How to fix Expected Android API level 21+ but was 19 in Android

Question

In my application i want get data from server, for get connect to server i used Retrofit, OkHttp.
But when running application, show me

Answer 1

Here I solve that problem downgrading this dependencies to this versions

api 'com.squareup.retrofit2:retrofit:2.3.0'
api 'com.squareup.retrofit2:converter-gson:2.3.0'
api 'com.squareup.okhttp3:okhttp:3.8.0'

And adding this code into onCreate of MainActivity

try {
      ProviderInstaller.installIfNeeded(this);
    } catch (GooglePlayServicesRepairableException e) {
      // Indicates that Google Play services is out of date, disabled, etc.
      // Prompt the user to install/update/enable Google Play services.
      GoogleApiAvailability.getInstance()
        .showErrorNotification(this, e.getConnectionStatusCode());

    } catch (GooglePlayServicesNotAvailableException e) {
      // Indicates a non-recoverable error; the ProviderInstaller is not able
      // to install an up-to-date Provider.
    }

Downgrade dependencies is neet because newest version need android API 21 or later.

That code above is to android update your security provider to protect against SSL exploits. See https://developer.android.com/training/articles/security-gms-provider.html to know more about it.