AppController.mm not found

First, Unity doesn’t support file sharing such as OneDrive or DropBox. Doing so may seem to work great for some amount of time but you are almost certainly going to lose data at some point in your project, or have mysterious errors.

Instead, use source control. See below:

Second AppController.mm (and all .mm files) are related to Apple / iPhone building, not Android, so I dunno what’s going on there.

Android build not building:

Recently (circa July 2022) there have been reports of Unity’s installer failing to install the Android Tools.

If it’s not that, then here’s how to troubleshoot:

First, make a blank project with a single blank scene and prove that it builds successfully.

If it does NOT build, then go fix your Unity installation, or your other tools, such as Android SDK, NDK, JDK, etc.

Until you can build a blank project to the target platform, don’t fiddle with anything else.

Once you can build a blank project, now bisect the problem by bringing over parts of your current project and building it one subsystem at a time, perhaps stubbing things out that might trigger compiler errors.

Most often things that prevent building are third-party libraries such as Firebase.

Once you identify the subsystem, go to the documentation for it and make sure you are doing it correctly.

It may also be helpful to work through a tutorial or two for that subsystem.

I’m sorry you’ve had this issue. Please consider using proper industrial-grade enterprise-qualified source control in order to guard and protect your hard-earned work.

Personally I use git (completely outside of Unity) because it is free and there are tons of tutorials out there to help you set it up as well as free places to host your repo (BitBucket, Github, Gitlab, etc.).

You can also push git repositories to other drives: thumb drives, USB drives, network drives, etc., effectively putting a complete copy of the repository there.

As far as configuring Unity to play nice with git, keep this in mind:

Here’s how I use git in one of my games, Jetpack Kurt:

Using fine-grained source control as you work to refine your engineering:

Share/Sharing source code between projects:

Setting up an appropriate .gitignore file for Unity3D:

Generally setting Unity up (includes above .gitignore concepts):

It is only simple economics that you must expend as much effort into backing it up as you feel the work is worth in the first place. Digital storage is so unbelievably cheap today that you can buy gigabytes of flash drive storage for about the price of a cup of coffee. It’s simply ridiculous not to back up.

“Use source control or you will be really sad sooner or later.” - StarManta on the Unity3D forum boards