how to create block screen with circle loader : i am doing an app that does background job that can take some time
i want to show a loader in that time

I want a black screen with a simple loader in the front of it
and show it \ hide it, 
when i do actions in the background

i want to do a simple half black square with loader circle
that also blocks presses to the screen

like in this picture: 

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/P2vet.png

how can i achieve that and that ?
