How to enable XAML Designer Window display in Visual Studio 2017?

Question

.NET

How to enable XAML Designer Window display in Visual Studio 2017?

Answer 1

create a WPF or UWP app and it opens fine by itself. otherwise it is not needed.
all designers in the studio (including WinForms) process layout files in conjunction with the code (although forms have code, only generated according to the designer's rules), therefore, designers are not available outside the project
if you have WPF or UWP - specify the problem

Answer 2

Judging by the picture, your studio separated xaml and xaml.cs, and did not understand them as a common entity. And now the xaml is showing as a plain text file. Perhaps the studio did not understand what type of template this project is (maybe the project is not newly created, but connected to an existing one?).
Create a new project in the same solution with the type WpfApplication and try the designer in it. Compare the csproj files between your defective project and the newly created project.