How to fix application.current.windows code?

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Hello, I have problem with Application.Current.Windows code. I don´t know, where is the problem. I found that the code should look like this:

C#

var window2 = Application.Current.Windows
    .Cast<Window>()
    .FirstOrDefault(window => window is Window2) as Window2;

and then

C#

var richText = window2.RadioButton

What I have tried:

I tried to modify to my code:

C#

var window1 = Application.Current.Windows
    .Cast<MainWindow>().FirstOrDefault(window => window is hra) as hra;
            var scitani = window1.scitani;

MainWindow is window where is the radiobutton with name scitani
hra is current window where I would like reference radiobutton

Error is: Cannot convert type 'type1' to 'type2' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion.

Can anyone tell me what to do with it?

Thank you

Posted 20-Apr-21 23:31pm

dejf111

Updated 20-Apr-21 23:52pm

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2 solutions

Solution 2

Cast tries to cast each element of the WindowsCollection to the new type, and if it isn't possible it throws the exception you have seen.
Cast<Window> works fine because every element in the collection is derived from Window - but unless every window in your application derives from MainWindow then your second version will fail.

Posted 20-Apr-21 23:52pm

OriginalGriff

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dejf111 21-Apr-21 5:57am

Thank you for advice!!!

OriginalGriff 21-Apr-21 7:08am

You're welcome!

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Richard Deeming · Accepted Answer · 2021-04-20T23:45:00

Quote:

C#

Application.Current.Windows.Cast<MainWindow>()

That will attempt to cast all open windows to MainWindow. If any of your open windows are of a different type, you will get this error.

Use OfType instead, and remember to check for null:

C#

MainWindow window1 = Application.Current.Windows.OfType<MainWindow>().FirstOrDefault();
if (window1 != null)
{
    var scitani = window1.scitani;
    ...
}

If you're absolutely certain that there will always be a MainWindow instance open, you could use First instead of FirstOrDefault, and skip the null check:

C#

MainWindow window1 = Application.Current.Windows.OfType<MainWindow>().First();
var scitani = window1.scitani;

NB: This will throw an exception if there are no windows of the specified type open.

Enumerable.Cast<TResult>(IEnumerable) Method (System.Linq) | Microsoft Docs[^]
Enumerable.OfType<TResult>(IEnumerable) Method (System.Linq) | Microsoft Docs[^]
Enumerable.FirstOrDefault Method (System.Linq) | Microsoft Docs[^]
Enumerable.First Method (System.Linq) | Microsoft Docs[^]