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Hi all,
I'm working on a project that consists of variuos forms. In some situations, i need to store some values in variables and use them in other form. How to do such thing?.
thanks in advance 
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Moham`d wrote: I'm working on a project that consists of variuos forms. In some situations, i need to store some values in variables and use them in other form. How to do such thing?.
Well, I would read this article on the subject[^]
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Colin Angus Mackay wrote: I would read this article on the subject
I did for kicks, and I must add it to my Must Read Articles in my CP blog 
"I'd like to help but I don't feel like Googling it for you."
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thanks for reply, this was helpfull
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i have two problem with mdiparent
1-i want to put listbox on mdiform but when i open childform the list box control still on top over the childform and hide it i want listbox to be hidden when childform is open
2-when i try to change mdiform backcolor it's apply new color why?1
ma_refay
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ma_refay wrote: 1-i want to put listbox on mdiform but when i open childform the list box control still on top over the childform and hide it i want listbox to be hidden when childform is open
Instead of putting the listbox directly on the mdiform, place it on the GroupBox control. On showing the child form call the Hide() method of the GroupBox control or set its Visible property to false.
ma_refay wrote: 2-when i try to change mdiform backcolor it's apply new color why?
 because you changed backcolor (kidding)
To change the back color of your mdiform, use BackgroundImage property, instead. The BackColor property doesn't change the back color of MDIContainer form (if it does then I don't know the way). Some controls inherit some properties of its parent. That is why when you set the BackColor of your MDI, it was get inherited by the control, which is placed on the mdi form.
Regards.
________________________________
Success is not something to wait for, its something to work for.
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hellow to all ..
i have a vb.net code that use ADO.NET
i need to make it work on C# ..
but when i write it down i got two erros ...
i don't know why ! it is ado.net code it have to work in anylanguage .
i got the error where the arrows are ..
thxx to anyhelp ..
{
string SQLContract,SQLContractPay;
int ContractIndx;
ClsInfo Assist_Var = new ClsInfo();
SQLContract = "INSERT Contract( " +
"ClientNum,ContractType,BDate,EDate," +
"UDate,ContratOption,PropertyNum,"+
"HierMeters,MeterPrice,Remarks)" +
"VALUES( " +
txt_Client_Name.Text + "," +
Assist_Var.PrepareStr("B") + "," +
Assist_Var.PrepareStr(dtFromDate.Text) + "," +
Assist_Var.PrepareStr(dtToDate.Text) + "," +
Assist_Var.PrepareStr(dtChange.Text) + "," +
Assist_Var.Val(txtYears.Text) + "," +
Assist_Var.Val(txtPropertyID.Text) + "," +
Assist_Var.Val(txtMeters.Text) + "," +
Assist_Var.Val(txtMeterPrice.Text) + "," +
Assist_Var.PrepareStr(txtRemarks.Text) + ");" +
"SELECT @Indx = @@IDENTITY" ;
OleDbConnection OleDbConn = new OleDbConnection(Assist_Var.SQLConnection());
OleDbConn.Open();
OleDbCommand OleDbCommand = new OleDbCommand();
OleDbCommand.CommandText = SQLContract;
OleDbCommand.CommandType = CommandType.Text;
OleDbCommand.Connection = OleDbConn;
OleDbParameter MyPara = new OleDbParameter();
------->>>> 'MyPara = new OleDbParameter("@Indx",SqlDbType.Int, 4);
MyPara.Direction = ParameterDirection.Output;
OleDbCommand.Parameters.Add(MyPara);
try
{
OleDbCommand.ExecuteNonQuery();
---->>>> 'ContractIndx = OleDbCommand.Parameters("@Indx").Value();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
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What I want to know is, why are you instantiating an OleDbParameter then attempting to write over it. In other words: Why are you creating an object then not using it?
microuser_2000 wrote: OleDbParameter MyPara = new OleDbParameter();
------->>>> 'MyPara = new OleDbParameter("@Indx",SqlDbType.Int, 4);
Well, looking at the documentation for OleDbParameter[^] it would appear that you are passing a SqlDbType when it expects an OleDbType.
microuser_2000 wrote: ---->>>> 'ContractIndx = OleDbCommand.Parameters("@Indx").Value();
This is because you have not translated the VB.NET code. The indexer property uses square brackets in C#. [] not parenthesis ()
Some other questions:
This appears to be connecting to a SQL Server database, why not use the equivalent classes in System.Data.SqlClient? It would be more efficient.
Why are you injecting values into the SQL statement? It blows a great big hole through any security you have in your application (if you have any at all) that allows an attacker almost direct access to the database. You might want to read about SQL Injection Attacks and some tips on how to prevent them[^]
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hello
sorry for the late reply ,
i wanna take the value of the indx after it has been inserted and to save it to use it in another statment ...
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microuser_2000 wrote: i wanna take the value of the indx after it has been inserted and to save it to use it in another statment ...
Excellent. So after following the advice I gave in my previous post what part are you stuck on now?
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Hi,
I'm building an app in C#. I won't bore you with the details, but basically I have two security questions. Any help would be much appreciated!
1. I will be saving files on a external server. I would like to encrypt the files before sending them. Different 'users' will be using this app. What are the best practices regarding C# to encrypt files? Public/Private key encryption? Where would I store the keys...in the registry? I'm well versed with regards the cryptography in theory, but do not have much experience in practise. What API's....where? Etc, etc...Any ideas?..
2. The application be will be using a third-party service, which requires a username/password. I suppose this username and password will be kept on a database somewhere, and the app will retrieve it. What are normal practises for this kind of thing? Store it on a database on server, and have the application request it? Should it be plain-text or encrypted? If so, how so? Remember, the idea is that users of the app can use this service, but should never know the username/password.
There's just a huge amount around on encryption, etc - but no real 'this is the right right way' methods. Any help appreciated.
By the way, this is for a fictitious company, so don't worry - this won't be a security risk!
Regards,
Cormac Redmond
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For encrypting files, well, if you're sending them to the server, are you doing this using .NET remoting? If so, there are some documented ways of encrypting .NET remoting streams. Alternately, you can use the System.Security.Cryptography.CryptoStream to encrypt the stream before streaming it to the server.
For #2, it's common to keep user names in plain text in the database. However, passwords do not need to be kept in plain text on the server. For this, you should simply encrypt hash the plain text using MD5 (again, look in System.Security.Cryptography) or some other hashing algorithm to hash the password, then save the hashed password to the database. When a user logs in, hash the password he typed, and compare it against the encrypted version in the database. If they match, the passwords match.
Last modified: 1hr 7mins after originally posted -- hash instead of encrypt, thank you dan
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Judah Himango wrote: For #2, it's common to keep user names in plain text in the database. However, passwords do not need to be kept in plain text on the server. For this, you should simply encrypt the plain text using MD5 (again, look in System.Security.Cryptography) or another encryption algorithms to encrypt the password, then save the encrypted password to the database. When a user logs in, encrypt the password he typed, and compare it against the encrypted version in the database. If they match, the passwords match.
That should be hash the password with MD5. Don't want to confuse the OP any more than he already is. Also advances in cryptographic attacks have gotten to the point where 128bit hashes are becoming questionable for the longterm, if possible something longer should be used instead.
--
Rules of thumb should not be taken for the whole hand.
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Yes, MD5 hash, rather.
Yes, a better option might be SHA.
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By hash, you mean use the users username+password as a key for the encryption?
I was thinking that - seems like the logical choice.
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No, actually what you do is hash your password. To use MD5 hashing, you could do it like this:
using System.Security.Cryptography;
using System.Text;
...
string password = "super secret password";
byte[] passwordBytes = UnicodeEncoding.UTF8.GetBytes(password);
MD5 md5 = MD5CryptoServiceProvider.Create();
byte[] hashedPassword = md5.ComputeHash(passwordBytes);
As you can see, this doesn't rely on any sort of key; in fact, you never need to store the user's real plain text password anywhere, just the MD5 (or other hashing algorithm) hash of that person's password. When the user goes to log in, hash his inputted password, and check it against the hashed passwords in the database. If they're equal, that means the user has specified a correct password.
This way is great for security -- even if someone got into your database or intercepted the password being sent to the server, it doesn't matter, because it's just the MD5 hash of the password, not the actual plain text password.
Make sense?
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Ah, good. All making sense now.
Cheers,
Cormac
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Thanks for the replies.
Using System.Security.Cryptography, etc - How would I go about decrypting the files on say, another machine? My real problem here is with keys; where to store them, how to keep them secure, etc.
Basically, I'm building a backup application, where there can be many users. It will use Amazons S3 service for storage. I want those files encrypted however before being sent to S3. The user should be able to access (download and decrypt) the files from any location. Hence we need a central server to:
1. Supply the app with the login/pass for S3, and
2. A list of what files on S3 belong to what users.
S3 isn't simply a file system, so it's not as easy as just storing files, hence the need for 2.
So I know about the namespaces to use, but not how to store keys, and access keys, etc etc.
Can you shed more light?
Regards,
Cormac Redmond
Cormac
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Ok, the MD5 option (or any other hashing algorithm option) works only for scenarios where you never need to decrypt the object. For example, this is a good option for passwords. See my other reply to you for more info about this.
However, for decryption, you're probably going to need a key to encrypt and decrypt. For this, there are several articles on code project covering this. Basically, you'd need to look at some of the transform classes in System.Security.Cryptography, such as RijndaelManaged. MSDN has this sample[^] on how to use CryptoStream to encrypt and decrypt a file using a key.
As far as where to store the key, I have no idea really. I don't think there's any standard place to store the key. Maybe someone else can better answer the "where to store the key" question.
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Ok, cheers for that!
I'll have a read of those articles!
Regards,
Cormac
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Hi!
I have a “Windows Application” type Visual Studio .NET 2005 solution. This project has one Windows Form, and a User Control. The Windwos Form has an instance of this User Control.
The User Control has a LinkLabelsList property, of type System.Collections.Generic.List <linklabel>.
public System.Collections.Generic.List <linklabel> LinkLabelsList
{
get { return (mv_linkLabelsList); }
set { mv_linkLabelList = value; }
}
In the Properties Grid of the User Control instance on the Windows Form, a browse button with “periods” ([...]) is visible against the LinkLabelsList property.
On clicking this “periods” button, the “Collection Editor” window opens up. Any number of “LinkLabel” entries can be added here in this “Collection Editor”.
When I am done with adding LinkLabels in the “Collection Editor”, I click the OK button in the “Collection Editor” dialog box, and it returns to the Windows Form editor. However, all the LinkLabel entries added, DISAPPEAR and it again shows an empty space instead of something like “(Collection)”.
How do I solve this problem?? How do I PERSIST THE ADDED ENTRIES for the property for the User Control, when it returns from the “Collection Editor”?
Your helps would be greatly appreciated.
Thanks,
Dinesh M Jayadevan
Thanks,
Dinesh M Jayadevan
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Is it possible to use C# to interface with Excel 2000, or is it necessary to have Excel 2003 or more recent?
-- modified at 15:56 Wednesday 27th December, 2006
It looks as though Office 2003 includes the Primary Interop Assemblies, whereas Office XP does not. I can only assume that Office 2000 is lacking the interop assemblies as well and that there is no backwards compatability. Does anyone know if there are PIA's for Office 2000? Because when trying to compile my app it's stopping on:
using Excel = Microsoft.office.Interop.Excel;
using System.Reflection;
and telling me that
Error 1 The type or namespace name 'office' does not exist in the namespace 'Microsoft' <BR> (are you missing an assembly reference?)
Error 2 Namespace '<global namespace>' contains a definition conflicting with alias 'Excel'
Are the PIAs my problem? Can anyone confirm this and/or suggest a solution, or am I indeed S.O.L.?
"Oh, I must've did somebody some good. I think I did. So I gave her the gun and I shot her!" - Led Zeppelin - In My Time of Dying
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The Apocalyptic Teacup wrote: It looks as though Office 2003 includes the Primary Interop Assemblies, whereas Office XP does not
A quick google search reveals you can download[^] the Office XP PIAs from Microsoft.
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Judah Himango wrote: A quick google search reveals you can download[^] the Office XP PIAs from Microsoft.
Hi Judah,
thanks for the reply. I saw that, but I am actually using Excel 2000. I was just noting that they were missing for Office XP and so I presume they are lacking for Excel 2000 as well.
I can't confirm this, however...
"Oh, I must've did somebody some good. I think I did. So I gave her the gun and I shot her!" - Led Zeppelin - In My Time of Dying
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Sorry for the second reply, but I thought I'd post this here in case anyone else was encountering the same problem. It seems I've gotten around the PIA problem using late binding rather than early binding. This way I get to avoid using the interop assemblies, so that previously:
using System.Reflection;
using Excel = Microsoft.Office.Interop.Excel
becomes
using System.Reflection;
Then I can instantiate Excel through, say, a button_click() event. Basically all I've done at the moment is to fill some Excel cells, but that is almost all I need. I can fill the cells and then call the charting routines from Excel itself using a macro!
"Oh, I must've did somebody some good. I think I did. So I gave her the gun and I shot her!" - Led Zeppelin - In My Time of Dying
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