:
AssemblyName assemblyName = AssemblyName.GetAssemblyName(HttpContext.Current.Server.MapPath("~\\Bin\\AnotherAssembly.dll"));
string typeAssemblyQualifiedName = string.Join(", ", "MyNamespace.MyType", assemblyName.FullName);
Type myType = Type.GetType(typeAssemblyQualifiedName);
The precondition is that you know the path of the assembly. In my case I know it because this is an assembly built from another internal project and its included in our project's bin folder.
In case it matters I am using Visual Studio 2013, my target .NET is 4.0. This is an ASP.NET project, so I am getting absolute path via HttpContext. However, absolute path is not a requirement as it seems from MSDN on AssemblyQualifiedNames

I cheated. Since the types I want to create (by name) are all in In a dll I control, I just put a static method in the dll in the assembly that takes a simple name, and calls type.GetType from that context and returns the result.
The original purpose was so that the type could be specified by name in configuration data. I've since change the code so that the user specified a format to process. The format handler classes implement a interface that determines if the type can parse the specified format. I then use reflection to find types that implement the interface, and find one that handles the format. So now the configuration specifies a format name, a not a specific type. The reflection code can look at adjacent dlls and load, them so I have a sort poor man's plug-in architecture.

Very late reply, but if anyone is dealing with this a decade later:
There is a very, very small chance that your class in Visual Studio has a Build Action set to "Content" instead of "Compile".
Click on your class in Solution Explorer, then look at the properties.
Check that Build Action is "Compile", not "Content".

Type namespace issue in C#

I have third party .Net assembly lets say ThridParty.dll which uses type "dotnet-namespace.dotnet-type from .Net assembly dotnetassembly.dll.
Now in new version of dotnetassembly.dll "dotnet-type" which was earlier in dotnet-namespace has been moved to new namespace lets say new-dotnet-namespace. Fully qualified name of dotnet-type has become new-dotnet-namespace.dotnet-type.
Now my question is, Is there any way I can tell runtime to look for type dotnet-type in new namespace i.e. new-dotnet-namespace instead of old namespace i.e. dotnet-namespace?
I know we can do use assembly redirection when we want to point new version of assembly but is it possible to redirect types within same assembly but to different namespace?
I don't have option to get new version of thridparty.dll which uses type from new namespace.

No, there is nothing in .Net Framework to redirect one type to another.
Note that namespace is just syntactic sugar to makes names shorter in source code, for .Net itself namespace is just part of the type name - so your question is essentially "can I point on type to another".
Solutions:
recompile
build proxy assembly
rewrite IL to point to new types.

How about:
public Type FindType(string typeName, string assemblyName)
{
Assembly assembly = AppDomain.CurrentDomain.GetAssemblies().SingleOrDefault(a => a.GetName().Name == assemblyName);
return assembly != null ? assembly.GetTypes().SingleOrDefault(t => t.Name == typeName) : null;
}
You would call this:
Type dotNetType = FindType("dotnet-type", "dotnetassembly");
This way you are independent of the type namespace.
As a side note, if you have two types with the same name in that assembly, this method will simply not work because it won't be able to know which type to return (in fact, it'll throw an exception). You can change SingleOrDefault to FirstOrDefault and make it return the first occurence.
Of course you'd lose all the compiler-time advantages, since you'll be looking up the type at runtime.

Activate type only without knowing the namespace of the type I am trying to activate

I'm not sure this is possible, and the existing answers to this question seem to imply that you need to know the namespace.
I am trying to activate a type, but would prefer to avoid specifying the Type's namespace. Is this possible? Of course I would know the Assembly ahead of time.
string qualifiedName = Assembly.GetAssembly(typeof(MyType)).FullName;
Type toActivate = Type.GetType("sometype, " + qulifiedName);
I've tried various ways, but hitting road blocks. Seems like I must know the namespace of the type. Is this true? Or am I missing something.
To recap, I have two things...
The name of the type, ie MyClass
Its executing assembl

You can list all types in the current application domain or executing assembly and do a Where to get the type you're looking for.
var types = AppDomain.CurrentDomain.GetAssemblies().SelectMany(t => t.GetTypes())
Or
var types = Assembly.GetAssembly(typeof(MyType)).GetTypes()
Followed by:
var myType = types.Where(t => t.Name == nameToFind);
Then you can decide whether a type was found, or if multiple, which one to use.

Reflection C# - GetType() Returns Null [duplicate]

This code:
Type.GetType("namespace.a.b.ClassName")
returns null.
I have in the usings:
using namespace.a.b;
The type exists, it's in a different class library, and I need to get it by it's name given as string.

Type.GetType("namespace.qualified.TypeName") only works when the type is found in either mscorlib.dll or the currently executing assembly.
If neither of those things are true, you'll need an assembly-qualified name:
Type.GetType("namespace.qualified.TypeName, Assembly.Name")

You can also get the type without assembly qualified name but with the dll name also, for example:
Type myClassType = Type.GetType("TypeName,DllName");
I had the same situation and it worked for me. I needed an object of type "DataModel.QueueObject" and had a reference to "DataModel" so I got the type as follows:
Type type = Type.GetType("DataModel.QueueObject,DataModel");
The second string after the comma is the reference name (dll name).

Try this method.
public static Type GetType(string typeName)
{
var type = Type.GetType(typeName);
if (type != null) return type;
foreach (var a in AppDomain.CurrentDomain.GetAssemblies())
{
type = a.GetType(typeName);
if (type != null)
return type;
}
return null;
}

If the assembly is part of the build of an ASP.NET application, you can use the BuildManager class:
using System.Web.Compilation
...
BuildManager.GetType(typeName, false);

Dictionary<string, Type> typeCache;
...
public static bool TryFindType(string typeName, out Type t) {
lock (typeCache) {
if (!typeCache.TryGetValue(typeName, out t)) {
foreach (Assembly a in AppDomain.CurrentDomain.GetAssemblies()) {
t = a.GetType(typeName);
if (t != null)
break;
}
typeCache[typeName] = t; // perhaps null
}
}
return t != null;
}

if your class is not in current assambly you must give qualifiedName and this code shows how to get qualifiedname of class
string qualifiedName = typeof(YourClass).AssemblyQualifiedName;
and then you can get type with qualifiedName
Type elementType = Type.GetType(qualifiedName);

As Type.GetType(String) need the Type.AssemblyQualifiedName you should use Assembly.CreateQualifiedName(String, String).
string typeName = "MyNamespace.MyClass"; // Type.FullName
string assemblyName = "MyAssemblyName"; // MyAssembly.FullName or MyAssembly.GetName().Name
string assemblyQualifiedName = Assembly.CreateQualifiedName(assemblyName , typeName);
Type myClassType = Type.GetType(assemblyQualifiedName);
The Version, Culture and PublicKeyToken are not required for assemblyName that's why you can use MyAssembly.GetName().Name.
About Type.GetType(String) :
If the type is in the currently executing
assembly or in Mscorlib.dll, it is sufficient to supply the type name
qualified by its namespace.

When I have only the class name I use this:
Type obj = AppDomain.CurrentDomain.GetAssemblies().SelectMany(t => t.GetTypes()).Where(t => String.Equals(t.Name, _viewModelName, StringComparison.Ordinal)).First();

If it's a nested Type, you might be forgetting to transform a . to a +
Regardless, typeof( T).FullName will tell you what you should be saying
EDIT: BTW the usings (as I'm sure you know) are only directives to the compiler at compile time and cannot thus have any impact on the API call's success. (If you had project or assembly references, that could potentially have had influence - hence the information isnt useless, it just takes some filtering...)

I am opening user controls depending on what user controls the user have access to specified in a database. So I used this method to get the TypeName...
Dim strType As String = GetType(Namespace.ClassName).AssemblyQualifiedName.ToString
Dim obj As UserControl = Activator.CreateInstance(Type.GetType(strType))
So now one can use the value returned in strType to create an instance of that object.

If the assembly is referenced and the Class visible :
typeof(namespace.a.b.ClassName)
GetType returns null because the type is not found, with typeof, the compiler may help you to find out the error.

Try using the full type name that includes the assembly info, for example:
string typeName = #"MyCompany.MyApp.MyDomain.MyClass, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null";
Type myClassType = Type.GetType(typeName);
I had the same situation when I was using only the the namesspace.classname to get the type of a class in a different assembly and it would not work. Only worked when I included the assembly info in my type string as shown above.

Make sure that the comma is directly after the fully qualified name
typeof(namespace.a.b.ClassName, AssemblyName)
As this wont work
typeof(namespace.a.b.ClassName ,AssemblyName)
I was stumped for a few days on this one

For me, a "+" was the key!
This is my class(it is a nested one) :
namespace PortalServices
{
public class PortalManagement : WebService
{
public class Merchant
{}
}
}
and this line of code worked:
Type type = Type.GetType("PortalServices.PortalManagement+Merchant");

This solution above seems to be the best to me, but it didn't work for me, so I did it as follows:
AssemblyName assemblyName = AssemblyName.GetAssemblyName(HttpContext.Current.Server.MapPath("~\\Bin\\AnotherAssembly.dll"));
string typeAssemblyQualifiedName = string.Join(", ", "MyNamespace.MyType", assemblyName.FullName);
Type myType = Type.GetType(typeAssemblyQualifiedName);
The precondition is that you know the path of the assembly. In my case I know it because this is an assembly built from another internal project and its included in our project's bin folder.
In case it matters I am using Visual Studio 2013, my target .NET is 4.0. This is an ASP.NET project, so I am getting absolute path via HttpContext. However, absolute path is not a requirement as it seems from MSDN on AssemblyQualifiedNames

I cheated. Since the types I want to create (by name) are all in In a dll I control, I just put a static method in the dll in the assembly that takes a simple name, and calls type.GetType from that context and returns the result.
The original purpose was so that the type could be specified by name in configuration data. I've since change the code so that the user specified a format to process. The format handler classes implement a interface that determines if the type can parse the specified format. I then use reflection to find types that implement the interface, and find one that handles the format. So now the configuration specifies a format name, a not a specific type. The reflection code can look at adjacent dlls and load, them so I have a sort poor man's plug-in architecture.

Very late reply, but if anyone is dealing with this a decade later:
There is a very, very small chance that your class in Visual Studio has a Build Action set to "Content" instead of "Compile".
Click on your class in Solution Explorer, then look at the properties.
Check that Build Action is "Compile", not "Content".

Build c# Generic Type definition at runtime

At present I'm having to do something like this to build a Type definition at runtime to pass to my IOC to resolve. Simplified:
Type t = Type.GetType(
"System.Collections.Generic.List`1[[ConsoleApplication2.Program+Person");
I know the generic type argument at runtime only.
Is there something that will allow me to do something like this (fake code):
Type t = Type.GetTypeWithGenericTypeArguments(
typeof(List)
, passInType.GetType());
Or shall I just stick to my hack, passInType.GetType() convert to string, build generic type string.. feel dirty

MakeGenericType - i.e.
Type passInType = ... /// perhaps myAssembly.GetType(
"ConsoleApplication2.Program+Person")
Type t = typeof(List<>).MakeGenericType(passInType);
For a complete example:
using System;
using System.Collections.Generic;
using System.Reflection;
namespace ConsoleApplication2 {
class Program {
class Person {}
static void Main(){
Assembly myAssembly = typeof(Program).Assembly;
Type passInType = myAssembly.GetType(
"ConsoleApplication2.Program+Person");
Type t = typeof(List<>).MakeGenericType(passInType);
}
}
}
As suggested in the comments - to explain, List<> is the open generic type - i.e. "List<T> without any specific T" (for multiple generic types, you just use commas - i.e. Dictionary<,>). When a T is specified (either through code, or via MakeGenericType) we get the closed generic type - for example, List<int>.
When using MakeGenericType, any generic type constraints are still enforced, but simply at runtime rather than at compile time.

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