I want to move picturebox with thread programming. Also, I want to get Picturebox's count with a Textbox in my solution, but it's my first try so I have problems with it. Could you please help me?
Thread th;
public void F_Thread()
{
for (int i = 0; i < Convert.ToInt16(textBox1.Text); i++)
{
this.pictureBox1.Left = this.pictureBox1.Left - 10;
Thread.Sleep(100);
}
}
private void button1_Click_1(object sender, EventArgs e)
{
th = new Thread(F_Thread);
th.Start();
}
Here is a cheap, minimal example of using Invoke to change a property of a control from a different thread:
public void F_Thread()
{
for (int i = 0; i < Convert.ToInt16(textBox1.Text); i++)
{
if (pictureBox1.InvokeRequired )
this.Invoke(new UpdatePBInvoker(UpdatePB), -10);
Thread.Sleep(100);
}
}
delegate void UpdatePBInvoker(int moveX);
private void UpdatePB(int moveX)
{
pictureBox1.Left = pictureBox1.Left + moveX;
}
Feel free to add more parameters; just make sure to keep the signatures of the function and the delegate the same:
delegate void UpdatePBInvoker(Control ctl, int moveX);
private void UpdatePB(Control ctl, int moveX)
{
ctl.Left = ctl.Left + moveX;
}
Call the 2nd version like this:
.. this.Invoke(new UpdatePBInvoker(UpdatePB), pictureBox1, -10);
Note the the check if ( someControl.InvokeRequired ) is optional and often added to allow for the option of not calling the function from a different thread; for theses cases one usually adds an else branch with the direct call: UpdatePB(...)
Also note that the thread may still run when you close the Form. To prevent errors make sure to abort it, maybe like this:
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
if ((th!= null && th.IsAlive) th.Abort();
}
If your thread would do more complicated things, especially aquiring locks, it should not be aborted but given a chance to finish and close itself, usually by setting a global flag. But in this case it should work ok. Also see MSDN on this topic..
I have some controls on the form of the Windows Forms application and I need to update its' texts at run-time from several threads.
Is it safe to just call BeginInvoke method like this:
BeginInvoke((MethodInvoker)delegate()
{
this.label.Text = "Some text";
});
from several threads at the same time? Should I do any additional synchronization in this case? Will it be processed by the same thread one by one and is this order guaranteed?
Thanks in advance.
Calling BeginInvoke puts the delegate on to the message queue to be processed by the UI thread, it will process the queue handling the messages one by one. So no, you do not need to do any additional synchronization (as long as the delegate is not accessing any resources that can't be accessed from the UI thread).
As for order, it is not guaranteed they will be processed in order but in practice most of the time the delegates will be processed in the order they where put in to the queue.
To address the question in the comments, instead of using multiple BeginInvoke calls you should be able to get away with just one.
You never really explained what your animation was so I am going to assume it is going to be that this.label will swap between ., .. and ... then you store the result text in this.label when you are done.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
animationTimer = new System.Windows.Forms.Timer();
animationTimer.Interval = 500;
animationTimer.Tick += animationTimer_Tick;
}
private System.Windows.Forms.Timer animationTimer;
private int dots = 0;
void animationTimer_Tick(object sender, EventArgs e)
{
//Make 1, 2, or 3 dots show up. This runs on the UI thread so we don't need to invoke.
this.label.Text = new String('.', dots + 1);
//Add one then reset to 0 if we reach 3.
dots += 1;
dots = dots % 3;
}
private void button1_Click(object sender, EventArgs e)
{
animationTimer.Start();
Task.Run(() => DoSomeSlowCalcuation());
}
private void DoSomeSlowCalcuation()
{
Thread.Sleep(5000);
this.BeginInvoke((MethodInvoker)delegate()
{
//We stop the timer before we set the text so the timer will not overwrite it.
animationTimer.Stop();
this.label.Text = "Some text";
});
}
}
This code is just a example to get my point across, if I where doing this I would use async/await for the button click and not use BeginInvoke at all.
private async void button1_Click(object sender, EventArgs e)
{
animationTimer.Start();
var result = await Task.Run(() => DoSomeSlowCalcuation());
animationTimer.Stop();
this.label.Text = result;
}
private string DoSomeSlowCalcuation()
{
Thread.Sleep(5000);
return "Some text";
}
We are learning multi-threadding today in class and we came across a very curious error. When doing a for loop in our new thread the upper bound of the for loop keeps getting passed. The thread is being killed but then another value will appear and end another thread.
For the purpose of debugging the error I changed the upper bound to 90 to avoid the OutOfRange Exception on the progressbar.
While outputting the counter to the progressing bar and updating the progress bar I got this in my output window.
If i commented out the updating on the progress bar (pbLoad.Value = i;) I got this in my output window
I have tried changing the loop to i<101 and also tried moving where the i++ was but it made no difference
EDIT: This is coming from the BeginInvoke. When i switched it to Invoke it worked but then I will get a deadlock when trying to use the cancel button.
Here is the code:
public partial class Form1 : Form
{
Thread backgroundThread;
bool stopExecution = false;
public Form1()
{
InitializeComponent();
}
private void btnStart_Click(object sender, EventArgs e)
{
stopExecution = false;
btnStart.Enabled = false;
backgroundThread = new Thread(DoDomethingThatTakesAWhile);
backgroundThread.Start();
}
private void DoDomethingThatTakesAWhile()
{
for (int i = 0; i <= 100; i++)
{
if (!stopExecution)
{
Thread.Sleep(100);
if (pbLoad.InvokeRequired)
{
MethodInvoker myMethod
= new MethodInvoker(
delegate
{
if (!stopExecution)
{
pbLoad.Value = i;
Debug.WriteLine(i); //i to output window
}
});
pbLoad.BeginInvoke(myMethod);
}
else
{
pbLoad.Value = i;
}
}
else
{
break;
}
}
}
private void btnCancel_Click(object sender, EventArgs e)
{
//backgroundThread.Abort();
stopExecution = true;
backgroundThread.Join();
pbLoad.Value = 0;
btnStart.Enabled = true;
}
}
When you call MethodInvoke it will not occurs at that moment, but some time later.
In your scenario you have a chance of following to occurs:
invoked code is finally executed;
the loop is already finished (and i become 101)
you are accessing i directly and you read 101.
And to fix it you can make a copy of i (by passing it as a parameter to invoked method):
pbLoad.BeginInvoke(new Action<int>(a =>
{
if (!stopExecution)
{
pbLoad.Value = a;
Debug.WriteLine(a); //a to output window
}
}), new object[] { i });
P.S: you don't need to check for InvokeRequired, unless you plan to call DoDomethingThatTakesAWhile method directly, which I assume is not the case.
You're using BeginInvoke which explicitly opens the possibility for races. I recommend synchronous invoking.
Furthermore, you are capturing i, not its value. This is racy and only works by accident because you're sleeping.
Either of the changes will fix the problem. Do both of them.
If you can, abolish this low-level use of synchronization and use async/await.
I have a Thread that retrieves objects from a third party API and stores them in a TreeView list List<TreeView>. My intention is that the TreeView inside the GUI displays the nodes, but I've had no success so far.
Since I've tried almost all kinds of Dispatcher.Invoke stuff, I think I need to raise an event and somehow pass the List<TreeView> object, but I have no clue on how to do so.
Anyhow, my goal is to update the TreeView from a thread different from the UI one.
Thanks in advance.
PS: I'm on WPF .NET 4.
My latest attempt:
private void runButton_Click(object sender, RoutedEventArgs e)
{
if (PfUtils.isAPIConnected() && !GUIlocked)
{
this.lockGUI();
paralell_thread = new Thread(new ThreadStart(RunPowerFlowSimulation));
paralell_thread.IsBackground = true;
paralell_thread.Name = "RunPowerFlow";
paralell_thread.ApartmentState = ApartmentState.STA;
paralell_thread.Start();
mainTabPanel.SelectedIndex = 1;
}
}
private void RunPowerFlowSimulation()
{
PfUtilsUtilsExtended pf = new PfUtilsUtilsExtended();
pf.performLoadFlow(statusLabel, pgbar1);
TreeView tv = pf.gerRelevantObjects(PfUtils.GetActiveProject(), statusLabel, pgbar1);
tv.Dispatcher.Invoke(new Action(() => { objectTreeView.ItemsSource = tv.Items; }));
this.UnLockGUI();
}
I have a c# application that uses a background worker thread, and quite successfully updates the UI from the running thread. The application involves shortest path routing on a network, and I display the network and the shortest path, on the UI, as the background worker proceeds. I would like to allow the user to slow down the display through use of a slider, while the application is running.
I found this as a suggestion, but it is in vb.net, I am not clear on how to get it to work in c#.
How can the BackgroundWorker get values from the UI thread while it is running?
I can pass the value of the slider to the backgroundworker as follows:
// Start the asynchronous operation.
delay = this.trackBar1.Value;
backgroundWorker1.RunWorkerAsync(delay);
and use it within the backgroundworker thread, but it only uses the initially-sent value. I am not clear on how to pick up the value from inside the backgroundworker when I move the slider on the UI.
I have previously used multiple threads and delegates, but if it is possible to utilize the background worker, I would prefer it for its simplicity.
5/10/2012
Thanks to all for your responses. I am still having problems, most likely because of how I have structured things. The heavy duty calculations for network routing are done in the TransportationDelayModel class. BackgroundWorker_DoWork creates an instance of this class, and then kicks it off. The delay is handled in TransportationDelayModel.
The skeleton of code is as follows:
In UI:
private void runToolStripMenuItem1_Click(object sender, EventArgs e)
{
if (sqliteFileName.Equals("Not Set"))
{
MessageBox.Show("Database Name Not Set");
this.chooseDatabaseToolStripMenuItem_Click(sender, e);
}
if (backgroundWorker1.IsBusy != true)
{
// Start the asynchronous operation.
delay = this.trackBar1.Value;
// pass the initial value of delay
backgroundWorker1.RunWorkerAsync(delay);
// preclude multiple runs
runToolStripMenuItem1.Enabled = false;
toolStripButton2.Enabled = false;
}
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
if (!backgroundWorkerLaunched)
{
// instantiate the object that does all the heavy work
TransportationDelayModel TDM = new TransportationDelayModel(worker, e);
// kick it off
TDM.Run(sqliteFileName, worker, e);
backgroundWorkerLaunched = true;
}
}
The TransportationDelayModel constructor is:
public TransportationDelayModel(BackgroundWorker worker, DoWorkEventArgs e)
{
listCentroids = new List<RoadNode>();
listCentroidIDs = new List<int>();
listNodes = new List<RoadNode>();
listNodeIDs = new List<int>();
listRoadLink = new List<RoadLink>();
roadGraph = new AdjacencyGraph<int, RoadLink>(true); // note parallel edges allowed
tdmWorker = worker;
tdmEvent = e;
networkForm = new NetworkForm();
}
so I have the tdmWorker, which allows me to pass information back to the UI.
In the internal calculations in TransportationDelayModel, I sleep for the delay period
if (delay2 > 0)
{
tdmWorker.ReportProgress(-12, zzz);
System.Threading.Thread.Sleep(delay2);
}
so the problem seems to be how to pass an updated slider value from the UI back to the object that is executing in the background worker. I have tried a number of combinations, sort of thrashing around, to no avail, either nothing happens or I get a message about not being allowed to access what is happening on the other thread. I realize that if I were doing all the work in the DoWork event handler, then I should be able to do things as you suggest, but there is too much complexity for that to happen.
Again, thank you for your suggestions and help.
6/2/2012
I have resolved this problem by two methods, but I have some questions. Per my comment to R. Harvey, I have built a simple application. It consists of a form with a run button, a slider, and a rich text box. The run button launches a background worker thread that instantiates an object of class "Model" that does all the work (a simplified surrogate for my TransportationModel). The Model class simply writes 100 lines to the text box, incrementing the number of dots in each line by 1, with a delay between each line based on the setting of the slider, and the slider value at the end of the line, something like this:
....................58
.....................58
......................58
.......................51
........................44
.........................44
The objective of this exercise is to be able to move the slider on the form while the "Model" is running, and get the delay to change (as in above).
My first solution involves the creation of a Globals class, to hold the value of the slider:
class Globals
{
public static int globalDelay;
}
then, in the form, I update this value whenever the trackbar is scrolled:
private void trackBar1_Scroll(object sender, EventArgs e)
{
Globals.globalDelay = this.trackBar1.Value;
}
and in the Model, I just pick up the value of the global:
public void Run(BackgroundWorker worker, DoWorkEventArgs e)
{
for (int i = 1; i < 100; i++)
{
delay = Globals.globalDelay; // revise delay based on static global set on UI
System.Threading.Thread.Sleep(delay);
worker.ReportProgress(i);
string reportString = ".";
for (int k = 0; k < i; k++)
{
reportString += ".";
}
reportString += delay.ToString();
worker.ReportProgress(-1, reportString);
}
}
}
This works just fine.
My question: are there any drawbacks to this approach, which seems very simple to implement and quite general.
The second approach, based on suggestions by R. Harvey, makes use of delegates and invoke.
I create a class for delegates:
public class MyDelegates
{
public delegate int DelegateCheckTrackBarValue(); // create the delegate here
}
in the form, I create:
public int CheckTrackBarValue()
{
return this.trackBar1.Value;
}
and the Model class now has a member m_CheckTrackBarValue
public class Model
{
#region Members
Form1 passedForm;
public static MyDelegates.DelegateCheckTrackBarValue m_CheckTrackBarValue=null;
#endregion Members
#region Constructor
public Model(BackgroundWorker worker, DoWorkEventArgs e, Form1 form)
{
passedForm = form;
}
When the background thread is launched by the run button, the calling form is passed
private void button1_Click(object sender, EventArgs e)
{
if (backgroundWorker1.IsBusy != true)
{
backgroundWorker1.RunWorkerAsync();
}
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
BackgroundWorker worker = sender as BackgroundWorker;
if (!backgroundWorkerLaunched)
{
// instantiate the object that does all the heavy work
Model myModel= new Model(worker, e, this);
Model.m_CheckTrackBarValue = new MyDelegates.DelegateCheckTrackBarValue(this.CheckTrackBarValue);
// kick it off
myModel.Run(worker, e);
backgroundWorkerLaunched = true;
}
}
Finally, in the Model, the Invoke method is called on the passed form to get the value of the trackbar.
public void Run(BackgroundWorker worker, DoWorkEventArgs e)
{
for (int i = 1; i < 100; i++)
{
int delay = (int)passedForm.Invoke(m_CheckTrackBarValue,null); // invoke the method, note need the cast here
System.Threading.Thread.Sleep(delay);
worker.ReportProgress(i);
string reportString = ".";
for (int k = 0; k < i; k++)
{
reportString += ".";
}
reportString += delay.ToString();
worker.ReportProgress(-1, reportString);
}
}
This works as well. I kept getting an error until I made the member variable static, e.g.
public static MyDelegates.DelegateCheckTrackBarValue m_CheckTrackBarValue=null;
My questions on this solution: Are there advantages to this solution as regards to the previous version? Am I making things too complicated in the way I have implemented this? Why does m_CheckTrackBarValue need to be static.
I apologize for the length of this edit, but I thought that the problem and solutions might be of interest to others.
You have to pass the TrackBar object to the BackgroundWorker, not delay. delay doesn't change once you set it.
To simplify the needed Invoke(), you can use a helper method, such as this one:
Async.UI(delegate { textBox1.Text = "This is way easier!"; }, textBox1, true);
I will assume that you are already familiarized with cross-thread invocation to update the UI. So, the solution is very simple: in your worker thread, after each iteration, invoke the UI to get the slider thumb position.
To use a backgroundworker, you add a method to the DoWork property, like this:
this.backgroundWorker1.WorkerSupportsCancellation = true;
this.backgroundWorker1.DoWork += new System.ComponentModel.DoWorkEventHandler(this.backgroundWorker1_DoWork);
this.backgroundWorker1.RunWorkerCompleted += new System.ComponentModel.RunWorkerCompletedEventHandler(this.backgroundWorker1_RunWorkerCompleted);
In the DoWork method, you need to check the variable where the updated delay is set.
This could be an integer field that is available on the containing Form or UI control, or it could be the TrackBar itself.