Develop Reference

using directive is unnecessary visual studio - random class

I want to use Random class but I got this error message:
using directive is unnecessary visual studio
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Net.Sockets;
using System.Random; //I got this error at this line
namespace Mikrotik
{
....

Quick-fix:
You only need using System; - inside your code you can use Random directly.
Background:
Please read the documentation for C#'s using directive: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-directive
I think you're imagining that using works like how import works in Java where you have to name each type you want to bring into scope or use .* to bring all types into scope. Instead, C#'s using only imports namespaces, making it roughly equivalent to Java's import being used exclusively with the .* syntax.
You're getting the error because there is no namespace System.Random, instead it's a type-name; so you just need using System; - in your code you can use Random as-is.
For pendantry: C#'s using directive has 3 different modes:
using namespace; - brings into scope all types in the specified namespace
using Alias = namespace.TypeName; - brings into scope a single type, but with an alias. The alias can match the original name.
using static namespace.TypeName; - brings only the static members of the specified type into scope.
Not to be confused with C#s using() {} statement, which is completely unrelated to importing types and namespaces.

missing a using directive or an assembly reference after adding them both

Solution contains 2 projects:
Geo.Data project, which contains CodeRepository class, defined in namespace Geo.Data
ConsoleApp1 project, in which I have Program.cs class, where I want to instantiate CodeRepository from the other project.
So, I add to ConsoleApp1 - project references - the assembly from Geo.Data\Bin\Debug\Geo.Data.dll; I also add a using directive on top of Program.cs: using Geo.Data;
using Geo.Data;
namespace ConsoleApp1
{
class Program
{
static void Main(string[] args)
{
Geo.Data.CodeRepository x = new Geo.Data.CodeRepository();
// here, if I add x. after the dot I can all methods listed (from class CodeRepository)
}
}
}
CodeRepository is coloured accordingly, so it's recognized as being part of Geo.Data
However, I do get an error when running the solution. Just don't see what I am doing wrong:
The type or namespace name 'Geo' could not be found (are you missing a
using directive or an assembly reference?) ConsoleApp1\Program.cs
As described earlier, I have already added both the using Geo.Data and the assembly reference to Geo.Data. Is this a conflict of diff namespaces or what? Thanks.
Also, after writing the first letter "G" in the using directive, it's suggested to me through intellisense to use Geo; so at that point it does find it. Problem is when I run the project. The error points to the using directive. Thanks!

If you want to reference Geo.Data as a library, you need to right-click the project in your solution explorer, select PROPERTIES, and change OUTPUT TYPE to CLASS LIBRARY (note that Geo.Data does NOT need to be a part of your solution if you do this - you would build Geo.Data elsewhere).
Otherwise, if you want Geo.Data to be part of your solution(edit, update, build at the same time), then add your reference by ADD REFERENCE and choosing SHARED PROJECTS from the right-side of the reference window.

SmartTag for adding a "using" statement for extension method

Lets say I have the following code that needs to be moved to another file/class:
namespace MyNamespace
{
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
class Class1
{
public void SomeMethod()
{
IEnumerable<int> l = new List<int>();
if (l.Count() == 0)
{
//...
}
}
}
}
If I move SomeMethod to another class (in another file) that does not have (say) a using System.Linq declaration, the l.Count() statement would not compile giving the very obvious message:
'System.Collections.Generic.IEnumerable<int>' does not contain a definition for 'Count' and no extension method 'Count' accepting a first argument of type 'System.Collections.Generic.IEnumerable<int>' could be found (are you missing a using directive or an assembly reference?)
If the new class/file does not have a using System.Collections.Generic declaration and you put your cursor on the IEnumerable<int> you will get a SmartTag that would suggest possible using-declarations. If you put your cursor on the Count() extension call you get no SmartTag to suggest the using System.Linq declaration.
Is there maybe an IDE extension out there that would help add a using statement for extension methods as explained above? This would help allot with refactoring code.

I have found a solution that would be free:
Download and install DevExpress CodeRush Express and then download and install the CR_ExtensionMethodsHelper community plugin.
You could also try the following commercial products (not free):
DevExpress CodeRush (with CR_ExtensionMethodsHelper community plugin; although there is a request pending to have this plugin supported natively)
ReSharper (I'm not using this one my self, but others have suggested it)

Missing Assembily Reference

I have produced a custom class serializer for a sole class contained in 'VcdcClassStructure.dll' using sgen as-per the documentation. The documents now state that all I need to do is
Add assembaly references to both 'VcdcClassStructure.dll' and the sgen-generated 'VcdcClassStructure.XmlSerializers.dll'.
Add references to the namespace that contains the newly generated serialization classes via
using VcdcClassStructure;
using Microsoft.Xml.Serialization.GeneratedAssembly;`
(I have confirmed that the namespaces are correct using DotPeek).
I have then changed my code from
XmlSerializer serializer = new XmlSerializer(typeof(message));
serializer.Serialize(writer, vcdMsg);
to
messageSerializer serializer = new messageSerializer();
serializer.Serialize(writer, vcdMsg);
but on compilation I am getting
The type or namespace name 'VcdcClassStructure' could not be found (are you missing a using directive or an assembly reference?)
and
The type or namespace name 'Xml' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)
I have reference the relevant assemblies and added the using code for the namespace. Why is the compiler complaining about these references?
Thanks for your time.
Edit. To prove that I have not missed any of the steps above.

I've checked, and the process described works correctly. I would have to assume, therefore, that you've made an error in the steps. It works fine (note: the type I created in the library was SomeType, hence the names):
You might want to try going through the steps again.

DataTable does not contain definition for AsEnumerable

Using linq to query a datatable returns the following error: CS0117: 'DataSet1.map DataTable' does not contain a definition for 'AsEnumerable'
Project includes reference for System.Data.Datasetextensions.
Here's the code.
using System;
using System.Collections;
using System.ComponentModel;
using System.Configuration;
using System.Reflection;
using System.Data;
using System.Linq;
using System.Data.Linq;
using System.Data.Common;
using System.Data.DataSetExtensions;
using System.Linq.Expressions;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
protected void Page_Load(object sender, EventArgs e)
{
var query1 = from mfg_nm in DataSet1.mapDataTable.AsEnumerable()
select mfg_nm;
}
running it w/out AsEnumerable() results in
var query1 = from mfg_nm in DataSet1.mapDataTable
select mfg_nm;
CS1660: Cannot convert lambda expression to type 'string' because it is not a delegate type.

The method you want is in the System.Data namespace, so that using directive is fine, but you also need a reference to the System.Data.DataSetExtensions assembly. Are you sure you've got that reference as an assembly reference?
It's not clear why you've got a using directive for a System.Data.DataSetExtensions namespace - does that not raise an error?
What is the exact error with the AsEnumerable() call? (I'm surprised about the error you're getting with the second form... that's not the error I'd have expected.)

Add System.Data.DataSetExtensions from "nuget" or "add reference"
Add this code:
using System.Data.DataSetExtensions;

In all cases where this happens, the reference to System.Data.DataSetExtensions.dll was missing. If in doubt, try creating a simple console project targeting .NET 4 with a reference to System.Data.DataSetExtensions.dll, to verify that adding the reference actually works.
Also note that you only need to use the System.Data namespace.
BTW mapDataTable is a DataTable, right?

I got this error message:
'System.Data.DataTable' does not contain a definition for 'AsEnumerable' and no extension method 'AsEnumerable' accepting a first argument of type 'System.Data.DataTable' could be found (are you missing a using directive or an assembly reference?)
Added
using System.Data;
Added "System.Data.DataSetExtensions" to the References section. It resolved the problem.

Google search "system.data.datatable does not contain a definition for asenumerable" brought me here, and my trouble was missing:
using System.Data;
Due to my implement the error message was a bit misleading. Hence, my answer to this question. Code was like...
public List<mytype> MyMethod(params) {
return new mynamespace.myclasslib.myclass().GetDataTable(params).AsEnumerable()
.etc
}
Once I tried to explicitly declare the DataTable, it became obvious that I was missing the using statement.

Try this code :
DataSet1.mapDataTable.Select().AsEnumerable()