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I know I'm missing something simple. I have a base class, Device, and a bunch of derived classes Dev1, Dev2... Depending on the type of device active at the moment, I have an abstract method for each derived type. Deciding which to use leads me to:
if (SelectedDevice.GetType() == typeof(Dev1))
{
SetDevice((Dev1)SelectedDevice);
}
else if (SelectedDevice.GetType() == typeof(Dev2))
{
SetDevice((Dev2)SelectedDevice);
}
else if ...
It works, but it just feels ugly.
Molly
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rather than comparing types explicitly, you could use the is keyword.
and what is wrong with a simple SetDevice(SelectedDevice);?
or perhaps SelectedDevice.Set()?
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My apologies for using the term 'abstract' a little too loosely. The SetDevice methods control display within a form, and are not part of the Device class.
I started with SetDevice(SelectedDevice); but the compiler kicks that back because it can't be resolved at compile time.
Molly
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You could establish an enum and then have an appropriate property in each class. Setting/getting a property probably has less impact on performance than casting.
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
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I've had this problem in the past. What I decided on was to have an enum and pass the type of the device to the base classes constructor. Something like...
public enum DeviceType
{
TypeA,
TypeB
}
public abstract class DeviceBase
{
private DeviceType deviceType;
internal DeviceBase(DeviceType deviceType)
{
this.deviceType = deviceType;
}
public DeviceType DeviceType
{
get { return deviceType; }
}
}
public class DeviceTypeA : DeviceBase
{
public DeviceTypeA()
: base(DeviceType.TypeA)
{ }
}
public class DeviceTypeB : DeviceBase
{
public DeviceTypeB()
: base(DeviceType.TypeB)
{ }
}
Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Why are you using VB6? Do you hate yourself? (Christian Graus)
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Why can't you do something like:
SelectedDevice.Set(this)
Which Set being virtual (abstract), so the right one is called without the IF and also, if newer classes appear, you don't need to change the "Deciding" code.
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MollyTheCoder wrote: I have a base class, Device, and a bunch of derived classes Dev1, Dev2
SetDevice((Device)SelectedDevice);
This one?
I are Troll 
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Is the casting required at all? Even if SetDevice is overloaded for each type there shouldn't be a problem should there? And if not, then you still don't need to cast to each type.
Edit: I just tried it and I see the problem.
More information about SetDevice would be helpful.
And, as Luc said, use is rather than comparing types.
Edit: Or perhaps SetDevice should handle determining which type of device it was passed:
private static void
SetDev
(
DevBase Dev
)
{
System.Console.WriteLine ( "DevBase" ) ;
if ( Dev is Dev1 ) SetDev ( (Dev1) Dev ) ;
else if ( Dev is Dev2 ) SetDev ( (Dev2) Dev ) ;
return ;
}
modified on Wednesday, December 30, 2009 2:01 PM
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I have a form with device information for for each type of device. Most of the information is similar, so I'm sharing a single form, using SetDevice() to setup fields and controls specific to each derived device type. (right now, all SetDevice methods are inside the form, not the Device classes).
SelectedDevice is instantiated as a Device, then cast to whichever derived class is appropriate. The cast is necessary because at compile-time, SelectedDevice is just a Device, but at run-time will have a specific derived type.
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I wonder whether or not dynamics in C# 4 will do it.
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PIEBALDconsult wrote: Or perhaps SetDevice should handle determining which type of device it was passed.
Wouldn't that mean creating a big SetDevice to handle all types, and just move the same code into SetDevice? Even if the code is a little less ugly thanks to is.
Molly
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Afaik, the 'is' keyword is not fully equal to x.GetType() == typeof(y) .
Let's say I have:
class A
class B:A (B inheriting from A)
Then following (pseudo-)code:
b = new B();
b is A returns true and
b = new B();
b.GetType() == typeof(A) returns false.
The latter option checks for an exact type match.
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Paul89 wrote:
b = new B();
b.GetType() == typeof(A);
The above test the immediate types A.GetType() != B.GetType() && B.GetType() != A.GetType()
for a better understanding try this:
b = new B();
a = new A();
typeof(A).ToString();
typeof(B).toString();
a.GetType().toString();
b.GetType().toString();
However this works like the is keyword:
B.IsSubclassOf(A) returns true
-or-
A.IsAssignableFrom(B) returns true
On the is key word:
'An is expression evaluates to true if the provided expression is non-null, and the provided object can be cast to the provided type without causing an exception to be thrown.'
modified on Wednesday, December 30, 2009 2:42 PM
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Thanks! I think is works for the code I've got today, but you probably saved me from myself on some future project.
Molly
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Or maybe not! 
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Who goes 400 pages deep (as of today) into a forum just to rub it in? 
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That'd be me. 
But I took a shortcut -- I saw on your profile that you had only posted a few questions, I checked those few.
I didn't actually know I'd find this.
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Today, I tried to move the logic of my code from the SQLServer to my C# code.
The task is simple: Create a new HierarchyID element which is the first child of the current.
At the server side, the code is
DECLARE @User hierarchyid
SELECT @User = hierarchyid::Parse('/1/')
INSERT USERS (LOGIN,HID)
VALUES ('UserName', @User.GetDescendant(NULL, NULL)
O.K. Now I try to do the same logic in code like this:
SqlHierarchyId NewHID = new SqlHierarchyId();
NewHID = SqlHierarchyId.Parse("/1/");
NewHID = NewHID.GetDescendant(null,null);
but I receive an error
"Error 6 Argument '1': cannot convert from null to 'Microsoft.SqlServer.Types.SqlHierarchyId"
What I find in the Microsoft's documentation at http://msdn.microsoft.com/en-us/library/microsoft.sqlserver.types.sqlhierarchyid.getdescendant(SQL.105).aspx[^]
sais that NULL is allowed.
Now what can I do in the case? Any Ideas?
p.s. I've designed a workaround meanwhile:
DECLARE @User hierarchyid
SELECT @User = hierarchyid::Parse('/1/')
SELECT @User.GetDescendant(NULL,NULL).ToString() as Child
...and I get a dataset filled with the value of the child. But this is stupid, isn't it?
modified on Wednesday, December 30, 2009 8:42 AM
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I want to call to a function every time that a function is add to my Event.
How can i do it?
Example for this kind of code:
public delegate void DoItDelegate(int i);
public partial class Form1 : Form
{
public DoItDelegate MyFunction;
public int Count=0;
public Form1()
{
InitializeComponent();
RegisterTheNewMethod();
MyFunction += new DoItDelegate(DoItFunction);
MyFunction.Invoke(32);
}
public void DoItFunction(int i)
{
Count++;
int j = i;
}
public void RegisterTheNewMethod()
{
Count = 0;
}
}
Every time that this kind of command (MyFunction += new DoItDelegate(DoItFunction);)is been called and the function is been added to the Event MyFunction i want to invoke some function (In this example RegisterTheNewMethod()).
How can i do it?
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Did you not read the answers to your earlier post? So why post the same again?
All those who believe in psycho kinesis, raise my hand.
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hi, I am not sure how to call method every time you add to a delegate. Why don't you call the method after the delegate is added .
e.g
MyFunction += new DoItDelegate(DoItFunction);
RegisterTheNewMethod();
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Hi,
i will be appreciated if someone could help me in this situation:
my PC: Pentium 2Core 2.1GHz 4Gb(Ram) windows 7 x64
The problem that I can not solve by myself is how to speed up calculations.
My method runs 850-970ms. method created for image processing (crops image ,recognize coped image and put calculated value into matrix)
When i am using threads (in this example 2 threads)
ThreadStart ts = new ThreadStart(ThreadOneP);
ThreadStart ts2 = new ThreadStart(ThreadTwoP);
Thread thread1 = new Thread(ts);
Thread thread2 = new Thread(ts2);
thread1.Start();
thread2.Start();
thread1.Join();
thread2.Join();
method takes 900-1070ms.
How to speed up that method will take about 400ms? it is possible?
P.S sorry for my English
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Well, that's a bit vague without knowing what the threads are actually doing.
The bit of code you posted isn't really incorrect, although the calling thread is blocked and you could do some work on that rather than create a new one then just block on its completion.
To improve performance, you need to take a look at your algorithm and make sure it can't be improved. Splitting the task onto more threads might be an idea as well so that machines with more processors can make use of them.
Perhaps try increases the thread priority of the workers?
Regards,
Rob Philpott.
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Also I just now try to set 7 thread 1 thread for each image row. but time consumption is the same as Using 2 threads 900-1000ms.
can you tell a little bit mote how to use thread priority, because i thing i i will set high priority for all threads there will be no effect.
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