I am following a tutorial online of C# programming, but the VSCode is not able to find my class definition in a separate file. I double-checked the class file is under the same namespace.
Here is my program.cs:
using System;
using System.Collections.Generic;
namespace GradeBook
{
class Program
{
static void Main(string[] args)
{
var book = new Book();
var grades = new List<double>() {12.7, 10.3, 6.11, 4.1};
grades.Add(56.1);
var result = 0.0;
foreach(var number in grades)
{
result += number;
}
result /= grades.Count;
Console.WriteLine($"Average Result is {result:N1}");
}
}
}
And I defined a class named Book, which is stored in a file called Book.cs. Here is the code in Book.cs:
namespace GradeBook
{
class Book
{
}
}
VSCode runs into an issue as follows:
The type or namespace name 'Book' could not be found (are you missing a using directive or an assembly reference?) [GradeBook]
I have checked that the class Book is using the same namespace; both program.cs file and Book.cs file is are in the same folder. How can I fix this issue?
I have checked that the class Book is using the same namespace; both program.cs file and Book.cs file is are in the same folder. How can I fix this issue
By making Book public - by default it is internal and thus inaccessible.
namespace GradeBook
{
public class Book
{
}
}
Learn more about access modifiers here: https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/access-modifiers
Related
I have the following Book class (it's to long to paste it all):
using System;
using System.Collections.Generic;
namespace GradeBook
{
internal class Book
{
and the BookTests class, that creates a variable of this Book type:
using System;
using Xunit;
namespace GradeBook.Tests
{
public class BookTests
{
[Fact]
public void Test1()
{
var book = new Book("");
}
}
}
both in separate projects.
It doesn't show error, despite of internal modifier, but i don't know why. The Book class also doesn't find a reference from second file.
I Have created two .cs files with namespaces ,classes and methods . I want to call the classes of one .cs file into another .cs file. Can u help me how to declare namespace and use the namespace so that i can call the classes of the preceding .cs file.
Please forgive if my explanation is not correct.
Suppose i have the following code.
ClassFile1
using system
namespace namespace1
{
class c1
{
Methods()
}
}
ClassFile2
using system
//here i need to declare the namespace1 .Can u help me how to declare namespace1 in this ClassFile2//
namespace namespace2
{
class c2
{
Methods()
}
}
You can reference the fully-qualified name of the class:
namespace SecondNamespace
{
public class SecondClass
{
private FirstNamespace.FirstClass someObject;
}
}
Or you can add a using directive to the file (note, this is at the file level, not the class level) to include a specific namespace when resolving type names:
using FirstNamespace;
namespace SecondNamespace
{
public class SecondClass
{
private FirstClass someObject;
}
}
Taken from here:
namespace SampleNamespace
{
class SampleClass
{
public void SampleMethod()
{
System.Console.WriteLine(
"SampleMethod inside SampleNamespace");
}
}
// Create a nested namespace, and define another class.
namespace NestedNamespace
{
class SampleClass
{
public void SampleMethod()
{
System.Console.WriteLine(
"SampleMethod inside NestedNamespace");
}
}
}
class Program
{
static void Main(string[] args)
{
// Displays "SampleMethod inside SampleNamespace."
SampleClass outer = new SampleClass();
outer.SampleMethod();
// Displays "SampleMethod inside SampleNamespace."
SampleNamespace.SampleClass outer2 = new SampleNamespace.SampleClass();
outer2.SampleMethod();
// Displays "SampleMethod inside NestedNamespace."
NestedNamespace.SampleClass inner = new NestedNamespace.SampleClass();
inner.SampleMethod();
}
}
}
Note also that sometimes in addition to the "using" entry (I'm not quite clear on how you app is structured, if it's all one project this is probably moot) you may also need to add the reference. Also not sure what environment you're using. From VSExpress while in the project/file that's the recipient click on Project - Add Reference, select solution and then select your namespace.
I'm quite new to C#, and have made a class that I would like to use in my main class. These two classes are in different files, but when I try to import one into the other with using, cmd says says
The type or namespace name "MyClass" could not be found (are you missing a using directive or an assembly reference?
I know that in Java I have to mess around with CLASSPATH to get things like this to work, but I have no idea about C#.
Additional details:
As you've probably figured out, I'm compiling and executing via command prompt. I'm compiling my non-main class using /target:library (I heard that only main classes should be .exe-files).
My code looks like this:
public class MyClass {
void stuff() {
}
}
and my main class:
using System;
using MyClass;
public class MyMainClass {
static void Main() {
MyClass test = new MyClass();
/* Doesn't work */
}
}
I have tried to encompass my non-main class with namespace MyNamespace { } and importing that, but it doesn't work either.
UPDATE: As of C# 6, if you want to use the static members of a class without specifying the class name, you can use the using static directive to import the static members into the current scope, like this:
using static MyNamespace.MyClass;
Although this is not what the original question is about, you get a similar error to the one OP gets, so I'm providing it for completeness.
Answer to OP's question:
using is for namespaces only - if both classes are in the same namespace just drop the using.
You have to reference the assembly created in the first step when you compile the .exe:
csc /t:library /out:MyClass.dll MyClass.cs
csc /reference:MyClass.dll /t:exe /out:MyProgram.exe MyMainClass.cs
You can make things simpler if you just compile the files together:
csc /t:exe /out:MyProgram.exe MyMainClass.cs MyClass.cs
or
csc /t:exe /out:MyProgram.exe *.cs
EDIT:
Here's how the files should look like:
MyClass.cs:
namespace MyNamespace {
public class MyClass {
void stuff() {
}
}
}
MyMainClass.cs:
using System;
namespace MyNamespace {
public class MyMainClass {
static void Main() {
MyClass test = new MyClass();
}
}
}
I know this is very old question but I had the same requirement and just discovered that after c#6 you can use static in using for classes to import.
I hope this helps someone....
using static yourNameSpace.YourClass;
Well what you have to "import" (use) the namespace of MyClass not the class name itself. If both classes are in the same namespace, you don't have to "import" it.
Definition MyClass.cs
namespace Ns1
{
public class MyClass
{
...
}
}
Usage AnotherClass.cs
using Ns1;
namespace AnotherNs
{
public class AnotherClass
{
public AnotherClass()
{
var myInst = new MyClass();
}
}
}
If they are separate class files within the same project, then you do not need to have an 'import' statement. Just use the class straight off. If the files are in separate projects, you need to add a reference to the project first before you can use an 'import' statement on it.
If the other class is compiled as a library (i.e. a dll) and this is how you want it, you should add a reference from visual studio, browse and point to to the dll file.
If what you want is to incorporate the OtherClassFile.cs into your project, and the namespace is already identical, you can:
Close your solution,
Open YourProjectName.csproj file, and look for this section:
<ItemGroup>
<Compile Include="ExistingClass1.cs" />
<Compile Include="ExistingClass2.cs" />
...
<Compile Include="Properties\AssemblyInfo.cs" />
</ItemGroup>
Check that the .cs file that you want to add is in the project folder (same folder as all the existing classes in the solution).
Add an entry inside as below, save and open the project.
<Compile Include="OtherClassFile.cs" />
Your class, will now appear and behave as part of the project. No using is needed. This can be done multiple files in one shot.
MyClass is a class not a namespace. So this code is wrong:
using MyClass //THIS CODE IS NOT CORRECT
You should check the namespace of the MyClass (e.g: MyNamespace). Then call it in a proper way:
MyNamespace.MyClass myClass =new MyNamespace.MyClass();
using is used for importing namespaces not classes.
So if your class is in namespace X
namespace X
{
public class MyClass {
void stuff() {
}
}
}
then to use it in another namespace where you want it
using System;
using X;
public class MyMainClass {
static void Main() {
MyClass test = new MyClass();
}
}
namespace MyNamespace
{
public class MyMainClass
{
static void Main()
{
MyClass test = new MyClass();
}
}
public class MyClass
{
void Stuff()
{
}
}
}
You have no need for using a namespace then because it is all encompased in the same namespace.
If you are unsure of what namespace your class is located, type the class (case sensitive you wish to use) then with your cursor on the class, use CTRL + . and it will offer you a manual import.
I having trouble finding assembly from a project. I have two Console Applications and one where i make a reference from the other. But then i can´t make the using-statement because it can´t find the project...
EDIT: my Program-class in Lab1PersonId:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Lab1PersonId
{
class Program
{
static void Main(string[] args)
{
}
}
}
EDIT:
using Lab1PersonId;
namespace Test
{
public class Program
{
static void Main(string[] args)
{
Lab1PersonId lab = new Lab1PersonId(); ***
}
}
}
Error on row ***:
Type name expected, but namespace named found
Your setup seems fine. You have added reference to the Lab1PersonId project inside your Test project, so normally you should be able to use classes that are defined in this assembly.
For example, you should first rebuild the Lab1PersonId project and then you should be able to add reference to some namespace that exists in it:
using Lab1PersonId;
I have a dll that I'm working with, it contains a class foo.Launch. I want to create another dll that subclasses Launch. The problem is that the class name must be identical. This is used as a plugin into another piece of software and the foo.Launch class is what it looks foe to launch the plugin.
I've tried:
namespace foo
{
public class Launch : global::foo.Launch
{
}
}
and
using otherfoo = foo;
namespace foo
{
public class Launch : otherfoo.Launch
{
}
}
I've also tried specifying an alias in the reference properties and using that alias in my code instead of global, that also didn't work.
Neither of those methods work. Is there a way I can specify the name of the dll to look in within the using statement?
You'll need to alias the original assembly and use an extern alias to reference the original assembly within the new one. Here's an example of the use of the alias.
extern alias LauncherOriginal;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace foo
{
public class Launcher : LauncherOriginal.foo.Launcher
{
...
}
}
Here's a walkthrough that explains how to implement that.
Also, you'd mentioned that you tried to use an alias before and encountered problems but you didn't say what they were, so if this won't work then please mention what went wrong.
as Chris said, you can use an alias on your original assembly.
If you can't you that, then you might be able to cheat by using a 3rd assembly
Assembly1.dll (your original)
namespace foo {
public class Launch {}
}
Assembly2.dll (dummy)
namespace othernamespace {
public abstract class Dummy: foo.Launch {}
}
Assembly3.dll (your plugin)
namespace foo{
public class Launch: othernamespace.Dummy{}
}
I'm not even proud of this!
Class name can be identical if it's defined in another namespace, but it boggles the mind why anybody would want to do that to themselves.
Maybe you need to use extern aliases.
For example:
//in file foolaunch.cs
using System;
namespace Foo
{
public class Launch
{
protected void Method1()
{
Console.WriteLine("Hello from Foo.Launch.Method1");
}
}
}
// csc /target:library /out:FooLaunch.dll foolaunch.cs
//now subclassing foo.Launch
//in file subfoolaunch.cs
namespace Foo
{
extern alias F1;
public class Launch : F1.Foo.Launch
{
public void Method3()
{
Method1();
}
}
}
// csc /target:library /r:F1=foolaunch.dll /out:SubFooLaunch.dll subfoolaunch.cs
// using
// in file program.cs
namespace ConsoleApplication
{
extern alias F2;
class Program
{
static void Main(string[] args)
{
var launch = new F2.Foo.Launch();
launch.Method3();
}
}
}
// csc /r:FooLaunch.dll /r:F2=SubFooLaunch.dll program.cs