This button disappeared from a new 3.1 version of AS Toolbar. Before it showed as:
Now it\'s missing:
Is is available from menu. Tools > Android
disappeared, so find it in File > Sync Project with Gradle Files
.
For me I did following to make it visible:
You should see the Updated Android.MainToolBarGradleGroup as follows:
In Android Studio under 3.1 it's placed in
Tools > Android > Sync Project with Gradle Files
You can use this shortcut Ctrl + Shift + A to get not only sync but also other action if you found trouble to get them.A window will appear and you can type some command that you would like IntelliJ to run. Just type "sync" in there and it will find that command Sync Project with Gradle Files, even if it's not visible on the menu.
I had to open /android/ on its own in Android Studio (you can click Open for Editing in Android Studio in the top right corner) and then you have this options in the toolbar and in File/Synch Project with Gradle Files (when viewing .gradle file).
It hasn't disappeared. They have just moved it between the Save and Sync files button on the far left end of the toolbar.
Edit: They like to keep playing with the toolbar.
Since Android Studio 3.3, the icon has been updated and moved back across to the right: