I have a simple foreach loop that I would like to paralellize, here's my code (not paralellized for now):
foreach (string filename in ofdmulti.FileNames)
{
img.Add(new DicomImage(filename)); // fill images
Progress_Bar_Loading_Images.PerformStep();
}
Now, my big problem is the progressbar.. I get an error because it seems I can't update the progressbar on another thread than the one that got created..
any hints?
Thanks!
Use Background Worker. It has built in support for doing cross-thread UI calls so you don't have to do anything special for it. Plus, it has events built in for updating progress bars. This tutorial walked me through it when I first needed to do exactly that.
Related
sorry if this is a silly question, I am new to C#, so please give me a break.
I am working on Revit API. currently, Revit API doesn't support multi-threading operations.
my question is how to stop a loop without calling a new thread?
I am trying to get a snapshot and I am waiting for the user to pick a snap, so I put an infinite loop till the condition meets
while (!Clipboard.ContainsImage()) //loop till user get a clipboard image
{
}
but what if I want to abort this???
I have tried
private void Abort_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Escape)
{
abort = true;
}
}
but this method requires threading ....any suggestions!!
You want to look into asynchronous processing patterns in Revit - check for instance The Building Coders description of IExternalEvent.
It might take a little while to wrap your head around it, but let me try to explain:
Split your code up into two parts: The first part runs up until the moment you ask the user to pick a snap (I'm assuming this happens in another application?). In a separate thread, poll the clipboard (or register your application as a clipboard viewer) in your while loop. Don't forget to Sleep() while you're polling! As soon as your polling thread finds a picture, create an instance of an IExternalEvent subclass and post it to Revit. When Revit has some spare time, it will execute the Execute method, passing in a UIApplication that you can use to do the rest of your code.
Revit doesn't let you access it's API from multiple threads at the same time, but during the Execute method of an IExternalEvent subclass, you are guaranteed to be in the correct thread for running code.
You can also look into the OnIdling event - basically, this gets called each time Revit has some spare time too. So instead of using a while loop in a separate thread, you could just place your clipboard checking code in the event handler for the OnIdling event and create a mechanism (a flag) to tell you wether you are currently waiting for a snap or not...
I am having issues on how to get around the following problem.
I have a class which which allows me to dynamically update and display a graph on a form. In order to update the values of the graph I have a method within the class of the form. I pass in the value to update the graph with to this method. Here is a high level example of what I am trying to do:
class GUICLass : Form {
//Code for drawing chart etc all here
public updategraphWithNewValue(double value){
// Code to update the graph
}
}
My other class is as follows:
class ValueProviderForGraph{
GUIClass graphForm = new GUIClass();
public calculateValuesAndPlot(){
for(int i = 0; i < 4000; i++){
graphForm.updategraphWithNewValue(i);
graphForm.update();
}
}
}
Now the issue I get from the above is that the form freezes while this operation is taking place. How could I go about getting around this, any help or advice would be much appreciated. I hope this high level example has enough information, if not please do let me know and I shall try and explain myself better.
Thanks.
Look into using BackgroundWorker. Its event-oriented interface should get you up and running quickly.
You can only update your form's controls from the thread that the control was originally created on.
If you are trying to update it from a different thread, you must marshal that call. There are numerous approaches on the web. My personal favorite (for WinForms) is the following:
https://stackoverflow.com/a/709846/141172
UPDATE
After re-reading your question at the urging of #StenPetrov, I suspect that you do not have a cross-thread issue after all, but that the UI thread is simply not processing messages while it updates the graph (this would cause the freezing during the operation).
If the UI thread is busy updating the graph, you will get that behavior. However, it looks like you are causing the graph to do an unnecessary update 3999 times. Try moving the line
graphForm.update();
outside of your for loop.
While I don't know exactly how your graph control works, I suspect the call to update() causes the entire graph to be re-rendered. You should only do that after all new data points have been added.
Do you need to update the UI often or not?
If you don't have to update the UI often, such as loading a large graph for viewing, then BackgroundWorker will do.
If you need the UI updated frequently you have to (a) make your graph calculations independent of UI, (b) run the graph calculations in a separate thread and (c) after the update is calculated use Form.Invoke(...) to update the UI
I know I'm having a massive derp moment here and this is probably quite easy to actually do - I have had a search around and read a few articles but i'm still struggling a little, so any feedback or pointers to useful resources would be greatly appreciated!
Anyway I have a class called PopulateDatagridViews which I have various functions in, one of which is called ExecuteSqlStatement, this function is simple enough, it initializes an SQL connection and returns a DataTable populated with the results of the SQL query. Within the same class I also have various functions that use string builders to build up SQL statements. (Not ideal, I know.)
I create a PopulateDatagridViews object in my GUI thread and use it to set various datagrid views with with the returned DataTables. For example:
dataGridViewVar.DataSource = populateDgv.GetCustomers();
Naturally a problem I'm having is that the more data to be read from the database, the longer the U.I is unresponsive. I would like to shift the process of retrieving data via the PopulateDatagridViews to a separate thread or BackgroundWorker so as prevent the main GUI thread from locking up whilst this is processed.
I realise I can create a BackgroundWorker to do this and place in the DoWork handler a call to the appropriate function within my PopulateDatagridViews.
I figure I could create a BackgroundWorker for each individual function inside my PopulateDatagridViews class, but surely there is a more efficient way to do this? I'd very much appreciate a point in the right direction on this as it's driving me around the bend!
Additional Info: I use version 4.0 of the .Net framework.
I strongly suggest that you use TPL (Task Parallel Library) http://msdn.microsoft.com/en-us/library/dd537609.aspx
In your case you will create first task to pull some data and than start second task after first is completed to update UI.
I`ll try to find code that i write for similar problem.
Edit: Adding code
Task<return_type> t1 = new Task<return_type>(() =>
{
//do something to take some result
return some_result; //return it
});
t1.Start();
Task t2 = t1.ContinueWith((some_arg_that_represent_previous_task_obj) =>{//ContinueWith guarantees that t2 is started AFTER t1 is executed!
//Update your GUI here
//if you need result from previos task: some_arg_that_represent_previous_task_obj.Result //Your dataset or whatever
}, TaskScheduler.FromCurrentSynchronizationContext()); //VERY important - you must update gui from same thread that created it! (you will have cross thread exeption if you dont add TaskScheduler.FromCurrentSynchronizationContext()
Hope it helps.
Well in that case I recommend reading this msdn article to get some ideas. Afterwards you should look for some tutorials, because the msdn is not the best source to learn things. ;o)
I've got a "Loading Progress" WPF form which I instantiate when I start loading some results into my Main Window, and every time a result is loaded I want the progress bar to fill up by x amount (Based on the amount of results I'm loading).
However what happens is that the Progress bar in the window stays blank the entire time, until the results have finished loading, then it will just display the full progress bar.
Does this need threading to work properly? Or is it just to do with the way I'm trying to get it to work?
//code snippet
LoadingProgress lp = new LoadingProgress(feedCount);
lp.Show();
foreach (FeedConfigGroup feed in _Feeds) {
feed.insertFeeds(lp);
}
//part of insertFeeds(LoadingProgress lbBox)
foreach (Feeds fd in _FeedSource) {
lpBox.setText(fd.getName);
XmlDocument feedResults = new XmlDocument();
feedResults.PreserveWhitespace = false;
try {
feedResults.Load(wc.OpenRead(fd.getURL));
} catch (WebException) {
lpBox.addError(fd.getName);
}
foreach (XmlNode item in feedResults.SelectNodes("/rss/channel/item")) {
//code for processing the nodes...
}
lpBox.progressIncrease();
}
If more code is needed let me know.
Consider accessing the progressbar from the external thread thru a delegate asynchronously using the ProgressBar's Dispatcher.Invoke.
This post might be helpful.
I suggest you to use another thread to do the processing. The progress bar is filled at the end, so you didn't make a mistake on its programming.
In general, you should avoid to do processing in the user interface thread.
So, how many feeds and how many items? I'll wait for you to count them in order to set the total length of the progress bar.
...
What was that? You wouldn't know the total until after most of the work is already done? Well, sounds like the progress bar isn't the correct control to use.
You're doing (at least what should be) asynchronous work here. Definitely do it in a worker thread. Definitely let the user know work is going on in the background. But don't use a progress bar. You can't know exactly what point in the process you are at and how much longer you have to go until all the long-lasting processes have completed. Most of your users will see that your progress bar as the lie it is and will laugh at your suck.
Just use the standard "work is going on in the background" fadey-circle-thingy on your RSS feed box (an Adorner would work nicely) and be done with it.
Using this video I managed to get it working, Dispatch.BeginInvoke (Except for one which needed to be Dispatcher.Invoke) was the way to go. If anyone wants the final code let me know and I can post it up.
OK, please disregard what has gone before. I'm not getting the errors anymore, so it seems my problem is with getting a Chart to update when I change the values to which the Chart is data bound.
//Disregard below here
Hi all. I have a WinForms application that has a panel, panel1. A background thread creates some other controls that then get added to panel1 like so
panel1.Controls.AddRange(myArrayOfControls);
This works great and I can see my controls get added. But, when new data comes in on another thread, I update values in the controls' parent objects and then need to Refresh() to get the display to update with the new values. Calling Refresh() in either context, the thread where the data comes in or the objects that receive the updated data causes an InvalidOperation exception because Invoke is required. I've tried using Invoke in my model objects and also the thread where the data is incoming and can't seem to shake the error.
If anyone has some guidance I'd greatly appreciate it.
UPDATE: Here's a little more info. I didn't think it would require it, but I was wrong. :)
I have an object class MyObject. This MyObject class gets created in a thread called topologyThread. Data comes in on dataThread. Instances of MyObject have a Panel instance variable and the Panel has child Controls including two Charts from the System.Windows.Forms.DataVisualization.Charting namespace. So, as data comes in on dataThread, I update the respective data values in the MyObject objects and then need to refresh the Charts to show the updated data.
I do know the data is processing fine. In my MyObject class, I'm logging the new values to Console in the setter for the property and see the new values show up.
You must do both operations (refresh and updating of control's parent object) from the main UI thread. If you are modifying a control from a background thread and not getting an exception that is bad luck because it is definitely an error.
The best way to do this is to use
theControl.Invoke(new MethodInvoker(MyUpdateMethod));
If you have a sample of how the update is done, we can give a better sample on how to properly call it from the background thread.
JaredPar is a pretty good answer. I would like to add to it a bit as to the reason your code sort of works.
With windows forms you can talk to the UI thread from other threads. This is really bad practice in all cases.
The catch is that when you do it, it is hard to catch because sometimes the UI will work as if nothing is wrong. item will get added or changed and the UI will reflect the changes. However other times running the same exact code, it will not work.
That is the catch with touching the UI from any thread other then the UI thread. The out come is inconsistent and that is why is very bad practice.
God I wish I could comment. :)
JaredPar's answer is good. It can cause problems in some instances (notably when the method is invoked before the form is finished being constructed). Here's a somewhat more robust implementation (using extension methods)
public static class ControlInvokeExtensions
{
public static void InvokeOnHostThread(Control host, MethodInvoker method)
{
if (IsHandleCreated)
Invoke(new EventHandler(delegate { method(); }));
else
method();
}
}
now you can call it this way
panel1.InvokeOnHostThread(() => panel1.Controls.AddRange(myArrayOfControls));
or if you're in the form:
InvokeOnHostThread(() => panel1.Controls.AddRange(myArrayOfControls));