I'm creating a library which relies on capturing the SynchronizationContext in order to post callbacks back to the UI thread.
A user was having a weird condition where the callbacks were being posted to the ThreadPool instead. After investigating a bit, I came up with the following two test cases:
1:
public partial class Form1 : Form
{
private Test test;
public Form1()
{
test = new Test();
InitializeComponent();
}
private class Test
{
public Test()
{
if (SynchronizationContext.Current == null)
throw new InvalidOperationException("It's null! :(");
}
}
}
2:
public partial class Form1 : Form
{
private Test test = new Test();
public Form1()
{
InitializeComponent();
}
private class Test
{
public Test()
{
if (SynchronizationContext.Current == null)
throw new InvalidOperationException("It's null! :(");
}
}
}
The 1st test runs fine, but the 2nd one throws an exception. Why?
In the second example new Test() runs (almost) as the very first code in the program. Probably, your Main function calls new Form1() which immediately calls new Test().
A SynchronizationContext must be set before it is present (obviously). There is nothing magic in the runtime that guesses that your app will use WinForms. Using WinForms is a dynamic runtime decision. WinForms will set its SynchronizationContext when you use WinForms (I forgot the exact trigger points).
In the first example the base constructor (new Form()) runs first which apparently installs the SynchronizationContext.
When you run code before any WinForms code runs no SynchronizationContext will/can be present.
There is nothing sane that your library can do about this. You could add an assert or manually set the WinForms sync context (there is a API for that) but that is hardly the business of a library. Libraries are not supposed to mess with global state. (Except if your library is clearly meant for WinForms-only use).
Related
I have two files, form1.cs and parser.cs. When I called my update method for NPCLogger.Text in the form1.cs file it works. but when I call it from parser.cs it does not? I've tried a lot of other solutions online and can't seem to get it working.
form1.cs
public void updateConsole(string text)
{
NPCLogger.Text += text;
}
private void ParseButton_Click(object sender, EventArgs e)
{
Parser parser = new Parser();
string link = UserLink.Text;
parser.Parsing(link);
updateConsole("12312"); // this works
}
parser.cs
public class Parser : Form
{
public bool debug = false;
public string aggroRadius = null;
public void Parsing(string userLink)
{
updateConsole("This does not work");
The compiler error you're seeing (but not including in the question...) is telling you that there is no updateConsole method in the Parser class. (Unless you've added one, and didn't include that in the question. In which case... what on Earth does that method do and why are you expecting a method on a different class to be invoked?)
When you attempt to call a method that's in the Parser class from the Form1 class, note how you do that:
parser.Parsing(link);
You don't just call Parsing(link) by itself, you call it on the parser variable, which is an instance of the Parser class. So, when you want to call a method that's in the Form1 class from the Parser class, why do you expect it to be any different?
You need a reference to your Form1 object. Given the code shown, probably the simplest way is to add it to the Parser constructor:
private Form1 form1Instance { get; set; }
public Parser(Form1 form1)
{
this.form1Instance = form1;
}
And pass the reference when calling the constructor:
Parser parser = new Parser(this);
Then, in Parser, you can use that property to reference the object:
this.form1Instance.updateConsole("This does not work");
As an aside... You're digging yourself into a rabbit hole. Now you have two forms trying to directly interact with each other's UI controls. It's going to get unwieldy quickly.
A form should be responsible for its own UI controls. Models/objects (not forms) should encapsulate the core logic of the application. Any given form would invoke that logic and use the returned result to update its UI.
I found a suggested solution to the cross-thread exception issue in another posting and have used it my code below, but I am finding it erratic at best. My tests indicate that it's correct operation is at the mercy of a race condition so I was hoping someone might be able to point out the obvious or provide a more robust solution.
I have a program with two simple forms, where the sole purpose of Form1 is to open Form2. Form2 only contains a RichTextBox and has code that starts a thread that accesses that RichTextBox in an arbitrary way. When execution reaches the InvokeRequired property it is usually (but not always) false, so it goes directly to the RichTextBox access where a cross-thread exception is generated. However, when I call Thread.Sleep(...) just before testing the InvokeRequired property it appears to work properly. However, I hate to use Sleep for this purpose simply because it seems like a kluge that may not always work. Is there a reliable, yet reasonable, way to do cross-thread communication? Thanks.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
var form2 = new Form2();
form2.ShowDialog();
}
}
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
Thread myThread = new Thread(new ThreadStart(myStartingMethod));
myThread.Start();
}
void myStartingMethod()
{
Test("Hello world!\n");
}
private delegate void myCallback(string text);
private void Test(string text)
{
// If I put Thread.Sleep(...something...) here it works better.
if (myRichTextBox.InvokeRequired)
{
myCallback d = new myCallback(Test);
Invoke(d, new Object[] { text });
}
else
{
// Cross-thread exception usually occurs, but not always.
int x = myRichTextBox.TextLength;
}
}
}
Update: Solution arrived since and is now accepted. Due to the clarity of the pseudo codes on this question the solution took only a few seconds. Trying to figure out the solution from the other seemingly "duplicate" questions took a lot of time already. I had the solution in 20 minutes from the moment I asked this question. So it is not a duplicate, probably the clearest of them all to date.
While several similar questions have been asked on this, I was still not able to put together a working code from them. My main application is not on a form, but in a separate class that is a plugin and executed by a host application.
So while it seems a duplicate question it is not. Please read on.
I have my main class doing stuff. Then I have a form that displays information to the user. I need to hide this form when the user switches away from the application (host application loses focus).
I am using very limited APIs so the only methods I have at my disposal events triggered by the host application.
I created a timer that fires every 100ms and checks whether the user had the application in focus. And if not a command is sent to the form to hide itself.
The reason for this approach is because the host application loosing focus is just one of the many scenarios that I need to hide the form and I need to channel all these through the same exact method.
All works from within the rest of the classes (the Hide() method is called from the rest of the application no problem.
But it does not work when the timer calls the Hide() method, because the timer is on a different thread when it fires. So the call becomes a cross-thread call.
The very specific question is that I need an exact sample code how to make this call from the timer event handler to the form's Hide() method thread-safe with Invoke.
Thanks.
This is the timer:
private void Controllel_Opened(object sender, EventArgs e)
{
myTimer.Elapsed += new System.Timers.ElapsedEventHandler(DisplayTimeEvent);
myTimer.Interval = 50;
myTimer.Start();
}
public static System.Timers.Timer myTimer = new System.Timers.Timer();
// This method checks different scenarios when the tool tip should be hidden and calls the hiding method
public static void DisplayTimeEvent(object source, System.Timers.ElapsedEventArgs e)
{
FormHandler.Hide();
}
Then the "FormHandler" class:
public static class FormHandler
{
private static Form1 frm1 = new Form1();
public delegate void Form1HideEventHandler();
public static event Form1HideEventHandler Form1Hide;
public static void Hide()
{
if (Form1Hide != null)
{
Form1Hide();
}
}
}
Then the form's code:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
FormHandler.Form1Hide += FormHandler_Form1Hide;
}
private void FormHandler_Form1Hide()
{
Hide();
}
}
I would like to get a solution with exact code if possible. Thanks.
private void FormHandler_Form1Hide()
{
if (InvokeRequired)
{
this.Invoke(new Action(() => { FormHandler_Form1Hide(); }));
}
else
{
Hide();
}
}
You need to use System.Windows.Forms.Timer instead. That will invoke back onto the dispatcher thread.
I'm trying to put some stuff that I use a lot into separate classes so it's easier to implement when starting a new project.
One of the things that I would like to do, is dynamically create a statusbar on my mainform. I have done this in a previous project and there it worked fine. So I copied the code and I changed the NameSpace for the mainform.
When I run the code it stops at the line
MainForm.Controls.Add(status);
When I look, it says Mainform is null.
Other than the Namespace I haven't changed anything.
Does anybody have an idea why this is happening?
Thanks
Kenneth
//THIS IS THE SEPARATE CLASS
public class Tools
{
public Form MainForm;
public void setupForm()
{
// LINK THE FORM
MainForm = myNamespace.Form1.MainForm;
// CREATE A STATUSBAR
StatusStrip status = new StatusStrip();
status.Name = "status";
// I'VE REMOVED SOME OF THE DYNAMIC CREATION STUFF FOR READABILITY
// ADD THE STATUSSTRIP TO THE FORM
MainForm.Controls.Add(status);
}
//THIS IS THE MAINFORM
public static Form1 MainForm;
public myNameSpace.Tools tools;
private void setupForm()
{
this.KeyPreview = true;
// LINK THE TOOLS CLASS
tools = new myNameSpace.Tools();
// SETUP THE FORM
tools.setupForm();
}
You have to pass a refernece of your main form to the Tools class. You can do this when you initialize tools or when you call the method setupForm. I implemented the second possibility for you:
//the call:
tools.setupForm(this);
//the implementation of the method
private void setupForm(Form1 MainForm)
{
//your method code
}
The normal way to separate responsibility is to inject the object you want to affect - not hijack it with a hardcoded reference.
Try injecting the form when you create your tools object:
tools = new myNameSpace.Tools(this);
Its null because you don't initiate or have a refference to the main window. You just create an alias for the namespace but not for the instance.
Pass the mainWondow as a parameter to the setupForm function. Then it will work.
Ok, I've got a strange problem. I am testing a usercontrol and have code like this:
[TestFixture]
public myTestClass : UserControl
{
MyControl m_Control;
[Test]
public void TestMyControl()
{
m_Control = new MyControl();
this.Controls.Add(m_Control);
Assert.That(/*SomethingOrOther*/)
}
}
This works fine, but when I change it to:
[TestFixture]
public myTestClass : UserControl
{
MyControl m_Control;
[Setup]
public void Setup()
{
m_Control = new MyControl();
this.Controls.Add(m_Control);
}
[TearDown]
public void TearDown()
{
this.Controls.Clear();
}
[Test]
public void TestMyControl()
{
Assert.That(/*SomethingOrOther*/);
}
}
I get an Object Reference Not Set To An Instance of an Object. I even output to the console to ensure that the setup/teardown were running at the correct times, and they were... but still it isn't newing up the usercontrols.
edit> The exact code is:
[TestFixture]
public class MoneyBoxTests : UserControl
{
private MoneyBox m_MoneyBox;
private TextBox m_TextBox;
#region "Setup/TearDown"
[SetUp]
public void Setup()
{
MoneyBox m_MoneyBox = new MoneyBox();
TextBox m_TextBox = new TextBox();
this.Controls.Add(m_MoneyBox);
this.Controls.Add(m_TextBox);
}
[TearDown]
public void TearDown()
{
this.Controls.Clear();
}
#endregion
[Test]
public void AmountConvertsToDollarsOnLeave()
{
m_MoneyBox.Focus();
m_MoneyBox.Text = "100";
m_TextBox.Focus();
Assert.That(m_MoneyBox.Text, Is.EqualTo("$100.00"), "Text isn't $100.00");
}
[Test]
public void AmountStaysANumberAfterConvertToDollars()
{
m_MoneyBox.Focus();
m_MoneyBox.Text = "100";
m_TextBox.Focus();
Assert.That(m_MoneyBox.Amount, Is.EqualTo(100), "Amount isn't 100");
}
}
I get the exception(s) at the respective m_MoneyBox.Focus() calls.
Solved - See Joseph's comments
I created a test case with exactly the same layout you presented here, but with a TextBox instead of a MyControl. I also added a constructor and a deconstructor and outputted all the various stages to the console to see the sequence of events. However, I never got an object reference exception.
In case you are interested, the sequence was [constructor called], [setup called], [test called], [tear down called]. The deconstruction never output anything to the screen for some reason.
My original thought was that the Controls property on myTestClass would not be initialized, but on my test it was, so I think it has something to do with your MyControl construction.
edit> I added the focus on my TextBox in my unit test as well but still no exception. Does your MoneyBox have any event handling going on behind the scenes during the Focus? That might be your culprit.
You haven't said where you're getting the exception, which would help - what does the stack trace look like?
It's very odd (IME) to derive from UserControl when you create a test fixture. Aside from anything else, I don't know that NUnit is going to call Dispose for you at any appropriate point... what's the purpose of it here? Can you not make your tests run with a "plain" test fixture?
I had exactly the same issue, so my apologies for answer to this old post.
The problem in your code (and mine) is that you are creating 2 different instances for MoneyBox and 2 more for TextBox. So, the initial assignation inside Setup, is valid only for Setup method and out_of_scope in the test methods.
Inside the Setup method you should use:
m_MoneyBox = new MoneyBox(); //GOOD
m_TextBox = new TextBox(); //GOOD
instead of
MoneyBox m_MoneyBox = new MoneyBox(); //BAD
TextBox m_TextBox = new TextBox(); //BAD
Just for anyone that could need it again