如何获取WPF中打开的窗口数的计数

Question

I have a requirement that, if one window is opened then user can not allow to open other window , for that I have tried following code.

if(System.Windows.Application.Current.Windows.Count == 0)
 {    
 //My code
 }

I am checking for currently opened window count, if it is greater then 1 then user can not open other window and that I will mention inside if statement,

but when I run this code it gives me the error

"Object reference not set to an instance of an object."

Any Solution

Answer 1

You would be probably getting this error because, even for the first windows to be loaded, you would be applying this check. For this you can apply null check in your code. and for list of loaded windows, you can get it using Application,

var loadedWindows = Application.Current.Windows.Cast<Window>()
                                               .Where(win => win.IsLoaded);

Answer 2

If you want to know how many windows are opened from your application instance, you can do this

 l_WindowCount = 0;

 foreach(var Window in App.Current.Windows)
 {
    l_WindowCount += 1
 }

if(l_WindowCount > 1)
{
//do what you want to do here
}