title: Save last emitted value of stream in Dart
body: <p>I make an app using firestore and a bottom navigation bar in Flutter. The problem is that when I switch between tabs, the build method is called everytime. The build method downloads data from firestore. Therefore, the app flickers when I switch tabs (the spinning bar is showed for a very short time). I tried to fix this by moving the firestore stream to the constructor. However, since the stream can emit before the build method, it loads forever. </p>
  
  <p>A solution could been to save the last value that was emitted. I tried to fix this using the shareReplay method in Rx, but they have not implemented in RxDart yet. So, what is the best practice to implement this?</p>