Android Multi-Phone Debugging

I’m working on an application that uses Android’s WiFi P2P functionality so that two phones can communicate directly with each other. Because of the nature of this application, I need to have two instances of this program running at once. The only problem is that Android Studio only let’s me have one debug target at a time. I thought of a few potential solutions.

  • * Deploy to one phone, start the application, then start debugging on the second
  • * Use a second computer and have each phone connected to a computer

Both of these solutions have shortcomings. They are both rather cumbersome. While this isn’t a supported scenario yet, there’s a better solution. We can use two instances of Android Studio on the same computer to open the project. We need a little bit of support from the operating system to pull this off. Android will otherwise see that we are opening a project that is already open otherwise. Before doing this, we need to make a symbolic link to our project.

A symbolic link is an entry in the file system that has its own unique path but points to existing data on the file system. Using symbolic links, a single file could be accessed through multiple paths. To Android Studio, these are two separate projects. But since it is the same data streams on the file system, the two “instances” will always be in sync. There are some files are are going to be unique to one instance or the other, but we will cover that in a

Symbolic links are supported on Windows, macOS, and on Linux. To make a symbolic link on macOS, use the ln command.

ln -s /original/path /new/linked/path

On Windows, use the mklink command.

mklink /j  c:\original\path c:\linked\path

Make sure that Android Studio is closed. Make a copy of your project’s folder. In the new copy that you just made, you are going to erase most of the files. Delete the folder app/src in the copy. Open a terminal and navigate to the root of the copied project. In my case the original project is called P2PTest and the other is called P2PCopy. To make the symbolic link for the src file I use the following command.

ln -s ../P2PTest/app/src app/src

Some other resources that I’ve looked at suggest doing the same thing for the the project’s build.gradle and the build.gradle for each module. For simple projects, the only module is the app. I tried this and while it worked fine for the project’s build.gradle, I would always get errors about a broken symbolic link when I tried with the build.gradle at the module level. In the end, I only did this for the project level.

## ln -s ../P2PTest/app/build.gradle app/build.gradle ## this line had failed results
ln -s ../P2PTest/build.gradle build.gradle

Because I could not make changes to the module’s build.gradle, if there are changes made to it then it will need to be copied between the instances of the project. Thankfully, most changes to a project will be in the source files. While it is possible to edit the source files from eithe project, I encourage only editing from the primary project. This will help avoid situations where you have unsaved changes to the same file in different editors and have to manually merge them.

When you are ready to debug, you can set one instance of Android Studio to one of your phones, and the other instance to the other phone. Here, I have two instances set to deploy to a Galaxy Note 5 and a Galaxy Note 8.

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