Re: method inheretance - C# Discussion Boards

8-Dec-08 6:29

Hello everyone,

I'm building my own library. But I'm kind of stuck and it is really tough to explain, but I will try:

I have a class, let's call this X. X has an interface and a base class. X also inherets another class (called Y).

Now I call some base functions and give X as a parameter.
But I would like to know if it is possible in another baseclass?

To sketch it up in code, it looks like this now:

class X : Y, InterfaceX
{
   public X()
   {
   }

   bool function1(String txt)
   {
      return base.function1(this, txt);
   }
}

class Y
{
   bool function1(InterfaceX x, String txt)
   {
      //do something
      return true/false;
   }
}

And what I would like to have is something like this:

class X : Y (& Z), InterfaceX
{
   public X()
   {
   }
}

class Y
{
   bool function1(InterfaceX x, String txt)
   {
      //do something
      return true/false;
   }
}

class Z
{

   bool function1(String txt)
   {
      return base.function1(this.getParent(), txt);
   }
}

Is this possible, and if it is, how can I implement this?

Thank you very much.

Alan Balkany8-Dec-08 8:11

Alan Balkany

8-Dec-08 8:11

Class X can't inherit from Y and Z because C# only supports single inheritance (unfortunately). You could have X inherit from Y, and Y inherit from Z. Or you could have X implement multiple interfaces.

Also you need the keyword "virtual" on the virtual methods in your base classes, and the keyword "override" on your overridden methods in the derived classes.

Another possibility is the Decorator design pattern, which lets you define inheritance (single or multiple) at runtime.

Deresen8-Dec-08 8:25

8-Dec-08 8:25

Thank you.

But the problem I have is that if I want to add a function to my Interface class and it is as simple as calling the base function with as parameter itself, shouldn't it be possible to do that in some kind of global class. Something like this:

class Main
{
   public Main()
   {
      X x = new X();
      x.function1("myText"); -> false
      X2 x2 = new X2();
      x2.function1("myText"); -> true
   }
}

interface InterfaceX
{
    int number { get; };
    bool function1(String txt);
}

class X :  Z, InterfaceX
{
    public int number
    {
       get { return 5;}
    }
   public X(){}
}
class X2 : Z, InterfaceX
{
    public int number
    {
       get { return 2;}
    }
    public X2() {}
}

class Z : Y, 
{
   public bool function1(String txt)
   {
      return base.function2(this.getParent(), txt);
   }
}

class Y
{
   public bool function2(InterfaceX x, String txt)
   {
      if(x.number < 3)
         return true;
      else
         return false;
   }
}

It's all about the this.getParent(), this doesn't work, but how can I get this working?

Alan Balkany8-Dec-08 8:32

Alan Balkany

8-Dec-08 8:32

I'm not sure what you're trying to do, but this.getParent () will only work if:

1. Class Z (or an ancestor of Z) defines a getParent () method, and
2. This getParent () method returns InterfaceX (or a descendant of InterfaceX).

Deresen8-Dec-08 9:14

8-Dec-08 9:14

With the this.getParent() I would like to get the 'parent' of Z.

So if I make an X : Z I would like to get X.
And if I make an BlahBlah : Z I would like to get BlahBlah.

I'm trying to get some work of my back.
In stead of implementing all the functions (of the interface) inside of every class, I would like to make a base class which implements these functions.

Alan Balkany8-Dec-08 9:40

Alan Balkany

8-Dec-08 9:40

If you put all the interface functions in a base class, they will automatically be available to all the derived classes.

If this doesn't work for you, you can define a class that implements all the interface functions, and define an instance of this in any class that that implements the interface. Then for each interface function, forward the call to this instance. This avoids having to re-implement the whole functions in each class that implements the interface.

For example:

interface InterfaceX
{
// Lots of interface function definitions...
}

class ImplementationOfInterfaceX : InterfaceX
{
// Implementation of each function...
}

class X : InterfaceX
{
ImplementationOfInterfaceX implX;

public int func1 (int par)
{
return implX.func1 (par); // I.e., a forwarded call instead of a 100-line function.
}

public float func2 (float par)
{
return implX.func2 (par);
}

...
}

Of course this would be much easier if C# allowed multiple inheritance. I'm hoping they will in a future version. It makes some things very easy. It seems to me they left it out because it allows complexity and confusion for some extreme contrived cases that no one in their right mind would do. Not a good justification for leaving it out (in my biased opinion).

Ben Fair8-Dec-08 10:34

Ben Fair

8-Dec-08 10:34

The crux of the problem is that you want class Z to pass an item into a function that accepts an InterfaceX item, but class Z is not necessarily an InterfaceX. So, the only way to do it as-is is to do this messy kind of check. Ideally, you'd have the call to function2 be in a class that is an InterfaceX. Passing a Z that is not an InterfaceX won't work, so you'll have figure out how you want to handle that situation. Here's a class Z that should work:

class Z : Y
{
    public bool function1(String txt)
    {
        if(this is InterfaceX)
            return base.function2((InterfaceX)this, txt);
        else
            return false; // maybe throw exception?
    }
}

Keep It Simple Stupid! (KISS)

Deresen8-Dec-08 10:51

How to verify existing and Installed components via code

8-Dec-08 10:51

Thank you very much, I'll try to do it this way.

Eitan O8-Dec-08 6:09

Eitan O

8-Dec-08 6:09

Hello,

I need to check and verify that some components are installed on the computer via C# code.

The components are:
MSMQ
IIS

I successfully implemented this issue using checking the existing of the relevant services.
and that they are running.

Is there any library that perform these checkings?
Is there any library that shows what do I have on this machine?
maybe an API that I can get the list from "Add/Remove Programs" of windows components?

Thanks,
Eitan

Using double quotes in a string

compninja258-Dec-08 5:51

compninja25

8-Dec-08 5:51

Hey all. I know I've done this in the past and I'm not having much luck searching online because it should...just work. I'm trying to save some javascript in a code behind and then calling it in the ASP.NET page using <%= Java%>. It's a simple time ticker that I want to reset all the time to countdown to Friday. My problem now is the string isn't accepting the \ as the escape for my double quotes.

public string Java
  {
      get
      {
          string java = "<script language="\"JavaScript\"">;";
          java += "TargetDate =\" " + friday + "\"";
          java += "BackColor = \"palegreen\";";
          java += "ForeColor = \"navy\"; ";
          java += "CountActive = true;";
          java += "CountStepper = -1;";
          java += "LeadingZero = true;";
          java += "DisplayFormat = \"%%D%% Days, %%H%% Hours, %%M%% Minutes, %%S%% Seconds.\";";
          java += "FinishMessage = \"It is finally FRIDAY!\"</script>;";
          return java;
      }
  }

* There might be a few extra "'s here and there as a result of copying and pasting out of VS *

every time I run the debugger, the string reads ect....

What's really weird is if I replace the double quote with a single quote, then the string acts the way I want it to, but not with the double quotes! (<script language="JavaScript"> ect...)

Has anyone ever seen this problem before? Is it possible something got screwed up with my VS 2008 install?

<div class="ForumSig">"You're damned if you do, and you're damned if you dont" - Bart Simpson</div>

J4amieC8-Dec-08 5:57

J4amieC

8-Dec-08 5:57

The debugger will always show the escape char '\'. Dont worry, it wont be in the output.

A few comments on your code:

1) Its Javascript. Java is a very different beast
2) Consider using a StringBuilder rather than lots of string concatenation using +=
3) Look at

Page.ClientScript.RegisterClientScriptBlock

. Its preferable to simply trying to output some script to the page using the old-asp method of <%= %>

Vikram A Punathambekar8-Dec-08 19:17

Vikram A Punathambekar

8-Dec-08 19:17

J4amieC wrote:
Consider using a StringBuilder rather than lots of string concatenation using +=

If the strings are known at compile time, the compiler will generate one big string for you. Try compiling this and taking apart the EXE with ildasm and you will see what I mean.

using System;

class Foo
{
	public static int Main(string[] args)
	{
		string s = "Hello, " + "world!";
		Console.WriteLine(s);
		
		return 0;
	}
}

Cheers,
Vıkram.

Stand up to be seen. Speak up to be heard. Shut up to be appreciated.

Deresen8-Dec-08 6:36

8-Dec-08 6:36

As J4amieC says, you can use the Stringbuilder. But you can also use String.Format();
Very easy to use:

String javaScript = String.Format(@"
<javascript> etc. </javascript>
<and other="" stuff="" here=""></and>
{0} <- a variable
{1} <- another variable", variable1, variable2);

Giorgi Dalakishvili8-Dec-08 7:10

Giorgi Dalakishvili

8-Dec-08 7:10

String.Format() uses StringBuilder internally.

Giorgi Dalakishvili

#region signature
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Asynchronous Registry Notification Using Strongly-typed WMI Classes in .NET [^]

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cor28798-Dec-08 7:22

cor2879

8-Dec-08 7:22

I do a lot of dynamically created JavaScript in my ASP.Net development. I use a pattern similar to this:

protected void Page_PreRender(object sender, EventArgs e)
{
	/* Call your method that registers JavaScript from here.  This event is called even if
	 * you only have a Call Back rather than a Post Back
	 */
	 
	 RegisterClientScript();
}

// This method contains any dynamic JavaScript that I wish to register on the page
protected void RegisterClientScript()
{
	// Check first to see if the page has already had the Javascript code registered.
	if (!(Page.ClientScript.IsStartupScriptRegistered("myJS"))
	{
		// Use a string builder to, well, build the string.  This limits the number of immutable strings that are added to memory and must
		// be eventually garbage collected.
		StringBuilder js = new StringBuilder();
		
		// Build the JavaScript code.  Note that inside the string we are actually using single quotes - this is legal in JavaScript for strings. 
		// In this way you don't even have to mess with escape characters.  At least not as often - there may still be occasions where you will
		// need single quotes.
		js.AppendLine("TargetDate = 'friday';");
		js.AppendLine("BackColor = 'palegreen';");
		js.AppendLine("ForeColor = 'navy';");
		js.AppendLine("CountActive = true;");
		js.AppendLine("CountStepper = -1;");
		js.AppendLine("LeadingZero = true;");
		js.AppendLine("DisplayFormat = '%%D%% Days, %%H%% Hours, %%M%% Minutes, %%S%% Seconds.';");
		js.AppendLine("FinishMessage = 'It is finally FRIDAY!'");
		
		/* Call the register startup script method.  This will call the above script to execute when the page renders.  The first parameter is any instance of the
		  * System.Type class, but usually you want to pass the type of this Page or Control.  Next is the key, then the JavaScript string itself.  The last boolean value
		  * specifies whether or not script tags should be added to the JavaScript code.  You can add them yourself or just do as I did and have the RegisterClientScript method
		  * do this for you.  To me this way is cleaner.
		  */
		Page.ClientScript.RegisterStartupScript(this.GetType(), "myJS", js.ToString(), true);
	}
}

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