Saving Data on Android

Adding security rules
Your 
WhatsUp
 app is still not safe. You'll add security rules next to restrict the 
access to data. Open Firestore database in the Firebase console and click on the 
Rules
 tab. Add the following rule:
service cloud.firestore { 
  match /databases/{database}/documents { 
    match /{document=**} { 
      allow read, write: 
if
 request.auth.uid != null; 
    } 
  } 
}
This rule allows 
read
 and 
write
 access on all documents for any signed in user. The 
allow
 expression specifies when the writing or reading the data is allowed.
When you're done with writing the rules to the editor click 
Publish
:
Usually, it takes a minute for the security rules to make an effect, but sometimes it 
can take up to 10 minutes. Before you start testing make sure you wait a couple of 
minutes.