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Hi All,
I have COM component which is referred in my C# application. Visual studio has generated interop for the COM and able to call the methods from C# code.
This component has a method with parameters being optional. Now I am not able to force the compiler to use default values of these optional parameter instead of explicitly passing them. In other words I don’t want to pass any values to call this method. I tried using System.Reflection.Missing.Value. but it throw error saying type missmatch. Method is looking for integer type value.
Is there any I can call this method without passing any parameters and creating a wraper to this assembly.
Thank you,
Krishnaraj Barvathaya B
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Optional parameters don't exist in C# unfortunately. The best you can do is create an overload and have the overload call the full method.
I hate to say it, but you can do this in VB! There was talk of it being introduced into C#4 but I don't know if it's made it or not.
void Method(int a)
{
Method(a, 0);
}
void Method(int a, int b)
{
}
DaveBTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
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I'm pretty sure optional parameters made it in. There's an inititive to introduce new features to both C# and VB.NET at the same time. This also means syncronizing the existing feature sets between the two languages where appropriate. For example, C# gets the optional parameters VB.NET supports, but VB.NET does NOT get the unsafe code and pointer support that C# has.  At least, not yet...
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Optional parameters did make it in to the underlying IL but they aren't exposed in C# yet (C# 4.0 will support them). There is an effort to keep the two languages more in-sync with one another but it isn't across the board with all language features, as you mentioned. Another exmaple is that C# will not get the "XML literal" syntax VB supports.
Scott Dorman Microsoft® MVP - Visual C# | MCPD
President - Tampa Bay IASA
[ Blog][ Articles][ Forum Guidelines]
Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai
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Thank you every one for your answers.
From your answers I am able to conclude that there is no straight forward way to call a method with optional parameter by forcing to use its default value. So I created a wrapper class in VB.net with number of overloaded methods to match its optional implementation. Looks to be working fine.
Krishnaraj Barvathaya B
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For the parameters you're not interested in, just pass either:
System.Type.Missing
System.Reflection.Missing.Value
(either will work)
David Anton
http://www.tangiblesoftwaresolutions.com
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This will work only in case the expected parameter is of reference type such as string. It doesn’t work if the method is looking for Integer type or any other primitive types. If you pass either System.Reflection.Missing. System.Type.Missing or System.Reflection.Missing.Value compiler shows up error saying type mismatch. So after lot of search, I think there is only way to break this barrier is by creating a wrapper class in VB.net and referencing the same.
Krishnaraj Barvathaya B
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Hi i have code on 64 bit system on windows 2008 server enterprise.
i want to read some value of my application in it through C# code, when i read by default it reads from wow6432 node only, but i need to read value from 32 bit node.
64 bit key value
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\COMPANY\product Name\1.0\folder
32 bit key value
HKEY_LOCAL_MACHINE\SOFTWARE\COMPANY\product name\1.0\folder
how write code to force reading value from folder32 in 32 bit registry hive?
i have set the flag for 32 bit system read that is:
UIntPtr HKEY_LOCAL_MACHINE = (UIntPtr)0x80000002;
const int KEY_WOW64_32KEY = 0x0200;
const int KEY_QUERY_VALUE = 0x1;
but still when i give like
RegistryHelper regHelper = RegistryHelper();
regHelper.BaseRegistryKey = Registry.LocalMachine;
regHelper.SubKey=@"HKEY_LOCAL_MACHINE\SOFTWARE\COMPANY\product name\1.0\folder"
string sPath = regHelper.ReadString("Path");
it gives sPath=null only.
it is searching in 64 bit node only. please help me resolve this issue.
thanks in Advance.
Hemal Kotak
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You are misunderstanding what WOW64 means.
WOW64 (windows on windows 64) is a windows 32bit emulator that runs on windows 64 bit. The wow64 folders/regs keys are for data from 32bit programs that are running on windows 64 (via the emulator).
You obviously are writing a 32bit program. Hence, it is running on WOW64. Which means when you write to the registry it goes in the WOW64 location. This is the correct behaviour. On windows 64, the registry is 64bit, and cannot be accessed by 32 bit programs. WOW64 allows a special area of the registry to be accessed by 32 bit programs.
(By the way, by default c# compiles in "architecture agnostic mode" which means it is both a native 32 and 64 bit program at the same time. If you are using C# you have obviously changed the settings to be for a 32bit cpu only. Consider changing it back. Right click on the project, go to properties, and look at the build tab. There is an option called "platform target" this should be set to "any cpu". If you do this, on a win64 system, the app will run as a native 64 bit app, so won't be using wow64 any more. I suspect you have it set to x86 which means 32bit cpus)
Simon
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Thanks Simon I will do that.
-Hemal
Hemal Kotak
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My app needs to take a pdf file and compress it into an .arc file (for a third party bit of software to pick up, so i have no choice in the compression format).
I have googled it but am struggling to find any c# solutions or opensource api's.
Any links, ideas etc most welcome
Mark
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Good day. I'm writing an application where I specify types in a config file and these types then need to be instantiated through reflection.
How can I create a System.String object through reflection? And a System.Int32 object with a value other than 0?
I've got the following code:
Type paramType = Type.GetType("System.String");
object obj = Activator.CreateInstance(paramType);
but when I try to do this for a System.String, it tells me that such a constructor doesn't exist (one with no parameters). When I run the code for a System.Int32 object, then the object is created, but I cannot pass the constructor a default value such as Activator.CreateInstance(typeof(int), 3, 5);
How can I create a type such as System.String, System.Int32 or such a type and assign a value when it's created, using reflection?
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Hi,
i'm not sure why you are using the Activator-object. The string has no constructor without parameters (check http://msdn.microsoft.com/en-us/library/system.string.string.aspx[^]), so you have to pass something to get a string object. What you could try is to use the ConstructorInfo of the Type.
<br />
ConstructorInfo oInfo = paramType.GetConstructor(new Type[] { typeof(char*) });<br />
object oString = oInfo.Invoke(new object[] { "This is a test."} );<br />
Hope this helps you a bit.
Regards
Sebastian
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The values in my app.config file actually looks like this.
<parameter type="System.String" value="32">
<parameter type="System.Int32" value="32">
Now, I can't call
int i = new int("32") or,
string myString = new string("32"),
since no such constructors exist. I need to somehow create objects of these types and assign these values to them. But I'm looking at a generic way of doing this.
(I don't want to write code like
object obj = null;
if(paramType is Int32)
obj = 32;
else if(paramType is String)
obj = "32";
I want to avoid code like this.
Any ideas?
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Take a look at the TypeConverter class.
object obj = TypeDescriptor.GetConverter(paramType).ConvertFromInvariantString("32");
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This one's the answer I was looking for. Thanks a lot for the help.
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Didn't know that values from the app.config are strongly typed. There are all coming as string, or?
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No, they're not strongly typed, otherwise it would have been much easier. They all come as a string.
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Ok. So i'm stuck here. How does you know if the app.config entry is an integer? Let me say it this way, somewhere in your app you have to consume the app.config entry in a typed way. Exactly at this point you know what you were expecting from the config file. What if you put an entry to the app.config with value 32, parsing the whole as int, but you are expecting a string in your app?
What do you want to achieve exactly?
Regards
Sebastian
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I want to have the following entry in my app.config file:
...
...
1: <Parameter type="System.Int32" value="32" />
2: <Parameter type="System.String value="Hallo" />
Ok. Now the "value" attribute of the "Parameter" tag will always be a string value when retrieved from the app.config.(that's how the Custom Configuration files were written). Now by looking at the "type" attribute, I want to cast/convert the value of the "value"-attribute to the type specified by the "type" attribute. Something like the following:
So for line 1: the following values will exist.
param.type = "System.Int32"; (String value);
param.value = "32"; (Also a string value as retrieved from app.config.
For line 2: it will be:
param.type = "System.String";
param.value = "Hallo"
Now what I'd like to do is something that would be similar to the following code:
param.type myVariableType = (param.type)param.value;
Where I have a type and cast the value I recieved from the app.config to that type.
(Look in one of the previous threads by Daniel Gruwald. I got an answer for this problem. It was to use the following code.
TypeDescriptor.GetConverter(Type.GetType(param.type)).ConvertFromInvariantString(param.value);
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Am I missing something, or the example below is really impossible.
The class called FirstImplementation derives from GenericClass, and the generic parameter used, FirstClass derives from Base. So from the outside I should be able to cast FirstImplementation to GenericClass<base></base>
public class Base
{
public int X { get; set; }
}
public class FirstClass : Base
{
public int Y { get; set; }
}
public abstract class GenericClass<T> where T: Base
{
public T Item { get; set;}
}
public class FirstImplementation : GenericClass<FirstClass>
{
public GenericClass<Base> Cast()
{
return (GenericClass<Base> )this;
}
}
modified on Thursday, January 15, 2009 6:18 AM
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That's not how generics work unfortunately. You can't do this
GenericClass<firstclass> var1;
GenericClass<base> var2;
var2 = (GenericClass<base> )var1;
Your var1 & var2 variables are different types. One is a generic class using base as it's type member, and one is using FirstClass as it's type member, you can't cast one to the other, just because FirstClass is a subclass of Base. var1 isn't a subclass of var2. What generics effectively do is define a new class using the type you specified. So it effectively equates to this:
public class GenericClassUsingBase
{
public Base Item
{
get;
set;
}
}
public class GenericClassUsingFirstClass
{
public FirstClass Item
{
get;
set;
}
}
You'll see if you try and cast these you can't do that either:
GenericClassUsingFirstClass var1;
GenericClassUsingBase var2;
var2 = (GenericClassUsingBase)var1;
They are basically different types, just because they are using type parameters that subclass each other doesn't make them subclasses of themselves.
Simon
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Thanks. Great explanation.
I guess I'm not the only one who bumps into this. Any known workarounds? Or rethink the whole implementation from scratch?
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gnjunge wrote: Any known workarounds?
That kind of depends what you are trying to do.
If you are trying to treat generics of a class tree as a tree themselves, I suspect you are slightly misusing the idea of generic classes. You might be better defining explicit classes instead of generic ones, and then having them all inherit from the same interface or abstract class instead if you need that.
What is it you are trying to archive?
Simon
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