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what could be the problem?
1.If you use Android emulator, please make sure your Android SDK location path if is changed by others applications(such as Android studio) like following screenshot. If this path is changed, all of your android emulator will missing.
2.Visual studio do not clean-rebuild your project after you make some changes(For example, change the target-framwork version) in your project. Please clean-rebuild your project when you meet the same issue at the nexttime.
Best Regards,
Leon Lu
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