The way nameof() works, I can write
var s = nameof(HomeController.Index);
Can I make my own compile-time method that works the same way and can take the same input? For example:
public static string MyMethod(Something input) // I'm not sure what Something should be
{
// do something with input to get method info
}
... // elsewhere in code
var s = MyMethod(HomeController.Index);
Update for context:
More specifically I would like to be able to make a helper method to be used in a Razor view. For example, I might call MyMethod(HomeController.Index) to return a string listing the controller name and the action name. It would be nice to be able to make such a method without having to pass both the controller type HomeController and the method name Invoke as separate parameters.
Update for more context and example:
My goal is to avoid magic strings when specifying controllers and actions in Razor views. Here's an example of how I am doing this currently by checking for the [Action] attribute on actions and trimming of the "Controller" suffix from controllers. But you can see that it's verbose.
<a asp-action="#(ControllerHelpers.GetActionName<HomeController>(nameof(HomeController.Index)))" asp-controller="#(ControllerHelpers.GetRouteName<HomeController>())">Link to Home</a>
I'm looking for a way to do something like this
<a asp-action="#ControllerHelpers.GetActionName(HomeController.Index)" asp-controller="#(ControllerHelpers.GetRouteName<HomeController>())">Link to Home</a>
and perhaps eventually my own tag helper like this. But even here I'd like to avoid having to separately pass both the controller and the action name (just for concision).
<a asp-controller-action="HomeController.Index">Link to Home</a>
You can do this via reflection, passing the method name as a string, and then using Type.GetMethod to get the method and then call Invoke on that, with the type instance.
However, the better thing to do here is to use a delegate. Specifically, you can do something like:
public static string MyMethod(Func<IActionResult> func)
And then:
var s = MyMethod(() => controller.Index());
Inside MyMethod, you'd invoke this like any other method, i.e. func().
That said, what you're trying to ultimately achieve here is unclear and suspect. You can't just invoke HomeController.Index; you need a HomeController instance. Manually newing up a controller, is pretty much always wrong, so there's probably a better way to achieve what you want, in general.
In other words, you seem to have an XY problem here. You're trying to do X, and you've decided Y is the way to do that (here, trying to pass a method reference and invoke that for some reason). But, you don't know how to do Y, either. Instead of asking about X, i.e. the thing you actually need help with, you're asking about Y, which almost assuredly isn't even a good way to do X, in the first place. Give us some more info on X, the thing you actually want, and we can probably give you a better method to achieve that.
I'm not 100% sure what you're asking for, but here's an example of how to do something like what you're asking for using delegates (MS delegate guide):
class MethodRunner
{
// use delegates to define the method signature that you'll operate on
public delegate void NoArgFormat();
public delegate void OneStringArgFormat(String arg);
//You can accept delegates as function arguments, then call them
//with a "live" object instance
public void RunMyMehtod(NoArgFormat methodToRun)
{
methodToRun();//runs the methd passed in
}
public void RunMyStringArgMethod(OneStringArgFormat methodToRun, String arg)
{
methodToRun(arg);
}
}
class Program
{
//This matches to "NoArgFormat" delegate definition
public void Method1()
{
Console.WriteLine("Method1");
}
//This matches the OneStringArgFormat
public void Method2(String arg)
{
Console.WriteLine(arg);
}
static void Main(string[] args)
{
Program p = new Program();
MethodRunner mr = new MethodRunner();
mr.RunMyMehtod(p.Method1);
mr.RunMyStringArgMethod(p.Method2, "First");
mr.RunMyStringArgMethod(p.Method2, "Second");
}
}
Sample output:
C:\Workspace\SampleApp\bin\Debug>SampleApp.exe
Method1
First
Second
Note: This question was asked at a time when C# did not yet support optional parameters (i.e. before C# 4).
We're building a web API that's programmatically generated from a C# class. The class has method GetFooBar(int a, int b) and the API has a method GetFooBar taking query params like &a=foo &b=bar.
The classes needs to support optional parameters, which isn't supported in C# the language. What's the best approach?
Surprised no one mentioned C# 4.0 optional parameters that work like this:
public void SomeMethod(int a, int b = 0)
{
//some code
}
Edit: I know that at the time the question was asked, C# 4.0 didn't exist. But this question still ranks #1 in Google for "C# optional arguments" so I thought - this answer worth being here. Sorry.
Another option is to use the params keyword
public void DoSomething(params object[] theObjects)
{
foreach(object o in theObjects)
{
// Something with the Objects…
}
}
Called like...
DoSomething(this, that, theOther);
In C#, I would normally use multiple forms of the method:
void GetFooBar(int a) { int defaultBValue; GetFooBar(a, defaultBValue); }
void GetFooBar(int a, int b)
{
// whatever here
}
UPDATE: This mentioned above WAS the way that I did default values with C# 2.0. The projects I'm working on now are using C# 4.0 which now directly supports optional parameters. Here is an example I just used in my own code:
public EDIDocument ApplyEDIEnvelop(EDIVanInfo sender,
EDIVanInfo receiver,
EDIDocumentInfo info,
EDIDocumentType type
= new EDIDocumentType(EDIDocTypes.X12_814),
bool Production = false)
{
// My code is here
}
From this site:
https://www.tek-tips.com/viewthread.cfm?qid=1500861
C# does allow the use of the [Optional] attribute (from VB, though not functional in C#). So you can have a method like this:
using System.Runtime.InteropServices;
public void Foo(int a, int b, [Optional] int c)
{
...
}
In our API wrapper, we detect optional parameters (ParameterInfo p.IsOptional) and set a default value. The goal is to mark parameters as optional without resorting to kludges like having "optional" in the parameter name.
You could use method overloading...
GetFooBar()
GetFooBar(int a)
GetFooBar(int a, int b)
It depends on the method signatures, the example I gave is missing the "int b" only method because it would have the same signature as the "int a" method.
You could use Nullable types...
GetFooBar(int? a, int? b)
You could then check, using a.HasValue, to see if a parameter has been set.
Another option would be to use a 'params' parameter.
GetFooBar(params object[] args)
If you wanted to go with named parameters would would need to create a type to handle them, although I think there is already something like this for web apps.
You can use optional parameters in C# 4.0 without any worries.
If we have a method like:
int MyMetod(int param1, int param2, int param3=10, int param4=20){....}
when you call the method, you can skip parameters like this:
int variab = MyMethod(param3:50; param1:10);
C# 4.0 implements a feature called "named parameters", you can actually pass parameters by their names, and of course you can pass parameters in whatever order you want :)
An easy way which allows you to omit any parameters in any position, is taking advantage of nullable types as follows:
public void PrintValues(int? a = null, int? b = null, float? c = null, string s = "")
{
if(a.HasValue)
Console.Write(a);
else
Console.Write("-");
if(b.HasValue)
Console.Write(b);
else
Console.Write("-");
if(c.HasValue)
Console.Write(c);
else
Console.Write("-");
if(string.IsNullOrEmpty(s)) // Different check for strings
Console.Write(s);
else
Console.Write("-");
}
Strings are already nullable types so they don't need the ?.
Once you have this method, the following calls are all valid:
PrintValues (1, 2, 2.2f);
PrintValues (1, c: 1.2f);
PrintValues(b:100);
PrintValues (c: 1.2f, s: "hello");
PrintValues();
When you define a method that way you have the freedom to set just the parameters you want by naming them. See the following link for more information on named and optional parameters:
Named and Optional Arguments (C# Programming Guide) # MSDN
Hello Optional World
If you want the runtime to supply a default parameter value, you have to use reflection to make the call. Not as nice as the other suggestions for this question, but compatible with VB.NET.
using System;
using System.Runtime.InteropServices;
using System.Reflection;
namespace ConsoleApplication1
{
public class Class1
{
public static void SayHelloTo([Optional, DefaultParameterValue("world")] string whom)
{
Console.WriteLine("Hello " + whom);
}
[STAThread]
public static void Main(string[] args)
{
MethodInfo mi = typeof(Class1).GetMethod("sayHelloTo");
mi.Invoke(null, new Object[] { Missing.Value });
}
}
}
I agree with stephenbayer. But since it is a webservice, it is easier for end-user to use just one form of the webmethod, than using multiple versions of the same method. I think in this situation Nullable Types are perfect for optional parameters.
public void Foo(int a, int b, int? c)
{
if(c.HasValue)
{
// do something with a,b and c
}
else
{
// do something with a and b only
}
}
optional parameters are for methods. if you need optional arguments for a class and you are:
using c# 4.0: use optional arguments in the constructor of the class, a solution i prefer, since it's closer to what is done with methods, so easier to remember. here's an example:
class myClass
{
public myClass(int myInt = 1, string myString =
"wow, this is cool: i can have a default string")
{
// do something here if needed
}
}
using c# versions previous to c#4.0: you should use constructor chaining (using the :this keyword), where simpler constructors lead to a "master constructor".
example:
class myClass
{
public myClass()
{
// this is the default constructor
}
public myClass(int myInt)
: this(myInt, "whatever")
{
// do something here if needed
}
public myClass(string myString)
: this(0, myString)
{
// do something here if needed
}
public myClass(int myInt, string myString)
{
// do something here if needed - this is the master constructor
}
}
The typical way this is handled in C# as stephen mentioned is to overload the method. By creating multiple versions of the method with different parameters you effectively create optional parameters. In the forms with fewer parameters you would typically call the form of the method with all of the parameters setting your default values in the call to that method.
Using overloads or using C# 4.0 or above
private void GetVal(string sName, int sRoll)
{
if (sRoll > 0)
{
// do some work
}
}
private void GetVal(string sName)
{
GetVal("testing", 0);
}
You can overload your method. One method contains one parameter GetFooBar(int a) and the other contain both parameters, GetFooBar(int a, int b)
You can use default.
public void OptionalParameters(int requerid, int optinal = default){}
For a larger number of optional parameters, a single parameter of Dictionary<string,Object> could be used with the ContainsKey method. I like this approach because it allows me to pass a List<T> or a T individually without having to create a whole other method (nice if parameters are to be used as filters, for example).
Example (new Dictionary<string,Object>() would be passed if no optional parameters are desired):
public bool Method(string ParamA, Dictionary<string,Object> AddlParams) {
if(ParamA == "Alpha" && (AddlParams.ContainsKey("foo") || AddlParams.ContainsKey("bar"))) {
return true;
} else {
return false;
}
}
Instead of default parameters, why not just construct a dictionary class from the querystring passed .. an implementation that is almost identical to the way asp.net forms work with querystrings.
i.e. Request.QueryString["a"]
This will decouple the leaf class from the factory / boilerplate code.
You also might want to check out Web Services with ASP.NET. Web services are a web api generated automatically via attributes on C# classes.
A little late to the party, but I was looking for the answer to this question and ultimately figured out yet another way to do this. Declare the data types for the optional args of your web method to be type XmlNode. If the optional arg is omitted this will be set to null, and if it's present you can get is string value by calling arg.Value, i.e.,
[WebMethod]
public string Foo(string arg1, XmlNode optarg2)
{
string arg2 = "";
if (optarg2 != null)
{
arg2 = optarg2.Value;
}
... etc
}
What's also decent about this approach is the .NET generated home page for the ws still shows the argument list (though you do lose the handy text entry boxes for testing).
I have a web service to write that takes 7 parameters. Each is an optional query attribute to a sql statement wrapped by this web service. So two workarounds to non-optional params come to mind... both pretty poor:
method1(param1, param2, param 3, param 4, param 5, param 6, param7)
method1(param1, param2, param3, param 4, param5, param 6)
method 1(param1, param2, param3, param4, param5, param7)... start to see the picture. This way lies madness. Way too many combinations.
Now for a simpler way that looks awkward but should work:
method1(param1, bool useParam1, param2, bool useParam2, etc...)
That's one method call, values for all parameters are required, and it will handle each case inside it. It's also clear how to use it from the interface.
It's a hack, but it will work.
I had to do this in a VB.Net 2.0 Web Service. I ended up specifying the parameters as strings, then converting them to whatever I needed. An optional parameter was specified with an empty string. Not the cleanest solution, but it worked. Just be careful that you catch all the exceptions that can occur.
For just in case if someone wants to pass a callback (or delegate) as an optional parameter, can do it this way.
Optional Callback parameter:
public static bool IsOnlyOneElement(this IList lst, Action callbackOnTrue = (Action)((null)), Action callbackOnFalse = (Action)((null)))
{
var isOnlyOne = lst.Count == 1;
if (isOnlyOne && callbackOnTrue != null) callbackOnTrue();
if (!isOnlyOne && callbackOnFalse != null) callbackOnFalse();
return isOnlyOne;
}
optional parameters are nothing but default parameters!
i suggest you give both of them default parameters.
GetFooBar(int a=0, int b=0) if you don't have any overloaded method, will result in a=0, b=0 if you don't pass any values,if you pass 1 value, will result in, passed value for a, 0 and if you pass 2 values 1st will be assigned to a and second to b.
hope that answers your question.
In the case when default values aren't available the way to add an optional parameter is to use .NET OptionalAttribute class - https://learn.microsoft.com/en-us/dotnet/api/system.runtime.interopservices.optionalattribute?view=netframework-4.8
Example of the code is below:
namespace OptionalParameterWithOptionalAttribute
{
class Program
{
static void Main(string[] args)
{
//Calling the helper method Hello only with required parameters
Hello("Vardenis", "Pavardenis");
//Calling the helper method Hello with required and optional parameters
Hello("Vardenis", "Pavardenis", "Palanga");
}
public static void Hello(string firstName, string secondName,
[System.Runtime.InteropServices.OptionalAttribute] string fromCity)
{
string result = firstName + " " + secondName;
if (fromCity != null)
{
result += " from " + fromCity;
}
Console.WriteLine("Hello " + result);
}
}
}
You can try this too
Type 1
public void YourMethod(int a=0, int b = 0)
{
//some code
}
Type 2
public void YourMethod(int? a, int? b)
{
//some code
}
I'm not sure exactly how to call this situation, but here it is:
I have 2 methods with different types, but from the "outside" they have the same signature. And when calling the method, I would like to invoke a specific method instead of the other - here is what I have:
public class SomeClass
{
public async Task<Response<T>> MyMethod<T>(string name, T myObj)
{
// some code here
}
public async Task<Response<T>> MyMethod<T>(string name, string myObj)
{
// some code here
}
}
For the compiler, the 2 methods above are different and have different signatures. But when calling:
var myClass = new SomeClass();
myClass.MyMethod("name", "something");
When calling MyMethod in the example, what's being called is MyMethod<T>(string name, T myObj), but what I would actually want to call is the second method. Is there a way to make it call a specific signature?
EDIT:
I found the if I give in one of the methods a different name to the second variable and then calling the method with the variable name as part of the call it does work, as in the following example:
public class SomeClass
{
public async Task<Response<T>> MyMethod<T>(string name, T myObj)
{
// some code here
}
public async Task<Response<T>> MyMethod<T>(string name, string myNewObj)
{
// some code here
}
}
var myClass = new SomeClass();
myClass.MyMethod<AnyOfMyTypes>("name", myNewObj: "something");
While this works, following Jon's response below, does it seem like something that is correct to do? As far as for the method name, I would like to keep it the same, and the other option is to change the signature by adding some dummy boolean variable.
The compiler certainly can't call the second method with that calling code, as it wouldn't know what to infer for T. If you specify a type argument though, it does call the second method:
myClass.MyMethod<string>("name", "something");
While that will work, I would strongly advise you to change the design if you possibly can. Rename one of the methods. I can reasonably call myself a C# expert, but I couldn't predict from inspection whether or not that would work. The overload resolution and type inference details in C# are really complicated, and it's unreasonable to expect every C# developer to know them inside out.
If you can give the methods different names, the code code is likely to be a lot simpler to read.
Following Jon's answer I'd suggest following solution to your problem:
private async Task<Response<T>> MethodForString<T>(string str)
{
// some code...
}
public async Task<Response<T>> Method<T>(T obj)
{
if (typeof(T) == typeof(string))
return MethodForString<T>(obj as string);
// some code...
}
Above is just a sample, but idea is simple: just check type of T and call appropriate method :)
This way, all your method call will remain exactly the same :)
The reason the first method is being called is because you have a generic type of T.
If you pass a string into this then it will hit the first method. It is better design to only have one method. If you want to be able to pass in any type then keep the first method, if you want just a string then keep just the second method. You should only have two methods if both have distinct clear purposes.
This
public class SomeClass
{
public async Task<Response<T>> MyMethod<T>(string name, T myObj)
{
// some code here
}
}
Or
public class SomeClass
{
public async Task<Response<T>> MyMethod<T>(string name, string myObj)
{
// some code here
}
}
Or
public class SomeClass
{
public async Task<Response<T>> MyMethod<T>(string name, string myObj)
{
// some code here
}
public async Task<Response<T>> MyMethod<T>(string name, int age, string address)
{
// some code here
}
}
Dont put a dummy variable into any of the methods, this will lead to problems debugging and be misleading for other developers.
Is it possible to get the name of another method in the same class but without using a manually written string?
class MyClass {
private void doThis()
{
// Wanted something like this
print(otherMethod.name.ToString());
}
private void otherMethod()
{
}
}
You may ask why: well the reason is that I must invoke the method later on like this Invoke("otherMethod"), however I don't want to hardcode this string myself as I can't refactor it anymore within the project.
One approach is you can wrap it into delegate Action, then you can access the name of method:
string name = new Action(otherMethod).Method.Name;
You can use reflection (example - http://www.csharp-examples.net/get-method-names/) to get the method names. You can then look for the method that you're looking for by name, parameters or even use an attribute to tag it.
But the real question is - are you sure this is what you need? This looks as if you don't really need reflection, but need to think over your design. If you already know what method you're going to invoke, why do you need the name? How about a using a delegate? Or exposing the method via an interface and storing a reference to some class implementing it?
Try this:
MethodInfo method = this.GetType().GetMethod("otherMethod");
object result = method.Invoke(this, new object[] { });
Btw. I also found (in the expansions of the internet) an alternative solution for only getting the string of a method. It also works with parameters and return types:
System.Func<float, string> sysFunc = this.MyFunction;
string s = sysFunc.Method.Name; // prints "MyFunction"
public string MyFunction(float number)
{
return "hello world";
}