问题

D:\rnworkspace\Hello>react-native run-android

JS server already running.
Running D:\Android\sdk/platform-tools/adb -s emulator-5554 reverse tcp:8081 tcp:
8081
Building and installing the app on the device (cd android && gradlew.bat install
Debug)...
:app:preBuild UP-TO-DATE
:app:preDebugBuild UP-TO-DATE
:app:checkDebugManifest
:app:preReleaseBuild UP-TO-DATE
:app:prepareComAndroidSupportAppcompatV72301Library UP-TO-DATE
:app:prepareComAndroidSupportRecyclerviewV72301Library UP-TO-DATE
:app:prepareComAndroidSupportSupportV42321Library UP-TO-DATE
:app:prepareComFacebookFrescoDrawee0110Library UP-TO-DATE
:app:prepareComFacebookFrescoFbcore0110Library UP-TO-DATE
:app:prepareComFacebookFrescoFresco0110Library UP-TO-DATE
:app:prepareComFacebookFrescoImagepipeline0110Library UP-TO-DATE
:app:prepareComFacebookFrescoImagepipelineBase0110Library UP-TO-DATE
:app:prepareComFacebookFrescoImagepipelineOkhttp30110Library UP-TO-DATE
:app:prepareComFacebookReactReactNative0392Library UP-TO-DATE
:app:prepareComFacebookSoloaderSoloader010Library UP-TO-DATE
:app:prepareOrgWebkitAndroidJscR174650Library UP-TO-DATE
:app:prepareDebugDependencies
:app:compileDebugAidl UP-TO-DATE
:app:compileDebugRenderscript UP-TO-DATE
:app:generateDebugBuildConfig UP-TO-DATE
:app:generateDebugAssets UP-TO-DATE
:app:mergeDebugAssets UP-TO-DATE
:app:generateDebugResValues UP-TO-DATE
:app:generateDebugResources UP-TO-DATE
:app:mergeDebugResources UP-TO-DATE
:app:bundleDebugJsAndAssets SKIPPED
:app:processDebugManifest UP-TO-DATE
:app:processDebugResources UP-TO-DATE
:app:generateDebugSources UP-TO-DATE
:app:processDebugJavaRes UP-TO-DATE
:app:compileDebugJavaWithJavac UP-TO-DATE
:app:compileDebugNdk UP-TO-DATE
:app:compileDebugSources UP-TO-DATE
:app:preDexDebug UP-TO-DATE
:app:dexDebug UP-TO-DATE
:app:validateDebugSigning
:app:packageDebug UP-TO-DATE
:app:zipalignDebug UP-TO-DATE
:app:assembleDebug UP-TO-DATE
:app:installDebug
Installing APK 'app-debug.apk' on 'emulator-5554 - 6.0'
Installed on 1 device.


BUILD SUCCESSFUL


Total time: 39.532 secs
Starting the app on emulator-5554 (D:\Android\sdk/platform-tools/adb -s emulator
-5554 shell am start -n com.hello/.MainActivity)...

error: unknown host service

解决