Develop Reference

Asynchronously add controls to Form during Form_Load

I'm working on a utility to copy a directory to multiple USB sticks. When Form1 loads, I would like for a label to display status "Detecting Disk Drives...", and then call a method to read the drives and populate the form with information. I have it working, except when the form loads it calls the method before displaying the label. Therefore it appears to be hung (the label is actually a white box on a gray background). I have tried timers and threads and everything I can think of, each with a different dead end. I have not yet found a way to have the label update before calling the method to read the drives.
The method getAndDisplayData() is wait 'hangs' my program. I would like for it not to be called until after the form has updated the text of lblDisplayStatus.Text
I also do not want the user to have to interact with the form before calling the method.
Here is my C# code:
private void USB_Utility_Load(object sender, EventArgs e)
{
lblDisplayStatus.Text = "Detecting Disk Drives...";
}
private void tabUSB_Prep_Enter(object sender, EventArgs e)
{
tabUSB_Prep.Controls.Clear();
getAndDisplayData();
}
Any help would be greatly appreciated.
Here is the code that I ended up with:
BackgroundWorker _worker;
private void USB_Utility_Load(object sender, EventArgs e)
{
_worker = new BackgroundWorker(); // Should be a field on the form.
_worker.DoWork += DoWork;
_worker.RunWorkerCompleted += RunWorkerCompleted;
lblDisplayStatus.Text = "Detecting Disk Drives...";
_worker.RunWorkerAsync();
}
//Background Worker
private void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
lblDisplayStatus.Text = "Done...";
displayData();
}
private void DoWork(object sender, DoWorkEventArgs e)
{
getData();
}

The old-fashioned way would be to use a BackgroundWorker to run the blocking work in getAndDisplayData and then update the label before starting the worker and again when the worker completes.
Now-adays I assume you could also use tasks to get the exact same result, but I haven't actually tried it as WinForms is not often first choice for new projects.
BackgroundWorker _worker;
public void Form_Load(object sender, EventArgs e) {
_worker = new BackgroundWorker(); // Should be a field on the form.
_worker.DoWork += DoWork;
_worker.RunWorkerCompleted += RunWorkerCompleted;
lblDisplayStatus.Text = "Detecting Disk Drives...";
_worker.RunWorkerAsync();
}
private void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {
lblDisplayStatus.Text = "Done...";
}
private void DoWork(object sender, DoWorkEventArgs e) {
getAndDisplayData();
}
About background workers

you can try this
private void USB_Utility_Load(object sender, EventArgs e)
{
lblDisplayStatus.Text = "Detecting Disk Drives...";
}
private void tabUSB_Prep_Enter(object sender, EventArgs e)
{
tabUSB_Prep.Controls.Clear();
Task<List<string>> t = new Task<List<string>>(DetectDrivesMethod());
t.ContinueWith((result)=>DisplayDrives(result.Result),TaskScheduler.FromCurrentSynchronizationContext);
t.Start();
}
You can tweak the code to fit your requirement. In DetectDriveMethod you will have logic to get data in background thread and in continue with, you can have logic to update UI. It is important that you pass syncronization context otherwise you will end up with Cross Thread exceptions.

If you want to use the new(ish) async/await pattern, you need to use the TaskScheduler to update the UI from the original thread. Here's an example:
// clear the form
tabUSB_Prep.Controls.Clear();
// This is just to show crossing a "context" works
string test = "";
// get the UI's current TaskScheduler
var scheduler = TaskScheduler.FromCurrentSynchronizationContext();
// This can be used to wrap a method that doesn't
// directly implement async/await
Task.Run(() =>
{
// Your method to GET the data (don't update the UI here)
test = "I can set a variable in this context!";
}).ContinueWith(task =>
{
if (task.Status == TaskStatus.RanToCompletion)
{
// update your UI here
// Again, this is just to show how crossing the context works
MessageBox.Show(test);
}
else
{
// update UI with an error message, or display a MessageBox?
}
}, scheduler);

Pass different method/function to DoWork event of Background worker

Please bear with my ignorance on this subject and on the terminology I have used. Please correct me where I am incorrect.
I have used a background Worker from the toolbox onto my form and I am passing a method to the DoWork event. What I have understood in this first attempt with background Worker is that I can use the background Worker that I've created only for 1 task. See code below:
private void btn1_Click(object sender, EventArgs e)
{
// Should call the uploadToDB1 using BackgroundWorker's DoWork event.
backgroundWorker1.RunWorkerAsync();
}
private void btn2_Click(object sender, EventArgs e)
{
// Should call the uploadToDB2 using BackgroundWorker's DoWork event.
backgroundWorker1.RunWorkerAsync();
}
private void uploadToDB1()
{
// Code for uploading to DB 1.
}
private void uploadToDB2()
{
// Code for uploading to DB 2.
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
try
{
uploadToDB1(); // I want to change this to uploadToDB2 i.e. a variable method, How do I assign a call to this?
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
}
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Visible = true;
progressBar1.Maximum = maxRecords;
lblProgress.Text = Convert.ToString(e.ProgressPercentage.ToString() + "/" + maxRecords);
progressBar1.Value = e.ProgressPercentage;
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
progressBar1.Visible = false;
lblProgress.Text = "";
}
I need to be able to dynamically pass a method to the DoWork event without having the need to create multiple background Workers as the actions in the rest of the events related to the background Worker remains unchanged.
Could you please advise how I should go about doing this?
Updated Code using TPL, however I am getting a cross thread error. Could you please help with a corrected code? Upload to DB 2 should happen only after upload to DB 1 is complete. So each time an upload happens the label and progress bar needs to be updated. I also need to pass different text to the label.
private void btn1_Click(object sender, EventArgs e)
{
Task.Factory.StartNew(uploadToDB1);
}
private void uploadToDB1()
{
for(i=0;i<dt.rows.count-1;i++)
{
// Code for inserting into DB1.
progressbar1.maximum=dt.rows.count-1;
progressbar1.value=i;
}
uploadToDB2();
}
private void uploadToDB2()
{
for(i=0;i<dt.rows.count-1;i++)
{
// Code for inserting into DB2.
progressbar1.maximum=dt.rows.count-1;
progressbar1.value=i;
}
}

What you can do, and is a bit of a hack, is pass an Action as an argument for invocation to your DoWorkAsync:
var bw = new BackgroundWorker();
bw.DoWork += (s, o) =>
{
Action actualWork = (Action)o.Argument;
actualWork();
}
and when you invoke DoWorkAsync:
Action action = () => DoSomething();
bw.RunWorkerAsync(action);
Instead, as #Sriram suggested, look into the Task Parallel Library, which will make you life a bit easier:
private async void btn1_Click(object sender, EventArgs e)
{
await Task.Run(UpdateFirst);
// Update UI here.
}
private async void btn2_Click(object sender, EventArgs e)
{
await Task.Run(UpdateSecond);
// Update UI again.
}
An extensive answer on TPL and the use of IProgess<T> can be found in How to provide a feedback to UI in a async method?

BackgroundWorker with ProgressBar - Cross-thread operation not valid

I have service call in my form application. When my button has been clicked I am calling my service method. Here is my code block:
void listBox_SelectedValueChanged(object sender, EventArgs e)
{
if (listBox.SelectedItem.Equals("Demo"))
{
progressBar1.Visible = true;
backgroundWorker1.RunWorkerAsync();
}
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
ObservableCollection<FilterInfo> filterInfos = new ObservableCollection<FilterInfo>();
FilterInfo myFilterObj = new FilterInfo("SUPERVISOR", userName);
filterInfos.Add(myFilterObj);
ObservableCollection<DEMOBec> demos = demoSvc.GetDemoByFilter(filterInfos, false);
dt = new Converter<DEMOBec>().ConvertDataTable(demos.ToList());
}
Before calling the service, I make my ProgressBar (Style = Marquee) visible. But I couldn't make it invisible in completed method because of Cross Thread problem.
When I tried to do something with in UI thread in BGWorker's Completed event,
void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
progressBar1.Visible = false;
}
I am getting an exception :
Cross-thread operation not valid: Control 'Form1' accessed from a thread other than the thread it was created on.
How can I handle this problem?

You need to use Invoke() method
private delegate void ToDoDelegate();
void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
Invoke(new ToDoDelegate(() => progressBar1.Visible = false));
}
more info for Invoke()
http://msdn.microsoft.com/de-de/library/System.Windows.Forms.Control.Invoke(v=vs.110).aspx

Here's alittle piece of code that I always love to use, I don't remember where I got it from I put it in my Dropbox a long time ago.
public static class ControlExtensions
{
public static TResult InvokeEx<TControl, TResult>(this TControl control,
Func<TControl, TResult> func)
where TControl : Control
{
return control.InvokeRequired
? (TResult)control.Invoke(func, control)
: func(control);
}
public static void InvokeEx<TControl>(this TControl control,
Action<TControl> func)
where TControl : Control
{
control.InvokeEx(c => { func(c); return c; });
}
public static void InvokeEx<TControl>(this TControl control, Action action)
where TControl : Control
{
control.InvokeEx(c => action());
}
}
Usage
this.InvokeEx( x => Progressbar1.Visible = false); //Note 'x' could be any variable
This way you won't have to type all that out each time, and it's so simple to use. Just add this right to the end of your form class (after the last bracket closes). You can use this to preform any cross thread operations safely.

Modify the Visibility of the ProgressBar on the UI thread.
Application.Current.Dispatcher.Invoke(DispatcherPriority.Normal, (Action)
delegate()
{
progressBar1.Visible = false;
});

I think the exception isn't raised in the RunWorkerCompleted event (as in comments said). My suggestion is, that the lines you try to access UI cmponents in the DoWork event fires it.
Try to put the data you need in the DoWork event into DoWorkEventArgs e. Tons of examples how to do it are provided on SO like this discussion.
When the work has finished, provide the "main UI thread" the modified/new data by using event args, too, like this:
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e) {
// do some work
e.Result = ... ; // modified/new data
}
and retrieve it in the following way:
void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) {
var newData = (CastToWhatever) e.Result;
}
Hope it helps =)
EDIT
Your code in backgroundWorker1_RunWorkerCompleted() is definitly not the source of the exception. It built a little and simple example to demonstrate my argment:
private void button1_Click(object sender, EventArgs e)
{
backgroundWorker1.RunWorkerAsync(textBox1.Text);
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
var num = Int32.Parse(e.Argument.ToString()) + 1;
backgroundWorker1.ReportProgress(num);
e.Result = num;
}
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = (int)e.ProgressPercentage;
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
textBox1.Text = e.Result.ToString();
}
What it does? On the WinForm there is a TextBox with a number, a ProgressBar and a Button to start a BackGroundWorker.
The worker gets the number from the TextBox (UI thread), DoWork increases it by 1 and saves it as result (new thread). Additionally it reports the increased number to the ProgressBar (cross-thread).
Finally RunWorkerCompleted reads out the result and stores the new value in the TextBox (UI thread).
So, please re-check your code ;-)

Progress bar c# - loading like process [duplicate]

This question already has answers here:
How to use a BackgroundWorker?
(2 answers)
Closed 1 year ago.
Hello I have a function which takes time to load. that's why i'm planning to put a progress bar on my winform so that the user would know that my program is still running. however, I do not know how I'm gonna solve it. is there someone here who could help guide me.
Here's what I'm planning to do:
private void btnProcess_Click(object sender, EventArgs e)
{
//function which takes time because it contacts to a server
}
I want to have a progressbar which increments and ends after my process has finished. Should I use a backgroundworker for this?
***I've followed this tutorial http://www.codeproject.com/Tips/83317/BackgroundWorker-and-ProgressBar-demo but it does not wait for a specific function or event to finish like a loading screen.
***My progressbar does not end after my buttonclick event has finished executing all its functions.
I've created:
private void myBackgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
for (int i = 0; i <= 100; i++)
{
myBackgroundWorker.ReportProgress(i);
System.Threading.Thread.Sleep(100);
}
}
private void myBackgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
myProgressBar.Value = e.ProgressPercentage;
}
private void btnProcess_Click(object sender, EventArgs e)
{
myBackgroundWorker.RunWorkerAsync();
//function which takes time because it contacts to a server
}
How Would I know when will my buttonclick event gonna end? so that my progress bar will end also?

These are the two really good examples
http://www.dreamincode.net/forums/topic/112547-using-the-backgroundworker-in-c%23/
http://www.dreamincode.net/forums/topic/246911-c%23-multi-threading-in-a-gui-environment/
Hope that helps
EDIT:
public partial class Form1 : Form
{
//--------------------------------------------------------------------------
public Form1()
{
InitializeComponent();
//Initialize backgroundworker
Shown += new EventHandler(Form1_Shown);
backgroundWorker1.WorkerReportsProgress = true;
backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
backgroundWorker1.ProgressChanged +=
new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged);
//counter
YourObject.Counter = 100;
}
//--------------------------------------------------------------------------
void btnClick_Clicked(object sender, EventArgs e)
{
//Trigger the background process
backgroundWorker1.RunWorkerAsync();
}
//--------------------------------------------------------------------------
void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
//Your freakishly long process,
//which needs to be run in the background
//to make it simple, I'll just do a for loop
for (int i = 0; i < 100; i++)
{
//The counter will keep track of your process
//In your case, it might not be a for loop
//So you will have to decide how to keep track of this counter
//My suggestion is to decrease/increase this counter
//right after importants action of your process
backgroundWorker1.ReportProgress(YourObject.Counter--);
}
}
void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
//The counter is updated and displayed with a progress bar
YourObject.Counter = e.ProgressPercentage;
}
}

Yeah, you should. It's pretty straightforward.
Make a background worker that executes whatever work btnProcess_Click does.
Have it report progress:
worker.WorkerReportsProgress = true;
And now you can have this progress report be triggered by an event you subscribe to.
worker.ProgressChanged += new ProgressChangedEventHandler(worker_ProgressChanged);
In doing so, you can create a progress bar than can update itself based on this worker_ProgressChanged event, triggered by your computation.
You can find plenty of implementations of this just by Googling. Good luck, hope this helps.

BackgroundWorker.ProgressChanged and RunWorkerCompletedhandler still want invoke?

I'd like to use a BackgroundWorker for background operations because I thought there is no need to take care of "BeginInvoke" etc. when updating WinForm-Controls. Is that right? As far as I know, you can update WinForms controls directly by using the ProgressChanged and RunWorkerCompleted eventhandlers.
But I can't, I although get the following exception:
Control control name accessed from a thread other than the thread it was created on
Some code:
public partial class ConfigurationForm : Form
{
public ConfigurationForm()
{
InitializeComponent();
backgroundWorker1.WorkerReportsProgress = true;
backgroundWorker1.WorkerSupportsCancellation = true;
label1.Text = String.Empty;
// [...]
}
private void StartButton_Click(object sender, EventArgs e)
{
if (backgroundWorker1.IsBusy != true)
{
label1.Text = "Converting...";
backgroundWorker1.RunWorkerAsync();
}
}
private void CancelButton_Click(object sender, EventArgs e)
{
if (backgroundWorker1.WorkerSupportsCancellation == true)
{
backgroundWorker1.CancelAsync();
}
progressBar1.Dispose();
this.Close();
}
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = e.ProgressPercentage;
// EXCEPTION here, why?
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
Converter c = new Converter();
c.Start(worker, e);
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
// EXCEPTION in all cases, why?
if (e.Cancelled == true)
{
label1.Text = "Canceled";
}
else if (e.Error != null)
{
label1.Text = "Error: " + e.Error.Message;
}
else
{
label1.Text = "Done!";
}
}
}
I have to say, this is not a WinForms application but an VSTO PowerPoint add-in. The Form above gets created by the add-in like this when the user is clicking an icon in the ribbon bar of PowerPoint:
//Do I need [STAThread] here? but doesn't seem to work anyway
private void button1_Click(object sender, RibbonControlEventArgs e)
{
ConfigurationForm config = new ConfigurationForm();
config.Show();
}
Can you tell me what's the problem here?

I posted the link but I don't actually think it is the best solution. Clearly the failure occurs because you never called Application.Run() or used Form.ShowDialog(). You can assign the context explicitly as shown but you can get some very tricky problems if you don't do it right. Like assigning it more than once.
The better fix is to ask it to automatically install itself. Which then ensures that whatever form you create will then install it only when it wasn't done before. Put this in front of the form creation code:
WindowsFormsSynchronizationContext.AutoInstall = true;
With the big advantage that if the code ever gets repeated, you won't create another instance of it and potentially screw up the thread's ExecutionContext.
Do consider ShowDialog() as another fix. If I'm not mistaken then you now also have a problem with tabbing and shortcut keystrokes.

Your assumption would be correct for Windows Forms. The way it works though is BackgroundWorkers uses the SynchronizationContext of the current thread. In a windows app, that will be a WindowsFormsSynchronizationContext, which does the marshalling for you.
In a VSTO app, it won't be. It will probably just be the default one, which simply executes the methods. The link from Hans Passant has the code you need to get it to work as expected. I.e.:
System.Threading.SynchronizationContext.SetSynchronizationContext(new WindowsFormsSynchronizationContext());
...create and start your background worker here...