Say I have a struct declared like the following:
public struct Test
{
public static int Width = 5;
...
public static int[] Value = new int[1]{ 0 };
}
Now what I want to do is call this from within another struct, but I have to clue how. What I'm trying to do would (in my mind) look like the following:
public struct AnotherStruct
{
public (type of struct) this[int key]
{
get
{
switch(key)
{
case 1:
return (another struct);
default:
return null;
}
}
}
}
My end goal is that I want to use code that looks like the following, without having to create an instance of the object:
structobject s = new AnotherStruct[5];
So this 'lookup table' will be created in another project and built, then called as a dll from my main project. Since I'm building the dll elsewhere and calling it, I'm hoping that I can get the dll loaded into memory once, and then I can just reference that memory from my main project. Then I'll have one allocated portion of memory and my code will just reference it, avoiding the need to create individual instances of this lookup table (thus avoiding the time overhead it takes to allocate the memory and store the new instance). The time I'd save would be hugely beneficial in the long run, so I'm hoping I can get this to work somehow.
I hope this isn't too confusing, but let me know if any clarification is needed.
Edit
This is being used on a website, so really I need an object that persists across all connections and is created once when the code is initially loaded. Same idea, but maybe that will make for a simpler solution?
Solution #2. Forgo the whole ID idea and just use the structure type and generics.
public struct St1
{
}
public struct St2
{
}
public class Factory<T>
where T : struct
{
static T _new = new T(); //cached copy of structure
public static T New { get { return _new; } }
}
class Program
{
static void Main(string[] args)
{
St1 x1 = Factory<St1>.New;
St1 x2 = Factory<St1>.New;
St1 x3 = Factory<St1>.New;
St2 y1 = Factory<St2>.New;
St2 y2 = Factory<St2>.New;
}
}
Solution #1. Using a common interface for all the structures and a dictionary collection
public interface IStr { }
public struct St1 : IStr
{
public static int ID = 1;
}
public struct St2 : IStr
{
public static int ID = 2;
}
public class StructFactory : System.Collections.ObjectModel.KeyedCollection<int, IStr>
{
public static StructFactory Default = new StructFactory();
protected override int GetKeyForItem(IStr item)
{
FieldInfo finfo = item.GetType().GetField("ID",
BindingFlags.Static | BindingFlags.Public);
return (int)finfo.GetValue(item);
}
public StructFactory()
{
Add(new St1());
Add(new St2());
}
}
class Program
{
static void Main(string[] args)
{
St1 x = (St1)StructFactory.Default[1];
St2 y = (St2)StructFactory.Default[2];
}
}
The syntax you use above won't work since it means "create an array of AnotherStruct with five elements in it." As mentioned in a comment, however, you really should look into using a factory pattern.
However, if you really want to use the pattern above, you could change it up slightly. Have your AnotherStruct array hold Type instances of each of your structs. Then, your "creation" line would look more like:
structobject s = (structobject)Activator.CreateInstance(AnotherStruct[5]);
You can use reflection on the Assembly (since you are wrapping it in a DLL) to get those Type objects.
And finally, unless you have a really good reason for using struct (and understand all of the nuances, of which there are several), stick with class.
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Sometimes it happens that I want to use a lot of Method As variables in Method B.
Usually its quite a pain to pass all the variables to this method, especially if I have to do this a lot of times (but cannot simply copy paste, because some things change) or am just to lazy.
Is there such a thing like a "inner Method"? Or some concept to handle this in an easy way?
What I want to do:
public void A()
{
int a = 4;
string b = "Hello World";
B(ref vals);
//Or like so
C(ref current);
}
public void B(ref AllValues)
{
a = 3;
...
}
public void C(ref MethodThatSharesAllValues method)
{
method.a = 3;
...
}
If they all are in the same class
You can configure them as class variables:
public class MyClass{
//set this as private/protected/public or nothing and you can also set a default value
int a;
public void A()
{
a = 4;
string b = "Hello World";
B();
C();
}
public void B()
{
a = 3;
...
}
public void C()
{
a = 3;
...
}
}
Elseway
public static class MyClassA{
public static int a = 0;
public static void MethodA(){
this.a = 3;
}
}
now from method B you can access MyClassA
int myExValueA = MyClassA.a;
Elseway you gotta pass them as parameters
hope this helps
You can create a class which will hold your parameters and then pass only an instance of this class
public void metA(Parameters input)
{
input.a = 5;
input.c = "hello";
metB(input);
}
public void metB(Parameters input)
{
input.b = 10;
}
public class Parameters
{
public int a;
public int b;
public string c;
}
You can declare the variables static in a class header and use them as you like, private if are in the same class, protected for child classes, internal or public else. Or box the variables in a class like this:
public class Foo
{
public int A { get; set; }
public int B { get; set; }
public string C { get; set; }
}
If passed variables are the same type you can use data structure like int[] or string[] or List<int> or List<string> and pass them without ref but this has the disadvantage that more than often you would not use all varibales from the structure as it is also the case with the class boxing variant.
Something like the following:
public void foo() {
int a = 10;
// ...
}
public void foo_bar() {
// "a" is not in scope for foo_bar, so this won't compile
a = 20;
// ...
}
would definitely be invalid. I don't think that this was what you were driving at in your question though.
You can do something somewhat similar to what you ask for using closures but they're a bit tricky to work with. Basically, something like this would be valid (and I'm not sitting in front of an IDE so forgive me if the syntax is a little off):
Func<int> GetCounter() {
int count = 0;
// This will capture the count variable from its context
Func<int> method = () => ++count;
return method;
}
While a fair number of languages (including some versions of C++ now I guess) have closures (or some similar variant), there seems to be little consistency in exactly how they work across languages (e.g. on whether the "count" variable should be immutable once it's captured) so it's important to check the documentation for the language you're using (in this case, C#) to understand exactly how they work.
In terms of the first code sample I provide, I doubt that that's what you were asking about, but just as a brief digression you probably wouldn't really want it to be the allowable anyway (and again I suspect that this isn't the syntax/semantics you're asking about) as it would quickly lead to unexpected/undefined behavior. For example:
If you have a local variable a that's initialized in Foo() and you refer to it in Foo_Bar() before you run Foo(), what should its value be?
If you run Foo() to initialize the variable, edit the variable in Foo_Bar(), and then run Foo() again, should you re-initialize the variable or allow it to remain what Foo_Bar() set it to?
Is it safe to garbage collect a local variable after the method call completes, or might it be referred to again?
See the following:
public class SomeObject
{
public int SomeProperty { get; set; } = 6;
// ...
}
public class SomeOtherObject
{
// ..
}
void foo() {
// What is the content of "a" before foo() runs?
object a = new SomeObject();
// Which "a" should this refer to - the one in foo() or the one in foo_bar()?
// Also, is this a valid cast given that we haven't specified that SomeOtherObject can be cast to SomeObject?
var b = (SomeObject)a;
// If we run foo() again, should "b" retain the value of SetProperty or set it back to the initial value (6)?
b.SetProperty = 10;
// ...
// Is it safe to garbage collect "a" at this point (or will foo_bar refer to it)?
}
void foo_bar() {
object a = new SomeOtherObject();
// ...
}
I have some delegates, two classes and a struct that look kind of like this:
delegate Value Combination(Value A, Value B);
class Environment
{
private Combination[][] combinations;
private string[] typenames;
private getString[] tostrings;
public Environment() { ... } //adds one 'Null' type at index 0 by default
public void AddType(string name, getString tostring, Combination[] combos) { ... }
public Value Combine(Value A, Value B)
{
return combinations[A.index][B.index](A, B);
}
public string getStringValue(Value A)
{
return tostrings[A.index](A);
}
public string getTypeString(Value A)
{
return typenames[A.index];
}
}
class Container
{
public string contents
{
get
{
return data.text;
}
}
public string contentType
{
get
{
return data.type;
}
}
private Value data;
public Container(Value val)
{
data = val;
}
public Container CombineContents(Container B)
{
return new Container(data.Combine(B.data))
}
}
struct Value
{
public string type
{
get
{
return environment.getTypeString(this);
}
}
public string text
{
get
{
return environment.getStringValue(this);
}
}
public readonly int type;
public readonly byte[] raw;
public readonly Environment environment;
public Value(int t, byte[] bin, Environment env)
{
type = t;
raw = bin;
environment = env;
}
public Value Combine(Value B)
{
return environment.Combine(this, B)
}
}
The reason for this structure is that Containers can have Values of various types, which combine with each other in user-defined ways according to the current Environment (which, like Container and Value, is differently named so as to avoid conflicting with the System.Environment class in my actual code- I used the name here to concisely imply its function). I cannot get around the problem with subclasses of Value and generic Containers since values of different types still need to be combinable, and neither Container nor the base Value class can know what type of Value combination should return.
It doesn't seem possible to define the Environment class in a global way, as the existing System.Environment class doesn't seem to allow storing delegates as user variables, and giving it a static method returning an instance of itself would render it unmodifiable*, and would require a new instance of the class to be created every time I want to do anything with Values, which seems like it should be a huge performance hit.
This causes two problems for me:
There is an extra reference padding out all my Values. Values are variable in size, but raw is almost always 8 bits or less, so the difference is significant, especially since in actual implementations it will be fairly common to have several million Values and Containers in memory at once.
It is impossible to define a proper 'null' Value, as a Value must have an Environment in it and the Environment must be mutable. This in turn means that Container constructors that do not take a Value as an argument are much more convoluted.
The only other way around this I can think of would be to have a wrapper class (either an extension of Environment or something with an environment as a parameter) which is required in order to work with Containers or Values, which has all extant Containers and Values as members. This would solve the 'null' problem and neaten up the Value class a bit, but adds a huge amount of overhead as described and makes for a really convoluted interface for the end user. Those problems are, with a good deal of work and some changes in program flow, solvable as well, but by that point I'm pretty much writing another programming language which is far more than I should need.
Is there any other workaround for this that I'm missing, or am I mistaken about any of my disqualifying factors above? The only thing I can think of is that the performance hit from the static implementation might be smaller than I think it would be due to cacheing (I cannot perform realistic benchmarking unfortunately- there are too many variables in how this could be used).
*Note that an environment doesn't strictly speaking need to be modifiable- there would be no problem, technically, for example, with something like
class Environment
{
private Combination[][] combinations;
private string[] typenames;
private getString[] tostrings;
public Environment(Combination[][] combos, string[] tnames, getString[] getstrings)
{
combinations = combos;
typenames = tnames;
tostrings = getstrings;
}
}
except that this would be much more awkward for the end user, and doesn't actually fix any of the problems I've noted above.
I had a lot of trouble trying to understand exactly what you were trying to achieve here! So apologies if I'm off the mark. Here is a singleton based example that, if I understand the problem correctly, may help you:
public class CombinationDefinition
{
public string Name;
public getString GetString;
public Combination[] Combinations;
}
public static class CurrentEnvironment
{
public static CombinationDefinition[] Combinations = new CombinationDefinition[0];
public static Environment Instance { get { return _instance.Value; } }
static ThreadLocal<Environment> _instance = new ThreadLocal<Environment>(() =>
{
Environment environment = new Environment();
foreach (var combination in Combinations)
environment.AddType(combination.Name, combination.GetString, combination.Combinations);
return environment;
});
public static Value CreateValue(int t, byte[] bin)
{
return new Value(t, bin, Instance);
}
}
Which can be used as:
CurrentEnvironment.Combinations = new CombinationDefinition[]
{
new CombinationDefinition() { Name = "Combination1", GetString = null, Combinations = null },
new CombinationDefinition() { Name = "Combination2", GetString = null, Combinations = null },
};
Value value = CurrentEnvironment.CreateValue(123, null);
string stringValue = CurrentEnvironment.Instance.getStringValue(value);
Important to note - CurrentEnvironment.Combinations must be set before the Environment is used for the first time as accessing the Instance property for the first time will cause the Environment to be instantiated by its ThreadLocal container. This instantiation uses the values in Combinationsto use the existing AddType method to populate the Environment.
You either need to make Environment a "Singleton" (recomended), or mark everything inside it as static. Another possibility is to use an IoC container, but that may be more advanced than you are ready to go for at this point.
The Singleton pattern usually declared a static Instance property that is initialized to a new instance of the class through a private constructor. All access is done through the static Instance property, which will be available globally. You can read more about Singletons in C# here.
static will allow you to access the members without instantiating an instance of the class and it will act as a "global" container.
Singleton Example:
class Environment
{
private static Environment _instance;
public static Environment Instance
{
get
{
if (_instance == null)
{
_instance = new Environment();
}
return _instance;
}
}
private Environment(){}
private Combination[][] combinations;
private string[] typenames;
private getString[] tostrings;
public Environment() { ... } //adds one 'Null' type at index 0 by default
public void AddType(string name, getString tostring, Combination[] combos) { ... }
public Value Combine(Value A, Value B)
{
return combinations[A.index][B.index](A, B);
}
public string getStringValue(Value A)
{
return tostrings[A.index](A);
}
public string getTypeString(Value A)
{
return typenames[A.index];
}
}
Example usage:
Environment.Instance.getStringValue(this);
Please excuse any syntax errors in code, I don't have access to Visual Studio at the moment.
As a very simplified and stupid example of what I'm dealing with, suppose I had the following class with a simple static int property:
public class MyClass
{
public static int MyVar { get; set; }
}
So, if I wanted to set that property via code, it would be easy enough with something such as:
MyClass.MyVar = 2;
But, how could I take care of (again, to simplify the example) passing in a string and have it converted to an int?
The only way I could think of doing it is to create a helper method such as:
public class MyClass
{
public static int MyVar { get; private set; }
public static void SetMyVar(string sMyVar)
{
MyVar = int.Parse(sMyVar);
}
}
And then in code run:
MyClass.SetMyVar("2");
I would love to know if there was a better way to accomplish this than having to add in that extra method.
Although you definitely shouldn't do this because it's confusing to read, you could create the property this way
class MyClass
{
private static int _property = 0;
public static object Property
{
get
{
return _property;
}
set
{
_property = Convert.ToInt32(value);
}
}
}
You would have to cast this to an int whenever you wanted to use it as an integer but this is best I could think of.
is this what you were trying to do?
class newclass
{
private static int MyVarValue = 0;
public static int MyVar
{
get;
set
{
MyVarValue = Convert.ToInt32(value);
}
}
}
This would not compile because the value that a property gets set to has to be of the same type as the property itself. But if you are taking a list of objects in a constructor and assigning them to the properties, there you can do something like this...
class newclass
{
private static int MyVarValue = 0;
public newclass(List<object> startingList)
{
MyVarValue = Convert.ToInt32(startingList[0]);
}
}
You can use the compiler's method overload resolution to pick a SetMyValue method depending on the type of the argument. Inside each SetMyValue method you have a mechanism to convert all of the different input values to the same underlying type.
Doing this is probably a bad idea - but here goes anyway. It doesn't have quite the semantics that you're asking for but it's close:
//A class with multiple 'set' methods that will silently handle
//type conversions
class MyClass{
private int myValue;
public int MyValue { { get return this.myValue; } }
public void SetMyValue(int value){
this.myValue = value;
}
public void SetMyValue(string value){
this.myValue = Convert.ToInt32(value);
}
}
In statically typed languages, switching types silently in a way that loses information is not a very wise idea. There are other, dynamically typed languages that let you play fast and loose with types but C# is not one of them. You have to go out of your way in C# to get dynamic typing.
Doing this is probably a pain in the butt from a maintenance standpoint. I would put some more thought into the underlying problem that you're trying to solve that lead to this question.
This is my first time posting on Stack Overflow, so hopefully I did everything right and you guys can help.
I'm wondering if in C# there's a way to access a static variable belonging to a class, when given only the type of the class. For example:
public class Foo
{
public static int bar = 0;
}
public class Main
{
public void myFunc(Type givenType)
{
int tempInt = ??? // Get the value of the variable "bar" from "Foo"
Debug.WriteLine("Bar is currently :" + tempInt);
}
}
// I didn't run this code through a compiler, but its simple enough
// that hopefully you should get the idea...
It's hard to describe the context of needing to know this, but I'm making a game in XNA and I'm trying to use reference counting to reduce the complexity of the design. I have objects in the game and power-ups that can apply an effect them (that stays on the objects). Power-ups can die but their effects can still linger on the objects, and I need to keep track of if any effects from a power-up are still lingering on objects (thus, reference counting). I plan to make a "PowerUpEffect" class (for each type of power-up) with a static integer saving the number of objects still affected by it, but the design of the rest of the game doesn't work well with passing the PowerUpEffect all the way down to the object for it to call a method of the PowerUpEffect class.
I'm hoping to pass only the PowerUpEffect's type (using something like "typeOf()") and use that type to reference static variables belonging to those types, but I have no idea how to do it or if it's even possible.
I'd be glad to even find work-arounds that don't answer this questions directly but solve the problem in a simple and elegant design. =)
Help! (and thanks!)
If you only have the Type handle, you can do this:
var prop = givenType.GetProperty("bar");
var value = prop.GetValue(null);
I would use a Dictionary instead, which are probably the most concise way of mapping one set of values to another. If you are associating int values with Types, then do something like:
public static readonly Dictionary<Type, int> sTypeValues =
new Dictionary<Type, int>
{
{ typeof(Type1), 5 },
{ typeof(Type2), 10 },
{ typeof(Type3), 2 },
{ typeof(Type4), 3 },
{ typeof(Type5), -7 }
};
your function then becomes:
public void myFunc(Type givenType)
{
int tempInt = sTypeValues[givenType];
Debug.WriteLine("Bar is currently :" + tempInt);
}
int tempInt = (int) givenType.GetField("bar").GetValue(null);
Okay, so you have a collection of powerups, and you want to have an integer associated with each of those powerups. Rather than having a lot of classes, each with a static integer, you can have a single static collection which holds onto all of the powerups and their associated integer values.
public static class MyPowerupInfo
{
public static Dictionary<PowerUp, int> PowerUps {get; private set;}
static MyPowerupInfo
{
PowerUps = new Dictionary<PowerUp, int>();
PowerUps.Add(*some power up object goes here*, 0);
//TODO add other power ups
}
}
Then to use it you can do something like:
int powerupCount = MyPowerupInfo.PowerUps[wickedAwesomePowerup];
or:
public static void IncrementPowerup(Powerup powerup)
{
MyPowerupInfo.PowerUps[powerup] = MyPowerupInfo.PowerUps[powerup]+1;
}
If am getting you correc, this might give you some idea:
using System;
using System.Reflection;
public class RStatic
{
private static int SomeNumber {get; set;}
public static object SomeReference {get; set;}
static RStatic()
{
SomeReference = new object();
Console.WriteLine(SomeReference.GetHashCode());
}
}
public class Program
{
public static void Main()
{
var rs = new RStatic();
var pi = rs.GetType().GetProperty("SomeReference", BindingFlags.Static | BindingFlags.Public); // i have used GetProperty in my case
Console.WriteLine(pi.GetValue(rs, null).GetHashCode());
}
}
Are you assuming if the name of the field you're trying to access (for example, for the class "foo", the field "bar") is a different field based on the Type parameter?
If the name of the field is known based on a finite number of allowable types, you should be able to determine it with a switch statement. For example:
public class Foo
{
public static int bar = 0;
}
public class Baz
{
public static int bing = 0;
}
public class Main
{
public void myFunc(Type givenType)
{
switch (givenType.ToString())
{
case "Foo":
Debug.WriteLine("Bar is currently :" + Foo.bar);
break;
case "Baz":
Debug.WriteLine("Bing is currently :" + Baz.bing);
break;
}
}
}
I am looking to find a way to take two objects that have identical properties and make a call to copy the property values from one object into the other. The the example below assume I have an instance of A and I want to use the data of that instance to hydrate a new instance or C (to keep things terse I used fields instead of properties in the example below)
public class A : B
{
public string prop1;
public int prop2;
}
public class B
{
public byte propX;
public float propY;
}
public class C
{
public byte propX;
public float propY;
public string prop1;
public int prop2;
}
public class Merger
{
public static object Merge(object copyFrom, object copyTo)
{
//do some work
//maybe <T> generically refactor?
}
}
The merger class is just a psuedo-example, doing this through generics would be optimal but the first thing I question is whether such a capability already exists. I could imagine using reflection to do this myself but just wanted to toss it out for better ideas first.
Real world context: This is actually an MVVM related issue as I am trying to use disparate classes coming back from EF to populate a ViewModel instance.
Check out tools and libraries like AutoMapper - those would handle cases like this with ease - and much more! No need to re-invent the wheel - just use the tool! :-)
You would basically define a map between classes A and C like this:
Mapper.CreateMap<A, C>();
and then later on, you can have AutoMapper do the mapping, based on that map, from an instance of A into an instance of C, something like this:
C yourC = Mapper.Map<A, C>(instanceOfA);
AutoMapper does a default mapping based on property names (and types), but you can extend and influence it in a great many ways to include mappings from one property to another, even if the names (or types) don't match 100%. It's quite flexible and well established - definitely worth a serious look!
using System;
using System.Linq;
using System.Reflection;
public class Merger
{
public static TTarget Merge<TTarget>(object copyFrom) where TTarget : new()
{
var flags = BindingFlags.Instance | BindingFlags.Public |
BindingFlags.NonPublic;
var targetDic = typeof(TTarget).GetFields(flags)
.ToDictionary(f => f.Name);
var ret = new TTarget();
foreach (var f in copyFrom.GetType().GetFields(flags))
{
if (targetDic.ContainsKey(f.Name))
targetDic[f.Name].SetValue(ret, f.GetValue(copyFrom));
else
throw new InvalidOperationException(string.Format(
"The field “{0}” has no corresponding field in the type “{1}”.",
f.Name, typeof(TTarget).FullName));
}
return ret;
}
}
class Program
{
static void Main(string[] args)
{
var a = new A { prop1 = "one", prop2 = 2, propX = 127, propY = 0.47f };
var c = Merger.Merge<C>(a);
Console.WriteLine(c.prop1); // prints one
Console.WriteLine(c.prop2); // prints 2
Console.WriteLine(c.propX); // prints 127
Console.WriteLine(c.propY); // prints 0.47
}
}
This isn't the best solution by far, but based on the object graph you've provided, you could probably accomplish this by XML serializing the first object, and XML deserializing the XML stream into the second object.
Your proposed Merger method could possibly look like this:
public class Merger
{
public static object Merge(object copyFrom, object copyTo)
{
var xmlContent = MyXMLSerializationMethod(copyFrom);
MyXMLDeserializationMethod(xmlContent, typeof(copyTo), out copyTo);
return copyTo;
}
}
Good post about using AutoMapper to solve this problem in the context of MVVM and MVC
http://www.bengtbe.com/blog/post/2009/04/14/Using-AutoMapper-to-map-view-models-in-ASPNET-MVC.aspx