C# 返回一个通用的 IEnumerable<T>
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returning a generic IEnumerable<T>
提问by Thousand
I'm messing around with generics and IEnumerable abit, but i'm kindof stuck. Here's what i'm trying to do: I want to have a method that returns any collection type - that implements IEnumerable (?) - (so e.g: List, Stack, Queue, ...)
我正在使用泛型和 IEnumerable abit，但我有点卡住了。这就是我想要做的：我想要一个返回任何集合类型的方法 - 实现 IEnumerable (?) - （例如：列表、堆栈、队列等）
furthermore, i want to be able to return any collection type, of any datatype.
so i want this method to be able to return a List<string>,as well as a Stack<int>, as well as a List<double>... etc etc.
此外，我希望能够返回任何数据类型的任何集合类型。所以我希望这个方法能够返回 aList<string>,和 a Stack<int>，以及 a List<double>... 等等。
public IEnumerable<T> returnSomething()
{
Stack<int> stackOfInts = new Stack<int>();
List<string> listOfStrings = new List<string>();
return stackOfInts;
}
this is what i've tried so far. this however doesn't work, i get this error:
这是我迄今为止尝试过的。但是这不起作用，我收到此错误：
Cannot implicitly convert type 'System.Collections.Generic.Stack<int>' to 'System.Collections.Generic.IEnumerable<T>'. An explicit conversion exists (are you missing a cast?)
however, if i replace the IEnumerable<T>in the method signature to IEnumerable<int>, i can return any collection of type int. This however means, that now i can't return the ListOfStringsanymore.
但是，如果我将IEnumerable<T>方法签名中的替换为，则IEnumerable<int>可以返回任何 int 类型的集合。然而，这意味着，现在我不能再返回ListOfStrings了。
would appreciate any suggestions or ideas :)
将不胜感激任何建议或想法:)
采纳答案by Mark Byers
You need to add a generic type parameterto your method:
您需要为您的方法添加一个泛型类型参数：
public IEnumerable<T> ReturnSomething<T>()
{
Stack<T> stackOfT = new Stack<T>();
return stackOfT;
}
The type parameter appears after the method name, but before the parameters. It is also possible to have a method with more than one type parameter.
类型参数出现在方法名称之后，但在参数之前。一个方法也可以有多个类型参数。
When you call the method you can specify the type:
当您调用该方法时，您可以指定类型：
IEnumerable<int> myInts = ReturnSomething<int>();
回答by oleksii
The trick is to declare<T>right, if you define generic <T>, then you have to stick to it in your methods, so if you have IEnumerable<T>then elsewhere in your method you must use <T>and not <int>or any other type.
诀窍是声明<T>正确，如果你定义了 generic <T>，那么你必须在你的方法中坚持它，所以如果你IEnumerable<T>在你的方法中的其他地方有那么你必须使用<T>而不是<int>或任何其他类型。
It is only latter when you actually useyou generic type you substitute generic <T>for a real type.
只有在您实际使用泛型类型时才将泛型替换<T>为真实类型。
See a sample
查看样本
class Foo<T>
{
public IEnumerable<T> GetList()
{
return new List<T>();
}
public IEnumerable<T> GetStack()
{
return new Stack<T>();
}
}
class Program
{
static void Main(string[] args)
{
Foo<int> foo = new Foo<int>();
IEnumerable<int> list = foo.GetList();
IEnumerable<int> stack = foo.GetStack();
Foo<string> foo1 = new Foo<string>();
IEnumerable<string> list1 = foo1.GetList();
IEnumerable<string> stack1 = foo1.GetStack();
}
}
回答by HatSoft
Yes you can return any type if you change IEnumerable<T> to IEnumerable<dynamic>
是的，如果您更改 I，您可以返回任何类型Enumerable<T> to IEnumerable<dynamic>
like this:
像这样：
public IEnumerable<dynamic> returnSomething()
{
.....
回答by burning_LEGION
public IEnumerable<T> returnSomething()
{
Stack<int> stackOfInts = new Stack<int>();
return (IEnumerable<T>) stackOfInts;
}
回答by Joe
The type parameter needs to be specified by the caller somewhere.
类型参数需要由调用者在某处指定。
Either when instantiating a generic class:
在实例化泛型类时：
public class MyClass<T>
{
public IEnumerable<T> returnSomething()
{
Stack<T> stackOfTs = new Stack<T>();
List<T> listOfTs = new List<T>();
return stackOfTs;
}
}
var v = new MyClass<int>();
foreach(var item in v.returnSomething())
{
}
Or when calling a generic method of a non-generic class:
或者在调用非泛型类的泛型方法时：
public class MyClass
{
public IEnumerable<T> returnSomething<T>()
{
Stack<T> stackOfTs = new Stack<T>();
List<T> listOfTs = new List<T>();
return stackOfTs;
}
}
var v = new MyClass();
foreach(var item in v.returnSomething<int>())
{
}
回答by sarder kamruzzaman polash
For more help full structure given below ...
如需更多帮助，请参阅下面给出的完整结构...
my model is
我的模型是
public class Student
{
public int studentId { get; set; }
public string studentName { get; set; }
public string subject { get; set; }
public string studentClass { get; set; }
public int RollNumber { get; set; }
}
IEnumerable return datalist
IEnumerable 返回数据列表
public static IEnumerable<Student> ReturnSomething()
{
IList<Student> studentList = new List<Student>()
{
new Student()
{studentId = 1, studentName = "Bill", subject = "Science", studentClass = "nine", RollNumber = 01},
new Student()
{studentId = 2, studentName = "Steve", subject = "Arts", studentClass = "ten", RollNumber = 03},
new Student()
{studentId = 3, studentName = "Ram", subject = "Commerce", studentClass = "nine", RollNumber = 05},
new Student()
{studentId = 1, studentName = "Moin", subject = "Science", studentClass = "ten", RollNumber = 06}
};
return studentList;
}
and last one is access code
最后一个是访问代码
Student student = new Student();
IEnumerable<Student> studentList = ReturnSomething();
foreach (Student VARIABLE in studentList)
{
student.studentName += VARIABLE.studentName + " "+ "Class= ";
student.studentClass += VARIABLE.studentClass + " ";
}
Console.WriteLine(student.studentName + student.studentClass);
Console.ReadKey();
