I'm trying to find a way to determine how many parameters a constructor has.
Now I've built one constructor with no parameters and 1 constructor with 4 parameters.
Is there, in C#, a way to find out how many parameters a used or given constructor has?
Thing is, I'm using a third constructor to read log files. These logs files are read as string[] elements and there should be just as many as there are arguments. If not, I have a corrupt log file.
But I'm using a lot of subclasses and each constructor has more parameters for their specific log-type.
So I wanted to know: is there a method to check the amount of parameters on a constructor?
And yes, this is a school assignment. I don't know what terms to look for really, so the VS2008 object browser is currently not of much use.
You should look at the System.Reflection Namespace. More specifically, you can get a list of the constructors of a class with:
System.Type.GetType("MYClassName").GetConstructors()
It sounds as if you need to re think your code a bit. From your description, having to dynamically determine the number of arguments in a constructor sounds a bit hairy. You might consider a factory design pattern since the type of object created is determined at runtime. If I misunderstand your problem then using reflection as pointed out by other answers will do the trick for you.
i'm not sure exactly what context you need this information, but if you need it dynamically at run-time try the System.Reflection namespace
otherwise the Intellisense drop-list should show you all the constructors available...
The amount of parameters is constant. I've defined them and they're not changing.
What's happening is I'm simulating a sort of publications tree and I'm making divisions in that(a.k.a. subclasses)
Thusly, all the constructors of my subclasses have the parameters or the classes they inherit from.
Thusly, the length is different for each type of publication.
I have a third constructor, just in case I need to visualise my publication data throuhg reading the log file.
But I have to take into account that the log file might be corrupt. Which includes the possibility that there is no data for all my parameters in the log file.
This is why I have to know how to find the amount of parameters in my constructor: I have to check howmuch data there is in my log compared to the amount of parameters I have.
Can't you make a constructor that takes a reference to the log file (or the current raw logfile entry), reads it, and throw an error if there's any problem?
I'm trying to understand why you'd need to look at the number of elements a constructor has. It seems a weak design from what I've seen so far to trust that the number of elements in the log file happens to identify the type of publication to create.
The short answer to your immediate question is what was stated in an earlier answer: reflect on the constructor for the class you're trying to create, and examine its parameters.
Related
I'd like to use C#'s reflection and custom attributes to simplify registering a series of types with a central management class (i.e. it provides static methods taking a string key and invoking/retrieving the proper method/parameter for the associated type). Looking at other questions here and a couple places elsewhere, it seems like the best way of doing so is to simply iterate through all public types of the assembly -- since it's intended to be a library -- and check if each type has the proper attribute before adding the relevant values to the underlying Dictionaries. The reflection and iteration will definitely be slow, but I can live with it since it should only occur once.
Unfortunately, I can't figure out how to get an attribute from a type. For methods and assemblies, I can use CustomAttributeExtensions.GetCustomAttribute<MyAttribute>(base) from System.Reflection.Extensions, but that doesn't provide an overload for Type; the same for Assembly.GetCustomAttribute(Assembly, Type) and the .IsDefined(...) methods used in this question. Other suggestions use methods on the Type itself that, from the documentation, seem to be loaded from mscorelib.dll, but it didn't seem to be showing up in Intellisense even after adding the reference and I'm not sure how that .dll interacts with .NET Standard, anyway (as in, does it reduce the ability to run on arbitrary platforms at all?)
Am I missing something obvious, or is it really this hard to get an Attribute back off of a Type?
Try typeof(YourType).GetTypeInfo().GetCustomAttributes();
I have a set of strings like this:
System.Int32
string
bool[]
List<MyType.MyNestedType>
Dictionary<MyType.MyEnum, List<object>>
I would like to test if those strings are actually source code representations of valid types.
I'm in an environment, that doesn't support Roslyn and incorporating any sort of parser would be difficult. This is why I've tried using System.Type.GetType(string) to figure this out.
However, I'm going down a dirty road, because there are so many edge cases, where I need to modify the input string to represent an AssemblyQualifiedString. E.g. nested type "MyType.MyNestedType" needs to be "MyType+MyNestedType" and generics also have to be figured out the hard way.
Is there any helper method which does this kind of checking in .Net 2.0? I'm working in the Unity game engine, and we don't have any means to switch our system to a more sophisticated environment with available parsers.
Clarification
My company has developed a code generation system in Unity, which is not easily changed at this point. The one thing I need to add to it, is the ability to get a list of fields defined in a class (via reflection) and then separate them based on whether they are part of the default runtime assembly or if they are enclosed within #if UNITY_EDITOR preprocessor directives. When those are set, I basically want to handle those fields differently, but reflection alone can't tell me. Therefore I have decided to open my script files, look through the text for such define regions and then check if a field is declared within in them, and if true, put it in a separate FieldInfo[] array.
The one thing fixed and not changeable: All script will be inspected via reflection and a collection of FieldInfo is used to generate new source code elsewhere. I just need to separate that collection into individual ones for runtime vs editor assembly.
Custom types and nested generics are probably the hard part.
Can't you just have a "equivalency map to fully qualified name" or a few translation rules for all custom types ?
I guess you know by advance what you will encounter.
Or maybe run it on opposite way : at startup, scan your assembly(s) and for each class contained inside, generates the equivalent name "as it's supposed to appear" in your input file from the fully qualified name in GetType() format ?
For custom types of other assemblies, please note that you have to do things such as calling Assembly.LoadFile() or pass assembly name in second parameter to GetType() before to be able to load them.
See here for example : Resolve Type from Class Name in a Different Assembly
Maybe this answer could also help : How to parse C# generic type names?
Could you please detail what is the final purpose of project ? The problem is a bit surprising, especially for a unity project. Is it because you used some kind of weird serialization to persist state of some of your objects ?
This answer is more a few recommandations and questions to help you to clarify the needs than a definitive answer, but it can't hold in a single comment, and I think it provide useful informations
I have been working on a project where I have a Worker class that generates a lot of data in a multi-threaded fashion. The type, size, and location of the data is variable based on a large set of parameters that can be set by an end user. Essentially this is a big test harness that I am using to investigate how certain things perform based on a variation of the data. Right now I have at least 12 different parameters for the Worker class. I was thinking about switching over to a separate WorkerOptions class that contains all of these values, and then have the UI create the WorkerOptions object and then pass that into the Worker. However, I could also expose public properties on the Worker class to allow the options to be set appropriately at Worker creation as well.
What is the best way to go about this, and why? I am sure this will generate some different opinions but I am open to listen to debate about why different people might do it a different way. Some things to consider are that currently once a Worker is created and running, its configuration doesn't change unless it stops. This could be subject to change, but I don't think it will.
EDIT
I am not a C# developer normally, I know enough to be able to write applications that function and follow common design patterns, but my expertise is in SQL Server, so I might ask follow up questions to clarify your meaning.
I have as guideline that the parameters that are necessary to use the instance should be passed in the constructor and all 'optional' parameters should be properties.
The properties will be initialized of course in the constructor to their default values.
If the number of arguments is not high I use default value arguments, but 12 is quite some amount.
I forgot to mention the separate class for options. Mostly I don't do such thing, unless there is some 'business logic' inside the options (like checking if some option combinations are not possible). If it is just for storage, you end up a with a lot of extra references to this option class (instances).
I'd combine the two approaches.
Make your WorkerOptions class use a constructor that requires all the required parameters, and allows the optional parameters to be set either via an overload, optional arguments, or properties, then pass that in as an argument.
Having the WorkerOptions class gives you a nice DTO to pass around in case refactoring leads you to create an additional layer between the UI and the worker class itself. Using required parameters in its constructor gives you compile-time checking to prevent runtime errors.
Personally, from what you have said, I prefer the WorkerOptions approach. For the following reasons:
It's cleaner, 12 constructor parameters is not out of the question, but it is perhaps a little excessive.
You can apply polymorphism and all the other OO goodness to your WorkerOptions. You might want to define an IWorkerOptions at some stage, or use Builder to construct different sub-classes of WorkerOption.
I would also make all WorkerOption instances immutable, or at least come up with a 'lock' or 'freeze' mechanism to prevent changes once a Worker has started execution.
I want to know how deserialization works and is it really needed to have the assembly on that system where the deserialization is happening.
If you haven't looked at MSDN yet, do so. It will tell you everything you need to know about the serialization/deserialization process...at least enough to use it. The link I gave you is specifically 'how to deserialize.'
As far as the more technical aspects, the pieces of information that will get serialized will be exactly what is required to fill that structure/class/object.
I'm not really sure what you mean by the 2nd part of your question about the assembly. However, if you are serializing a struct (for instance), then in order to deserialize to another machine, or application, you must have that exact same struct available: name, fields, data types, etc.
If you're looking for the exact details, you can boot up an instance of Reflector and point it to mscorlib and look into the various classes in the System.Runtime.Serialization namespace. Here's the high-level idea (as I understand it):
The first step is ensuring that the type system that wrote binary stream is the same as the type system that is reading the binary stream. Since so little meta-information is attached to the output, problems can arise if we're not looking at the same type. If we have two classes named A, but the writer thinks an A is class A { int m_a, m_b; } and the reader thinks A is class A { int m_b, m_a; }, we're going to have problems. This problem is much worse if the types are significantly different. Keep this in mind, it will come back later.
Okay, so we're reading and writing the same types. The next step is finding all the members of the object you want to serialize. You could do this through reflection with a call like typeof(T).GetFields(~System.Reflection.BindingFlags.Default), but that will be super-slow (rule of thumb: reflection is slow). Luckily, .NET's internal calls are much faster.
Step 1: Now we get to writing. First: the writer writes the strong-name assembly that the object we're serializing resides in. The reader can then confirm that they actually have this assembly loaded. Next, the object's namespace-qualified type is written, so the reader can read into the proper object. This basically guarantees that the reading type and writing type is the same.
Step 2: Time to actually write the object. A look at the methods of Formatter lets us know that there is some basic functionality for writing ints, floats and all sorts of simple types. In a pre-determined order (the order they are declared, starting from the fields of the base class), each field is written to the output. For fields that are not the simple types, recurse back to step 1 with the object in that field.
To deserialize, you perform these same steps, except replace all the verbs such as 'write' with verbs like 'read.' Order is extremely important.
Background
I have a few scripts that run as part of my build process that look at the various source code files and generate some more source code for me.
The scripts use CodeDom to generate them and they read the .cs files using a simple text reader.
Question
One of the scripts is looking for use of a specific class attribute called PageMenuItem and its purpose is to build a static list of page menu items.
It does this right now by reading all of the .cs files and looks for "PageMenuItem" attributes, then it counts the number of arguments and tries to figure out which constructor is being used so it can pull apart the various pieces of information.
There are 7 constructors for PageMenuItem with various parameters, so it is getting very difficult to determine from the .cs source code which constructor is being used and therefore how to parse out the information.
Instead of trying to parse the text myself, I would like to simply construct a PageMenuItem object in memory and then use its properties.
So, I need a way of taking the attribute declaration from the .cs file and construct a new instance of PageMenuItem from it.
Is that possible?
Another way of asking this question:
Given this string:
string myCodeStatement = "[MyAttribute(\"asdf\", \"foo\")]";
How can I create an object of the type MyAttribute so that I can work with that object? I have full access to the source code that defines MyAttribute.
Seems like you could introspect the class files, or alternately add an annotation to the constructor that would make your parsing job simpler. Aspect oriented techniques might help -- capture every time that constructor is called, and as it is, add the item to your list.
You can use the CSharpCodeProvider to do this. There is a Microsoft Support article describing the process.
Is invoking the compiler an option? You could build the source files themselves and use reflection to walk the attributes, or you could create a dummy source file that you mark up with those attributes. Either way, once it's compiled, you can reflect in to access the attribute's properties.
This script is part of the build process, so it needs to be pretty quick. Also, it generates source code that is going to get compiled, so I want to avoid "double compiling" my project.
I also don't want to have to compile and load an assembly just to reflect against it, which seems "expensive" to do several hundred times during my build process.
I decided that I just needed to fix up how I am parsing the attributes now. ---
I'm already reading the source code and trying to count the number of attributes. I decided I could modify that code to just parse the arguments into their types and then use Activator.CreateInstance() using my parsed arguments. Activator will figure out which constructor to use and I will get an instance of my attribute class and can use its properties.
I already know which types are available in the attribute's constructor, so I wrote a little method that parses the stuff between the parans into their correct type (string, int, guid, etc) and then I pass that object array to the Activator.
The Activator does the hard work of finding the correct constructor and gives me back an instance of my attribute class.