Generally, “A System Image Must be Selected to Continue “ is an android studio error, encountered when attempting to run your Android application through Android Virtual Device(AVD), sometimes this error can read as, “No System Images available. Are you connected to the internet?”.
This error tells you that, intel x86 atom system image is not available in the android SDK.
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How to solve System Image Must be Selected Error in android studio 3.0 and above
This error is encountered for most new installations of the android studio. To solve this error, just create a new application and attempt to run, you might see this message on your screen: “No System Images available. Are you connected to the internet?” That simply tells you that you will need to be connected to the internet to download Intel x86 atom system image.
On the AVD screen, you will see a refresh button at the bottom of the window, click it to refresh System Images from the internet. Please have a look at the image below
After refresh, several links will appear, select your preferred image according to the version of android you would like to test your applications on. Then accept software license and install into your SDK as shown in the image below
Please note download may take a while, again it might depend on your internet connections. Now you are ready to test Android applications on Android Virtual Device.