Confusion with typecast of nullable bool in getter method of a property

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Dear experts
I have the following test code:

C#

public class Person : INotifyPropertyChanged
{
    private bool? valid;

    public bool Valid
    {
        get
        {
            // Test only, expecting an exception in the next statement.
            valid = null;

            // Exception of typecast only shown while debugging *1)
            return ((bool)valid);
        }
        // ....
    }

    // ....
}

*1) typecast
Here I expect an exception and in debugger the exception will be shown.
But running the application _without_ debugger no exception will be shown, but there is one... only not shown. Btw, I do not have any try/catch which hides the exception.

This in contrast to ...

C#

private void buttonNullableBoolTest_Click(object sender, EventArgs e)
{
    bool? nullableBool = null;
    bool testBool= (bool)nullableBool; 
}

... which throws and Shows also _without_ debugger the exception "System.InvalidOperationException: Nullable object must have a value."

The question is: Why the application does not show the exception?
Any idea, what I do not understand/misinterpret this time here?
Thank you in advance.

[Edit]
Sorry, now after some more tests I see that I need to be more precise in my question.

a.) In case I access the property directly in my code e.g. if (person.Valid)... then the exception is shown also out of debugger. So here everything is like expected.

b.) But in case I bind the property to e.g. a button's Enabled property by the help of BindingSource than the app does not show the exception. It looks like .NET does hide the exception in this case :(

[Edit2]
Only for information: Binding directly in code with buttonBindingTest.DataBindings.Add(new Binding("Enabled", person, "Valid")); does also works with the expected behaviour (the app does show the exception one time).... but with the side effect that Binding will disappear :confused:

What I have tried:

Described in the question above.

Posted 22-Jul-16 0:03am

User 11060979

Updated 22-Jul-16 3:06am

v6

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Comments

Rob Philpott 22-Jul-16 6:34am

Just a thought, but is it something to do with the thread you're on? The second example clearly happens on the gui thread, but the NotifyPropertyChange suggest that a second thread might be in play.

That's the sort of thing the debugger may be being helpful with.

[no name] 22-Jul-16 6:39am

Thank you for your comment. Both tests running on a very simple test app, no threads nothing Special else.

BillWoodruff 22-Jul-16 8:08am

May I suggest that sometimes it is a waste of time to try and deeply analyze how the compiler and run-time behave when you are trying to force .NET to do something that doesn't quite make sense ? Why not just make the Property Type a nullable bool and get back to work.

[no name] 24-Jul-16 2:42am

Thank you for your feedback. You wrote "... that sometimes it is a waste of time ..."

Yes and no; why I tried to analyze this in deep?
a.) There is always a chance - at least if I write the code - that there is a bug. And in case such a bug is silently catched, it is hard to find it.
b.) I could not believe, that .NET catches silently an exception without giving me a chance to know about it.

Finally I found at MSDN, that .NET does support that I will be informed:
Event: BindingSource.DataError
Description: Occurs when a currency-related exception is silently handled by the BindingSource.
https://msdn.microsoft.com/query/dev11.query?appId=Dev11IDEF1&l=DE-DE&k=k(System.Windows.Forms.BindingSource.DataError);k(TargetFrameworkMoniker-.NETFramework,Version%3Dv4.5);k(DevLang-csharp)&rd=true[^]

Philippe Mori 22-Jul-16 9:19am

I would guess that binding simply do not update value if an exception is thrown similar to what would happen if you bind to a property that do not exist.

[no name] 22-Jul-16 9:21am

It's much worse, in some Situation the app completely freezes.

3 solutions

Solution 1

try this

C#

bool? nullableBool = null;
       bool? testBool = (bool?)nullableBool; // validate the testBool before usage

       // or

       bool? nullableBool = null;
       bool testBool = nullableBool.HasValue ? nullableBool.Value : false;  // if null, it will be assigned as false

for Nullable Types use HasValue Property [^]

Posted 22-Jul-16 0:22am

Karthik_Mahalingam

Updated 22-Jul-16 0:23am

v3

Comments

[no name] 22-Jul-16 6:25am

Thank you for your reply. I know how to manage it correctly. But the question is why I don't get an exception message for the getter method when I run the app without Debugger.

Karthik_Mahalingam 22-Jul-16 6:31am

i tried to run that without debugging in console app
i still get the exception "Nullable object must have a value."

[no name] 22-Jul-16 6:38am

Thank you for your Feedback.

Karthik_Mahalingam 22-Jul-16 8:12am

welcome :)

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Richard Deeming · Accepted Answer · 2016-07-22T03:06:00

Solution 3

The BindingSource is the reason. It suppresses exceptions thrown when reading the properties. You have to subscribe to the BindingComplete event to see the errors:
How to: Handle Errors and Exceptions that Occur with Databinding[^]

Posted 22-Jul-16 3:06am

Richard Deeming

Comments

[no name] 22-Jul-16 9:08am

Yeah great, thank you very much. So basically my mistake using Binding witout reading the documentation :)

/[Edit]
Only for Information: This does solve "only" the Problem during binding process, but not when the exception happens after successful binding.

OriginalGriff · Accepted Answer · 2016-07-22T00:28:00

When I try it in my app built for release I do get a runtime error: "Nullable object must have a value."

C#

Person p = new Person();
Console.WriteLine(p.Valid);

So I would suspect you have a try - catch somewhere which is picking up on it.
Check your settings for debug:
"Debug" menu..."Exceptions..."
In the dialog, check the "thrown" and "user-unhandled" columns and see if there is anything you can do to get the same results as the release version.

[Update]

Sorry for the delay...I was thinking! (And that takes me some time...)
I can duplicate your problem and get an exception in VS but not when "live" very simply, without using a BindingSource, just by moving the Valid getter access to a different thread:

C#

    {
    BackgroundWorker work = new BackgroundWorker();
    work.DoWork += work_DoWork
    work.RunWorkerAsync();
    }

void work_DoWork(object sender, DoWorkEventArgs e)
    {
    Person p = new Person();
    Console.WriteLine(p.Valid);
    }

Which implies that the bound event is being executed on a different thread, which "swallows" the exception for some reason.

So... What I suspect is happening: the DataBinding is executing the code on a different thread, and when the exception is unhandled, the system shuts down the thread and doesn't notify you outside of the debugger.
A quick test:

C#

    BackgroundWorker work = new BackgroundWorker();
    work.DoWork += work_DoWork;
    work.RunWorkerAsync();
    ...
void work_DoWork(object sender, DoWorkEventArgs e)
    {
    try
        {
        Person p = new Person();
        Console.WriteLine(p.Valid);
        }
    catch (Exception ex)
        {
        File.WriteAllText(@"D:\Temp\aaaaa.txt", DateTime.Now.ToString() + " " + ex.Message);
        }
    }

And the exception is logged each end every time.

What do you do about it? Good question: I'd suggest a try-catch but exactly where you put it, I don't know...

Confusion with typecast of nullable bool in getter method of a property

3 solutions

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Solution 1

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