Dash progress bar during loading page

HI Everybody!

I try to make a dashboard where I have to do a lot calculation and preparation in my code before I can make my charts. So first I have to calculate the data, put them into pandas dataframes and after use them for my charts.

I can to this before I start the dash app.server but I would like to first load my dashboard and after calculate the data which I would like to visualize with a progress bar.

Can show somebody any example for this kind of solution?