Keeping the Device Awake | Android Developers

Scheduler.zip To avoid draining the battery, an Android device that is left idle quickly falls asleep. However, there are times when an application needs to wake up the screen or the CPU and keep it awake to complete some work. The approach you take depends on the needs of your app. However, a general rule of thumb is that you should use the most lightweight approach possible for your app, to minimize your app's impact on system resources.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:keepScreenOn="true">
    ...</RelativeLayout>

public class MainActivity extends Activity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
  }

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Android Studio: No classes.dex in built apk

Recently, when I deploy my simple Android application to emulator in Android Studio, it always fails with error: Failure [INSTALL_FAILED_DEXOPT]
Check the logcat log: it shows: "The apk does not include classes.dex".

The Workaround: Build the app manually in command line: *gradlew.bat clean assembleDebug*

Please read full article from Android Studio: No classes.dex in built apk