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post #41 of 49
Quote:
Originally Posted by Fantasy View Post

Thank you guys so much. I have spent all of yesterday trying to understand why my abstract component class is being called instead of the the derived class. Now it works perfectly. I really can't thank all of you enough. smile.gif

bad code
Code:
abstract class component 
{
     public void Draw()
     {
     }
}

class Panel : component 
{
     public new void Draw()
     {
          base.Draw();
     }
}

class PanelTest : Panel 
{
     public new void Draw()
     {
          base.Draw();
     }
}

Right code
Code:
abstract class component 
{
     public virtual void Draw()
     {
     }
}

class Panel : component 
{
     public virtual void Draw()
     {
          base.Draw();
     }
}

class PanelTest : Panel 
{
     public override void Draw()
     {
          base.Draw();
     }
}

There's not abstract methods in your abstract class, so you don't need it.
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post #42 of 49
Quote:
Originally Posted by tompsonn View Post

Not telling him to do it here - but "new" allows the child class to hide a method in the base class (not the same as overriding).

http://msdn.microsoft.com/en-us/library/6fawty39%28VS.80%29.aspx

Ya - i didn't connect the dots - new (for method hiding) is a seldom used feature in c# (in my experience anyways). Alot of times it can be confusing because the runtime won't call the method in the same way overridden methods are. If you're using new, a good alternative is just to call the method something different instead of using the name of the method in the base class.
post #43 of 49
Thread Starter 
ok I thought you would add abstract to a class so you can't create a new object of the class. like
Code:
//doesn't work.
Component c = new Component(); 

I didn't want anyone to make a new object out of Component class. that's why I added the abstract keyword.
Edited by Fantasy - 3/16/13 at 7:19am
    
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post #44 of 49
Quote:
Originally Posted by Fantasy View Post

ok I thought you would add abstract to a class so you can't create a new object of the class. like
Code:
//doesn't work.
Component c = new Component(); 
Yeah, that's true.
post #45 of 49
Quote:
Originally Posted by voidsstr View Post

Ya - i didn't connect the dots - new (for method hiding) is a seldom used feature in c# (in my experience anyways). Alot of times it can be confusing because the runtime won't call the method in the same way overridden methods are. If you're using new, a good alternative is just to call the method something different instead of using the name of the method in the base class.

I use it when I need to shove in some ad-hoc functionality or bolt on some code that wasn't meant to be there (read: hacks) and I don't control the original source.

Quote:
Originally Posted by Fantasy View Post

ok I thought you would add abstract to a class so you can't create a new object of the class. like
Code:
//doesn't work.
Component c = new Component(); 

I didn't want anyone to make a new object out of Component class. that's why I added the abstract keyword.

Private constructor, not abstract class smile.gif (Although abstract class will be easier haha, so its fine to use that too. I have).
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post #46 of 49
Thread Starter 
Quote:
Originally Posted by tompsonn View Post

Private constructor, not abstract class smile.gif (Although abstract class will be easier haha, so its fine to use that too. I have).

That makes more sense blushsmiley.gif
    
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post #47 of 49
Quote:
Originally Posted by tompsonn View Post

Quote:
Originally Posted by voidsstr View Post

Ya - i didn't connect the dots - new (for method hiding) is a seldom used feature in c# (in my experience anyways). Alot of times it can be confusing because the runtime won't call the method in the same way overridden methods are. If you're using new, a good alternative is just to call the method something different instead of using the name of the method in the base class.

I use it when I need to shove in some ad-hoc functionality or bolt on some code that wasn't meant to be there (read: hacks) and I don't control the original source.

Quote:
Originally Posted by Fantasy View Post

ok I thought you would add abstract to a class so you can't create a new object of the class. like
Code:
//doesn't work.
Component c = new Component(); 

I didn't want anyone to make a new object out of Component class. that's why I added the abstract keyword.

Private constructor, not abstract class smile.gif (Although abstract class will be easier haha, so its fine to use that too. I have).
That's another way of doing it lol
post #48 of 49
Quote:
Originally Posted by Fantasy View Post

Right code
Code:
abstract class component 
{
     public virtual void Draw()
     {
     }
}

class Panel : component 
{
     public virtual void Draw()
     {
          base.Draw();
     }
}

class PanelTest : Panel 
{
     public override void Draw()
     {
          base.Draw();
     }
}

Be careful with the Draw() method in Panel. It is not overriding the one in component, it is shadowing it. It is the same as if you placed the new keyword there, except that you've implicitly shadowed component.Draw() rather than explicitly shadowing it. You usually don't want to shadow methods unless you have a specific reason to do so. You normally do it by accident, and then introduce unexpected bugs (unless you have Resharper which will scream at you even if you do it deliberately smile.gif ). You can use override multiple times in an inheritance hierarchy like this.
    
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post #49 of 49
Quote:
Originally Posted by randomizer View Post

Quote:
Originally Posted by Fantasy View Post

Right code
Code:
abstract class component 
{
     public virtual void Draw()
     {
     }
}

class Panel : component 
{
     public virtual void Draw()
     {
          base.Draw();
     }
}

class PanelTest : Panel 
{
     public override void Draw()
     {
          base.Draw();
     }
}

Be careful with the Draw() method in Panel. It is not overriding the one in component, it is shadowing it. It is the same as if you placed the new keyword there, except that you've implicitly shadowed component.Draw() rather than explicitly shadowing it. You usually don't want to shadow methods unless you have a specific reason to do so. You normally do it by accident, and then introduce unexpected bugs (unless you have Resharper which will scream at you even if you do it deliberately smile.gif ). You can use override multiple times in an inheritance hierarchy like this.
+1.
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