In the last few days I've been trying to learn how to use ASP.NET Web Forms together with multithreading the hard way by building a simple applet using both and I've been struggling with aspects of interactions between different threads and the UI.
I've resolved some multithreading issues in some other questions (and also learned after waaaaaay too long that web forms and WPF are not the same thing) but now I'm running into trouble finding the best way to update UI elements based on data acquired in multiple threads.
Here's my code:
Default.aspx
public partial class _Default : System.Web.UI.Page
{
private NlSearch _search;
private static int _counter = 0;
private static SortedList<long, SearchResult> resultsList = new SortedList<long, SearchResult>();
protected void Page_Load(object sender, EventArgs e)
{
_search = new NlSearch();
}
protected void AddSearchMethod(object sender, EventArgs e)
{
var text = SearchForm.Text;
new Task(() => MakeRequest(text));
}
protected void UpdateMethod(object sender, EventArgs e)
{
resultsLabel.Text = "";
foreach (var v in resultsList.Values)
{
resultsLabel.Text += v.SearchTerm + ": " + v.Count + " occurances<br/>";
}
}
protected void ClearSearchMethod(object sender, EventArgs e)
{
resultsLabel.Text = "";
resultsList.Clear();
}
protected void MakeRequest(string text)
{
_counter++;
SearchResult s = new SearchResult
{
SearchTerm = text,
Count = _search.MakeRequests(text)
};
resultsList.Add(_counter, s);
}
}
I've tried quite a few versions of the same basic thing. NlSearch.MakeRequest (called by MakeRequests) sends an HTTP POST request to an outside web site imitating a search bar input, and then extracts an integer from the markup indicating how many results came back.
The current simple UI revolves around a SearchForm textfield, an "Add Search" button, an "Update Label" button a "Clear Search" method, and a ResultsLabel that displays results. The AddSearch button creates a new task that calls MakeRequest, which calls the method to send the HTTP request and then stores the results in the order they were sent in a static sorted list.
So now ideally in a good UI I would like to just update the label every time a thread returns, however I've tried using ContinueWhenAll and a few other task functions and the problem seems to be that other threads do not have the ability to change the UI.
I have also tried running a new thread on page load that updates the label every few seconds, but this likewise failed.
Because I haven't been able to implement this correctly, I've had to use the "Update Label" button which literally just tells the label to display what's currently in the static list. I would really like to get rid of this button but I can't figuer out how to get my threads to make UI changes.
In general, trying to do threading in a web app is a bad idea. Web servers are designed for this, but spinning off new threads or processes should be avoided if at all possible. While there used to be a mechanism (and maybe there still is) to "push" results to a client, there are better solutions available today.
What you're describing is exactly the problem that AJAX is intended to solve.
You mentioned WPF in your question -- are you perhaps instead looking for a Windows application, like WinForms? I think that perhaps the term "web forms" has confused the situation. Web forms are just webpages with some (okay, a lot) of added in Microsoft functionality.
It sounds like you're trying to send updates to a webpage from a thread in code. The web doesn't work that way. I'd suggest reading through the ASP.NET Page Life Cycle Overview if you're actually trying to design webpages. Other answers have suggested AJAX functionality (which is where the web page executes some JavaScript that goes out and talks to a web server).
Have you ever hear about AJAX before? I think you're a thinking as application dev instead of web dev.
If you want to run your code asynchonous you may want to use the Async Await keywords instead of managing threads yourself. See information about Asynchronous Programming with Async and Await
Do not let your threads get tangled up ;)
Related
I have poked around here to try and find a resolved issue to help me solve my problem. Unfortunately I don't know enough about C# and Forms/Services to be able to interpret many of the answers, so I thought I'd post my issue here, in it's uniqueness, and see if I can get a sufficient answer.
I recently got an internship for a local company, learning C# and SQL to manage their shipping/inventory logistics.
I have gotten pretty good at creating windows forms with VisualStudios2017, and my knowledge of Java helps me pick up C# pretty quickly.
However, recently I was given the task of developing a Windows Service, which will run in the background, and do some repetitive task every minute or so.
Since I am familiar with the "Drag and Drop" techniques of adding features to windows forms, My supervisor suggested I use a Timer in my service, so, that's what I did, I did a "Drag and Drop" to add the timer component to my service, and renamed it "timerMainTick"
Here is My code. I want to start simple, all this code does is move to some local directory (henceforth referred to as $DIR), create a folder $DIR/GabbServiceDir, and make a text file $DIR/GabbServiceDir/AnotherTest.txt". However, every time the timer ticks, it is supposed to create (if it does not already exist) a new text document "$DIR/GabbServiceDir/Test.txt" and append the date-time to it every 2.5 seconds. This does not happen.
namespace GabbService
{
public partial class GabbService : ServiceBase
{
public string dir = "../../Users/Tyler/GabbServiceDir";
public GabbService()
{
InitializeComponent();
}
protected override void OnStart(string[] args)
{
Directory.CreateDirectory(dir);
timerMainTick.Interval = 2500; //miliseconds = 2.5seconds
File.AppendAllText(dir + "/AnotherTest.txt","asdiofbhjasdflikjbasdf\r\n");
timerMainTick.Enabled = true;
timerMainTick.Start();
}
protected override void OnStop()
{
}
private void timerMainTick_Tick(object sender, EventArgs e)
{
timerMainTick.Enabled = false;
File.AppendAllText(dir + "/Test.txt", DateTime.Now.ToString() + "\r\n");
timerMainTick.Enabled = true;
}
}
}
And a picture of the directory and it's contents after the service was started.
This is in Powershell, in $DIR/GabbServiceDir
PS C:\Users\Tyler\GabbServiceDir> ls
Directory: C:\Users\Tyler\GabbServiceDir
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a---- 6/23/2017 9:54 PM 72 AnotherTest.txt
PS C:\Users\Tyler\GabbServiceDir> cat .\AnotherTest.txt
asdiofbhjasdflikjbasdf
timerMainTick is Windows.Forms.Timer, and many of the solutions provided indicate to use a different kind of timer, the System.Timers.Timer.
This is all well and good, and may fix my problem, but the issue comes when trying to do something when this new type of timer ticks. When I double click the Windows.Forms.Timer in the Service Designer, it automagically writes a bunch of source, and gives me a method to begin writing code in, that magically executes when the timer ticks. I am not yet familliar with all of the magic that is going on in the backround, because I've only begun to learn C# as of the day I got this internship. I don't know what to name the methods for custom objects so that the "backround magic" will work, thus I am unable to interperate some of the solutions provided for problems similar to mine.
Perhaps someone could enlighten me.
For instance. Say I go into the Designer Source Code, and add a component
private System.Timer.Timer timerSystemTimer;
Then, in the Service source code and alter the method that was previously
private void timerMainTick_Tick(object sender, EventArgs e)
To
private void timerSystemTimer_Tick(object sender, EventArgs e)
I get an error immediately:
The more reading I do the more I see lots of event handlers being passed around and I have yet to comprehend what they do. Perhaps what I need is a link to some good literature. I am capable of looking for this on my own but I imagine many people here may have links to other bits of good literature more specific to what I want to comprehend here.
*Something I have found so far that may be useful to people in my situation:
https://msdn.microsoft.com/en-us/library/aa288459(v=vs.71).aspx
Error in VS - You added timerSystemTimer but did not remove timerMainTick component which still references timerMainTick_Tick as handler of it's Tick event. Compiler does not find this handler method anymore since you changed it to timerSystemTimer_Tick.
Adding different timer - Never modify designer file code. You could add a System.Timers.Timer instance to your class code, instantiate it in OnStart and provide handler for Elapsed event. Here's a sample for you.
I'm working on a really big project developed by two teams, one (mainly) for the database, and one (where I am) mainly for the GUI and helper classes as an interface between GUI and DB.
Obviously, there are errors in communication, and - of course - we can't assume 100Mbit bandwidth & super-fast server computer.
Language is C# .NET, target "framework" is WPF and Silverlight.
When a user clicks a button, the GUI asks the DB (through helper classes) for information. Let's say... pizza types. The server should answer "{Funghi,Frutti di mare,Prosciutto}". When DB sends his answer, we receive a "database.Ready" event and fill our datagrid.
BUT if the user clicks the button while we haven't received the answer yet, the GUI sends an another request to the database. And the whole system tries to serve the user.
But it can't, because when the second request is sent, the first is disposed when we want to read it. So NullReferenceExceptions occur.
I've solved this by implementing kind of a semaphore which closes when user input occurs and opens when the Ready event (the functions it calls) finishes working.
Problem:
If I don't receive the Ready event, no user input is allowed, but this is wrong.
Question:
Is there a common (or at least, working) solution to stop waiting for the Ready event and...
1) re-sending the request a few times, hoping we receive our pizza types?
AND/OR
2) Dropping the request, tell the user that database failed to send the answer, and re-open the semaphore?
I can't post code here as this code is the property of a corporation, I'd rather like to have theoretical solutions, which are okay for professionals too.
Sorry for the long post, and thank you for your answers!
I assume that you are already using a background thread to dispatch the query to the database and wait for it's response. You can use the Task API that was introduced in .NET 4.0 to cancel such a request. For that, you pass in a CancellationToken that signals the status to the executing task. You can obtain a CancellationToken via a CancellationTokenSource as shown in the following code:
public partial class MainWindow : Window
{
private readonly CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
public MainWindow()
{
InitializeComponent();
}
private void Button_CallDatabase(object sender, RoutedEventArgs e)
{
Task.Factory.StartNew(CallDatabase, _cancellationTokenSource.Token);
}
private void Button_OnNavigate(object sender, RoutedEventArgs e)
{
// If you navigate, you can cancel the background task and thus
// it will not execute any further
_cancellationTokenSource.Cancel();
}
private void CallDatabase()
{
// This simulates a DB call
for (var i = 0; i < 50; i++)
{
Thread.Sleep(100);
}
// Check if cancellation was requested
if (_cancellationTokenSource.Token.IsCancellationRequested)
{
Debug.WriteLine("Request cancelled");
return;
}
Debug.WriteLine("Update Controls with DB infos.");
}
}
Note that this example is simplified, you can and should use this in another component (e.g. view model).
If you still want to use the Ready event, you could also just unregister from it when you navigate away, so that no further actions will be performed when it is raised.
I am a very newbie programmer. Does anyone of you know how to do Web automation with C#?
Basically, I just want auto implement some simple action on the web.
After I have opened up the web link, i just want to perform the actions below automatically.
Automatically Input some value and Click on "Run" button.
Check In the ComboBox and Click on "Download" button.
How can I do it with C#? My friend introduce me to use Powershell but I guess .Net do provide this kind of library too. Any suggestion or link for me to refer?
You can use the System.Windows.Forms.WebBrowser control (MSDN Documentation). For testing, it allows your to do the things that could be done in a browser. It easily executes JavaScript without any additional effort. If something went wrong, you will be able to visually see the state that the site is in.
example:
private void buttonStart_Click(object sender, EventArgs e)
{
webBrowser1.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(webBrowser1_DocumentCompleted);
webBrowser1.Navigate("http://www.wikipedia.org/");
}
void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
HtmlElement search = webBrowser1.Document.GetElementById("searchInput");
if(search != null)
{
search.SetAttribute("value", "Superman");
foreach(HtmlElement ele in search.Parent.Children)
{
if (ele.TagName.ToLower() == "input" && ele.Name.ToLower() == "go")
{
ele.InvokeMember("click");
break;
}
}
}
}
To answer your question: how to check a checkbox
for the HTML:
<input type="checkbox" id="testCheck"></input>
the code:
search = webBrowser1.Document.GetElementById("testCheck");
if (search != null)
search.SetAttribute("checked", "true");
actually, the specific "how to" depends greatly on what is the actual HTML.
For handling your multi-threaded problem:
private delegate void StartTestHandler(string url);
private void StartTest(string url)
{
if (InvokeRequired)
Invoke(new StartTestHandler(StartTest), url);
else
{
webBrowser1.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler(webBrowser1_DocumentCompleted);
webBrowser1.Navigate(url);
}
}
InvokeRequired, checks whether the current thread is the UI thread (actually, the thread that the form was created in). If it is not, then it will try to run StartTest in the required thread.
Check out SimpleBrowser, which is a fairly mature, lightweight browser automation library.
https://github.com/axefrog/SimpleBrowser
From the page:
SimpleBrowser is a lightweight, yet
highly capable browser automation
engine designed for automation and
testing scenarios. It provides an
intuitive API that makes it simple to
quickly extract specific elements of a
page using a variety of matching
techniques, and then interact with
those elements with methods such as
Click(), SubmitForm() and many more.
SimpleBrowser does not support
JavaScript, but allows for manual
manipulation of the user agent,
referrer, request headers, form values
and other values before submission or
navigation.
If you want to simulate a real browser then WatiN will be a good fit for you. (Selenium is another alternative, but I do not recommend it for you).
If you want to work on the HTTP level, then use WebRequest and related classes.
You could use Selenium WebDriver.
A quick code sample below:
using OpenQA.Selenium;
using OpenQA.Selenium.Firefox;
// Requires reference to WebDriver.Support.dll
using OpenQA.Selenium.Support.UI;
class GoogleSuggest
{
static void Main(string[] args)
{
// Create a new instance of the Firefox driver.
// Note that it is wrapped in a using clause so that the browser is closed
// and the webdriver is disposed (even in the face of exceptions).
// Also note that the remainder of the code relies on the interface,
// not the implementation.
// Further note that other drivers (InternetExplorerDriver,
// ChromeDriver, etc.) will require further configuration
// before this example will work. See the wiki pages for the
// individual drivers at http://code.google.com/p/selenium/wiki
// for further information.
using (IWebDriver driver = new FirefoxDriver())
{
//Notice navigation is slightly different than the Java version
//This is because 'get' is a keyword in C#
driver.Navigate().GoToUrl("http://www.google.com/");
// Find the text input element by its name
IWebElement query = driver.FindElement(By.Name("q"));
// Enter something to search for
query.SendKeys("Cheese");
// Now submit the form. WebDriver will find the form for us from the element
query.Submit();
// Google's search is rendered dynamically with JavaScript.
// Wait for the page to load, timeout after 10 seconds
var wait = new WebDriverWait(driver, TimeSpan.FromSeconds(10));
wait.Until(d => d.Title.StartsWith("cheese", StringComparison.OrdinalIgnoreCase));
// Should see: "Cheese - Google Search" (for an English locale)
Console.WriteLine("Page title is: " + driver.Title);
}
}
}
The great thing (among others) about this approach is that you can easily switch the underlying browser implementations, just by specifying a different IWebDriver, like FirefoxDriver, InternetExplorerDriver, ChromeDriver, etc. This also means you can write 1 test and run it on multiple IWebDriver implementations, thus testing how the page works when viewed in Firefox, Chrome, IE, etc. People working in QA sector often use Selenium to write automated web page tests.
I'm using ObjectForScripting to automate WebBrowser, A Javascript callback to C# function and then function in c# extract data or automate many-thing.
I have clearly explained in the following link
Web Automation using Web Browser and C#
.NET does not have any built-in functionality for this. It does have the WebClient and HttpRequest/HttpResponse classes, but they are only building blocks.
You cannot easily automate client-side activity, like filling out forms or clicking on buttons from C#. However, if you look into JavaScript, you may be able to better automate some of those things. To really automate, you would need to reverse engineer the call made by clicking the button, and connect to the url directly, using the classes #John mentions.
I built a little web application that displays charts. I was thinking that it might be useful for the superuser of the app to do a complete data refresh, however this process takes around 10 minutes to complete. I was thinking perhaps the user could click a button that would start off a new thread to do a data refresh and subsequent clicks would kill the thread and restart the data population process. The user would then be free to browse about the site and view the charts as their data is populated.
Is there a simple method of accomplishing something like this?
You can twist ASP.NET to do this sort of thing, but it violates a few good general rules for ASP.NET development -- and could really cause problems in a server farm.
So, the most obvious route is to do this work in a web service. You can have the method return a chunk of HTML if you want. You could also add status methods to see how the thread is progressing.
Other options include: Handing the intense processing off to a database server (sounds like this might be a good use of OLAP) or, another cheap trick might be to set up the click to fire off a scheduled task that runs on the server. Can you provide some additional detail about the environment? Single server? Data storage platform, version of .net?
Ok, I didn't use either answer so here is what I did. I decided that it would be better if subsequent clicks would terminate instead of the currently executing one. Thanks for your answers guys.
//code behind
protected void butRefreshData_Click(object sender, EventArgs e)
{
Thread t = new Thread(new ThreadStart(DataRepopulater.DataRepopulater.RepopulateDatabase));
t.Start();
}
//DataRepopulater.cs
namespace DataRepopulater
{
public static class DataRepopulater
{
private static string myLock = "My Lock";
public static void RepopulateDatabase()
{
if(Monitor.TryEnter(myLock))
{
DoWork();
Monitor.Exit(myLock);
}
}
}
Are there any build in UI capabilities when using Windows Workflow..
Lets say I have a workflow that takes an hour to run where different activities are happening all the time. While it's running I want to see what activity is currently active, what activities have already ran etc..
Do I have to code this UI myself or does WF have built in features that graphically show the status etc of the workflow?
To find out which state a workflow is in, I subscribe to the WorkflowIdled event and do something like this:
private delegate void UpdateDelegate();
void workflowRuntime_WorkflowIdled(object sender, WorkflowEventArgs e)
{
StateMachineWorkflowInstance stateMachineInstance = new StateMachineWorkflowInstance(MyManager.WorkflowRuntime, MyInstance.Id);
UpdateDelegate LclUpdateDelgate = delegate()
{
// Update the workflow state on the form thread
if (stateMachineInstance.CurrentState != null)
LabelWorkflowState.Text = stateMachineInstance.CurrentStateName;
else
LabelWorkflowState.Text = "";
};
this.Invoke(LclUpdateDelgate);
}
There is no built in UI.
But you can create one, either by subscribing to events on the WorflowInstance (see other answer), or by using the Tracking Service.
The former is simple to set up for a quick solution but the latter will work with multiple host processes and long running (unloaded) workflow instances.
Check out the this code sample over at MSDN:
http://msdn.microsoft.com/en-us/library/ms741706.aspx