Re: Lock(This) - C# Discussion Boards

10-Aug-09 9:35

Make the interface generic?

public interface Abase<T>
{
    T Xyz() ;
}

(Not tested.)

modified on Monday, August 10, 2009 6:57 PM

DaveyM6910-Aug-09 7:00

DaveyM69

10-Aug-09 7:00

I agree with PIEBALDconsult, an interface is probably the cleanest way to do this:

public class A<T> : IA where T : class
{
    public int Xyz()
    {
        return 1;
    }
}
public interface IA
{
    int Xyz();
}

// where a is an instance of A<T>
if (a is IA)
    int returnValue = (a as IA).Xyz();

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
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PIEBALDconsult10-Aug-09 12:59

10-Aug-09 12:59

Why use is and as? Pick one.

DaveyM6910-Aug-09 21:25

DaveyM69

10-Aug-09 21:25

Force of habit. Say a was passed as a parameter (object o). Without the is, you would have to catch the NullReferenceException at the as if it wasn't an A<T> instance, and without the as (or some other cast/conversion), there would be no way to access the Xyz method.

PIEBALDconsult10-Aug-09 22:02

10-Aug-09 22:02

A<T> a = o as A<T> ;
if ( a != null ) a.Xyz() ;

if ( a is A<T> ) ((A<T>) o).Xyz() ;

Aw crap, how'd it get to be 01:00? I'd better get to bed.

Lock(This)

jpk42010-Aug-09 5:06

jpk420

10-Aug-09 5:06

Hello All ,

I was readinf the lock concept and find that there is problem with lock(this) or lock(public type).
what is the problem doing like that ?

Please explain me with an example

Ennis Ray Lynch, Jr.10-Aug-09 5:30

Ennis Ray Lynch, Jr.

10-Aug-09 5:30

A good starting point for research is the documentation[^]. I think you would be surprised at the information available in MSDN.

Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting.

A man said to the universe:
"Sir I exist!"
"However," replied the universe,
"The fact has not created in me
A sense of obligation."
--Stephen Crane

Luc Pattyn10-Aug-09 5:52

10-Aug-09 5:52

Nah. MSDN documentation is like holiday brochures without pictures, nothing interesting there. Laugh | :laugh:

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Ennis Ray Lynch, Jr.10-Aug-09 5:55

Ennis Ray Lynch, Jr.

10-Aug-09 5:55

Actually, the particular article I referenced while sparse does indicate the common problems and a common solution in the remarks section. Although, most MSDN is total crap.

jpk42010-Aug-09 5:57

jpk420

10-Aug-09 5:57

I check the documentation . I did not get that what was the problem .

any way we are making lock on that object . So what matters if that is private or public?

Please help me out

Luc Pattyn10-Aug-09 6:06

10-Aug-09 6:06

you could as well ask why private and protected members exist at all. Why not make everything public?

it is a matter of encapsulation, separation of concern, improving reliability, etc.

Smile | :)

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jpk42010-Aug-09 6:28

jpk420

10-Aug-09 6:28

No That i not mean at all . what i got confused is anyhow i am locking that object . So untill i done with my work no body can tamper it with .

So even if i declare private or public i am holding a lock on that . So how that acces specifier will affect that .

Sorry to trouble u .. bUt a good example will clear my doubt .. my brain is not able to leav this doubt unanswered.

Luc Pattyn10-Aug-09 6:38

10-Aug-09 6:38

when your locker object is public I can lock it without your code being aware of it; so all your code would break right away. Don't make public what doesn't have to be public, that is one of the OO principles.

Smile | :)

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PIEBALDconsult10-Aug-09 7:04

10-Aug-09 7:04

Yet with Reflection I can see your privates. Cool | :cool:

Luc Pattyn10-Aug-09 7:10

10-Aug-09 7:10

You'd better think twice before applying reflection on me... $Shucks | :-\$

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Re: treeview scroll event

Leonardo Muzzi10-Aug-09 7:18

Leonardo Muzzi

10-Aug-09 7:18

The problem with Lock(this) and Lock(type) is that these objects are public, so an external code could lock on them. So if your class is named YourClass, I can make a code like this:

YourClass obj = new YourClass();
lock(obj){ ... }

And that would probably deadlock your internal code. Same problem for a public type. Since it is commom to lock an object that you want to protect, it's not too dificult for a code like this to happen.

The best approach is to create an object just for locking on it, instead of locking the class object. Make this locking object "static" and you get the same effect of locking a type.

Regards,

Leonardo Muzzi

q in datagridview

mohammad alnoed10-Aug-09 4:56

mohammad alnoed

10-Aug-09 4:56

Hi All,

I am having problems adding a new row to a datagridview control in my form. I have a simple form
with datagridview. When the user types in an item number in the first columen by event
the system will populate the datagridview with the relevant data from the database.

Re: q in datagridview

RobScripta10-Aug-09 9:13

RobScripta

10-Aug-09 9:13

I presume you want to fill in other columns in the new row based on the item number in the first column.
You can use the validated event of the cell:

- You get an DataGridViewCellEventArgs object with rowindex and columnindex
if Columnindex == 0
{
// Collect the data from the database
DataTable dt1 = datatablefunction(relevantsql);
//Write the data in the appropiate cells
this.DataGridView.rows[e.RowIndex].Cells["NameOfCell"].value = dt1.rows[0]["ColumnName"].toString();
}

This is all aircode, but I hope this helps.

Rob

treeview scroll event

Surya Ayyagari10-Aug-09 3:49

Surya Ayyagari

10-Aug-09 3:49

I have treeview which is in panel. As it grows scroll bar of the treeview appear. I want capture the scroll bar value and set the value to another treeview in another panel. But I could see that there is no scroll event for treeview. How can do that?

Thanks in Advance
Regards
Surya D'Oh! | :doh:

0x3c010-Aug-09 4:31

0x3c0

10-Aug-09 4:31

Unfortunately I can't provide any sample code because I can't get access to Visual Studio, but in terms of a scroll event, I'd create a class which inherits from TreeView and overrides the WndProc method. If m.Msg == WM_MOUSEWHEEL, then you've got a scroll message; you just have to interpret m.WParam and m.LParam properties in a fashion. When the derived class provides a Scroll event, use that instead of the TreeView control

Between the idea
And the reality
Between the motion
And the act
Falls the Shadow

Re: treeview scroll event

Surya Ayyagari10-Aug-09 17:52

Surya Ayyagari

10-Aug-09 17:52

thanks for the help. I will try that.

Best Regards
Surya

Form Events

Member 368144310-Aug-09 2:36

Member 3681443

10-Aug-09 2:36

Hi All,

I'm having some problems finding the correct Forms event from which to fire my code. I want to run a sequence of code automatically once a form is displayed on the screen.

Form_load isn't correct as my code finished before the form is displayed.
Form_Shown doesn't seem to trigger consistently.
Form_Activated triggers multiple times
Form_Validated doesn't seem to trigger consistently.

What event should i use?

I basically want the code to fire as if the form was displayed on the screen and I hit a "Start Button".

Thanks in advance.

Daniel.

Re: Form Events

Luc Pattyn10-Aug-09 2:51

Database Problem, Unknown Information in a Access DataBase by the MEMO type!

10-Aug-09 2:51

Shown should fire exactly once, the first time the form has become visible.
MSDN: "Occurs whenever the form is first displayed."

Smile | :)

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maysam gamini10-Aug-09 2:05

maysam gamini

10-Aug-09 2:05

Recently i get a project about a clinic software and i have a little problem with the previous database information. so i thought that you are the best one that could answer me,

let me describe a little...

the previous software has a feature that allow to the doctor to write the patients information by hand writing with a electrical pen, it so like paint brush software and it save this information in the database like bellow,

AORtHQTwD4AEAh4CSBEHSBFEgID8BwRIEEU1B0gRRP8BRQgFSBFE/wEEAwE4ABgiIDIJAPT/AgHpIjpFMwkA+J8CAVogOkU4CAD+AwAAAIB/AA8OEvkjjT/PI40/EQAAgD8eKLQBhvAdR4DpyGhwAAAAAAAAAAAAAAIAZ4yvRgAAnp8AACGhwAAAAAAKIgqE+ry+sL1Y4RhHXsCF8iV5DHKLKIJsTICFqxzDyy14ueEKIgmH5jDmMYFA51D5XSIqh+Ow47GwWG2Sug26
Confused | :confused:

so i don't know what exactly it is, but i guess it could be a Multimedia Format Like jpeg or anything else like that, do you know what it could be, and how can i solve this problem!

thank you very much!
With best Regards!
--
Maysam Gamini
Bachelor Of Information Technology
Faculty Of Engineering, Isfahan University

E-mail address: Mit.gamini@gmail.com
E-mail address: Ir.webbiz@gmail.com

Phone: +9821-20105677
Cell No: +98912-3778746

Re: Database Problem, Unknown Information in a Access DataBase by the MEMO type!

Luc Pattyn10-Aug-09 2:54