Develop Reference

UI not updating while looping through IP Addresses

I have a simple work to do, On button click it will get all Network IP addresses from a range, loop through them and put the active in a list. While performing the process a panel will be shown on which ip address will be displayed that is being checked. Code runs fine but form hangs up, application go to not responding and ip address not displayed even panel is not shown. how to do that?
my code is:
private void btnAutoSearch_Click(object sender, EventArgs e)
{
panel_Search.Visible = true; // Not Working
Cursor.Current = Cursors.WaitCursor;
string ipBase = getIPAddress();
string[] ipParts = ipBase.Split('.');
ipBase = ipParts[0] + "." + ipParts[1] + "." + ipParts[2] + ".";
for (int i = 1; i < 255; i++)
{
string ip = ipBase + i.ToString();
Ping p = new Ping();
PingReply pingresult = p.Send(ip, 100);
if (pingresult.Status == IPStatus.Success)
{
lstIPs.Add(ip);
lblConnecting.Text = ip; // Not Working
}
}
GridConn.Rows.Clear();
foreach (string s in lstIPs)
{
Device obj = new Device();
obj.IPAddress = s;
lblConnecting.Text = s;
int vSMSLimit = 0;
int.TryParse(txtSMSLimit.Text, out vSMSLimit);
obj.SMSLimit = 0;
if (obj.ConnectToHostServer())
{
obj.SendConnectionMessage();
obj.ReceiveConnectionMessage();
MyDevices.lst.Add(obj);
GridConn.Rows.Add(true, obj.IPAddress, obj.PhoneModel, obj.PhoneStatus, obj.SoftwareVersion);
}
}
Cursor.Current = Cursors.Default;
panel_Search.Visible = false;
}

The issue is that the UI must be updated from the 'Main' thread (always called UI thread), but if you do other processing on this thread then the UI itself will lock up. So you should put long running process onto another thread.
This will cause the problem however that this thread cannot update the UI, as it is not the Main/UI thread. So then you have to invoke the UI thread yourself to update it.
Luckily there is simple way of doing this using the BackgroundWorker class in C# which can help you a lot. But you need to separate out your UI and background tasks.
//Define worker
BackgroundWorker myBGWorker;
//Initalise worker and start it from your button
private void btnAutoSearch_Click(object sender, EventArgs e)
{
panel_Search.Visible = true; // Not Working
Cursor.Current = Cursors.WaitCursor;
myBGWorker = new BackgroundWorker()
//This method will execute your processing on a background thread
myBGWorker.DoWork += new DoWorkEventHandler(bgw_DoWork);
//This method will execute when your background worker finishes
//It runs on the Main/UI thread
myBGWorker.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bgw_RunWorkerCompleted);
//This method will execute when the background thread wants to update the progress
//It runs on the Main/UI Thread
myBGWorker.ProgressChanged += new ProgressChangedEventHandler(bgw_ProgressChanged);
//Tell it we will be reporting progress
myBGWorker.WorkerReportsProgress = true;
//Start!
myBGWorker.RunWorkerAsync()
}
private void bgw_DoWork(object sender, DoWorkEventArgs e)
{
string ipBase = getIPAddress();
string[] ipParts = ipBase.Split('.');
ipBase = ipParts[0] + "." + ipParts[1] + "." + ipParts[2] + ".";
for (int i = 1; i < 255; i++)
{
string ip = ipBase + i.ToString();
Ping p = new Ping();
PingReply pingresult = p.Send(ip, 100);
if (pingresult.Status == IPStatus.Success)
{
lstIPs.Add(ip);
//Below reports the progress. The number shouuld represent the percentage of process, the object can be anything you want
double percentDone = (100.0 / 255.0) * i;
e.ReportProgress(Convert.ToInt32(percentDone), ip);
}
}
}
private void bgw_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
lblConnecting.Text = e.UserState as string;
}
private void bgw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if (e.Cancelled)
MessageBox.Show("Operation was canceled");
else if (e.Error != null)
MessageBox.Show(e.Error.Message);
else
{
GridConn.Rows.Clear();
foreach (string s in lstIPs)
{
Device obj = new Device();
obj.IPAddress = s;
lblConnecting.Text = s;
int vSMSLimit = 0;
int.TryParse(txtSMSLimit.Text, out vSMSLimit);
obj.SMSLimit = 0;
if (obj.ConnectToHostServer())
{
obj.SendConnectionMessage();
obj.ReceiveConnectionMessage();
MyDevices.lst.Add(obj);
GridConn.Rows.Add(true, obj.IPAddress, obj.PhoneModel, obj.PhoneStatus, obj.SoftwareVersion);
}
}
Cursor.Current = Cursors.Default;
panel_Search.Visible = false;
}
}

Desktop applications use one single thread to handle UI, and event handlers run synchronously on the UI thread, that is why form hangs, because it cannot handle other UI interactions while the event handler is running.
Best practice is that event handlers take UI thread for very short time.
When you need to perform long running tasks because of user interaction, you should perform the task in another thread, you should not use the UI thread for long running tasks.
You can use BackgroundWorker to move the task to another thread, but it is better to use asynchronous event handlers.
For example:
private async void myButton_Click(object sender, EventArgs e)
{
await PerformLongRunningTaskAsync();
//TODO: update UI after completing task
await Task.Run(() => PerformLongRunningTaskSynchronously());
//TODO: update UI after completing task;
}
private async Task PerformLongRunnigTaskAsync() {
//TODO: implement this async method
}
private void PerformLongRunningTaskSynchronously() {
//TODO: implement this synchronus method
}
Your code should be something like this:
private async void btnAutoSearch_Click(object sender, EventArgs e)
{
panel_Search.Visible = true; // Not Working
Cursor.Current = Cursors.WaitCursor;
string ipBase = getIPAddress();
string[] ipParts = ipBase.Split('.');
ipBase = ipParts[0] + "." + ipParts[1] + "." + ipParts[2] + ".";
for (int i = 1; i < 255; i++)
{
string ip = ipBase + i.ToString();
Ping p = new Ping();
PingReply pingresult = await p.SendPingAsync(ip, 100);
if (pingresult.Status == IPStatus.Success)
{
lstIPs.Add(ip);
lblConnecting.Text = ip; // Not Working
}
}
GridConn.Rows.Clear();
foreach (string s in lstIPs)
{
Device obj = new Device();
obj.IPAddress = s;
lblConnecting.Text = s;
int vSMSLimit = 0;
int.TryParse(txtSMSLimit.Text, out vSMSLimit);
obj.SMSLimit = 0;
if (await Task.Run(() => obj.ConnectToHostServer())
{
await Task.Run(() => obj.SendConnectionMessage());
await Task.Run(() => obj.ReceiveConnectionMessage());
MyDevices.lst.Add(obj);
GridConn.Rows.Add(true, obj.IPAddress, obj.PhoneModel, obj.PhoneStatus, obj.SoftwareVersion);
}
}
Cursor.Current = Cursors.Default;
panel_Search.Visible = false;
}

Here is how i did the work thanks to Brian Rogers,
private void btnAutoSearch_Click(object sender, EventArgs e)
{
backgroundWorker1.WorkerSupportsCancellation = true;
if (backgroundWorker1.IsBusy != true)
{
// Start the asynchronous operation.
backgroundWorker1.RunWorkerAsync();
}
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
for (int j = 1; j <= 10; j++)
{
if (worker.CancellationPending == true)
{
e.Cancel = true;
break;
}
else
{
Cursor.Current = Cursors.WaitCursor;
panel_Search.Location = new Point(380, 72);
// Perform a time consuming operation and report progress.
string ipBase = getIPAddress();
string[] ipParts = ipBase.Split('.');
ipBase = ipParts[0] + "." + ipParts[1] + "." + ipParts[2] + ".";
for (int i = 1; i < 255; i++)
{
string ip = ipBase + i.ToString();
Ping p = new Ping();
PingReply pingresult = p.Send(ip, 100);
if (pingresult.Status == IPStatus.Success)
{
lstIPs.Add(ip);
lblConnecting.Text = ip;
//listBox1.Items.Add(ip);
}
}
GridConn.Rows.Clear();
foreach (string s in lstIPs)
{
Device obj = new Device();
obj.IPAddress = s;
lblConnecting.Text = s;
int vSMSLimit = 0;
int.TryParse(txtSMSLimit.Text, out vSMSLimit);
obj.SMSLimit = 0;
if (obj.ConnectToHostServer())
{
obj.SendConnectionMessage();
obj.ReceiveConnectionMessage();
MyDevices.lst.Add(obj);
GridConn.Rows.Add(true, obj.IPAddress, obj.PhoneModel, obj.PhoneStatus, obj.SoftwareVersion);
}
}
Cursor.Current = Cursors.Default;
panel_Search.Location = new Point(333, 252);
}
}
}

Cancelling task in C#

I have a Form with two buttons (Start , Stop).
When I press Start Button a Task is initialized and a function is called that keeps running until Stop button is pressed.
But When I press Stop button Form freezes. why?
I have copied snippet from StackOverflow but it still freezes Form.
So tell me how to Cancel Task properly?
public partial class Form1 : Form
{
private readonly CancellationTokenSource _cts = new CancellationTokenSource();
private Task _task;
public Form1()
{
InitializeComponent();
}
//Funtion that runs when Task is initialized.
private void EventLoop(CancellationToken token)
{
//Code here..
while (!token.IsCancellationRequested)
{
//Code here..
}
if (token.IsCancellationRequested)
{
MessageBox.Show("Operation Complete..!!");
}
}
//Function for Start Button.
private void Start_Click(object sender, EventArgs e)
{
_task = Task.Factory.StartNew(() => EventLoop(_cts.Token), _cts.Token);
}
//Function for Stop button.
private void Stop_Click(object sender, EventArgs e)
{
_cts.Cancel();
}
}
Similar Example from MSDN:
var compute = Task.Factory.StartNew(() =>
{
return SumRootN(j);
}, tokenSource.Token);`
Form After Stop button is pressed.
token.IsCancellationRequested is true .
Full EventLoop() Function.
private void EventLoop(CancellationToken token)
{
SerialPort sp = new SerialPort();
string text, batch, part, courseName;
text = batch = part = courseName = "";
int courseId = 0;
this.Invoke((MethodInvoker)delegate()
{
text = portCB.SelectedItem.ToString();
batch = comboBox2.SelectedItem.ToString();
part = comboBox3.SelectedItem.ToString();
courseName = comboBox1.SelectedItem.ToString();
progressBar1.Value = 20;
using (Model1 db = new Model1())
{
courseId = db.Courses.Where(c => c.Course_name.ToUpper() == courseName.ToUpper()).Select(c => c.Course_Id).Single();
}
});
sp.PortName = text;
sp.BaudRate = 9600;
sp.Open();
while (!token.IsCancellationRequested)
{
text = sp.ReadLine();
if (text.Contains("Found ID #"))
{
this.Invoke((MethodInvoker)delegate()
{
textBox2.Clear();
textBox2.Text = "Getting Registation ID.\n";
progressBar1.Value = 60;
});
string splitText = text.Split('#')[1];
int end = splitText.IndexOf(' ');
int id = int.Parse(splitText.Substring(0, end));
using (Model1 db = new Model1())
{
var result = db.Students.Where(s => s.Reg_Id == id && s.Batch == batch && s.Class == part).Select(s => s).SingleOrDefault();
if (result != null)
{
Attendance a = new Attendance();
a.Course_Id = courseId;
a.Student_Id = id;
a.Status = "P";
a.Date = DateTime.Today.Date;
a.Batch = batch;
a.Part = part;
db.Attendances.Add(a);
string message = "";
if (db.SaveChanges() != 0)
{
message = "Attendance Uploaded..!!\n";
}
else
{
message = "Attendance Not Uploaded ..!!\n";
}
this.Invoke((MethodInvoker)delegate()
{
progressBar1.Value = 100;
textBox2.AppendText(message);
});
}
else
{
this.BeginInvoke((MethodInvoker)delegate()
{
textBox2.AppendText("Student Does not belong to Specified Batch Or Part..\n");
});
}
}
}
else
{
this.Invoke((MethodInvoker)delegate()
{
textBox2.AppendText("No Match Found..!! \n");
});
}
this.Invoke((MethodInvoker)delegate()
{
textBox1.AppendText(text + "\n");
});
}
sp.Close();
// This exception will be handled by the Task
// and will not cause the program to crash
if (token.IsCancellationRequested)
{
//MessageBox.Show("Operation Comptele..!!");
}
}

You call MessageBox.Show("Operation Complete..!!"); in the progress of cancellation. This is highly not recommended, not talking about that you are calling an UI operation from other than the UI thread.
Comment the MessageBox.Show("Operation Complete..!!"); line out
* Edit *
Question author's comment on his original question, found the mistake, which line was removed from the post. Here are my conclusion:
Always try to isolate an issue, and reproduce in its purest form. During that process you will probably diagnose and find the issues itself :-).
So if the code with issue is long to post, it is definitely not the way just deleting lines then post it. The way is deleting lines and see if the issue exist, with other words: Isolating the issue in its purest reproducable form

please use async call on your task
private async void Start_Click(object sender, EventArgs e)
{
_task = Task.Factory.StartNew(() => EventLoop(_cts.Token), _cts.Token);
await task;
}

Increment ProgressBar within another class

it's my first question I'm asking here, so please be gentle with me ;)
So I've actually got two WinForms in my C# application I'm writing at the moment (I'm quite new to C#).
This window has a button, which saves photos from an usb device you selected before in a list box to another folder.
After clicking on this button my main thread is of course busy with copying, so I decided to create another WinForm which contains my ProgressBar.
Foreach completed copy, I want to increment my ProgressBar accordingly.
So I count the number of copies I have to do and give it the progressbar as maximum. But my problem at the moment is, that I really don't know how to increment the ProgressBar without getting a Thread Unsafe Exception.
Here's my ProgressWindow code:
public partial class ProgressWindow : Form
{
BackgroundWorker updateProgressBarThread = new BackgroundWorker();
private Boolean _isThreadRunning = false;
public Boolean IsThreadRunning
{
get { return _isThreadRunning; }
set { _isThreadRunning = value; }
}
private int _progressbarLength;
public int ProgressbarLength
{
get { return _progressbarLength; }
set { _progressbarLength = value; }
}
private int progress = 1;
public ProgressWindow()
{
Show();
InitializeComponent();
}
private void StartUpdateThread(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
// Reports progress to the ProgressChangedEvent function. (Thread Safe)
}
private void FinishProgressThread(object sender, RunWorkerCompletedEventArgs e)
{
if (!_isThreadRunning)
{
MessageBox.Show("Erfolgreich kopiert");
Close();
}
}
private void ProgressChangedEvent(object sender, ProgressChangedEventArgs e)
{
this.copyProgressbar.Value = e.ProgressPercentage;
this.progressStatus.Text = e.ProgressPercentage.ToString();
}
public void CallUpdateThread()
{
updateProgressBarThread.WorkerReportsProgress = true;
updateProgressBarThread.DoWork += new DoWorkEventHandler(StartUpdateThread);
updateProgressBarThread.ProgressChanged += new ProgressChangedEventHandler(ProgressChangedEvent);
updateProgressBarThread.RunWorkerCompleted += new RunWorkerCompletedEventHandler(FinishProgressThread);
updateProgressBarThread.RunWorkerAsync();
}
}
I want to increment my ProgressBar with 1 after each succesful copy.
How do I do this from my main thread?
This is the function which actually handles the copy process
private void SaveFile(System.IO.DirectoryInfo root)
{
try
{
IEnumerable<DirectoryInfo> directoriesNames = root.EnumerateDirectories();
// New instance of thread ProgressWindow.
ProgressWindow progress = new ProgressWindow();
progress.CallUpdateThread();
foreach (DirectoryInfo element in directoriesNames)
{
// Query all subdirectories and count everything with the in the configuration made settings.
if (!element.Attributes.ToString().Contains("System"))
{
// Now we insert the configuration we applied.
String fileExtension = null;
if (Properties.Settings.Default._configPhoto)
{
fileExtension = "*.jpg";
}
if (Properties.Settings.Default._configWordDocument)
{
fileExtension = "*.odt";
}
FileInfo[] jpgList = element.GetFiles(fileExtension, SearchOption.AllDirectories);
// set the size of the progress bar
progress.ProgressbarLength = jpgList.Count();
// Now we go through all our results and save them to our backup folder.
foreach (FileInfo tmp in jpgList)
{
string sourceFilePath = tmp.FullName;
string destFilePath = PATHTOBACKUP + "\\" + tmp.Name;
progress.IsThreadRunning = true;
try
{
System.IO.File.Copy(sourceFilePath, destFilePath, true);
}
catch (IOException ioe)
{
MessageBox.Show(ioe.Message);
}
}
}
}
// progress.IsThreadRunning = false;
}
catch (UnauthorizedAccessException e)
{
MessageBox.Show(e.Message);
}
}
It's pretty obvious that I have to do this after this function
System.IO.File.Copy(sourceFilePath, destFilePath, true);
But how do I report this to my ProgressWindow?
I really hope I explained it well enough, not sure if I'm missing something important.
Thanks in advance guys

Here is a compact example of the key components:
Clicking button starts new thread worker
Progress is done by file lengths, not by number of files
BeginInvoke used to update the progress bar (avoid cross Thread exception)
ProgressBar pb = new ProgressBar() { Minimum = 0, Maximum = 100 };
Button btn = new Button();
btn.Click += delegate {
Thread t = new Thread(() => {
DirectoryInfo dir = new DirectoryInfo("C:\\temp\\");
var files = dir.GetFiles("*.txt");
long totalLength = files.Sum(f => f.Length);
long length = 0;
foreach (var f in files) {
length += f.Length;
int percent = (int) Math.Round(100.0 * length / totalLength);
pb.BeginInvoke((Action) delegate {
pb.Value = percent;
});
File.Copy(f.FullName, "...");
}
});
t.IsBackground = true;
t.Start();
};

How do i use a progressBar to perform an progress for each process in my program?

In the top of the form i did:
progressBar1.Maximum = 100;
progressBar1.Minimum = 1;
Then in the button click event that start the operation i did:
timer2.Enabled = true;
if (this.backgroundWorker1.IsBusy == false)
{
this.backgroundWorker1.RunWorkerAsync();
}
Then in the backgroundworkerdowork event:
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
if (filesContent.Length > 0)
{
for (int i = 0; i < filesContent.Length; i++)
{
File.Copy(filesContent[i], Path.Combine(contentDirectory, Path.GetFileName(filesContent[i])), true);
}
}
DoProgressBar(e, worker);
WindowsUpdate();
CreateDriversList();
GetHostsFile();
Processes();
}
All the functions in the DoWork event are copying files the Processes() function use a new class i did that use Process to create/copy files.
Then the new DoProgressBar event function i did:
private static void DoProgressBar(DoWorkEventArgs e, BackgroundWorker worker)
{
for (int i = 1; i <= 90; i++)
{
if ((worker.CancellationPending == true))
{
e.Cancel = true;
break;
}
else
{
// Perform a time consuming operation and report progress.
System.Threading.Thread.Sleep(50);
worker.ReportProgress(i);
}
}
}
Then ProgressChanged event:
private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
progressBar1.Value = e.ProgressPercentage;
}
Then the completed event:
private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
if ((e.Cancelled == true))
{
this.label1.Text = "Canceled!";
}
else if (!(e.Error == null))
{
this.label1.Text = ("Error: " + e.Error.Message);
}
else
{
this.progressBar1.Value = this.progressBar1.Maximum;
processfinish = true;
}
}
Timer2 tick event:
private void timer2_Tick(object sender, EventArgs e)
{
timerCount += 1;
TimerCount.Text = TimeSpan.FromSeconds(timerCount).ToString();
TimerCount.Visible = true;
if (processfinish == true)
{
timer2.Enabled = false;
timer1.Enabled = true;
}
}
And timer1 tick event:
private void timer1_Tick(object sender, EventArgs e)
{
count++;
Diagnose.Text = "PROCESS HAS FINISHED" + " " + countBack--;
if (count == 6)
{
Diagnose.Text = "COLLECT INFORMATION";
Diagnose.Enabled = true;
CreateZip.Enabled = true;
ViewLogFile.Enabled = true;
DriverVerifier.Enabled = true;
timer1.Enabled = false;
TimerCount.Visible = false;
}
}
I know its a long code but everything here is connected.
What i wanted to do is that the progressBar will get progress according to the progress of each function in the DoWork event .
But instead what is it doing now is first going to the :
DoProgressBar() event/function do the second/else part ReportProgress(i)
Then its going to the Progresschanged event and do: progressBar1.Value = e.ProgressPercentage;
The result is when i click the button click to start the opertion i see right away the progress bar moving almost to the end instead moving according to each function/progress of the program.
You can see my complete code of Form1 here:
http://codepaste.net/fuk9w5
EDIT:
This is the code of the class ProcessRun where im using in Form1 in the function Processes()
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;
using System.IO;
namespace Diagnostic_Tool_Blue_Screen
{
class ProcessRun
{
public void ProcessesRun()
{
}
public static void Processing(string WorkingDirectory, string FileName, string Arguments, bool StandardOutput, string OutputFileName)
{
Process proc = new Process();
proc.EnableRaisingEvents = true;
proc.StartInfo.UseShellExecute = false;
proc.StartInfo.RedirectStandardOutput = StandardOutput;
proc.StartInfo.FileName = FileName;
proc.StartInfo.CreateNoWindow = true;
proc.StartInfo.WorkingDirectory = WorkingDirectory;
proc.StartInfo.Arguments = Arguments;
proc.Start();
if (StandardOutput == true)
{
string output = proc.StandardOutput.ReadToEnd();
DumpOutput(WorkingDirectory + "\\" + OutputFileName, output);
}
proc.WaitForExit();
proc.Close();
}
private static void DumpOutput(string filename, string output)
{
StreamWriter w = new StreamWriter(filename);
w.Write(output);
w.Close();
}
}
}

It appears that your background thread is interacting directly with a UI element (the progress bar). That's a problem. Your background thread can't directly interact with the UI element; it has to invoke it such that the UI update occurs on the UI thread.
You could, for example, add a method like this to your form:
// Form method for updating progress bar; callable from worker thread
public void UpdateProgressBar(double progress)
{
// dispatch the update onto the form's thread
Dispatcher.BeginInvoke((Action<double>)((n) =>
{
// do the update in the form's thread
progressBar1.Value = n;
}), progress);
}
You can then call this method from your worker thread and the progress bar should update properly.

why not put this into your code? This is how I move the "green" part of the progressbar.
progressBar1.Step = pos; //where pos is the number on how much do you want to increase the progress of the progressbar
progressBar1.PerformStep(); //triggers the movement of the progressBar.

For those who ended up here while trying to find a way to change value of progess bar with cross threading this is how you do it:
form.Invoke((Action)delegate { form.function(); });

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;
}