Develop Reference

C# Invoking ListView not working (Background Thread)

Im working with WinForms.
I want to populate ListView from background thread but when im Invoking listview my program stops and shows an error. The error is "Cannot acces a disposed object. Object name is: ListView." And when i put this method
lvValidate.Invoke((Action)delegate
{
lvValidate.Items.Add(listitem);
});
in a try-catch block my program starts lagging. I dont know where is the problem,but my Invoke method is:
static class Intercept
{
internal static void Invoke(this Control control, Action action)
{
control.Invoke(action);
}
}
The error only showing when i close the form and open another form (in the same program). In the Form which contains the ListView the data is unreadable and it seems loads a thousands times.
Here's what my DoWork,ProgressChanged,RunWorkerCompleted event does.
private void bgwLoad_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
string commandText = "SELECT * FROM works";
MySqlCommand command = new MySqlCommand(commandText, connection);
MySqlDataAdapter da = new MySqlDataAdapter(command);
connection.Close();
connection.Open();
reader = command.ExecuteReader();
connection.Close();
DataTable dt = new DataTable();
da.Fill(dt);
for (int i = 0; i < dt.Rows.Count; i++)
{
DataRow dr = dt.Rows[i];
ListViewItem listitem = new ListViewItem(dr["ID"].ToString(), dr["Date"].ToString());
listitem.SubItems.Add(dr["Date"].ToString());
listitem.SubItems.Add(dr["Name"].ToString());
listitem.SubItems.Add(dr["WorkNumber"].ToString());
listitem.SubItems.Add(dr["WorkCode"].ToString());
listitem.SubItems.Add(dr["CoreThread"].ToString());
listitem.SubItems.Add(dr["Tech"].ToString());
listitem.SubItems.Add(dr["From"].ToString());
listitem.SubItems.Add(dr["To"].ToString());
listitem.SubItems.Add(dr["Validate"].ToString());
listitem.SubItems.Add(dr["Validate2"].ToString());
lvValidate.Items.Add(listitem);
}
}
private void bgwLoad_ProgressChanged(object sender, System.ComponentModel.ProgressChangedEventArgs e)
{
}
private void bgwLoad_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
{
picLoading.Visible = false;
}

Try the following:
Dispatcher.CurrentDispatcher.Invoke(() => {
lvValidate.Items.Add(listitem);
});
EDIT:
Or Try this:
public static void AddItem(ListItem listitem)
{
if (lvValidate.InvokeRequired)
{
AddItemDelegate d = new AddItemDelegate (AddItem);
lvValidate.Invoke(d, new object[] { listitem });
}
else
{
lvValidate.Invoke(new Action(() =>
{
lvValidate.Items.Add(listitem);
}));
}
}
delegate void AddItemDelegate(ListItem listitem);
Then call:
AddItem(listitem);

According to your comments, you are trying to retrieve Data from a DB using a DataAdapter, then handing out the Data piecemeal. This will not work for several reasons:
DataAdapter
The DataAdapter Classes all have in common that they only work, while the DBConnection is actively open. That is why you get "Cannot acces a disposed object". Because by the time you try to use it, it the connection is already Disposed. And disposing is not a thing you should ever delay. Or split up at all. Keep the using (that you hopefully got) right where it is, inside the DoWork().
For that reason you always have to copy the data of the DataAdapter into a non-Adapter collection. Really any old list would do. This will temporarily double the Memory load and might procude some stuff for the GC to clean up, but is really they only adviseable way.
Bulk Writes only in Completed
While you can theoretically hand out Partial Reads/process results via Progress Reporting, this is not adviseable to try. Writing a GUI has a massive overhead. The first and only time I did that, I ended up locking up my GUI thread with Write and Draw Operations. It looked like I had never done Multitasking. Updating a Progress bar is just about low cost enough to never really cause issues.
The default pattern is to only over write relevant amount of data after you got it all.
If you run into a exception or cancel, the pattern is to asume that all data is faulty and not have it on the UI.
I like to call the BackgroundWorker "Multitasking/-Threading Training Wheels". They teach you all those things. The firt part, by making the handing out akward. The second part, by actually throwing a Exception if you try to use the Result in invalid cases.
You propably retreive too much
Perhaps the most common mistake with DB's, is trying to retrieve a lot of data to then do processing or filtering in the Client. A common mistake, so avoid it.
There is a limit to how much data a User can process whatever you would define as 1 page. Never more then 100 Data Fields at once is my advice. If you got do Filtering, Pagination or the sort, always do it in the Query. Moving this stuff to the client moves a lot of unesessary data over the Network to then be slower at processing/Filtering then the DB would ever have been.
Example code
This actually is my first BGW Project. I updated it a bit over the years, but the bulk of it is still valid:
#region Primenumbers
private void btnPrimStart_Click(object sender, EventArgs e)
{
if (!bgwPrim.IsBusy)
{
//Prepare ProgressBar and Textbox
int temp = (int)nudPrim.Value;
pgbPrim.Maximum = temp;
tbPrim.Text = "";
//Start processing
bgwPrim.RunWorkerAsync(temp);
}
}
private void btnPrimCancel_Click(object sender, EventArgs e)
{
if (bgwPrim.IsBusy)
{
bgwPrim.CancelAsync();
}
}
private void bgwPrim_DoWork(object sender, DoWorkEventArgs e)
{
int highestToCheck = (int)e.Argument;
//Get a reference to the BackgroundWorker running this code
//for Progress Updates and Cancelation checking
BackgroundWorker thisWorker = (BackgroundWorker)sender;
//Create the list that stores the results and is returned by DoWork
List<int> Primes = new List<int>();
//Check all uneven numbers between 1 and whatever the user choose as upper limit
for(int PrimeCandidate=1; PrimeCandidate < highestToCheck; PrimeCandidate+=2)
{
//Report progress
thisWorker.ReportProgress(PrimeCandidate);
bool isNoPrime = false;
//Check if the Cancelation was requested during the last loop
if (thisWorker.CancellationPending)
{
//Tell the Backgroundworker you are canceling and exit the for-loop
e.Cancel = true;
break;
}
//Determin if this is a Prime Number
for (int j = 3; j < PrimeCandidate && !isNoPrime; j += 2)
{
if (PrimeCandidate % j == 0)
isNoPrime = true;
}
if (!isNoPrime)
Primes.Add(PrimeCandidate);
}
//Tell the progress bar you are finished
thisWorker.ReportProgress(highestToCheck);
//Save Return Value
e.Result = Primes.ToArray();
}
private void bgwPrim_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
pgbPrim.Value = e.ProgressPercentage;
}
private void bgwPrim_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
pgbPrim.Value = pgbPrim.Maximum;
this.Refresh();
if (!e.Cancelled && e.Error == null)
{
//Show the Result
int[] Primes = (int[])e.Result;
StringBuilder sbOutput = new StringBuilder();
foreach (int Prim in Primes)
{
sbOutput.Append(Prim.ToString() + Environment.NewLine);
}
tbPrim.Text = sbOutput.ToString();
}
else
{
tbPrim.Text = "Operation canceled by user or Exception";
}
}
#endregion

How do I bypass code in the RunWorkerCompleted event if an error occurs?

I wrote a program that creates an XML file from the contents of an Excel spreadsheet. The program works and I am now making it more robust by adding error checking. For example, if the Excel spreadsheet does not contain a required XML tag, the program displays an error and returns from the main program. When an error occurs, the RunWorkerCompleted() event fires, and code executes that shouldn't execute because an error occurred. My question is how to determine if an error occurred so I can bypass certain code in the RunWorkerCompleted() event.
I tried calling bgw.CancelAsync() in the main program where the error is detected, but RunWorkerCompletedEventArgs e.Cancelled is false so it doesn't work.
Here are some excerpts from my code. The progress bar is started in the click event of a button. It works, but I had to declare cellsProcessed, rowCount, and colCount as global because I couldn't figure out how to pass them to bgw_DoWork().
private void button_create_Click(object sender, EventArgs e)
{
// Define the event that fires when the progress bar finishes
bgw.RunWorkerCompleted += bgw_Complete;
rowCount = xmlRange.Rows.Count; // Declared as global
colCount = xmlRange.Columns.Count; // Declared as global
// Start the progress bar thread
if (!bgw.IsBusy)
{
bgw.RunWorkerAsync();
}
// Read the header in row 1 and return an error if it isn't valid
for (colIdx = 1; colIdx <= colCount; colIdx++)
{
if ((xmlRange.Cells[1, colIdx] != null) && (xmlRange.Cells[1, colIdx].Value2 != null))
{
cellContents = xmlRange.Cells[1, colIdx].Value2.ToString();
switch (colIdx)
{
case 1:
if (cellContents != "Tag")
{
error = true;
errText = "Cell A1 must contain 'Tag'";
}
break;
case 2:
if (cellContents != "Type")
{
error = true;
errText = "Cell B1 must contain 'Type'";
}
break;
if (error)
{
bgw.CancelAsync();
MessageBox.Show(errText, "Error", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
// Close Excel resources
xmlWorkbook.Close();
xmlSpreadsheet.Quit();
Marshal.ReleaseComObject(xmlRange);
Marshal.ReleaseComObject(xmlWorksheet);
Marshal.ReleaseComObject(xmlWorkbook);
Marshal.ReleaseComObject(xmlSpreadsheet);
GC.Collect();
return;
}
private void bgw_DoWork(object sender, DoWorkEventArgs e)
{
if (bgw.CancellationPending)
{
e.Cancel = true;
}
else
{
label_pctComplete.Text = "Completed " + progressBar.Value.ToString() + "%";
bgw.ReportProgress((100 * ++cellsProcessed) / (rowCount * colCount));
}
}
private void bgw_Complete(object sender, RunWorkerCompletedEventArgs e)
{
if (!e.Cancelled)
{
label_pctComplete.Visible = false;
progressBar.Visible = false;
// Inform the user that the XML file was created
label_created.Visible = true;
label_created.Text = "Done!...Created " + textBox_outputFile.Text;
// Enable the button so the user can view the XML Limit File
button_openLimitFile.Enabled = true;
}
}
private void bgwProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar.Value = e.ProgressPercentage;
}
Thank you for any help.

Sleep Thread With IF condition in C#

In my C# windows form, I want to set notification label with loop and thread before fill the data into data grid view . for that I try to use below method and thread.
My Thread is
public void Run()
{
System.Windows.Forms.MessageBox.Show("this is System Thread");
m = new Dashboard();
string text = "";
Int32 a = 0;
do
{
Thread.Sleep(1000);
notiCount++;
/*Notifications ne = new Notifications(m.loadNotification);
ne.Invoke(text);*/
//Thread.Sleep(1000);
}
while (notiCount <= 10) ;
}
My method is
private void loadINtransfer(string status)
{
Int32 x = 0;
string text="";
SystemThreadings s = new SystemThreadings();
Thread t = new Thread(s.Run);
t.Start();
Thread.Sleep(100);
do
{
if (s.notiCount == 0)
{
text = "Request Data";
Thread.Sleep(1000);
this.loadNotification(text);
// MessageBox.Show("request");
}
else if (s.notiCount == 3)
{
text = "Fetching Data";
Thread.Sleep(1000);
//MessageBox.Show("request");
this.loadNotification(text);
}
else if (s.notiCount == 6)
{
text = "Loading Data";
Thread.Sleep(1000);
this.loadNotification(text);
//MessageBox.Show("loading");
}
else if (s.notiCount == 9)
{
text = "Done";
Thread.Sleep(1000);
this.loadNotification(text);
//MessageBox.Show("done");
}
//Thread.Sleep(200);
}
while (s.notiCount != 10);
//Thread.Sleep(5000);
MessageBox.Show("attach");
dt = dl.loadTransfer(status);
dgvDashboard.AutoGenerateColumns = false;
dgvDashboard.DataSource = dt;
}
but it only show Done part. other if parts are passing but not show. And I want to wait some time the all parts before load data to grid view. how can I do this. Please help Me.

As I alluded to in the comments, this is pretty well a poster-child use case for BackgroundWorker. I created a new Windows Forms application, added a button and a label (I didn't bother to rename them), and then double-clicked the button to add an event handler. After adding the BackgroundWorker code, this is what Form1.cs ended up looking like:
using System;
using System.ComponentModel;
using System.Threading;
using System.Windows.Forms;
namespace WindowsFormsApp1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
var bw = new BackgroundWorker();
bw.DoWork += Bw_DoWork;
bw.WorkerReportsProgress = true;
bw.ProgressChanged += Bw_ProgressChanged;
bw.RunWorkerCompleted += Bw_RunWorkerCompleted;
bw.RunWorkerAsync();
}
private void Bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
MessageBox.Show("attach");
//dt = dl.loadTransfer(status);
//dgvDashboard.AutoGenerateColumns = false;
//dgvDashboard.DataSource = dt;
}
private void Bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
if (e.ProgressPercentage == 0)
{
label1.Text = "Request Data";
}
else if (e.ProgressPercentage == 3)
{
label1.Text = "Fetching Data";
}
else if (e.ProgressPercentage == 6)
{
label1.Text = "Loading Data";
}
else if (e.ProgressPercentage == 9)
{
label1.Text = "Done";
}
}
private void Bw_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
int notiCount = 0;
do
{
Thread.Sleep(1000);
notiCount++;
worker.ReportProgress(notiCount);
}
while (notiCount <= 10);
}
}
}
Notice that we're not having to sleep or wait on the UI thread. When progress has been made, we're notified and can access the UI to update it. And when the work is complete, we again get notified.
The only Thread.Sleep we have is within the background worker, and I assume there is standing for actual useful work being done.
You absolutely should not have any Thread.Sleep calls in any constrained context such as the UI thread, where there aren't likely to be any other threads available to service other uses which may want to use your thread whilst you're just blocking it. Even Sleeping a threadpool thread is acting as a bad "team player" in modern multi-threaded applications.

Cross thread operation not valid when use backgroundworker in c#

private bool ImportData()
{
bool result = false;
try
{
intdevid = int.Parse(cmbDeviceName.SelectedValue.ToString());
FetchDevicedata(intdevid);
//FTPTCompletedBatchTransfer();
FetchMaxReportId();
GetFTPFile(strDeviceIP, strDeviceUsername, strDevicePwd, strDevicePath + "//RunningBatch//RunningBatch.db", "RunningBatch.db"); // Copy RunningBatch.db to Debug Folder from Remote
LoadRunningData(); // Get Running Data in dataset from running.db
if (DecodeBatchData_R() == false)
{
MessageBox.Show("Running Batch Data Not Found");
}// save in batch master and row data table
GetFTPFile(strDeviceIP, strDeviceUsername, strDevicePwd, strDevicePath + "//CompletedBatch//CompletedBatch.db", "CompletedBatch.db");
LoadCompletedData();
if (DecodeBatchData() == false)
{
MessageBox.Show("Completed Batch Data not found");
}
result = true;
}
catch (Exception ex)\\here error:Cross-thread operation not valid: Control 'cmbDeviceName' accessed from a thread other than the thread it was created on.
{
clsLogs.LogError("Error: " + ex.Message + this.Name + " || ImportData");
result = false;
}
return result;
}
private void btnimport_Click(object sender, EventArgs e)
{
//////////////////copy checkweigher .db to database folder
dsCheckRptId = new DataSet();
///////////////////////////////////////////////////////////
if (cmbDeviceName.Text.ToString().Trim() == "--Select--")
{
MessageBox.Show("Please Select Proper Device");
cmbDeviceName.Focus();
return;
}
var deviceId = (int)cmbDeviceName.SelectedValue;
bgw.RunWorkerAsync(deviceId);
progressBar1.Visible = true;
label2.Visible = true;
}
void bgw_DoWork(object sender, DoWorkEventArgs e)
{
for (int i = 1; i <= 100; i++)
{
var deviceId = (int)e.Argument;
e.Result = ImportData();
System.Threading.Thread.Sleep(100);
bgw.ReportProgress(i);
}
}
void bgw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = e.ProgressPercentage;
label2.Text = String.Format("Progress: {0} %", e.ProgressPercentage);
}
void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
var result = (bool)e.Result;
if (cmbDeviceName.SelectedValue != null && cmbDeviceName.SelectedValue.ToString().Trim() != "0" && cmbDeviceName.SelectedValue.ToString().Trim() != "System.Data.DataRowView" && cmbDeviceName.SelectedValue.ToString().Trim() != "")
if (result)
{
MessageBox.Show("Data Import Completed Successfully for " + strDevicename);
clsLogs.LogEvent(3, "Data Import Completed Successfully for " + strDevicename);
}
else
{
MessageBox.Show("Data Import Fail For " + strDevicename);
clsLogs.LogEvent(3, "Data Import Fail for " + strDevicename);
}
progressBar1.Visible = false;
label2.Visible = false;
}
;When I run this background worker coding, there's an error stating "Cross-thread operation not valid: Control 'cmbDeviceName' accessed from a thread other than the thread it was created on. ."
How do I solve this problem guys?

WinForms controls are not thread safe, thus cross-thread operations on controls are not valid. You can access controls only from thread which created those controls. In your code you are accessing cmbDeviceName combobox from background thread. Best option to solve this is passing intdevid as RunWorkerAsync argument:
// executed on main thread
var deviceId = (int)cmbDeviceName.SelectedValue;
backgroundWorker.RunWorkerAsync(deviceId);
And get this argument in your DoWork handler:
private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
// executed on background thread
var deviceId = (int)e.Argument;
// ...
}
Suggested reading: Safe, Simple Multithreading in Windows Forms

GUI Update with multiple Backgroundworker C#

Here i'm using multiple backgroundworkers to do one network related operation.Basically its a process of checking the user is registered with my page or not. I'm having nearly 1000 accounts to check, hence i'm using datagridview to import users and fetch the username from same for checking purpose. My code working fine and displays the result, But the problem is when updating the status in datagridview its not that much effective. In that long process method i used to set status text for every process of method, like login process started logged in failed to login .But Backgroundworker does not updating the status column. It displaying the status after all backgroundworker completes only. Can anyone give me an idea for how to update the status for each account ??
thanks in advance
It my code:
int threadNum;
public BackgroundWorker bcheker;
private void toolStripButton2_Click(object sender, EventArgs e)
{
if (wbcheckStatus == WorkerStatus.NotStarted || wblogcheckStatus == WorkerStatus.Completed)
{
threadNum = -1;
SetControlsStatus(ProgramStatus.BChecking);
toolStripButton2.Image = aTumblr.Properties.Resources.control_stop;
for (int i = 0; i < 4; i++)
{
bcheker = new BackgroundWorker();
bcheker.DoWork += new DoWorkEventHandler(bcheker_dowork);
bcheker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bchecker_completed);
bcheker.ProgressChanged +=bcheker_ProgressChanged;
bcheker.WorkerReportsProgress = true;
bcheker.WorkerSupportsCancellation = true;
bcheker.RunWorkerAsync();
}
}
else
{
threadNum = 10000;
bcheker.CancelAsync();
SetControlsStatus(ProgramStatus.BlogChecking);
}
}
public void bcheker_dowork(object sender, DoWorkEventArgs e)
{
while (!bcheker.CancellationPending)
{
int rownum = Interlocked.Increment(ref threadNum);
if (rownum >= bchecktableModel.Rows.Count)
{
break;
}
Thread.Sleep(1000);
BlogChecker bc = new BlogChecker(bchecktableModel[rownum, 1].Text, bchecktableModel[rownum, 2]);
bc.check();
wblogcheckStatus = WorkerStatus.Running;
}
if (bcheker.CancellationPending)
{
wblogcheckStatus = WorkerStatus.Completed;
SetControlsStatus(ProgramStatus.BCheckingDone);
}
}
public void bcheker_ProgressChanged(Object sender, ProgressChangedEventArgs e)
{
}
public void bchecker_completed(object sender, EventArgs e)
{
if (threadNum == bchecktableModel.Rows.Count+1)
{
SetControlsStatus(ProgramStatus.BCheckingDone);
wblogcheckStatus = WorkerStatus.Completed;
}
}

First of all, It looks like you have an issue of multiple handlers registering to the DoWorkEvent.
I am not sure what is happening, but I would check How many time the bcheker_dowork method is being called.
In order to report about your progress, use the BackgroundWorker.ReportProgress method.
public void bcheker_ProgressChanged(Object sender, ProgressChangedEventArgs e)
{
//Update your progress here
}

Also, in your DoWork() method, you shouldn't be using "bcheker" as that will simply refer to the last BackgroundWorker created. Instead, cast the sender parameter to a local BackgroundWorker variable and use that.