Android SDK version error- how to downsize(?)

Question

I had two API version(21,27) in my SDK platform and my Virtual Device was also targeting API 21. The problem was MediaPlayer in my MainActivity was not working. I checked volume , it was obviously turned on but could here no sound. So i thought the higher API version(In my case, API 27) might be causing the problem so i uninstalled it. and now every singe code has turned into red-which means error occured)as u can see. enter image description here

would you give insight of what is the cause and how to fix it? Thanks you so much in advance.

Answer 1

download every api version and try

start with api 27 and keep coming down but you don't have to delete the sdk version

Answer 2

You just need to click the "Sync Project with gradle file", available in AndroidStudio

This will also download necessary SDK version in case missing.

Answer 3

Latest android studio version should use latest build tools and better to target with current popular version just like:

your project build.gradle should set like that:

    compileSdkVersion 26
    buildToolsVersion "27.0.3"
 defaultConfig {
        minSdkVersion 21
        targetSdkVersion 27

set your min support sdk if the app support from SDK 21 to 27. Should install back the latest sdk 27