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Hi,
I have an email application and when checking mails I use a new thread (so it doesnt stuck the whole program while downloading data).
the problem is that this method (runned by the new thread) fires some events, and some of that events have observer methods that modify a textbox (txtLog).. and it throws this exception InvalidOperationException..
How do i resolve this?
The weird thing is that some observer methods modify a status bar and there the exception isnt thrown
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Hi,
you need to invoke a delegate, have a look at the SetText method of this article[^] (SerialPort.DataReceived event also runs on a separate thread).
Luc Pattyn [Forum Guidelines] [My Articles]
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Thanks,
why does cross threading work with a label on a status and not on a textbox?
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Hi,
I don't know, I am not convinced your observation is correct: Controls are NOT thread-safe and since they typically are all interconnected in some way, you should not touch any Control from a thread other than the main thrad (aka GUI thread). Sine .NET 2.0, when you do, an InvalidOperationException is to be expected.
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May I use a lock(new Object()) for making it thread-safe instead of the InvokeRequired thing?
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No. There is only one correct way to deal with threads and Controls.
Locks and Controls don't work well together, the GUI needs to be un(b)locked at all times.
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Hi
In case of thread cross exceptions you can also use a BackgroundWorker component to run the other thread.BackgroundWorker raise some events and you can handle them.These events will be run in the main thread so no cross thread exception will be thrown if you try to set properties of some controls.
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beatles1692 wrote: raise some events and you can handle them.These events will be run in the main thread
That comment seems a little misleading to me...
If you raise your own event from a BackgroundWorker thread, which would be from a
DoWork event handler, event handlers for your event will not be executed on the UI thread -
they will run on the background thread.
You would have to invoke those events on the UI thread just like you would
from any other thread.
Mark Salsbery
Microsoft MVP - Visual C++
![Java | [Coffee]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/coffee.gif)
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You are right.
I meant:
"BackgroundWorker raises some events and you can handle them"
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Sorry to revive this thread but I have a question:
If I have my model separated from the UI, lets say they are two projects,
If the model is the one running the different threads instead of the UI.. (and the model raises events) then I wouldnt have this problem of crossing threads and the Invoke solution?
Or I would have it either way?
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I have coded to retrieve data from SQL Server to ListView on C Sharp.
Unfortunately, ID field goes wrong. Obviously, it has four records then it display on a listview with double recode. See my codes ....
dbConnection.sqlCnn.Open();
string sSQL = "SELECT * FROM TBL_USER";
SqlCommand sCommand = new SqlCommand(sSQL, dbConnection.sqlCnn);
SqlDataReader sReader = sCommand.ExecuteReader();
while (sReader.Read() == true)
{
_ID.Add(sReader[0].ToString());
for (int i = 0; i < _ID.Count; i++)
//for (int i = 0; i < sReader.FieldCount; i++ )
{
lstItems = new ListViewItem((i + 1).ToString());
lstItems.SubItems.Add(sReader[1].ToString());
lstItems.SubItems.Add(sReader[2].ToString());
lstItems.SubItems.Add(sReader[3].ToString());
lstItems.SubItems.Add(sReader[4].ToString());
lstItems.SubItems.Add(sReader[5].ToString());
this.lsv_user.Items.Add(lstItems);
}
}
sReader.Close();
dbConnection.sqlCnn.Close();
Thanks
Chuon Visoth
Angkor Wat - Cambodia
asp.net - c sharp beginner
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Hi,
your code does not make sense to me.
the while loop iterates over the records, that is OK.
the for loop should not be there: IMO each record only provides data for one item in the ListView.
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Well, I have commented on //for (int i = 0; i < sReader.FieldCount; i++ ) so, it isn't used.
Exactly, if we do a right code, it will display a correct recode (only four records on listview). In db it has only four records. After I have coded (code i have posted), it displays many records (duplicate records) on the listview. One record in db it shows many records on listview.
Do you make sense?
Chuon Visoth
Angkor Wat - Cambodia
asp.net - c sharp beginner
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misCafe wrote: Do you make sense?
Yes he does, you on the other hand don't.
It seems that you are confussing 'records' and 'fields', records are the rows in the database and fields are the columns. The code that you have provided shows that you are adding the same row for every field (column) you have. sReader is the record (row), sReader[i] is the field (column). Hence why you go through the DataReader record by record (sReader.ReadLine()), and for each record you then go through it field by field, as shown in my other post.
I hope that clears things up.
My failometer is detecting vast quantities of FAIL!
"Its SQL - hardly programming..." (Caslen)
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![Rose | [Rose]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/rose.gif)
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you have two for loops, only one of them is commented out.
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misCafe wrote: while (sReader.Read() == true)
{
_ID.Add(sReader[0].ToString());
for (int i = 0; i < _ID.Count; i++)
//for (int i = 0; i < sReader.FieldCount; i++ )
{
lstItems = new ListViewItem((i + 1).ToString());
lstItems.SubItems.Add(sReader[1].ToString());
lstItems.SubItems.Add(sReader[2].ToString());
lstItems.SubItems.Add(sReader[3].ToString());
lstItems.SubItems.Add(sReader[4].ToString());
lstItems.SubItems.Add(sReader[5].ToString());
this.lsv_user.Items.Add(lstItems);
}
}
With that, you are adding the same record to the ListView n(sReader.FieldCount) times. Your problem is the line in bold, you are adding the same ID/name ((i + 1).ToString()) for each record. Each ListViewItem should have a different name or be blank (no parameter).
I think I know what you are trying to do, so I hope this helps:
if (sReader.FieldCount > 0)
{
_ID.Add(sReader[0].ToString());
lstItems = new ListViewItem(sReader[0].ToString());
for (int i = 1; i < sReader.FieldCount; i++)
{
lstItems.SubItems.Add(sReader[i].ToString());
}
this.lsv_user.Items.Add(lstItems);
}You just need to replace the content of your while loop.
My failometer is detecting vast quantities of FAIL!
"Its SQL - hardly programming..." (Caslen)
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Thank you very much again.
I understand what you said and it is solved now.
Chuon Visoth
Angkor Wat - Cambodia
asp.net - c sharp beginner
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hi guys,
in the setup project i added checkboxes dialog to user interface section. i have two checkboxes to install two products accordingly.
if the user unchecks the both of the checkboxes, i want the next button to be disabled.
do you know how to do that?
thanks
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Is there anyway to do this without closing/reopening the file?
I found this in some code I wrote a few years, and after cringing and hitting google, failed to do so.
m_fsXMLLib = new FileStream(m_fileName, FileMode.Create, FileAccess.ReadWrite, FileShare.None);
m_fsXMLLib.Close();
m_fsXMLLib = new FileStream(m_fileName, FileMode.Open, FileAccess.ReadWrite, FileShare.Read);
My intent is to keep anyone from trying to read the file while it's being written and in an inconsistent state. After saving the file, I want it kept open to prevent anyone else from being able to modify it while letting them have read only rights.
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains.
-- Pride and Prejudice and Zombies
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Hi Dan,
interesting question.
IMO a pure .NET solution does not exist. This is what I would try:
- create the FileStream with Share.None
- write and flush the data
- now P/Invoke to CreateFile, specify Share.Read and a zero FileMode (which .NET compiles but refuses to run) as explicitly allowed here[^]
- finally close the original FileStream.
That may run all right and yield a file readable for others.
Luc Pattyn [Forum Guidelines] [My Articles]
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Show formatted code inside PRE tags, and give clear symptoms when describing a problem.
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Thanks, I'll give it a shot when I get back into the office on tuesday.
It is a truth universally acknowledged that a zombie in possession of brains must be in want of more brains.
-- Pride and Prejudice and Zombies
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I am writing a web application that I want to use windows authentication for. The only problem is that the users using it may not always be running it from there own machine. I want to check the roles for the current windows user and if they have the required role take them directly into the application. If the current user does not have the required role I will take them to a sign-on page so they can enter their windows user i.d. and password. Then I will check if that user has the required role. The problem is that I can only find a way to check the roles for the current windows user.
Is there a way to validate the user that signs in to the application rather than the windows user and check the roles or groups they are in?
Thank you
Marty
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Use the techniques from this article to impersonate the user given their username and password. Create a new System.Security.Principle.WindowsIdentity object from the token you'll get back from LogonUser. Use my code from this post, where currentPrinciple is the WindowsIdentity you created
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Thank you, I will try this as soon as possible.
Marty
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