Caused by: java.lang.ClassNotFoundException: Didn't find class "io.grpc.helloworldexample.HelloworldActivity" on path: DexPathList

FAQ:  Android app 编译好后安装到手机，运行时闪退，报如下错误：

java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{io.grpc.helloworldexample/io.grpc.helloworldexample.HelloworldActivity}: java.lang.ClassNotFoundException: Didn't find class "io.grpc.helloworldexample.HelloworldActivity" on path: DexPathList[[zip file "/data/app/io.grpc.helloworldexample-aHJfGmXKi-KoAnqDIRZHhQ==/base.apk"],nativeLibraryDirectories=[/data/app/io.grpc.helloworldexample-aHJfGmXKi-KoAnqDIRZHhQ==/lib/arm64, /system/lib64, /vendor/lib64]]

问题原因：

重复拷贝工程，并且重名工程都在as中打开过，导致as产生混淆，找不到相应类：

解决办法：

直接禁用Instant run, 这个效果最直接

disable Instant Run Go to File -> Settings -> Build,Execution, Deployment -> Instant Run -> Uncheck the checkbox for instant run. Run your app once and this apk file work properly..

试了下下面其他的办法，对GRPC上的这个问题解决没有效果，只能禁用即时编译，看来这个即时编译就是一个摆设，不实用，毛病问题太多！！！

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其他的解决办法（供参考）：

DELETE THAT FOLDER .gradle.

deleted "build" folder under "app" folder.

Change the application name in AndroidManifest to full path
Clean Project
Rebuild Project
Build APK

My problem solved using use multi dex:

android {
defaultConfig {

// Enabling multidex support.
multiDexEnabled true
}
...
}
dependencies
{
compile 'com.android.support:multidex:1.0.0'
}

// in AndroidManifest.xml:
<application
android:name="android.support.multidex.MultiDexApplication" >
...
</application>

public class MyApplication extends MultiDexApplication

Make sure this Diable preDexLibraries

In your app module .gradle file

android {
dexOptions {
  preDexLibraries false
 }

}