I myself met in the use of the process issue, Baidu looking for a long time to find the right method.
Given as follows:
Emulator: emulator: ERROR: Unknown AVD name [Nexus_5X_API_29_x86], use -list-avds to see valid list.
Solution I saw there three：
1, re-create a simulator, this method is not valid to me.
pass out
2, the
copy avd under .android directory under your own computer to the next sdk path (ps: because the custom installation when I installed the sdk choice, so sdk path is not in the default path below, the default path of my computer is c: \ user \ 18242 \ sdk here and we may not the same for reference only) but this method is not valid to me.
So pass the
3、The solution to my problem, Is to modify your environment variables ANDROID_SDK_HOME, it will become a value corresponding platform-tools installation path under your sdk
my installation path is like this, you put your path corresponds to put on it, and then in the path in additional it 
here% ANDROID_SDK_HOME% = D: \ SDK_Android_studio
because I was in front of the set value ANDROID_SDK_HOME.
Append path is for the system to find the ADB, just in case and back problems.
This is the first time made the article, just wanted to pit himself in memory of the encounter, and if you are like, I did not indicate the source, then you do not mind, thank you.
up Liu
