I have a problem that has been driving me nuts for days.. I've tried so many tutorials and code snippets from this and many other websites. I am building a P2P application and i have problems accessing the main thread.
Here is the simple flow of my application:
1. frmMain is shown - user clicks on login button
2. frmlogin is shown - user enters his name
3. after "logging in" - two threads are created (threadTCPlistener and threadUDPlistener)
4. frmDataGrid is shown
Server listen = new Server();
Thread listeningUDPThread = new Thread(new ThreadStart(listen.startUDPServer));
listeningUDPThread.IsBackground = true;
listeningUDPThread.Start();
Thread listeningTCPThread = new Thread(new ThreadStart(listen.startTCPServer));
listeningTCPThread.IsBackground = true;
listeningTCPThread.Start();
frmDataGrid dg = new frmDataGrid();
dg.Show();
5.Threads work in one separate class called "Server". In there they wait for incoming connections, and when TCP thread accepts a connection it starts receinving a file. Upon receiving the file, I would like to change the GUI in the frmDataGrid to add a new row to grid view. I've done something like this:
public void downloadFile()
{
//--receiving of the file--
frmDataGrid fdg = new frmDataGrid();
//filename is the name of received file, and 100's are just for testing (for now).
fdg.verifyUIRequest(fileName, 100, 100);
}
I am calling a method from frmDataGrid VerifyUIRequest that looks like this:
public void verifyUIRequest(string filename, int done, int percent)
{
if (dgvDown.InvokeRequired)
{
dgvDown.Invoke((MethodInvoker)delegate { updateDownDgv(filename, done, percent); });
}
else
{
updateDownDgv(filename, done, percent);
}
After this, the main thread should call the "updateDownDgv" method but the problem is that nothing is happening with my data grid. Here is the code for updating:
public void updateDownDgv(string filename, int done, int percent)
{
foreach (DataGridViewRow r in dgvDown.Rows)
{
if ((string)r.Cells[0].Value == filename)
{
r.Cells[1].Value = done;
r.Cells[2].Value = percent;
}
dgvDown.Invalidate();
return;
}
DataTable tab = (DataTable)dgvDown.DataSource;
DataRow row = tab.NewRow();
row[0] = filename;
row[1] = percent;
row[2] = done;
//MessageBox.Show(done.ToString());
tab.Rows.Add(row);
dgvDown.DataSource = null;
dgvDown.DataSource = tab;
}
I have tried doing this withh begin invoke, with some lambda expressions but nothing succeded. Can anyone please point me to an error or help in some other way? I would really appreciate it.
PS This is my first post, so if it is poorly formatted, i apologize in advance. :)
EDIT:
So the problem is obviously with instances, so I've done something like this:
from Server class where I create an instance of my frmDataGrid class, i now call it's constructor that takes 3 arguments.
frmDataGrid fdg = new frmDataGrid(fileName, 100, 100);
in that constructor, in frmDataGrid, I call verifyUIRequest. But then another error occurs, and I can't seem to figure it out. It stops at
if (dgvDown.InvokeRequired)
{...
error is as folows:
"Object reference not set to an instance of an object", i.e. NullReferenceException. What could be the error?
You are creating a brand new data grid in your downloadFile method. You should be updating the main grid and calling methods on that from your thread methods, not creating a new one that you drop on the floor when the downloadFile method exits.
Related
I've spent 4 hours on this and totally failed.
I know that i need to use BackgroundWorker but all the tutorials refer to running a progress script on the actual form you are running the worker on.
I have a large datagrid, which the user can use a check box to "select all" and then press "UPDATE ALL"
This updates every grid with a bunch of options they choose.
For some users this may be 5 records which is nothing, but some might update 200 records with 5 options which takes about... 10-15 secs to iterate through them.
I have tried so many variations of running BGworker which loads a FrmLoading.Showdialog
Or trying to have BGworker "do work" running the code and then the main thread having the FrmLoading.Show()
However nothing is working.
If i have the update code in the background worker, it fails because the datagrid and everything is in a different thread.
The other way round, and it just hangs on FrmLoading.Show()
Any advice would be great.
I just can't seem to get my head around how to get this working for what seems to be an easy idea!
Current Update Code:
foreach (DataGridViewRow rowx in dataGridpatients.Rows)
{
//MessageBox.Show(Convert.ToBoolean(rowx.Cells["clnselected"].Value).ToString());
if (Convert.ToBoolean(rowx.Cells["clnselected"].Value) == true)
{
//if cycle has a value.
if (cmbcycle.SelectedIndex != -1)
{
rowx.Cells["clncycletype"].Value = cycle;
rowx.Cells["clnpackscollect"].Value = packs;
}
//if location has a value
if (cmblocation.SelectedIndex != -1)
{
location = Convert.ToInt32(cmblocation.SelectedValue);
rowx.Cells["clnlocation1"].Value = location;
}
if (cmbsize.SelectedIndex != -1)
{
size = Convert.ToInt32(cmbsize.SelectedValue);
rowx.Cells["clnpacksize"].Value = size;
}
if (chkDelivery.Checked == true)
{
rowx.Cells["clnDelivery"].Value = true;
}
if (chkSignSheet.Checked == true)
{
rowx.Cells["clnSigningSheet"].Value = true;
}
}
countupdated++;
}
foreach (DataGridViewRow row in dataGridpatients.Rows)
{
row.Cells["clnselected"].Value = false;
row.DefaultCellStyle.BackColor = Color.White;
}
cmbsize.SelectedIndex = -1;
cmblocation.SelectedIndex = -1;
cmbcycle.SelectedIndex = -1;
chkDelivery.Checked = false;
chkSignSheet.Checked = false;
#countupdated++;
I also have #CountSelected.
What i want to do is run this code above but have a popup overlay (dialog) with my logo + "Updating X%"
Where X = countupdated/countselected * 100
I now know i need to use the background worker and invoke for the above, but literally have no idea regarding how to invoke the grid and go from there.
I understand i need to invoke the variables I'm using
(eg. cmbcycle.SelectedIndex)
I know iterating through 150 records and updating individual cells is probably wrong,
My other option is creating a datatable from "selected" cells on that datatable
then Running the update via SQL instead of iterating through a bound table.
Then after the SQL i can re-create the table which will now have the new cell values updated in it?
Would that be a more appropriate way to do it?
Max rows on this table would be 200. Average ~70 so we are never talking 500 or 1000
EDIT:
So the checked answer works to run the background worker and refer to the controls on the form.
The issue is that if i do this:
backgroundWorker1.RunWorkerAsync();
splashy.ShowDialog();
Then the splash screen pops up after the background worker ends
If i do this:
splashy.ShowDialog();
backgroundWorker1.RunWorkerAsync();
Then the popup semi-forms and hangs until the end of the background worker, at which time it closes
because of the RunWorkerCompleted event.
EDIT:
I have no updated the code in DoWork and used Invokes to refer to the controls.
This works and the code runs fine.
I now need a popup ot appear showing the progress through the updates.
splashy.InvokeBy(() =>
{
splashy.Show();
});
backgroundWorker1.RunWorkerAsync();
Does not work. It causes the popup but freeze
splashy.ShowDialog();
backgroundWorker1.RunWorkerAsync();
Allows the Dialog to show (not 'frozen' and distorted) However the Lab (lblprogress) does not update.
This is because the form never get to the RunWorker method, it is stuck at ShowDialog.
It would be a good idea to make modifications on your DataSource itself and then bind it with the DataGridView.
But as from your existing code if you want to access your controls/UI to update or change values from BackgroundWorker.RunWorkerAsync method or any other Thread call for that matter, you can create an extension method to .Invoke() the controls like:
public static class MyExtensions
{
public static void InvokeBy(this Control ctl, MethodInvoker method)
{
if (ctl.InvokeRequired)
ctl.Invoke(method);
else method();
}
}
Keep this static class under the same Namespace as your main class for convenience.
Thus this code:
foreach (DataGridViewRow rowx in dataGridpatients.Rows)
{
//your codes
}
Will become:
dataGridpatients.InvokeBy(() =>
{
foreach (DataGridViewRow rowx in dataGridpatients.Rows)
{
//your codes
}
});
Similarly,
if (cmbcycle.SelectedIndex != -1)
{
//your codes
}
Will become:
cmbcycle.InvokeBy(() =>
{
if (cmbcycle.SelectedIndex != -1)
{
//your codes
}
});
This way you van safely access your controls, while keeping your UI responsive at the same time. Update your Popup Status UI the same way!
This answer is based around o_O's answer.
The main issue is that i wanted the UI to actually update and the background worker to supply the splash.
Instead of running all the 'hard code' in the BGW, i left it in the original thread, but called a BGW to display a popup Dialog form.
so at the start of the "hard code" I used:
backgroundWorker1.RunWorkerAsync();
This called:
FrmSplash splashy;
private void backgroundWorker1_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
splashy = new FrmSplash();
splashy.ShowDialog();
}
In order to remove the dialog box, at the end of the code in the GUI thread, i used:
splashy.InvokeBy(() =>
{
splashy.Close();
}
);
backgroundWorker1.CancelAsync();
Which uses the extension supplied by O_o
public static class MyExtensions
{
public static void InvokeBy(this Control ctl, MethodInvoker method)
{
if (ctl.InvokeRequired)
ctl.Invoke(method);
else method();
}
}
I have also built a label update into splashy
So i could call
splashy.InvokeBy(() =>
{
splashy.SetStatus(countupdated.ToString());
}
);
As i iterated through the datagridview rows. This updated the label on the splash screen :)
Fairly frustrating since this seems to be well documented and the fact that I accomplished this before, but can't duplicate the same success. Sorry, I'll try to relate it all clearly.
Visual Studio, C# Form, One Main Form has text fields, among other widgets.
At one point we have the concept that we are "running" and therefore gathering data.
For the moment, I started a one second timer so that I can update simulated data into some fields. Eventually that one second timer will take the more rapid data and update it only once per second to the screen, that's the request for the application right now we update at the rate we receive which is a little over 70 Hz, they don't want it that way. In addition some other statistics will be computed and those should be the field updates. Therefore being simple I'm trying to just generate random data and update those fields at the 1 Hz rate. And then expand from that point.
Definition and management of the timer: (this is all within the same class MainScreen)
System.Timers.Timer oneSecondTimer;
public UInt32 run_time = 0;
public int motion = 5;
private void InitializeTimers()
{
this.oneSecondTimer = new System.Timers.Timer(1000);
this.oneSecondTimer.Elapsed += new System.Timers.ElapsedEventHandler(oneSecondTimer_elapsed);
}
public void start_one_second_timer()
{
run_time = 0;
oneSecondTimer.Enabled = true;
}
public void stop_one_second_timer()
{
oneSecondTimer.Enabled = false;
run_time = 0;
}
Random mot = new Random();
private void oneSecondTimer_elapsed(object source, System.Timers.ElapsedEventArgs e)
{
run_time++;
motion = mot.Next(1, 10);
this.oneSecondThread = new Thread(new ThreadStart(this.UpdateTextFields));
this.oneSecondThread.Start();
}
private void UpdateTextFields()
{
this.motionDisplay.Text = this.motion.ToString();
}
motionDisplay is just a textbox in my main form. I get the Invalid Operation Exception pointing me towards the help on how to make Thread-Safe calls. I also tried backgroundworker and end up with the same result. The details are that motionDisplay is accessed from a thread other than the thread it was created on.
So looking for some suggestions as to where my mistakes are.
Best Regards. I continue to iterate on this and will update if I find a solution.
Use a System.Forms.Timer rather than a System.Timers.Timer. It will fire it's elapsed event in the UI thread.
Don't create a new thread to update the UI; just do the update in the elapsed event handler.
Try this
private void UpdateTextFields()
{
this.BeginInvoke(new EventHandler((s,e)=>{
this.motionDisplay.Text = this.motion.ToString();
}));
}
This will properly marshall a call back to the main thread.
The thing with WinForm development is that all the controls are not thread safe. Even getting a property such as .Text from another thread can cause these type of errors to happen. To make it even more frustrating is that sometimes it will work at runtime and you won't get an exception, other times you will.
This is how I do it:
private delegate void UpdateMotionDisplayCallback(string text);
private void UpdateMotionDisplay(string text) {
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.motionDisplay.InvokeRequired) {
UpdateMotionDisplayCallback d = new UpdateMotionDisplayCallback(UpdateMotionDisplay);
this.Invoke(d, new object[] { text });
} else {
this.motionDisplay.Text = text;
}
}
When you want to update the text in motionDisplay just call:
UpdateMotionDisplay(this.motion.ToString())
This is my coding
Thread groupid = new Thread(() =>
{
while(true)
{
GroupIds.ForEach(delegate(String name)
{
if (tabControl1.TabPages.ContainsKey(name))
{
}
else
tabControl1.TabPages.Add(name);
});
}
});
For some reason, if I start the thread (which this loop checks if a new value in the list appears, then creating a new page. This code works to the point, it will show a new tab created with the value, then after about 1 second it says "Project is unresponsive" a.k.a it crashed. So I don't know how to fix it, I've tried !tabControl1.TabPages.Contains(name), and a different looping style. Even without the thread, it makes the new page then crashes immediately.
Accessing the tabControl blocks the ProgramThread. So you're actually blocking that thread non-stop. Especially in such a tight loop, it will look like the application is unresponsive.
if (!tabControl1.TabPages.Contains(tabPage2))
{
tabControl1.TabPages.Insert(1, tabPage2);
}
this will check whether table page already exist, if not this will allow you to create one
.
You can try something like this:
for (int i = 0; i < TabControl.TabPages.Count; i++)
{
if (TabControl.TabPages[i].Name == MyName)
{
TabControl.TabPages.Remove(RdpTabControl.TabPages[i]);
}
}
I am currently working on a home project for myself.
The program is written in C# using winforms.
The problem I'm currently experiencing is as followed:
I have a listview in my mainform called lvwGames
When I run the program without debugging, it runs fine.
However when I start with a debug, I get an error. This has something to do with the background worker thread.
Allow me to post some code to assist me.
private void MainViewLoad(object sender, EventArgs e)
{
RefreshGamesListView();
}
Nothing special here.
The reason I am calling RefreshGamesListView() is because I have to refresh on several occasions.
The method being called looks like this.
public void RefreshGamesListView()
{
pbRefreshGamesList.Value = 0;
bgwRefreshList.RunWorkerAsync();
}
So when the method is called, the background worker is called and runs the dowork method.
This one is quite big.
private void BgwRefreshListDoWork(object sender, DoWorkEventArgs e)
{
List<Game> games = _mainController.RetrieveAllGames();
int count = 1;
foreach (Game game in games)
{
string id = game.id.ToString();
var li = new ListViewItem(id, 0);
li.SubItems.Add(game.title);
li.SubItems.Add(game.Genre.name);
li.SubItems.Add(game.Publisher.name);
li.SubItems.Add(game.Platform.name);
li.SubItems.Add(game.CompletionType.name);
li.SubItems.Add(game.gameNotice);
lvwGames.Items.Add(li);
double dIndex = (double)(count);
double dTotal = (double)games.Count;
double dProgressPercentage = (dIndex / dTotal);
int iProgressPercentage = (int)(dProgressPercentage * 100);
count++;
bgwRefreshList.ReportProgress(iProgressPercentage);
}
}
When i run the code in debug, when the code is on lvwGames.Items.Add(li);
It gives me the following error:
Cross-thread operation not valid: Control 'lvwGames' accessed from a thread other than the thread it was created on.
I have absolutely no clue why.
I think it is code specific. But it can also mean I don't get the background worker completely, and specifically when to use it properly.
The reason I'm using it is because I'm loading a large large list from the database, I want to keep responsiveness in the UI when the list is loaded, and inform the users how far it is, using a progress bar.
If any code is missing, or you actually understand why this is happening PLEASE explain me why in this case its causing the error. You don't need to fix it for me. I just want to know WHY it's caused.
Thanks for taking the time to read this post. I hope to be able to continue using the debugger soon. :)
You need to call Conrol.Invoke when accessing visual controls from background threads.
if (_lvwGames.IsHandleCreated) {
Action addGameToList = () => {
string id = game.id.ToString();
var li = new ListViewItem(id, 0);
li.SubItems.Add(game.title);
....
_lvwGames.Items.Add(li);
};
if (_lvwGames.InvokeRequired) {
_lvwGames.Invoke(addGameToList);
} else {
addGameToList();
}
}
From Manipulating Controls from Threads
...For example, you might call a method that disables a button or
updates a display on a form in response to action taken by a thread.
The .NET Framework provides methods that are safe to call from any
thread for invoking methods that interact with controls owned by other
threads. The Control.Invoke method allows for the synchronous
execution of methods on controls...
This is because you're attempting to access a UI control (lvwGames) from a background thread. The way to make it work requires you to marshal the information back to the main UI thread and update the control from there:
private void BgwRefreshListDoWork(object sender, DoWorkEventArgs e)
{
List<Game> games = _mainController.RetrieveAllGames();
int count = 1;
foreach (Game game in games)
{
string id = game.id.ToString();
var li = new ListViewItem(id, 0);
li.SubItems.Add(game.title);
li.SubItems.Add(game.Genre.name);
li.SubItems.Add(game.Publisher.name);
li.SubItems.Add(game.Platform.name);
li.SubItems.Add(game.CompletionType.name);
li.SubItems.Add(game.gameNotice);
// This is the new line you need:
lvwGames.Invoke(new MethodInvoker(delegate { lvwGames.Items.Add(item) }));
double dIndex = (double)(count);
double dTotal = (double)games.Count;
double dProgressPercentage = (dIndex / dTotal);
int iProgressPercentage = (int)(dProgressPercentage * 100);
count++;
bgwRefreshList.ReportProgress(iProgressPercentage);
}
}
Normally you would check the InvokeRequired property first as mentioned in other answers, but there is really no need if you are always calling it from the background thread. Your DoWork method will always require an invoke call, so you might as well just go ahead and write it like that.
This happening cause, just like compiler cliams, you are going to update UI control content from another thread. You can not do that, as UI control can be updated only within main thread.
Please have look on this SO answer with example code provided:
Invoke from another thread
The background worker is not working properly if you run in debug mode in studio. If you have calls that use the windows handle to retrieve messages, then they will fail. If you for instance have a progressChanged event handler and this changes a text in a textbox that might fail.
I had this scenario: A Form that has a background worker. If I just start the worker without getting a dialog box up first then it works ok. If I show a dialog and then start the background worker then it fails. When I run the program normally it does not fail. It is somehow the debug environment that destroys the link between the events and the foreground window. I have changed my code to use invoke, and now all works both in when running in release and when I debug.
Here is a link explaining what can be done to make a program thread safe.
http://msdn.microsoft.com/en-us/library/ms171728(VS.80).aspx
I did not do the same as the sample to microsoft. I made delegates, assigned to the functions I needed to run. and called invoke on them.
sample pseudo code:
class MyClassWithDelegates
{
public delegate void ProgressDelegate( int progress );
public ProgressDelegate myProgress;
public void MyProgress(int progress)
{
myTextbox.Text = ..... ; // this is code that must be run in the GUI thread.
}
public MyClassWithDelegates()
{
myProgress = new ProgressDelegate(MyProgress);
}
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
Invoke( myProgress, e.ProgressPercentage );
}
}
All code that potentially have to be run in the GUI thread of the application must be Invoked to be safe.
I'm using WatiN to parse my web site. I have a button that starts the process. I open a browser window and navigate where I need to go, then I create a new task that calls a method called DoWork.
My problem is that if I call a new method at the end of DoWork to do something else I get strange results when I try to have the program navigate my website, however, if I don't call this new method from DoWork and just hook the new method up to a button click all works fine. So my question is am I not properly calling my new method from the background process method, Dowork?
Code:
IE browser = new IE("http://www.mywebsite.com/");
string startYear;
string endYear;
int NumRows;
Task myThread;
public Form1()
{
InitializeComponent();
}
private void Start_Click(object sender, EventArgs e)
{
startYear = txtStartYear.Text;
endYear = txtEndYear.Text;
//website navigation work removed for brevity
browser.Button(Find.ById("ContentPlaceHolder1_btnApplyFilter")).Click();
int numRows = browser.Div(Find.ById("scroller1")).Table(Find.First()).TableRows.Count -1;
NumRows = numRows;
lblTotalRows.Text = numRows.ToString();
myThread = Task.Factory.StartNew(() => DoWork());
}
public void DoWork()
{
List<string> myList = new List<string>(NumRows);
txtStartYear.Text = startYear;
txtEndYear.Text = endYear;
for (int i = 1; i < NumRows; i++)
{
TableRow newTable = browser.Div(Find.ById("scroller1")).Table(Find.First()).TableRows[i];
string coll = string.Format("{0},{1},{2},{3},{4}", newTable.TableCells[0].Text, newTable.TableCells[1].Text, newTable.TableCells[2].Text, newTable.TableCells[3].Text, newTable.TableCells[4].Text);
myList.Add(coll);
label1.Invoke((MethodInvoker)delegate
{
label1.Text = i.ToString();
});
}
//database work removed for brevity.
browser.Button(Find.ById("btnFilter")).Click();
newMethod();
}
public void newMethod()
{
int start = int.Parse(startYear);
start++;
startYear = start.ToString();
int end = int.Parse(endYear);
end++;
endYear = end.ToString();
browser.SelectList(Find.ById("selStartYear")).SelectByValue(startYear);
browser.SelectList(Find.ById("selEndYear")).SelectByValue(endYear);
//removed for brevity
}
}
To reiterate, if I call newMethod from Dowork the line browser.SelectList(Find.ById("selStartYear")).SelectByValue(startYear) doesn't behave properly, but if I remove the call to newMethod from Dowork and just hook newMethod up to a button it works fine. I'm wondering if it has to do with DoWork being a background task?
When I say it doesn't behave properly I mean that when you select an item from the drop down list the page auto posts back, however the above line of code selects it but the page doesn't post back, which shouldn't be possible. If I don't call the method within DoWork I don't have this issue.
You're modifying a UI element from a non-UI thread. You've already got code which deals with that within DoWork, via Control.Invoke - you need to do the same kind of thing for newMethod. It would probably be easiest just to invoke the whole method in the UI thread:
// At the end of DoWork
Action action = newMethod;
label.BeginInvoke(action);
(I'm using label.BeginInvoke as I'm not sure whether the browser itself is a "normal" control - but using label will get to the right thread anyway. If browser.BeginInvoke compiles, that would be clearer.)
I suspect it's a problem with the select list control. When I browse websites, I sometimes select drop down items by keyboard. Sometimes, it just doesn't postback, while using mouse always guarantee a postback.
I think you might be better off putting an extra button and do a browser.Button(Find.ById("btnFilter")).Click(); kind of thing to invoke a postback.
If the functions in the browser doesn't perform the proper cross thread checking, what Jon Skeet said should help.