Android Emulator: Installation error: INSTALL_FAILED_VERSION_DOWNGRADE

It means you're trying to install an app with the same packageName as an app that's already installed on the emulator, but the one you're trying to install has a lower versionCode (integer value for your version number).

You might have installed from a separate copy of the code where the version number was higher than the copy you're working with right now. In either case, either:

• uninstall the currently installed copy

• or open up your phone's Settings > Application Manager to determine the version number for the installed app, and increment your <manifest android:versionCode to be higher in the AndroidManifest.

• or https://stackoverflow.com/a/13772620/632951

First uninstall your application from the emulator:

adb -e uninstall your.application.package.name

Then try to install the application again.

This was happening in my project because I was using an XML resource to set the version code.

AndroidManifest.xml:
android:versionCode="@integer/app_version_code"

app.xml:
<integer name="app_version_code">64</integer>

This wasn't a problem in prior versions of adb, however, as of platform-tools r16 this is no longer being resolved to the proper integer. You can either force the re-install using adb -r or avoid the issue entirely by using a literal in the manifest:

android:versionCode="64"

You can also consider adding -d flag to adb install. It should ignore this error.

adb install -r -d abc.apk