C# Discussion Boards - CodeProject

Re: Please give me an idea.

15-Jan-04 4:38

If you look at the documentation for the AutoScrollPosition property, it states that negative values are returned for the X and Y properties of the Point returned from the property if a user has scrolled away from the starting position (0,0). Make sure you negate these values before factoring them into your new position for child panels.

See DirectX 9.0 - Get Ambient with DirectSound[^] which should contain a sample like this (judging by the way the program works).

Please give me an idea.

god4k14-Jan-04 21:31

god4k

14-Jan-04 21:31

Dear, Sir

I will develop an application that automatic check what update on database on the Web Server.
Please give me an idea and overview about it. To get what update via Internet I should use what classs.

I ever create database application, but I never create application that connect to the internet.

And I think I should use thread in this application. Is.... correct?

Thank You.

Sorry for bad English.
Smile | :)

;);P

((

Jinwah14-Jan-04 23:47

Jinwah

14-Jan-04 23:47

You need to read about ADO.NET. Disconnected data sources is the main area.

HTH

Luke

PS: Never appologise for your english (most of us "english" do not speak it very well and the majority cannot even speak another language including me Wink | ;)

Re: Please give me an idea.

Heath Stewart15-Jan-04 4:29

Inserting and Updating BLOBS

15-Jan-04 4:29

As Jinwah was getting at, see the System.Data.DataSet class documentation in the .NET Framework SDK, as well as System.Data.Common.DbDataAdapter - specifically, one of its derived classes depending on what database you're accessing (like System.Data.SqlClient.SqlDataAdapter for a SQL Server database).

You give the DbDataAdapter the appropriate SELECT, INSERT, UPDATE, and DELETE commands (it has properties for each), which you can either use the DataAdapter designer in VS.NET or a CommandBuilder to generate, or type them yourself but generating an example to get an idea might be a good idea.

Then, whenever you update, remove, or insert information in the DataSet, you call DbDataAdapter.Update(DataSet) which will use the change type information for each DataRow and will call the appropriate DbCommand on the DbDataAdapter. There are several examples of this on the CodeProject web site, as well as examples in the .NET Framework SDK.

Guinness4Strength14-Jan-04 18:28

Guinness4Strength

14-Jan-04 18:28

I have the following code:

<br />
<br />
try<br />
{<br />
	string ConnString;<br />
	ConnString="Provider=SQLOLEDB;";<br />
	ConnString+="data source=127.0.0.1;";<br />
	ConnString+="initial catalog=AutoConvert;";<br />
	ConnString+="password=password;";<br />
	ConnString+="persist security info=False;";<br />
	ConnString+="user id=sa;";<br />
	OleDbConnection dbConn = new OleDbConnection(ConnString);<br />
	dbConn.Open();<br />
	<br />
	FileStream fs = File.Open("c:\\temp\\output.dat",FileMode.Open);<br />
	BinaryReader BR = new BinaryReader(fs);<br />
	byte [] BLOB=BR.ReadBytes(Convert.ToInt32(fs.Length));<br />
	DataBase.InsertBLOB(dbConn,"Documents","BatchName","1234567",true,"Document",BLOB);<br />
	dbConn.Close();<br />
<br />
}<br />
catch(Exception Err)<br />
{<br />
	Console.WriteLine(Err.Message);<br />
}<br />
<br />
<br />
<br />
<br />
static public void InsertBLOB(OleDbConnection db,string Table,string LookUpField,string LookUpData,bool IsLookUpString,string BLOBField,byte [] BLOB)<br />
{<br />
	try<br />
	{<br />
		string Command;<br />
		if(IsLookUpString)<br />
			Command= String.Format("UPDATE {0} SET {1}=@{1} WHERE({2}='{3}')",<br />
						Table,BLOBField,LookUpField,LookUpData);<br />
		else<br />
			Command= String.Format("UPDATE {0} SET {1}=@{1} WHERE({2}={3})",<br />
						Table,BLOBField,LookUpField,LookUpData);<br />
		OleDbCommand addEmp = new OleDbCommand(Command, db); <br />
		addEmp.Parameters.Add("@"+BLOBField,BLOB);<br />
		addEmp.ExecuteNonQuery();<br />
	}<br />
	catch(Exception Err)<br />
	{<br />
		throw new Exception(Err.Message);<br />
	}<br />
}<br />

addEmp.ExecuteNonQuery throws an exception witht he message:
"You must define @Document"
I copied the code almost directly from MSDN, but I can't get it to work...Any ideas ?
Oh and in my AutoConvert Catalog I have the table Documents with an image field of length 16 called Document.

Heath Stewart15-Jan-04 4:24

15-Jan-04 4:24

First of all, if you're connecting to a SQL Server, you should be using the class in System.Data.SqlClient. These classes - including the SqlParameter (as opposed to OleDbParameter) are optimized for SQL Server.

Finally, you must define the type of your SqlParameter like so:

SqlParameter parm = addEmp.Parameters.Add("@" + BLOBField, SqlDbType.Image;
parm.Value = BLOB;

See http://msdn.microsoft.com/library/en-us/cpguide/html/cpconwritingblobvaluestodatabase.asp[^] for an example.

Guinness4Strength15-Jan-04 4:44

Guinness4Strength

15-Jan-04 4:44

Thanks for the help as always Heath, I thought SqlConnection and OleDbConnection class were interchangable...

Heath Stewart15-Jan-04 6:54

15-Jan-04 6:54

You can use the System.Data.OleDb classes to access SQL Server, but they are not optimized for any one database - they just use the OLE DB driver using only the common abstract implementations. As far as mixing these two collections of classes together, that's not really supported because most methods in the derived classes take specific types indicitive of their namespace (like a SqlCommand can take a SqlConnection, not a generic DbConnection).

Best way of tracking remoting clients?

Guinness4Strength15-Jan-04 8:20

Guinness4Strength

15-Jan-04 8:20

I've been a VC++ programmer for about 4 years now and I'm learning C#, you been a great help thus far Heath...thanks

Alex Korchemniy14-Jan-04 18:21

Alex Korchemniy

14-Jan-04 18:21

A solution that I'm developing has a server and multiple clients. The clients access Client-Activated object on the remoting server. What would be the best way of keeping track of the connections?

I have a SQL server on the same machine and I'm thinking about doing it like this: on init - add an entry in the connection table. when the object is disposed it will remove itself from the table. However, there are a few problems.

+ if the client crashes -> when the lease runs out the connection will be unregistered. right?
+ What about if the server crashes - I'll just clean up the connection table on startup.

Does anyone have any suggestions?

occcy14-Jan-04 21:22

occcy

14-Jan-04 21:22

Your SQL-Server solution works, but there is an easier way to tracking your clients (I think):
Create an ArrayList and add each ClientObject by creation.
Use delegates to remove ClientObjects, when there lease is running out.
If the server crashes, the ArrayList will be removed automatically Wink | ;)

Heath Stewart15-Jan-04 3:57

15-Jan-04 3:57

Actually, this is not so good but your solution to use a lease is what I was going to recommend anyway. I originally recommend using a database as we do for our app (which is driven by a SQL Server anyway) because if your remoting object goes down for some reason, your list is lost. The database (in our case, which is replicated and stored on a RAID array) will persist this information so that when the remoting object comes back up, it can grab the information and return to its original state.

Heath Stewart15-Jan-04 4:03

15-Jan-04 4:03

As I hinted at before, implement ILease and return that in an override for GetLifetimeService on your remoting object. If a sponser cannot be contacted or has not renewed the time on the lease, you remove the row from the RDBMS for that sponsor (a client). In an internal remoting application, your lease can ping the sponsers to determine if they still exist. If you expose your remoting object on IIS (which automatically gets exposed as a Web Service, thus using HTTP which is one-way), you'll just have to wait until the sponsor does not renew their lease and remove the row.

If the remoting object (the server) crashes, this really isn't a problem. As long as the database is still up and running, the remoting object will grab the existing information (this is the reason I mentioned you should persist connection information in a database or something) and restore its state. Clients can't really connect why the remoting object is down, so you don't have to worry about new information. Now if the server(s) that has/have both your remoting object and the database go down, the scenario isn't much different from before. Just use transacted statements to increment and decrements your client connections table and they will be logged so that they can be completed in such a case.

Alex Korchemniy15-Jan-04 4:37

Alex Korchemniy

15-Jan-04 4:37

Actually, this is for a different but similar project. Smile | :)

I had everything covered the only thing was : If the activated object crashes and the client app never decides to re-activate the object. The information will remain on the server, and the admin app on the server will read the entry in the database as a live connection.

Heath Stewart15-Jan-04 9:41

15-Jan-04 9:41

That would be a problem, then. I guess the only thing you could do in such a case is to prevent the admin application from worrying about what's in that table and instead get the remoting object and this admin app to interact instead of using a table as a sort of intermediary.

Custom Attributes

pnolan14-Jan-04 13:53

pnolan

14-Jan-04 13:53

Does anyone know how to MODIFY the value of a custom attribute associated with a class property at runtime?

I havn't been able to find a single example of this on the net.

Thanks Heaps,

Patrick.

Re: Custom Attributes

Heath Stewart15-Jan-04 3:55

I still didn't found what I was looking for - C# Service installation

15-Jan-04 3:55

You can't modify attributes at runtime. You can, however, use an ICustomTypeDescriptor to return an array of attributes that you can create at runtime (note, this interface is only used by certain classes like the TypeDescriptor in System.ComponentModel).
See the documentation for ICustomTypeDescriptor.GetAttributes for more information.

If you use reflection instead of a TypeDescriptor to get attributes, you won't be able to change anything unless you programmatically create an attribute and add it to your array/list/collection.

Finally, if this is a custom attribute, you can give the attribute's property a set accessor as well, but this is to change only a property. This is highly NOT recommend, though, because attributes are meta-data that describe classes, etc. The attributes in the base class library don't allow such changes. If you need to modify values like this, you should consider a abstract or virtual property for a particular type that child classes can override, or using an interface for a good polymorphic design.

Pinho14-Jan-04 12:53

Pinho

14-Jan-04 12:53

Hi There,

Yes, besides being a great music it's the situation I'm in right now. Smile | :)

I've searched and searched and I cannot find what I want, I'm starting to think that it's not possible. Mad | :mad:

I've developed a service using C#, and used one of the great advantages of .NET, the possibility to easily install a service, I've done everything I wanted, except for this:

Is it possible to set the name of the service during installation? Confused | :confused:

I must/want to give this option so that the user can install several instances of that service each with a different name. (Gateway I,Gateway II, etc).

If this is impossible what are the alternatives?

Thanks for all the replies,

Luis Pinho

Re: I still didn't found what I was looking for - C# Service installation

Heath Stewart15-Jan-04 3:50