c# Does casting create a new object?

[matthewaveryusa]

I have a little dilemma I would like to straighten out.

I have a class Car with 100's of parameters.
I add a bunch of Car instances to a listbox. They are now plain old objects.
Then when I selected an item from the listbox, I would like to cast the object back to Car and print the parameters on screen.
so I have 2 options:

option 1:

Textbox1.Text = ((Car) Listbox1.SelectedItem).param1.ToString();
Textbox2.Text = ((Car) Listbox1.SelectedItem).param2.ToString();
...
Textbox100.Text = ((Car) Listbox1.SelectedItem).param100.ToString();

option 2:

Car c = new Car();
c = (Car) Listbox1.SelectedItem;
Textbox1.Text = c.param1.ToString();
Textbox2.Text = c.param2.ToString();
...
Textbox100.Text = c.param100.ToString();
 

Option 1 Could be more efficient if the cast is pointing to the object, while option 2 creates a new object, which could be more efficient if a cast creates a new object each and every time. Which one is right, which one is wrong? A reference to the MSDN website would be nice

thanks a lot!
Matt

[nukefusion]

I would say that option 2 is almost certainly the better way to do this.
A cast obviously requires some sort of performance overhead and in code sample 2 you only have to perform the cast once.
In code sample 1 you have to cast each and everytime.

I can't say whether it would cost you more in terms of performance to declare the new object in sample 2 than it would to cast X amount of times in sample one, however I do know declaring a new object in sample 2 is unnecessary. Here's how I would do it:

Car c = (Car) Listbox1.SelectedItem; 
Textbox1.Text = c.param1.ToString(); 
Textbox2.Text = c.param2.ToString(); 
... 
Textbox100.Text = c.param100.ToString(); 

[r035198x]

Better use

Car c = (Car) Listbox1.SelectedItem;

instead of

 Car c = new Car();
c = (Car) Listbox1.SelectedItem;

There is no need for creating that new Car object which you simply discard afterwards.

P.S Your code looks like it could have been done cleaner using arrays or ArrayLists.

[matthewaveryusa]

I'm sorry for my ignorance but what is the difference between these two snippets with regards to c.

car some_other_car = new car();
car c = new car();
c = some_other_car;

and

car some_other_car = new car();
car c = some_other_car;

?

[Shashi Sadasivan]

@matthewaveryusa
You mean to c#...
objects in c# get referenced when you do that....
so c will point to the same meory location as some_other_car

[balabaster]

Alas it was a design decision by the language team at MS that the WITH statement not be included in C# or you could do:

with (car)ListBox1.SelectedItem{
  textbox1.text = .param1;
  textbox2.text = .param2;
}

of course, when you point a variable to an object instance, it points to the reference, so you're really not creating a new object, what you're really doing here is saying: Create a reference c to ListBox1.SelectedItem and treat it as the object type car.

car c = (car)listbox1.selectedItem;
textbox1.text = c.param1;
textbox2.text = c.param2;

Alas, this is one of those instances where C# isn't quite as syntactically efficient as if it had adopted some of VBs keywords - those instances are few and far between though.

In VB you can do:

With Cast(ListBox1.SelectedItem, Car)
  TextBox1.Text = .Param1
  TextBox2.Text = .Param2
End With

It would've been nice if you could do it that way in C# (as my first code block suggests).

[matthewaveryusa]

Oh boy, good thing you sorted this out for me. This can become an issue when threading :)