I am trying to create a user interface using XAML. However, the file is quickly becoming very large and difficult to work with. What is the best way for splitting it across
You can split up XAML files by using a ResourceDictionary. The ResourceDictionary can be used to merge other files:
In the ResourceDictionary, you can also declare Styles that you can use at your elements, such that the main XAML file gets smaller.
Another possibility to get a smaller XAML file is to define your own controls that you then use in your main app.