ERROR: Module 'app': platform 'android-28' not found. and Design editor is unavailable until after a successful project sync

Solution 1:

Go to Tools->sdk manager->install API Level 28 then restart.

Solution 2:

  1. go to Tools
  2. Select SDK Manager
  3. Under SDK Platforms select Android 9.0 (Pie) (API 28)
  4. Then Apply and Download the API

Solution 3:

I face the same problem. First, install API Level 28 & Restart the Android studio.

Solution 4:

First of all! you need to update your sdk manager that too essential tools are: build tools platform tools tools and android Emulator

.....

Now go to LOGCAT , click on configure sdk..... put it to latest and click autoconfig button for each bar.

thats it rebuild it! You are done with 100 percent% successful error solving, Your Activity.xml file will be displayed with out any warning or error!

Solution 5:

After reinstalling and upgrading my android studio to android 4, I faced the same challnge. but what I did was to go to tool->sdk manager and then install some other APIs including the error messages API 28 not installed and it works fine.