如何在XAML public中创建一个控件，以便在其他类中看到

I'm working in wpf application i made a checkbox in the XAML, then my code calls a function in a class and in this function there is an if condition where its checking on whether the checkbox is checked or not but the checkbox is not seen in this class, so how to do this?I'm working in wpf application i made a checkbo