How to open 2 Visual Studio instances, with same Git projects and different branches

I need to open 2 Visual Studio instances: one will be to just look at the code of the Project X / Branch 1, and the other will be used to code in the Project X / Branch 2.

How can I do that without losing changes when committing?

The issue here isn't to do with Visual studio, but how Git works. When you check out a branch in git, it places that branch into your working tree or (file structure, whatever you wish to call it).

With git you can only have one branch checked out at a time, but wait there is a solution! By utilising the git worktree command, you can create a second worktree for the same repository in a different directory. You can then open that work tree in visual studio to have two different branches checked out.

Let's say you have C:\projects\the_project and you want to make a new work tree at e.g, C:\projects\the_project_2, open git bash, navigate to the project's directory and run

git worktree add ../the_project_2 <branch>

where is the branch you want checked out in the new work tree.

This will create a new directory "C:\projects\the_project_2") and checkout the branch into it, without having to re-clone the repository.

For more information see the git worktree documentation.

Note: Earlier versions of Visual Studio does not know how to treat additional work trees, and will not recognise them as git repositories.

If you need to open the code in Visul Studio it is necessary to checkout the branch. As you can't checkout two different branches in the same directory at the same time, you can't avoid to checkout each branch in a separate directory.

But you can set the remote of one directory to the other git directory, so that you can synchronize locally and don't Need to have any external.

Assume you want to have both branches as subdirectories of a root common directory ProjectX:

cd ProjectX
git clone -b branch1 <remote repo of project X> directory_branch1 
git clone -b branch2 directory_branch1 directory_branch2

Update May 2019: As git woorktree is now working and supported by GUI based tooling, this is probably the solution to use today.

If you don't care for the git connection of the source branch (the one you just look at but not modify), you can always make a copy of the folder containing the solution when said branch is active. then you can open a non-source controlled version of that branch once the target branch is active

"clone the repo twice to different directories" is the quickest easiest workflow as @ewan said in the comments.