Use resources in WPF

I make a bitmap build action to "Resource"
And use it like
BitmapSource="Imags\\1.png";

it works fine .

The dir looks like :

FolderA \ UI \ App2.xaml
FolderA \ UI \ Images\1.png
FolderB \ UI \ App1.xaml

As I mentioned , App2.xaml use resource fine . How can I use the resource in the App1.xaml ?

Thanks very much. ....

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To be code or not . It is a problem.