Can't start a Handler on the main thread

I'm working on a .jar api to read Google Fit data from Unity3D. The problem that I'm facing right now is that when I want to execute this block of code:

private void buildFitnessClient() { mClient = new GoogleApiClient.Builder(myContext).addApi(Fitness.HISTORY_API) .addScope(new Scope(Scopes.FITNESS_ACTIVITY_READ_WRITE)) .addConnectionCallbacks(new ConnectionCallbacksListener()) .enableAutoManage(this, 0, new ConnectionFailedListener()).build(); }

I get the error: java.lang.IllegalStateException: Must be called from main thread of process

This error is due to the this reference in the last sentence of the line of code.

Now online I found that I could fix this by starting a Handler on the Main Looper, I tried this with this code:

new Handler(Looper.getMainLooper()).post( new Runnable() { @Override public void run() { try { buildFitnessClient(); } catch (Exception ex) { Log.i(TAG, ex.getMessage() + "\n"); } } });

For some reason my Unity app instantly crashes, usually I can get the error since I use a try catch statement. With this problem it instantly crashes and there is no log I can check.

When I create my Handler without the mainlooper, like:

new Handler()

or

new Handler(Looper.myLooper())

The code runs, but the java.lang.IllegalStateException error remains, and the Thread.currentThread() obviously remains the same.

The thread that the program runs on is a thread created by Unity.

Thanks in advance!