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Activator.CreateInstance(Type) returns an Object .
Activator.CreateInstance Method (System) | Microsoft Docs[^]
As a result, you are calling eventMessager.Publish<object>(instanceOfYourType) .
That uses the run-time type of the parameter to find the subscriber. This will be a Subject<YourClass> instance.
You then try to cast that instance to Subject<object> , which fails because the Subject<T> class is not covariant on its type parameter.
Covariance and Contravariance in Generics | Microsoft Docs[^]
You can't even get away with casting the subscriber to the IObserver<T> interface, since that interface is contravariant.
You're going to need to use reflection to invoke the method. I'd suggest using a separate method to avoid making the regular method slower:
public void PublishNew(Type eventType)
{
if (subscriberLookup.TryGetValue(eventType, out object subject))
{
object @event = Activator.CreateInstance(eventType);
Type t = typeof(IObserver<>).MakeGenericType(eventType);
MethodInfo onNext = t.GetMethod("OnNext");
onNext.Invoke(subject, new[] { @event });
}
}
...
eventMessager.PublishNew(w[0]);
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
modified 5-Sep-18 13:17pm.
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Ah, that works perfectly, thank you.
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Richard Deeming wrote: I'd suggest using a separate method to avoid making the regular method slower:
I found some other lower level code that the author claimed was 10 times faster than Activator.CreateInastance:
public class ObjectCreateMethod
{
delegate object MethodInvoker();
MethodInvoker methodHandler = null;
public ObjectCreateMethod(Type type)
{
CreateMethod(type.GetConstructor(Type.EmptyTypes));
}
public ObjectCreateMethod(ConstructorInfo target)
{
CreateMethod(target);
}
void CreateMethod(ConstructorInfo target)
{
DynamicMethod dynamic = new DynamicMethod(string.Empty,
typeof(object),
new Type[0],
target.DeclaringType);
ILGenerator il = dynamic.GetILGenerator();
il.DeclareLocal(target.DeclaringType);
il.Emit(OpCodes.Newobj, target);
il.Emit(OpCodes.Stloc_0);
il.Emit(OpCodes.Ldloc_0);
il.Emit(OpCodes.Ret);
methodHandler = (MethodInvoker)dynamic.CreateDelegate(typeof(MethodInvoker));
}
public object CreateInstance()
{
return methodHandler();
}
}
But you have solved my problem, so this does not bother me as much.
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Hi Folks,
I have a referenced .dll in one of the projects in my solution, and from what I can tell during debugging most of it appears to be used and accessed without issue.
However, when calling a 'getModelDataContext' function from the model.designer.cs file that should be within the .dll, nothing seems to happen. It appears to not be reachable ('under the caret') when I try to jump to its definition. It is not breaking though when it hits this function, but it is not returning a valid data connection, and then a subsequent function call is using an empty data set and failing at that point.
Does anyone have any ideas how I can approach this please?
Many thanks,
AJ
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Look at the source code (if you have it), or the documentation provided by whoever created the DLL. You should be able to collect more information from the debugger by single-stepping through the code.
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Thank you, that's a good idea. I'll see if I can get into the source code for some further investigation.
All the best,
AJ
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This was based on silly oversight on my part. Although I was unable to access the functions and files through the .dll itself. After looking through the source code I found that it was in fact accessing everything and the result it was producing was in fact perfectly fine as per the underlying code.
The issue truned out to be with the data I had been sent to test the API with as it did not match a suitable record in another system used to retrieve additional record data.
I'm still not sure why I was unable to navigate to the file in question through the .dll but thankfully, as I was able to get into the original sorce code, I managed to work aroung this.
Thank you Richard for your input!
AJ
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Hello,
I am trying to get a leg up at my job, so this is not a homework assignment.
I need help to begin to understand Constructor Injection.
there are five types; Default, Parameterized, Copy, Static and Private. The constructor creates an instance for the class, and initializes Private fields.
Where would Injection be used?
What are the risks of modifications to the constructor, does it break the "target" code?
How do constructors allow for unit testing?
What is unit testing?
What book can you recommend to learn C#? I have some experience in C, Visual Studio, and way back Assembly.
Thanks in advance, I am sure I will have other questions also.
Tom.
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You have many questions in one message.
I have created a "Zelda" example with lot of constructors. I hope you find it useful.
Hint: Start a new console application in C#, called ConsoleApplication1. Paste the code, set break points and debug.
using System;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
var maxArrows = Link.ArrowMaximum;
var link = new Link();
IWeapon weapon = new KokiriSword();
link = new Link(10);
link = new Link(weapon);
link = new Link("Go to Lost woods");
var fierceDeityLink = new FierceDeityLink();
}
}
public interface IWeapon
{
int Damage { get; }
}
public class NoWeapon : IWeapon
{
public int Damage { get; private set; }
public NoWeapon()
{
Damage = 0;
}
}
public class KokiriSword : IWeapon
{
public int Damage { get; private set; }
public KokiriSword()
{
Damage = 1;
}
}
public class BigGoronSword : IWeapon
{
public int Damage { get; private set; }
public BigGoronSword()
{
Damage = 100;
}
}
public class Link
{
public static int ArrowMaximum { get; private set; }
public int Rupies { get; private set; }
public bool RecuredZelda { get; private set; }
public string HintFromNavi { get; private set; }
public IWeapon Weapon { get; private set; }
static Link()
{
ArrowMaximum = 100;
}
public Link()
{
Rupies = 5;
Weapon = new NoWeapon();
}
private Link(bool recusedZelda)
{
RecuredZelda = recusedZelda;
}
public Link(int rupies)
{
Rupies = rupies;
}
public Link(IWeapon weapon)
{
Weapon = weapon;
}
protected Link(int rupies, bool recuedZelda, IWeapon weapon) : this(rupies)
{
RecuredZelda = recuedZelda;
Weapon = weapon;
}
internal Link(string hintFromNavi)
{
HintFromNavi = hintFromNavi;
}
}
public class FierceDeityLink : Link
{
public FierceDeityLink() : base (int.MaxValue, true, new BigGoronSword())
{
}
}
}
Answers for your other questions:
Where would Injection be used?
Lots of places. Depends on the logic of the code. Read here.
What are the risks of modifications to the constructor, does it break the "target" code?
Impossible to say without reviewing the code.
Try... and learn from mistakes.
How do constructors allow for unit testing?
Constructors are used to create objects from classes. That has nothing to do with unit testing.
What is unit testing?
Something which is very useful and you should adapt immediately. Read here.
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Hello,
Even though webcam quality is 5mp , webcam seems and takes low quality of picture via below codes.
Is there any way to fix this and raise quality to maximum possible?
namespace DXApplication2
{
public partial class Form1 : DevExpress.XtraEditors.XtraForm
{
public Form1()
{
InitializeComponent();
}
private FilterInfoCollection webcam;
private VideoCaptureDevice cam;
private void Form1_Load(object sender, EventArgs e)
{
this.WindowState = FormWindowState.Maximized;
webcam = new FilterInfoCollection(FilterCategory.VideoInputDevice);
foreach (FilterInfo VideoCaptureDevice in webcam)
{
comboBox2.Items.Add(VideoCaptureDevice.Name);
}
comboBox2.SelectedIndex = 0;
}
if (pictureBox3.Image != null)
{
iTextSharp.text.Image png2 = iTextSharp.text.Image.GetInstance(pictureBox3.Image, System.Drawing.Imaging.ImageFormat.Jpeg);
png2.Alignment = Element.ALIGN_CENTER;
if (png2.Height > png2.Width)
{
float percentage = 0.0f;
percentage = 400 / png2.Height;
png2.ScalePercent(percentage * 100);
}
else
{
float percentage = 0.0f;
percentage = 320 / png2.Width;
png2.ScalePercent(percentage * 100);
}
pdf1.Add(png2);
}
private void cam_NewFrame(object sender, NewFrameEventArgs eventArgs)
{
Bitmap bit = (Bitmap)eventArgs.Frame.Clone();
pictureBox1.Image = bit;
}
private void button6_Click(object sender, EventArgs e)
{
pictureBox2.Image = pictureBox1.Image;
}
modified 13-Feb-19 21:02pm.
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i need to get a picture (.BMP or image) convert to .dpx format. The DPX is Digital Picture Exchange , so how can i convert image to DPX format in C# ?
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.NET (and thus C#) does not natively support DPX files, so to write them you will need to either write the code to convert and save them yourself, or use a prewritten library for that. This one seems well appreciated: GraphicsMagic @ CodePlex Archive[^] - I've not used it myself though.
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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When some exception occurs in a class of the .Net framework, we see the public function of a public class called by our code only, the further details (private functions, or even non-public classes) used by the public function are hidden in the StackTrace of the exception object, when the exception occurred somewhere down there.
Now I have some functionality where I'd like to have such a feature, too:
For testing, we use MS Test. I added some extensions, e.g. "ThrowsAssert " (based on Asserting Exceptions in MSTest with Assert.Throws()[^]). When such an Assert fails, I get a long StackTrace like:
bei TestUtilities.ExceptionAssert.OnNoExceptionThrown[T](String _customMessage) in C:\Users\bernhard.hiller\SVN\Product-SW\trunk\C_TestUtilities\ExceptionAssert.cs:Zeile 29.
bei TestUtilities.ThrowsAssert.Throws[T](Action _task, String _expectedMessage, ExceptionMessageCompareOptions _messageOptions, ExceptionInheritanceOptions _inheritOptions, String _customMessage) in C:\Users\bernhard.hiller\SVN\Product-SW\trunk\C_TestUtilities\ThrowsAssert.cs:Zeile 42.
bei MyAssembly.Tests.MyClassTests.MyFunctionTest() in C:\Users\bernhard.hiller\SVN\Product-SW\trunk\MyAssemblyTests\MyClassTests.cs:Zeile 36.
or even longer...
Is there some way to "hide" all those functions of class ThrowsAssert and ExceptionAssert in the StackTrace?
Oh sanctissimi Wilhelmus, Theodorus, et Fredericus!
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As far as I'm aware, the only way to hide methods from the stack trace is to get the compiler to inline them - since they are no longer called, they are no longer available to stack tracing. Unfortunately for you, there is no way that I know of to force the compiler to inline a method - you can force it to not inline, but the reverse does not apply. I understand that you can (in v4.5 and later) hint that you might like it inlined: MethodImplOptions Enum (System.Runtime.CompilerServices) | Microsoft Docs[^] using the AgressiveInlining field, but that is just a suggestion, not an order!
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Take the "stack trace", run it through a "string reader", and eliminate the entries you don't want (via a class or method "name" related to the exception).
I do all my "trace filtering" in the
Application_DispatcherUnhandledException
event handler.
At that point, I can even "continue execution" via "e.handled" (if the situation calls for it).
"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal
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I got a class and I have created an array in the class
<pre>class myclass
{
string array = new string[5];
for (int i = 0; i< array.Length; i++)
{
array[i] = "whatever"
}
}
now I want to transfer this array into my main, maybe create new array at main and just transfer the info. how do i create and
string GetArray() in class to return an array, and how do I get the info into main. thanks
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I have a VB.NET class library with a single public function with a single parameter that calls a method to produce the string return value. I referenced it in the C# project, and added a using statement for the namespace. However, I have no success in even coding to use the function from the dll. Can someone point me in the right direction? There are lots of answers to the problem on the web, but none work for me. Here is a portion of the VB dll code. GetSeparators() prepares and returns the string. I am developing the library to get information from a COM library. I have not found a convenient code for C# to use the COM library. The VB dll is NET 3.5 and the C# app is NET 4.6.1.
Public Class HYSYSFetch
<pre>
Private _filename As String
Private _sepstring As String = ""
Public Function FetchSeparators(filename As String) As String
_filename = filename
GetSeparators()
Return _sepstring
End Function</pre>
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All you have to do is create an instance of the containing class, and call the function on that
private void MyFunction()
{
HYSYSFetch hsf = new HYSYSFetch(...);
string result = hsf.FetchSeparators(strPathToFile);
} If that doesn't work, you need to tell us exactly what you get as an error message, and show us the exact code you tried.
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Thank you. This is something I have done a hundred times with projects. But I never used a VB dll with a C# project. I shall remember that the right solution is the simple one.
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Once they are compiled, VB and C# DLLs are the same thing - you can treat them as if they were written in any language. (The same applies to any language which compiles to IL, so F#, Cobol, C++ - all "look the same" once compiled.)
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Griff, Once you cleared the fog and got me started, the rest was easy. Everything works smoothly when the C# application calls the VB.NET library functions. Thanks again.
I needed the VB library because C# doesn't easily communicate with a COM object. And I already had the VB code in a VB application. I develop most of my class libraries with C#, just to keep in practice. My VB application that uses Selenium Basic (Selenium wrapper for VB & VBA) doesn't play with Firefox latest editions. So my need to use C# to make use of Selenium which doesn't work with VB. My main use is to get information from a process simulator and transfer it to a web page, thus eliminating transcribing errors. This takes several technologies to get it to work.
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You're welcome!
Sent from my Amstrad PC 1640
Never throw anything away, Griff
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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Well, I spoke too soon. The VB dll is not playing well with the C# app. The C# app doesn't recognize a particular method in the dll. Call to a different method works OK. Throws an error, something about Reflection and the wrong number of arguments. But the number of arguments is correct; there is only one. I had an earlier version working, but the C# app was not getting the proper data from the dll which fetches data from a COM app. I'll have to go back to an earlier version and trace the problem.
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