Re: Error Could not open form interface design in C# ? - C# Discussion Boards

Re: Accessing the parameters of a method assigned to a delegate

19-Feb-17 10:47

Is this at all possible?

Consider these simplified classes:

static class Class1
{
    internal static int GetValue(int First, int Second)
    {
        return First + Second;
    }
}
static class Class2
{
    internal static String  GetSignatureFromMethod<TResult>(Func<TResult> Method)
    {
        // Do Stuff
        // Here I want to access the values of First and Second from Class1.GetValue

        String SomeCalculatedValue = A calculation depending on the existence of Val1, Val2 + the result of Method();
        return SomeCalculatedValue;
    }
}
class Program
{
    static void Main(string[] args)
    {
        int Val1 = 3;
        int Val2 = 4;

        Func<int> Function = () => Class1.GetValue(Val1, Val2);

        Console.WriteLine(Class2.GetSignatureFromMethod(Function));
        Console.ReadKey();
    }
}

I haven't found a way of doing this generically.
My searches indicate that it's not possible to do using reflection, at least not without deep knowledge of IL code.

Wrong is evil and must be defeated. - Jeff Ello

Dave Kreskowiak19-Feb-17 11:33

Dave Kreskowiak

19-Feb-17 11:33

No, not like that. By the time your Main gets to Class2.GetSignatureFromMethod the parameter values are no longer on the stack. They just don't exist anymore.

You've picked a very difficult problem that cannot be done without that knowledge of IL. The thing is that you have to grab the parameter values while the code is still in the method that you called. If you call ANY other method while the method your interrogating is running the stack gets deeper and you have to walk the stack to go get the correct parameter values. How far down the stack do you have to go? This is entirely dependent on your interrogation code.

A guide to posting questions on CodeProject

Click this: Asking questions is a skill.
Seriously, do it.

Dave Kreskowiak

Re: Accessing the parameters of a method assigned to a delegate

Jörgen Andersson19-Feb-17 21:09

Re: Accessing the parameters of a method assigned to a delegate

19-Feb-17 21:09

Thanks for confirming. Thumbs Up | :thumbsup:

Seems I'm stuck with a parameter array and/or a whole load of overloads for the GetSignatureFromMethod.
Or I have to get the architecture changed.

Wrong is evil and must be defeated. - Jeff Ello

Gerry Schmitz19-Feb-17 15:06

Gerry Schmitz

19-Feb-17 15:06

Not saying it's best for your situation, but you may want to consider using "dynamic" objects, parameter object arrays (like WriteLine()), and / or Name-Value collections for interfacing.

"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal

Re: Accessing the parameters of a method assigned to a delegate

Jörgen Andersson19-Feb-17 21:04

Re: Accessing the parameters of a method assigned to a delegate

19-Feb-17 21:04

I would have preferred to avoid that kind of solution, but since I can't think of any alternatives...

Wrong is evil and must be defeated. - Jeff Ello

Gerry Schmitz20-Feb-17 8:25

Gerry Schmitz

20-Feb-17 8:25

If it's "all your code", than I would change all methods to have an "object sender" (and perhaps an "args-type" instance); and "reflect" on that.

Same pattern as the WPF / Windows Forms (ui) event model.

"(I) am amazed to see myself here rather than there ... now rather than then".
― Blaise Pascal

Re: Accessing the parameters of a method assigned to a delegate

Richard Deeming20-Feb-17 2:44

Re: Accessing the parameters of a method assigned to a delegate

20-Feb-17 2:44

With a compiled delegate, it's going to be almost impossible.

In your specific example, the Function.Target property will return an instance of an anonymous type, with a field for each captured variable, and one for the delegate:

Function.Target == new
{
    Val1 = 3,
    Val2 = 4,
    Function = Func<int>
}

However, without reading the IL of Function.Method, you have no way of knowing which field corresponds to which argument.

Things get even more interesting if the anonymous closure type is shared between multiple closures, or you're not using a closure at all.

You might be able to extract the information if you use an Expression<Func<T>>[^] instead of a Func<T>. In simple cases, the following seems to work:

Expression<Func<int>> expr = () => Class1.GetValue(Val1, Val2);
var body = (MethodCallExpression)expr.Body;
var parameters = body.Method.GetParameters();
for (int index = 0; index < body.Arguments.Count; index++)
{
    var arg = (MemberExpression)body.Arguments[index];
    var instance = arg.Expression == null ? null : ((ConstantExpression)arg.Expression).Value;
    var field = (FieldInfo)arg.Member;
    object value = field.GetValue(instance);
    Console.WriteLine("{0} = {1}", parameters[index].Name, value);
}

/*
Output:
First = 3
Second = 4
*/

However, this code is rather fragile, and likely to break if you pass in any "interesting" expressions.

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Jörgen Andersson28-Feb-17 20:34

Windows form application connectivity

28-Feb-17 20:34

I've meant to respond to this post for a while as it deserves a proper answer, but I had to leave for Germany to go to a funeral so I haven't really had the time until now.
But the very long answer that I thought out boiled down to a very short one in the end.

I'm going to explore the Expression methodology, more for educational purposes than anything else, but since it indeed seems to be quite fragile I'm going for a different architecture for now.
Thanks for the insight!

Wrong is evil and must be defeated. - Jeff Ello

Member 1301073119-Feb-17 8:54

Member 13010731

19-Feb-17 8:54

Hello,

I think I am level basic at programming, but I'm not lazy to search on internet when I have a problem.

Although I need help because I searched on the internet for hours and when I found something what was looking good, it didn't help me.

And because of that I'm asking you guys if you would help me please. In code's comments are my problems. Thank you for replies.

<pre>
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace kg
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            // and I need to get "price" to Calculate_Click() = my biggest problem 

            double price = 0;

            if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 0)
                price += 82.36;
            if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 1)
                price += 125.23;
            if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 2)
                price += 163.98;
            // and so on...
        }

        private void Calculate_Click(object sender, EventArgs e)
        {
            MaterialPriceLabel.Text = price; // Why is the "price" underlined? 
        }
    }

NotPolitcallyCorrect19-Feb-17 9:47

NotPolitcallyCorrect

19-Feb-17 9:47

Member 13010731 wrote:
Why is the "price" underlined?

Because you didn't google search "variable scope"

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Speed of light - 186,000 mi/sec
Speed of stupid - instantaneous.

Richard Deeming19-Feb-17 9:48

19-Feb-17 9:48

You need to learn about variable scope.
3.7 Scopes (C#)[^]

A local variable declared in one method is not available outside of that method. Can you imagine how confusing it would be if that was not the case? If every single local variable had to have a unique name across your entire class or project, so that it didn't conflict with other local variables in other methods?

To make it available to other methods in the same class, make it a field:

public partial class Form1 : Form
{
    private double price = 0;
    
    public Form1()
    {
        InitializeComponent();
        
        if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 0)
            price += 82.36;
        if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 1)
            price += 125.23;
        if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 2)
            price += 163.98;
        // and so on...
    }
    
    private void Calculate_Click(object sender, EventArgs e)
    {
        MaterialPriceLabel.Text = price;
    }
}

Fields (C# Programming Guide)[^]

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Member 1301073120-Feb-17 1:48

Member 13010731

20-Feb-17 1:48

Thanks, I really appreciate it. You helped me a lot, but when I click button, in the "MaterialPriceLabel" appear 0 every time (there should be for example: 82.36) and I think my "if part" of the code is good. So problem would be in the sending of value to the "price", I think. Can you give me some advice please?

public partial class Form1 : Form
{
    private double price = 0;
    
    public Form1()
    {
        InitializeComponent();
        
        if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 0)
            price += 82.36;
        if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 1)
            price += 125.23;
        if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 2)
            price += 163.98;
        // and so on...
    }
    
    private void Calculate_Click(object sender, EventArgs e)
    {
        MaterialPriceLabel.Text = price.ToString();
    }
}

Richard Deeming20-Feb-17 1:53

20-Feb-17 1:53

You need to debug your code.

Click on the left-hand margin in the editor next to the first "if" statement to set a breakpoint. You should see a small red circle appear. Then run your application and step through the code to see what's happening.

Using Breakpoints - MSDN[^]
Using Breakpoints for Debugging in Visual Studio 2015 | Visual Studio Shorts | Channel 9[^]

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer

Member 1301073120-Feb-17 4:23

Member 13010731

20-Feb-17 4:23

I've got only one problem. I'm trying debug and it works, nevertheless debugging didn't help me.

public partial class Form1 : Form
    {

        private double price = 0; 

        public Form1()
        {

            InitializeComponent();

            if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 0) 
                price += 82.36;                                             // If this is true, value of price should be 82.36 but, when I click on Calculate it's 0.

            if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 1)  
                price += 125.23;
            if (Material.SelectedIndex == 0 && Thickness.SelectedIndex == 2)
                price += 163.98;


        }

        private void Calculate_Click(object sender, EventArgs e)
        {
            MaterialPriceLabel.Text = cena.ToString(); // When I click, it shows 0 every time
        }
    }

Please help me how to get value of price to Calculate_Click.

Richard Deeming20-Feb-17 4:48

20-Feb-17 4:48

Step through the code, and you'll find that none of your if conditions are matched, so the price field is never updated.

You need to debug your code. I can't do that for you.

"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer