Develop Reference

C# Background Worker Append TextBox

first off I'd like to say I'm brand new to C# so I am not too aware with how the background worker is supposed to be implemented. I have a GUI program that basically pings a domain a returns the response to a textbox. I am able to get it to work normally, however, it freezes the code because it is running on the same thread which is why I am trying to implement a background worker.
Here is the basic setup
private void button1_Click(object sender, EventArgs e)
{
url = textBox1.Text;
button1.Enabled = false;
button2.Enabled = true;
bgWorker.DoWork += new DoWorkEventHandler(bgWorker_DoWork);
bgWorker.RunWorkerAsync();
}
private void bgWorker_DoWork(object sender, DoWorkEventArgs e)
{
do
{
if (bgWorker.CancellationPending)
break;
Invoke((MethodInvoker)delegate { monitor(); });
} while (true);
}
public void monitor()
{
textBox2.AppendText("Status of: " + url + "\n");
Status(url);
System.Threading.Thread.Sleep(30000);
}
private void Status(string url)
{
// This method does all the ping work and also appends the status to the Text box as it goes through , as OK or down
}
I have not worked with bgworkers before and as you can imagine it's confusing. I've looked at tons of other articles and I can't seem to get it. Sorry if the code looks crazy, I'm trying to learn.

Use Microsoft's Reactive Framework (NuGet "System.Reactive.Windows.Forms" and add using System.Reactive.Linq;) and then you can do this:
private void button1_Click(object sender, EventArgs e)
{
var url = textBox1.Text;
Observable
.Interval(TimeSpan.FromMinutes(0.5))
.SelectMany(_ => Observable.Start(() => Status(url)))
.ObserveOn(this)
.Subscribe(status => textBox2.AppendText("Status of: " + status + "\n"));
}
You then just need to change Status to have this signature: string Status(string url).
That's it. No background worker. No invoking. And Status is nicely run on a background thread.

You've got several mistakes. First,
Invoke((MethodInvoker)delegate
{
monitor();
});
will call monitor() on your UI thread. In almost all cases you should not call methods on other threads. You especially should not call methods that block or do anything that takes more than a few milliseconds on your UI thread, and that is what this does:
System.Threading.Thread.Sleep(30000);
Instead of calling a method on another thread; submit immutable data to the other thread and let the thread decide when to handle it. There is an event already built in to BackgroundWorker which does that. Before you call bgWorker.RunWorkerAsync() do this:
url = new Uri(something);
bgWorker.WorkerReportsProgress = true;
bgWorker.WorkerSupportsCancellation = true;
bgWorker.ProgressChanged += Bgw_ProgressChanged;
private void Bgw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
textBox2.AppendText("Status of: " + url + ": " + e.UserState.ToString()
+ Environment.NewLine);
}
Your bgWorker_DoWork should look more like this:
void bgWorker_DoWork(object sender, DoWorkEventArgs e)
{
while (!bgw.CancellationPending)
{
System.Threading.Thread.Sleep(new TimeSpan(0, 0, 30));
var status = ResultOfPing(e.Argument as Uri);
bgw.ReportProgress(0, status);
}
e.Cancel = true;
}
and you should call it like this:
bgWorker.RunWorkerAsync(url);
You've got a second problem. BackgroundWorker creates a thread, and your thread is going to spend most of its time blocked on a timer or waiting for network responses. That is a poor use of a thread. You would be better off using completion callbacks or async/await.

The background worker is running on a thread pool thread, but your call to Status and Sleep is running on the UI thread. You need to move that stuff back into bgWorker_DoWork.

Try this code:
public partial class Form1 : Form
{
bool cancel;
public Form1()
{
InitializeComponent();
}
public void StartPinging()
{
this.cancel = false;
startButton.Enabled = false;
stopButton.Enabled = true;
responseBox.Clear();
responseBox.AppendText("Starting to ping server.");
responseBox.AppendText(Environment.NewLine);
var bw = new BackgroundWorker
{
WorkerReportsProgress = false,
WorkerSupportsCancellation = true
};
bw.DoWork += (obj, ev) =>
{
while (!cancel)
{
// Ping Server Here
string response = Server.PingServer();
this.Invoke(new UiMethod(() =>
{
responseBox.AppendText(response);
responseBox.AppendText(Environment.NewLine);
}));
}
};
bw.RunWorkerCompleted += (obj, ev) =>
{
this.Invoke(new UiMethod(() =>
{
responseBox.AppendText("Stopped pinging the server.");
responseBox.AppendText(Environment.NewLine);
startButton.Enabled = true;
stopButton.Enabled = false;
}));
};
bw.RunWorkerAsync();
}
delegate void UiMethod();
private void startButton_Click(object sender, EventArgs e)
{
StartPinging();
}
private void stopButton_Click(object sender, EventArgs e)
{
responseBox.AppendText("Cancelation Pressed.");
responseBox.AppendText(Environment.NewLine);
cancel = true;
}
}
public class Server
{
static Random rng = new Random();
public static string PingServer()
{
int time = 1200 + rng.Next(2400);
Thread.Sleep(time);
return $"{time} ms";
}
}

Erwin, when dealing with C# - threads and UI elements usually you will come across cross-thread operations i.e. Background thread with UI threads. This interaction needs to be done in thread safe way with the help of Invoke to avoid invalid operations.
Please look into below resource: InvokeRequired section.
https://learn.microsoft.com/en-us/dotnet/framework/winforms/controls/how-to-make-thread-safe-calls-to-windows-forms-controls

Threads running in random order in C#

I think the title speaks for itself. Simply I have some threads that run with a random order instead of the order I planned.
This is a sample code:
event strHandler strChanged;
delegate void strHandler(string str);
public Form1()
{
InitializeComponent();
strChanged += new strHandler(updatestr);
}
public void updatestr(string str)
{
Thread th = new Thread(new ParameterizedThreadStart(updatethr));
th.IsBackground = true;
th.Start(str);
}
object obj = new object();
private void updatethr(object str)
{
lock (obj)
{
SystemUtilities.SetControlPropertyThreadSafe(textBox1, "Text", (string)str);
Thread.Sleep(1000);
}
}
private void button1_Click(object sender, EventArgs e)
{
this.Text = write();
}
private string write()
{
string res = "";
strChanged(res);
for (int i = 0; i <= 5; i++)
{
res += i.ToString();
strChanged(res);
}
return res;
}
Note: SystemUtilities.SetControlPropertyThreadSafe(textBox1, "Text", (string)str) is a function (used to avoid cross thread exception) that set textBox1.Text to str.
When you press button1 this.Text will be set instantly to the result of write() function ("012345").
The string returned is res that is build inside write() starting from an empty string and, iteratively, appending numbers from 0 to 5.
When the string is created and for each number added to res, the event strChanged is raised calling updatestr method.
Every time that updatestr is called a thread is created and it starts calling updatethr.
Here textBox1.Text is set to str (that should be progressively "", "0" , "01", "012", "0123", "01234", "012345") and wait a second before exiting the method.
Using lock statement the threads created in updatestr should wait the end of the previous threads before modifying textBox1.Text.
Running this code I obtain sequences of values for textBox1.Text that don't match the expected sequence as if the threads don't start in order with their creation in updatestr.
Why does this happen? How can I fix that? Thanks in advance!
EDIT: If want to try this code you can replace SystemUtilities.SetControlPropertyThreadSafe(textBox1, "Text", (string)str) with System.Windows.Forms.MessageBox.Show(str)

I believe you are looking for a different threading strategy. It appears you need a single thread, to maintain order, that's different from the Form's main thread to finish an operation. By using a BlockingCollection, you can sequentially have a different thread operate on the string.
I would rewrite the code this way:
event strHandler strChanged;
delegate void strHandler(string str);
public Form1()
{
InitializeComponent();
Thread th = new Thread(new ThreadStart(updatethr));
th.IsBackground = true;
th.Start();
strChanged += new strHandler(updatestr);
}
BlockingCollection<string> bc = new BlockingCollection<string>();
public void updatestr(string str)
{
bc.Add(str);
}
private void updatethr()
{
while(true)
{
string str = bc.Take();
SystemUtilities.SetControlPropertyThreadSafe(textBox1, "Text", (string)str);
// Not sure why you need this here, other than simulating a long operation.
// Thread.Sleep(1000);
}
}
private void button1_Click(object sender, EventArgs e)
{
this.Text = write();
}
private string write()
{
string res = "";
strChanged(res);
for (int i = 0; i <= 5; i++)
{
res += i.ToString();
strChanged(res);
}
return res;
}

Delegate loads the Alert Form but I can't use any of the components.. its stuck

The problem is below. Here's my code...
// Contents of Form1.cs
// Usual includes
namespace ProcessMonitor
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
public Boolean getStatus()
{
// Returns true if the system is active
if (label1.Text.Equals("Active"))
return true;
return false;
}
private void button1_Click(object sender, EventArgs e)
{
if(getStatus())
{
label1.Text = "Not Active";
button1.Text = "Activate";
}
else
{
label1.Text = "Active";
button1.Text = "Deactivate";
}
}
private void Form1_Load(object sender, EventArgs e)
{
Monitor mon = new Monitor(this);
mon.Run();
}
}
}
// Contents of Monitor.cs
// Usual includes
using System.Management;
using System.Diagnostics;
using System.Threading;
namespace ProcessMonitor
{
class Monitor
{
Form1 parent;
private void ShowAlert(Alert al)
{
al.Show();
}
public Monitor(Form1 parent)
{
this.parent = parent;
}
public void InvokeMethod()
{
//This function will be on main thread if called by Control.Invoke/Control.BeginInvoke
Alert frm = new Alert(this.parent);
frm.Show();
}
// This method that will be called when the thread is started
public void Run()
{
var query = new WqlEventQuery("__InstanceCreationEvent", new TimeSpan(0, 0, 0, 0, 1),
"TargetInstance isa \"Win32_Process\");
while (true)
{
using (var watcher = new ManagementEventWatcher(query))
{
ManagementBaseObject mo = watcher.WaitForNextEvent();a
//MessageBox.Show("Created process: " + ((ManagementBaseObject)mo["TargetInstance"])["Name"] + ",Path: " + ((ManagementBaseObject)mo["TargetInstance"])["ExecutablePath"]);
ManagementBaseObject o = (ManagementBaseObject)mo["TargetInstance"];
String str = "";
foreach (PropertyData s in o.Properties)
{
str += s.Name + ":" + s.Value + "\n";
}
this.parent.Invoke(new MethodInvoker(InvokeMethod), null);
}
}
}
}
}
Alert.cs is just a blank form with a label that says “new process has started”. I intend to display the name of the process and location, pid, etc. by passing it to this alert form via the Thread (i.e. class Monitor). I have deliberately made the thread load in form_load so that I can resolve this error first. Adding it as a thread properly after the main form loads fully is a later task. I need to fix this first..
The delegate creates the Alert form but I can’t click on it, its just stuck. Need help to solve this.

Your while loop in Run is blocking the UI thread.
by passing it to this alert form via the Thread
You never actually create a new thread or task here - you just run code which executes in the UI thread, and causes an infinite loop. This will prevent the main form, as well as your Alert form, from ever displaying messages.
You need to push this into a background thread in order for it to work, ie:
private void Form1_Load(object sender, EventArgs e)
{
ThreadPool.QueueUserWorkItem(_ =>
{
Monitor mon = new Monitor(this);
mon.Run();
});
}

RunWorkerCompleted firing too fast

i got some really simple code, but cant get it to work. I'm using BackgroundWorker. Problem is that RunWorkerCompleted is fired way to fast. Instantly after running i get message "Work completed", but application remains frozen for couple of seconds as 'DataType data = new DataType(path);' is beign executed. After that i got all my DataGridViews etc filled correctly. If i swap this single line with Thread.Sleep everything seems to work well. Any ideas?
public frmWindow(string path)
{
InitializeComponent();
DataType d;
backgroundWorker1.RunWorkerAsync(path);
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
string path = e.Argument as string;
DataType data = new DataType(path);
e.Result = data;
}
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
d = e.Result as DataType;
MessageBox.Show("Work completed");
}

How about you use Debug.Write instead of MessageBox.Show with timers to show when the Methods are entered and exited.
While it is possible for this same background thread to act on your UI, its almost always NOT a good thing to do--UI is not threadsafe.
BackgroundWorker backGroundWorker1;
public frmWindow(string path)
{
InitializeComponent();
DataType d;
backGroundWorker1 = new BackgroundWorker();
backGroundWorker1.DoWork += (s, e) =>
{
System.Diagnostics.Debug.Write("Work started at: " + DateTime.Now + Environment.NewLine);
string path = e.Argument as string;
DataType data = new DataType(path);
e.Result = data;
};
backGroundWorker1.RunWorkerCompleted += (s, e) =>
{
d = e.Result as DataType;
System.Diagnostics.Debug.Write("Work completed at: " + DateTime.Now + Environment.NewLine);
};
backGroundWorker1.RunWorkerAsync();
}

Multi threading in WPF using C# (with background worker)

I have written code to save an image which is generated by the application. The size of the image is around 32-35 MB. While saving the image to a BMB file, it is taking a long time, around 3-5 secs. For this purpose, I have used a background worker but when running the background worker, it shows an error like..."can't access the object as it is created on different thread".
Following is the code:
private void btnSaveDesign_Click(object sender, RoutedEventArgs e)
{
Microsoft.Win32.SaveFileDialog sfd = new Microsoft.Win32.SaveFileDialog();
sfd.Title = "Save design as...";
sfd.Filter = "BMP|*.bmp";
if (sfd.ShowDialog() == true)
{
ww = new winWait();
ww.Show();
System.ComponentModel.BackgroundWorker bw = new System.ComponentModel.BackgroundWorker();
bw.DoWork += new System.ComponentModel.DoWorkEventHandler(bw_DoWork);
bw.RunWorkerCompleted += new System.ComponentModel.RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
fName = sfd.FileName;
cache = new CachedBitmap((BitmapSource)imgOut.Source, BitmapCreateOptions.None, BitmapCacheOption.OnLoad);
bw.RunWorkerAsync();
}
}
void bw_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
{
ww.Close();
}
void bw_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
{
BmpBitmapEncoder encoder = new BmpBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(cache)); //here... it says cant access...
using (FileStream file = File.OpenWrite(fName))
{
encoder.Save(file);
}
}
I have declared "cache" as a global object. (A similar trick worked when I was programming in Windows Forms with VB.NET.)
ww is the wait window that I want to be displayed while the precess is being executed.
How to do this? Is there any other simple method for multi threading in WPF?

When WPF objects are created they are assigned to a Dispatcher object. This disallows any threads other than the creating thread to access the object. This can be circumvented by freezing the object by calling the freeze method. You would need to call Freeze on your bitmapsource object. Once you have frozen your object it becomes uneditable

Your problem comes about because you are accessing an object which is not created by the background worker thread. Normally this would happen if you access a UI control which is created in the main thread and accessed from different thread.
Use the code below.
Dispatcher.Invoke
(
new Action(
delegate()
{
BmpBitmapEncoder encoder = new BmpBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(cache));
using (FileStream file = File.OpenWrite(fName))
{
encoder.Save(file);
}
}
)
);

I think you have to pass cache as a parameter to the new thread:
bw.RunWorkerAsync(cache);
and get it from the DoWork method:
var cache=(CacheType) e.Argument;

.NET framework provides a simple way to get started in threading with
the BackgroundWorker component. This wraps much of the complexity and
makes spawning a background thread relatively safe. In addition, it
allows you to communicate between your background thread and your UI
thread without doing any special coding. You can use this component
with WinForms and WPF applications. The BackgroundWorker offers
several features which include spawning a background thread, the
ability to cancel the background process before it has completed, and
the chance to report the progress back to your UI.
public BackgroudWorker()
{
InitializeComponent();
backgroundWorker = ((BackgroundWorker)this.FindResource("backgroundWorker"));
}
private int DoSlowProcess(int iterations, BackgroundWorker worker, DoWorkEventArgs e)
{
int result = 0;
for (int i = 0; i <= iterations; i++)
{
if (worker != null)
{
if (worker.CancellationPending)
{
e.Cancel = true;
return result;
}
if (worker.WorkerReportsProgress)
{
int percentComplete =
(int)((float)i / (float)iterations * 100);
worker.ReportProgress(percentComplete);
}
}
Thread.Sleep(100);
result = i;
}
return result;
}
private void startButton_Click(object sender, RoutedEventArgs e)
{
int iterations = 0;
if (int.TryParse(inputBox.Text, out iterations))
{
backgroundWorker.RunWorkerAsync(iterations);
startButton.IsEnabled = false;
cancelButton.IsEnabled = true;
outputBox.Text = "";
}
}
private void cancelButton_Click(object sender, RoutedEventArgs e)
{
// TODO: Implement Cancel process
this.backgroundWorker.CancelAsync();
}
private void BackgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
// e.Result = DoSlowProcess((int)e.Argument);
var bgw = sender as BackgroundWorker;
e.Result = DoSlowProcess((int)e.Argument, bgw, e);
}
private void BackgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
workerProgress.Value = e.ProgressPercentage;
}
private void BackgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Error != null)
{
MessageBox.Show(e.Error.Message);
}
else if (e.Cancelled)
{
outputBox.Text = "Canceled";
workerProgress.Value = 0;
}
else
{
outputBox.Text = e.Result.ToString();
workerProgress.Value = 0;
}
startButton.IsEnabled = true;
cancelButton.IsEnabled = false;
}