I have the main form class which contains a list box I want to change. The box is populated with items created in a time-consuming method. Right now it looks like this (inventing an example by hand, might not be valid C#):
List<string> strings = StaticClassHelper.GetStrings(inputString);
foreach(string s in strings)
{
listBox1.Add(s);
}
//meanwhile, in a different class, in a different file...
public static List<string> GetStrings(inputString)
{
List<string> result = new List<string>();
foreach(string s in inputString.Split('c'))
{
result.Add(s.Reverse());
Thread.Sleep(1000);
}
return result;
}
What I would like to do instead is regularly update the list box as new strings are found. The other answers I found work when the thread method is in the same class, so you can set up an event handler. What do I do here?
Here is how I like to do this, I create a method on the form like this:
public void AddItemToList(string Item)
{
if(InvokeRequired)
Invoke(new Action<string>(AddItemToList), Item);
else
listBox1.Add(Item);
}
I prefer invoke in this case to make sure the items are added synchronously, otherwise they can get out of order. If you don't care about the order then you can use BeginInvoke which will be a tad faster. Since this method is public, you can all it from any class in your application as long as you can get a reference to your form.
Another advantage of this is that you can call it from either your UI thread or a non-UI thread and it takes care of deciding whether or not it needs Invokeing. This way your callers don't need to be aware of which thread they are running on.
UPDATE
To address your comment about how to get a reference to the Form, typically in a Windows Forms app your Program.cs file looks something like this:
static class Program
{
static void Main()
{
MyForm form = new MyForm();
Application.Run(form);
}
}
This is typically what I would do, particularly in the case of a "Single Form" application:
static class Program
{
public static MyForm MainWindow;
static void Main()
{
mainWindow = new MyForm();
Application.Run(form);
}
}
And then you can access it pretty much anywhere with:
Program.MainWindow.AddToList(...);
The class containing the ListBox needs to expose a method to add a string - since this method might be called on a different thread, it needs to use
listBox1.Invoke( ...)
to create a thread-safe calling mechanism
Would it be possible for you to rewrite GetStrings as an Iterator? Then in your UI you could start a background thread which iterates over the results of GetStrings, updating the listbox each time. Something like:
public static System.Collections.IEnumerable GetStrings(inputString)
{
foreach(string s in inputString.Split('c'))
{
yield return s.Reverse();
Thread.Sleep(1000);
}
}
And in the UI (Assuming C# 4):
Task.Factory.StartNew(() =>
{
foreach (string s in StaticClassHelper.GetStrings(inputString))
{
string toAdd = s;
listBox1.Invoke(new Action(() => listBox1.Add(toAdd)));
}
}
Probably cleaner ways to go about it, but this should get you what you're looking for.
Related
I have a UserControl that was built following the MVVM pattern with an exposed function for other apps to send "commands" for the control to do. The commands in this case are strings. I'm trying to find a way to stop the GUI from hanging when a lot of commands are being sent in a short period. Each command should wait for the last one to finish.
Most of these commands do work on a 3rd party map control that is displayed in the main control's view.
The flow goes like this:
App sends command string to control.
Control calls a parse function to parse the string.
After parsing is complete, a certain class is called depending on the command.
Stuff happens i.e. create a model, update ObservableCollection, update the map control, etc.
Here's an example:
The usercontrol:
///The code behind for the control
public partial class MainControl : UserControl
{
public MainControl()
{
InitializeComponent();
}
//Other apps call this function
public void ExecuteCommand(string command)
{
CommandParser.StartParse(command);
}
}
Class to parse the commands:
//Handles parsing a string command and calling the right class
public static class CommandParser
{
public static void StartParse(string command)
{
//parses the command into a string array to hold different parts
DoCommand(parsedCommand);
}
private static void DoCommand(string[] command)
{
switch(command[0])
{
case "addpoint":
AddCommand.AddObj(command);
break;
case "createstyle":
CreateCommand.CreateObj(command);
break;
}
}
}
Two classes that take the parsed command and do something:
//Adds objects to the third party map control
public static class AddCommand
{
public static void AddObj(string[] command)
{
//Adds a point to the third party map control
MapControl.AddPoint(new Point(90, -90)); //just an example
}
}
//Creates model objects to add to observablecollections in viewmodels
public static class CreateCommand
{
public static void CreateObj(string[] command)
{
//create a model
//get the correct viewmodel
viewModel.StylesCollection.Add(styleModel); //StylesCollection is an ObservableCollection
}
}
Very basic example but should show the flow of everything. So imagine getting a a few thousands commands; Creating a model is fast, but because the map control (which is part of the GUI) is being updated every time, or an ObservableCollection (that has a control's itemsource bound to it) is being modified, the GUI hangs when receiving and doing all these commands.
In (the probably unlikely) case that there is a considerable amount of work that can be done off the UI thread, you may implement multi threading. A very basic way of doing this would be as so.
First, create a new thread to run:
var task = new Thread(YourTask);
task.Start();
Then in the thread method where the calculations are done, delegate the result to the UI thread by calling Dispatcher.Invoke. Make sure you don't call Invoke too often (e.g. not more than 10 times per second), as this will again block the UI thread.
public void YourTask()
{
// do calculations and get results
Application.Current.Dispatcher.Invoke(
new Action(() =>
{
// update the UI
}));
}
Use case
I'm developing a small application in C# that is called by another application to retrieve data from the Internet. It runs as a process on its own, but almost all of the interaction with it, is managed by the calling application. Therefor it does not have a GUI. However I'd like to add a progress bar using WPF that is shown during certain data retrievals that could take up to a minute. It's fairly easy to make an estimate of how much work is done and how much is left and therefor I find a progress bar suitable.
Research done
I have a fair understanding of threading after reading large parts of Albahari's pdf on threading (http://www.albahari.info/threading/threading.pdf). I have also read through a lot of posts on SO and MSDN in this matter. Most posts suggest the use of a background worker for the time consuming data retrieval while keeping the GUI in the main thread and therefor suggest solutions using a background worker. That feels awkward in this scenario though, where the main task is data retrieval and not GUI interaction.
I've spend a bunch of hours trying to make sense of different tutorials and forum posts while trying to conform them to my problem, but I have not succeeded and now I'm pretty much back to square one. Basically I'd like to end up with the following two classes outlined below:
ProgressBarWindow
public partial class ProgressBarWindow : Window
{
public ProgressBarWindow()
{
InitializeComponent();
}
public void setValue(int value)
{
// This function should be available from the main thread
}
}
Querier
Public class Querier
{
public List<Item> getItems()
{
// call ProgressBarWindow.setValue(0);
...
// call ProgressBarWindow.setValue(100);
// call ProgressBarWindow.Close();
}
}
It's my understanding that UI must run under single threads and therefor my ProgressBarWindow object could not be instantiated in a new thread while at the same time be available to the main thread (kind of).
Dispatcher.BeginInvoke appears to be my savior here but so far I haven't been able to figure out what should go into the Querier class and what to go in the ProgressBarWindow class. How can I make the two threads interact with the same instance of ProgressBarWindow?
Please ask if you need more details and I will try to clarify.
You can use the Progress class to update the UI with the current progress of a long running operation.
First create an instance of Progress in your UI:
Progress<int> progress = new Progress<int>(currentProgress =>
{
progressBar.Value = currentProgress;
//todo do other stuff
});
Then pass it to the long running process:
public List<Item> getItems(IProgress<int> progress)
{
progress.Report(0);
//todo do something
progress.Report(100);
}
Here is a generic function which i generally use:
public static void Invoke(this UIElement element,Action action)
{
element.Dispatcher.Invoke(action, null);
}
And to use it, simply call:
this.Invoke(() => ProgressBarWindow.SetValue(0));
So, in the getItems() function, you would have something along the lines of:
public List<Item> getItems()
{
ProgressBarWindow wnd;
MainWindow.Invoke(() => wnd = new ProgressBarWindow())
MainWindow.Invoke(() => wnd.SetValue(0))
...
MainWindow.Invoke(() => wnd.SetValue(100))
MainWindow.Invoke(() => wnd.Close())
}
Make sure you always have a way to get to the main window is anything (the one running from either App.xml, or App.Run(...). You can then issue any GUI actions through it (even if you have to create a new Loader window for example, as long as it's done within the main thread)
App.xaml
public partial class App : Application
{
private void Application_Startup_1(object sender, StartupEventArgs e)
{
Task.Factory.StartNew<List<int>>(() => Querier.GetItems());
}
}
ProgressBarWindow.xaml.cs
public partial class ProgressWindow : Window
{
public ProgressWindow()
{
InitializeComponent();
Querier.Start +=()=> Visibility = Visibility.Visible;
Querier.Stop += () => Visibility = Visibility.Collapsed;
Querier.ReportProgress +=OnReportProgress;
}
public void OnReportProgress(int value)
{
txtBox.Text = value.ToString();
}
}
ProgressBarWindow.xaml
<Grid>
<TextBox x:Name="txtBox"></TextBox>
</Grid>
Querier
public class Querier
{
public static event Action Start;
public static event Action Stop;
public static event Action<int> ReportProgress;
public static List<int> GetItems()
{
if (Start != null)
App.Current.Dispatcher.BeginInvoke(Start,null);
for (int index = 0; index <= 10; index++)
{
Thread.Sleep(200);
if (ReportProgress != null)
App.Current.Dispatcher.BeginInvoke(ReportProgress, index*10);
}
if (Stop != null)
App.Current.Dispatcher.BeginInvoke(Stop, null);
return Enumerable.Range(1, 100).ToList();
}
}
I am just trying to give an idea hope this will help.
I'm writing a simple Windows forms application to get me into the swing of things with Threads. So far what I have is working, but what I would like to do is contain it all in a seperate class rather than directly in my forms code.
I have a background thread that starts and retrieves data from a database. I then display that data in to a listbox.
private delegate void UpdateListValues(List<ListBoxItem> itemList);
private void form_main_Shown(object sender, EventArgs e)
{
// Set the loading text.
list_selection.Items.Add(ListHelpers.LoadingItem());
// Start the data access on a seperate thread.
Thread worker = new Thread(GetInvoicingData);
worker.IsBackground = true;
worker.Start();
}
private void GetInvoicingData()
{
// Query database
List<ListBoxItem> values = DAC.GetInvoicingAccounts();
// Display results
BeginInvoke(new UpdateListValues(DisplayList), new object[] { values });
}
private void DisplayList(List<ListBoxItem> itemList)
{
// Display each result
list_selection.Items.Clear();
for (int i = 0; i < itemList.Count; i++)
{
list_selection.Items.Add(itemList[i]);
}
}
The problem is that in the DisplayList method, I won't be able to access the list box (list_selection) because it's part of the form class. Does anyone have any suggestions on how I can do this.
Also, I'm new to threading so feel free to tell me I'm doing it absolutely wrong. I just used the example from http://www.codeproject.com/Articles/23517/How-to-Properly-Handle-Cross-thread-Events-and-Upd to get me to where I am now.
Thanks
How about something like this:
// Added the form's class declaration to highlight separation of thread code into a separate class, but may not be exactly the same as yours depending on naming
public class Form1 : Form
{
private readonly DataRetriever _dataRetriever;
private void form_main_Shown(object sender, EventArgs e)
{
// Set the loading text.
list_selection.Items.Add(ListHelpers.LoadingItem());
// Create the DataRetriever, and provide it with a delegate to DisplayList for returning data
_dataRetriever = new DataRetriever(DisplayList);
// Start retrieving data on a separate thread...
_dataRetriever.GetData();
}
private void DisplayList(List<ListBoxItem> itemList)
{
if (InvokeRequired)
{
// Ensure the update occurs on the UI thread
Invoke((Action)(() => DisplayList(itemList)));
return;
}
// Display each result
list_selection.Items.Clear();
foreach (var item in itemList)
{
list_selection.Items.Add(item);
}
}
}
// Separate class to hold thread code
public class DataRetriever
{
public delegate void UpdateCallbackDelegate(List<ListBoxItem> itemList);
private readonly UpdateCallbackDelegate _updateCallback;
public DataRetriever(UpdateCallbackDelegate updateCallback)
{
_updateCallback = updateCallback;
}
public void GetData()
{
var thread = new Thread(GetInvoicingData)
{
IsBackground = true
};
thread.Start();
}
private void GetInvoicingData()
{
// Not sure whether "DAC" is a static class, if it needs to be constructed
// in the DataRetriever's constructor, or passed to it as a parameter
_updateCallback(DAC.GetInvoicingAccounts());
}
}
As you can see, all the thread code is now in a separate class DataRetriever, and a delegate provided when constructing it to enable the retrieved data to be passed back to the form once the retrieval is complete. The method that handles the callback ensures that the call is marshalled to the UI thread to prevent cross-thread exceptions.
I would like to point out that this is not presented as the "best" way to do this, but merely as an answer to the question (how to separating threading code into a separate class). As others have mentioned, there are already mechanisms in place to do this sort of thing (e.g. BackgroundWorker). Some complexity has been omitted for clarity. For example, in the implementation presented here, if you were to call GetData() multiple times (with each call occurring before the previous ones have returned their data), you would have multiple queries occurring simultaneously, and as they are running asynchronously, may return their data in an arbitrary order. This may or may not be an issue in your case.
I'm trying to update a text box from a class called 'hex' to the main form. Within the class 'hex' I have the following code:
Main m = new Main();
m.updateTextBox(convertedHex);
the code passed the variable to the main form to the method called 'updateTextBox' as shown below:
public void updateLog(string input)
{
textBox2.AppendText(input);
}
Sorry if this seems like a silly questions I have been stuck for a while, all the links on my google searches are now purple so I was hoping if someone could explain this to me. Many thanks.
Add this kind of method inside your Main class where textBox is created and call it from outside.
Lets say you added the code in your Program.cs class to start new
// Add this code in Program.cs (or similar where you start the gui
public static readonly Main MainLogWindow = new Main();
// Add this code in Main.cs class
private delegate void NameCallBack(string varText);
public void UpdateTextBox(string input) {
if (InvokeRequired) {
textBox.BeginInvoke(new NameCallBack(UpdateTextBox), new object[] {input});
} else {
textBox.Text = input;
// textBox.Text = textBox.Text + Environment.NewLine + input // This might work as append in next line but haven't tested so not sure
}
}
Call it like: Program.MainLogWindow.UpdateTextBox("test test"); from anywhere assuming that you have MainLogWindow open
This will also allow you to call updates from within other threads.
You have not given us very much information to go on. But as I said in my comment if your startup form is Main, the code that you are showing is creating a new Main Form and any changes made to it will not appear in your UI. You need to pass the form instance to the Hex class constructor. I would do something like this(assuming that the namespaces are the same, they are on the same thread, and your Hex Class is not Static. if on different threads you need to use the Method shown by MadBoy)
public partial class Form1 : Form
{
Hex hex;
public Form1()
{
InitializeComponent();
hex = new Hex(this);
}
}
class Hex
{
Form1 m;
public Hex( Form1 frm)
{
m = frm;
m.updateTextBox("Hello World");
}
}
Your class, presumably a business object, generally shouldn't be concerned with updating the UI. It doesn't particularly need to know that you even have a UI. But there are a couple of different useful approaches you could use.
1) Simply have your UI invoke your business object's method, and let the method return a value, and then the UI can choose to display it.
// inside Main form
var hex = new Hex();
string convertedHex = hex.GetConvertedHex(someArgument);
UpdateTextBox(convertedHex);
2) Have your business object expose an event. The arguments for the event would include whatever string that needs to be broadcast to whomever subscribes to the event. The UI would then be one of the subscribers.
Of the two ideas, I would generally opt for the first unless you actually do need an event model.
jest simple no need to do all of this make text box public from the properties and pass the current form object to the class throudh a method like this
public void mthod(){
//crete a obj of the class
cls1 obj=new clas1();
obj.smethod(this);
}
now in the class can cal it like this
smethod(from1 obj){
obj.textbox.text="";
}
I have a layered worker class that I'm trying to get progress reports from. What I have looks something like this:
public class Form1
{
private void Start_Click()
{
Controller controller = new Controller();
controller.RunProcess();
}
}
public class Controller
{
public void RunProcess()
{
Thread newThread = new Thread(new ThreadStart(DoEverything));
newThread.Start();
}
private void DoEverything()
{
// Commencing operation...
Class1 class1 = new Class1();
class1.DoStuff();
Class2 class2 = new Class2();
class2.DoMoreStuff();
}
}
public class Class1
{
public void DoStuff()
{
// Doing stuff
Thread.Sleep(1000);
// Want to report progress here
}
}
public class Class2
{
public void DoMoreStuff()
{
// Doing more stuff
Thread.Sleep(2000);
// Want to report progress here as well
}
}
I've used the BackgroundWorker class before, but I think I need something a bit more free form for something like this. I think I could use a delegate/event solution, but I'm not sure how to apply it here. Let's say I've got a few labels or something on Form1 that I want to be able to update with class1 and class2's progress, what's the best way to do that?
Using events is the most straightforward solution. When you subscribe to the event from the main thread, the handler should check the Control.IsInvokeRequired to know whether it must call itself again through Invoke(...) to get the message passed to the right thread.
John is correct. You want to utilize events and for that you'll need to use a delegate or delegates. This might give you some ideas.
http://www.yoda.arachsys.com/csharp/threads/winforms.shtml
If you do not want to block the processing threads during notification, you can use Control.BeginInvoke() for fire & forget behavior.
To decrease the number of calls and update progress on a regular interval, you may want to encapsulate the states of different operations in classes.
This way you can just write states to e.g. volatile fields - of presumably another, aggregate-state class - and use a timer on the GUI thread to re-read state and refresh labels accordingly.