passing "this" by reference - C# Discussion Boards

19-Apr-07 0:37

OK, I'm not sure about that, I'd suggest writing to Chris and asking him.

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog
"I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

C# Newbie Please Help!

ashley4838518-Apr-07 14:30

ashley48385

18-Apr-07 14:30

well just want to say hiya to start with.

i need a bit of healp on C# GUI programming.
the problem i have is this.

i need to vreate a C# forms appliction that access data from the registry.say the CPU speed for example.
then it need to display it on the forums.how do i do this.

thanks guys!
D'Oh! | :doh:

Ashley

pbraun18-Apr-07 14:44

18-Apr-07 14:44

If you're wanting the CPU speed, you should be looking at WMI since the CPU speed is not kept in the registry. Look in your help files for "Registry Class". The examples there are quite good for basic information. If you have questions beyound that information, by all means please ask.

Phil

ashley4838518-Apr-07 14:51

ashley48385

18-Apr-07 14:51

hi phil thanks for replying.
all i need to do is access the reg or WMI and display the info on a GUI win app project.
i dont suppose you have any example code at all do you.

thanks!

pbraun18-Apr-07 15:02

18-Apr-07 15:02

There are many examples of that on this web site. Do a search for "Registry" or WMI and you will get a number of hits. Be sure to limit your search to C# and you will get mostly C# articles. You should download the examples and go through them.

Phil

ashley4838518-Apr-07 15:09

ashley48385

18-Apr-07 15:09

do you have a link to just one of them.
the only ones i can find are console and does not help me at all.
i cant seem to find anything on forms programming.

thanks!
x

pbraun18-Apr-07 15:24

passing "this" by reference

18-Apr-07 15:24

Ok, now I understand the problem you are having. I believe it is this:

You have a control on your form such as a text box in which you want to place a value. The value might be the current CPU usage or other value. But you can't seem to display it on the form.

Try doing the following:

Add a button to your form
Add a textbox to your form

Double click on the button which will generate the _Click(...) stub. In this stub do the following:

Pseudo code

int myValue = 110; // Replace this line with a query to WMI or the Registry
TextBox.Text = myValue.ToString();

End Pseudo code

The second line in the pseudo code block I believe is the information you seem to be missing.

Phil

cbin18-Apr-07 14:25

cbin

18-Apr-07 14:25

hi,
I originally wrote an object as a struct, and now I am changing it to a class.
In one of my member methods I want to pass "this" by reference to a method in another class and I get teh below error when I try to build? Is this common? Anyone know why it works with a struct and not a class?

Cannot pass '<this>' as a ref or out argument because it is read-only

thanks

cb

Re: passing "this" by reference

Luc Pattyn18-Apr-07 14:48

Luc Pattyn

18-Apr-07 14:48

Hi,

for structs, ints and other simple data types, "this" is the value itself
(hence the name "value types"); you may add the "ref" keyword to obtain a
reference to it (similar to a pointer in C/C++).

for class instances, "this" is a reference (hence "reference types"),
so it behaves as a pointer would in C/C++; hence you should drop the "ref"
all together when switching from struct to class.

Smile | :)

Luc Pattyn

[My Articles]

Re: passing "this" by reference

Tim Paaschen18-Apr-07 19:43

Tim Paaschen

18-Apr-07 19:43

Hi,

as Luc already suggested, you can just drop the 'ref' from your method's parameter and everything should work. I will just add some explanation why you must not pass 'this' as a ref parameter.

If you have a value object (a struct) and you pass it by value (no 'ref' parameter) to the method, the method gets its own copy and the original will not be affected by any changes made in the method. If the value object is passed by reference, all changes do affect the original.
If you have a reference object (a class) and you pass it by value, the reference itself is copied. Thus you have two references to the same object. If the method changes the referenced object, the changes will affect the original. However, if the method changes the reference itself (e.g. set it to 'null'), this will not affect the original reference. If you pass the reference object as a reference parameter, you are able not only to manipulate the referenced object but also the reference itself. Sometimes this is the desired behaviour, but you definitely don't want enable any method to set your 'this' reference to 'null'. Therefore 'this' is read-only and must not be passed by reference.

Hope this helps.

Regards,
Tim

Reading data from one application to another

yirmyah18-Apr-07 12:45

yirmyah

18-Apr-07 12:45

Hi,

I need help in reading an edit box from one application (java) to a C# application.

Currently (using Spy++ / Winspector as reference) I have been able to locate the parent handle of the java application using FindWindow like so:

IntPtr hWndParent = FindWindow(null, "Application Name");

I then find the correct child handle by looping through all the child handles until I get to the actual edit box on the java application using FindWindowEx like so:

IntPtr hWndChild = FindWindowEx(hWndParent, IntPtr.Zero, null, null);

Now that I have the address of the edit box, I am wanting to pull the actual data stored in the edit box and save it into the C# application.

jn

Re: Reading data from one application to another

Christian Graus18-Apr-07 14:45

Re: Reading data from one application to another

18-Apr-07 14:45

You need to use p/invoke to call GetWindowText on that text box via it's handle.

yirmyah18-Apr-07 15:19

yirmyah

18-Apr-07 15:19

I have read that GetWindowText will not work if I am reading any control outside of the application that is outside of the calling application.

Re: Reading data from one application to another

Dave Kreskowiak18-Apr-07 15:31

Dave Kreskowiak

18-Apr-07 15:31

True! You can also send the WM_GETTEXT message to the window handle without running into that restriction.

But, of course, it gets worse! There nothing that say that the target edit box has to respond to either request! You could go through all this junk and find out that the edit box doesn't care about that message and won't respond to it.

Dave Kreskowiak
Microsoft MVP
Visual Developer - Visual Basic
2006, 2007

Using Databound ComboBox

polishprogrammer18-Apr-07 12:03

polishprogrammer

18-Apr-07 12:03

I have a database application that uses a DataGridView to display all records and textboxes, comboboxes, checkboxes, etc., to display each individual record. The user edits the individual record controls to update (or add) records. The comboboxes text field is bound to the appropriate data item in the datatable. Unfortunately, though I can select a new item from the combobox, that item does not get updated to the datasource when I save any updates. The textboxes and such do get updated. Can anyone explain to me why this is the case? Thanks.

RichTextBox

Saikek18-Apr-07 11:29

Saikek

18-Apr-07 11:29

Hello! Sorry for my million annoying questions, but i have another one.

So:
I have i RichTextBox, and i click in the center of some word.
How can i get a full word ?

(is there some methods, or i have to move left and right to spaces?)

Thanks!

One nation - underground

Re: RichTextBox

Judah Gabriel Himango18-Apr-07 15:56

Judah Gabriel Himango

18-Apr-07 15:56

With the System.Windows.Forms.RichTextBox, yes, you have to do your own code to figure out the word given a location.

If you use the Windows Presentation Foundation (WPF) RichTextBox, there's some built-in things to help you get the run/word/paragraph at a particular point, IIRC.

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Judah Himango

C# and C++

netJP12L18-Apr-07 10:31

netJP12L

18-Apr-07 10:31

Hi guys, I am not sure why everyone is moving on C# besides it microsoft technlogy, provide drag and drop functionality and easy to do programming and coloured syntax. If C++ is powerfull why there wasn't any work get done on it. Infact Windows is also written in C/C++. How come there wasn't any VS2005 kind of editor for C/C++ programmers that could have the "." style object lists . Wouldn't it better if we could have more developement in C++ Apis,syntaxs, memory managements, plug and play controls and component based control progrmaming so we can get more control over what we want to achieve rather than calling C/C++ API functions in C# programming.

Thanks

Christian Graus18-Apr-07 10:45

18-Apr-07 10:45

netJP12L wrote:
How come there wasn't any VS2005 kind of editor for C/C++ programmers that could have the "." style object lists .

VS2005 does C++, and does it pretty well.

C# is easier to use, and easier to write most types of Windows apps. I write some pretty complex and non standard code in C#, it works just fine. If Microsoft were to go under, C# is subject to an external standard, but, either way, I'd lose my platform as well. I know C++, I have been a C++ MVP, as it happens ( I am now a C# MVP, should change my sig ). But, C# is a better tool for a lot of jobs, in my experience. Why would a client pay me double to have the same functionality, have it take twice as long, so they can say it's written in C++ ?

pbraun18-Apr-07 14:58

18-Apr-07 14:58

I agree with Christian and his points. I still feel that I should point out though, that there are very specific cases when C/C++ is a better choice. A case that comes to mind is when outright speed is essential, an example would be a driver. However, C# allows much more rapid user interface development with a lot less coding.

Phil

Christian Graus18-Apr-07 16:06

18-Apr-07 16:06

I agree, there are times when you need C++. Writing the .NET framework is an obvious example :P

netJP12L18-Apr-07 16:19

netJP12L

18-Apr-07 16:19

Thanks for your response, I do agree what you said but why microsoft or some other regulatory body didn't take the initiative to redesign the C/C++ codeing style and made it what C# offers to programmers rather than coming up with a new language. I mean, lets say in the future someone else come up with new easy language syntax and bit something different everyone gonna be moving towards that then. Why don't we focus entire on Parent language rather than producing child languages.

pbraun18-Apr-07 18:07