Marshaling - C# Discussion Boards

Re: Force Scroll in DataGrid

4-Aug-02 21:28

Use the CurrentCell property to change which cell is visible (ie, set it to the first column in the last row).

It looks really stupid this way; but here is the code to do that

myGrid.CurrentCell = new DataGridCell(rowIndex, 1);

[rant]
Who ever thought it would make sense to assign a cell to the current cell property must've been smoking something at the time. To me this says replace the contents of the current cell with this new cell. Its not until you look at the documentation for DataGridCell that you realize it is used only to identify a cell by location and not to hold the actual contents of it. Dead | X|

[/rant]

James
"Java is free - and worth every penny." - Christian Graus

mike.5-Aug-02 8:15

mike.

5-Aug-02 8:15

Thanks.

I do agree that it doesn't look "elegant".
I also agree it would seem there is "something" missing, but could just be the 'ol VB6er in me..

Marshaling

Kastro4-Aug-02 10:52

4-Aug-02 10:52

I have a control that overrides WndProc. I handle WM_NCCALCSIZE and in the case where LParam is true I need to store a pointer to a value in the Result field of the Message structure. I do so as follows:

msg.Result = Marshal.AllocHGlobal(4)
Marshal.WriteInt32(msg.Result, WVR_REDRAW)

I never call Marshal.FreeHGlobal since the Result is used outside the scope of WndProc.

Will this code cause a memory leak? If so, is there any way to do this without a memory leak?

Thanks

Rama Krishna Vavilala4-Aug-02 11:18

4-Aug-02 11:18

msg.Result = WVR_REDRAW;

will be just fine

Kastro4-Aug-02 11:29

4-Aug-02 11:29

That won't compile for me since Result is an IntPtr and WVR_REDRAW is just an Integer...

Rama Krishna Vavilala4-Aug-02 11:32

4-Aug-02 11:32

Ok,

msg.Result = new IntPtr(WVR_REDRAW);

As far as I'm concerned you are a lower form of life than B*** S***** and M***** M******** combined. Colin Davies on some guy called R*** G****

Kastro4-Aug-02 11:42

4-Aug-02 11:42

That doesn't work either.. That creates a pointer to memory location WVR_REDRAW, the value at that location is not controlled by me.. I need to set Result to an IntPtr that points to a location containing the value WVR_REDRAW... The only way that I know of to do this is with the AllocHGlobal and WriteInt32 calls...

Rama Krishna Vavilala4-Aug-02 11:44

4-Aug-02 11:44

Kastro wrote:
That doesn't work either..

No my code was right IntPtr is a value type so you will not have any problems.

You don't need AllocHGlobal

As far as I'm concerned you are a lower form of life than B*** S***** and M***** M******** combined. Colin Davies on some guy called R*** G****

Kastro4-Aug-02 11:52

4-Aug-02 11:52

From the .NET help docs:

public IntPtr(
    int value
);

value - A pointer or handle contained in a 32-bit signed integer."

IntPtr is a value type, but the value that it stores is an address.

My original code works (presumably leaking memory though). When I switch to using new IntPtr(WVR_REDRAW) it doesn't work...

Rama Krishna Vavilala4-Aug-02 12:01

4-Aug-02 12:01

IntPtr is a value type of size same as the default pointer size for the platform. It can be used for numbers or pointers. All it is is that it size varies the number stored in it can be anything.

In window messages LParam, and WParam are 32 bit ints or 64 bit ints depending on the platform. In window messages LParam and WParam mean different things depending on the context. Same thing about LResult it can be used to return integers or pointers. In case of WM_NCCALCSIZE windows expect an integer to be returned so if return as new IntPtr(WVR_REDRAW) it is ok.

Kastro4-Aug-02 12:03

4-Aug-02 12:03

Ok, I figured out what's going on... You are right about just using new IntPtr(WVR_REDRAW).. I used Spy++ to see what result was being returned for the WM_NCCALCSIZE message...

For my code I was getting WVR_ALIGNBOTTOM | WVR_REDRAW | 0019F008

From what you suggested I get WVR_REDRAW...

What you suggested wasn't working (as far as the control went) because of other reasons...

Also is the wording of the help file incorrect then? That's what led me to believe what I did.

James T. Johnson4-Aug-02 13:23

4-Aug-02 13:23

Kastro wrote:
Also is the wording of the help file incorrect then?

Not entirely, IntPtr is used to represent an integer value that varies in size depending on the platform. A specific use of such an integer is a pointer. There isn't anything special about a pointer, except that its value refers to a location in memory.

James
"Java is free - and worth every penny." - Christian Graus

Async WebRequest

leppie4-Aug-02 9:50

leppie

4-Aug-02 9:50

Hi
I have a problem with running more than 2 async WebRequest's when launched. To explain better. Only 2 at a time responds, while the others wait for a "slot" to open. Then once one "slot" is open, the next async WebRequest will continue.

I am invoking all the requests from a foreach loop in the main program thread. I was thinking there is maybe a 2 operation limit, but can find no such mention.

IAsyncResult res = ds.WebRequest.BeginGetResponse( new AsyncCallback( this.ResponseCallback) , ds);

But ResponseCallback only get called when a slot opens up.

Any help will be accepted. Confused | :confused:

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

James T. Johnson4-Aug-02 13:19

4-Aug-02 13:19

This is the behavior of IE; to test it yourself upload 3 largish files to a website and create a webpage linking to them. Load the page up then right click and save target as on 3 of them; 2 will go immediately while the third will wait. I can't remember the agreed upon reasoning for this at the moment.

Unfortunately not much you can do about it unless you create your own class which will do the downloading. But there is a chance such a class already exists Smile | :)

James
"Java is free - and worth every penny." - Christian Graus

leppie5-Aug-02 1:53

leppie

5-Aug-02 1:53

James T. Johnson wrote:
Unfortunately not much you can do about it unless you create your own class which will do the downloading.

Thanx James, this is exactly what I am doing Smile | :)

I have tried calling Stream.Read each from its own thread, but with no joy either Frown | :(

Now only one download starts and with a second one following that and all others timing out.

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

James T. Johnson5-Aug-02 2:16

5-Aug-02 2:16

You aren't going to be able to use the WebRequest class at all; because the problem is how the WebRequest class works, by shifting the burden to the IE implementations which has the 2 connections to the same server limit.

The "work around" is to create your own WebRequest type class using the base Socket class to handle the communication with the HTTP server.

Given the TcpClient class this might not be very hard, if you have the HTTP 1.1 spec open since most communication is done via text.

James
"Java is free - and worth every penny." - Christian Graus