You need to override onSaveInstanceState(Bundle savedInstanceState)
and write the application state values you want to change to the Bundle
parameter like this:
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
super.onSaveInstanceState(savedInstanceState);
// Save UI state changes to the savedInstanceState.
// This bundle will be passed to onCreate if the process is
// killed and restarted.
savedInstanceState.putBoolean("MyBoolean", true);
savedInstanceState.putDouble("myDouble", 1.9);
savedInstanceState.putInt("MyInt", 1);
savedInstanceState.putString("MyString", "Welcome back to Android");
// etc.
}
The Bundle is essentially a way of storing a NVP ("Name-Value Pair") map, and it will get passed in to onCreate()
and also onRestoreInstanceState()
where you would then extract the values from activity like this:
@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
Or from a fragment.
@Override
public void onViewStateRestored(@Nullable Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
// Restore UI state from the savedInstanceState.
// This bundle has also been passed to onCreate.
boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
double myDouble = savedInstanceState.getDouble("myDouble");
int myInt = savedInstanceState.getInt("MyInt");
String myString = savedInstanceState.getString("MyString");
}
You would usually use this technique to store instance values for your application (selections, unsaved text, etc.).
I use the following from inside an activity:
private boolean isMyServiceRunning(Class<?> serviceClass) {
ActivityManager manager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
for (RunningServiceInfo service : manager.getRunningServices(Integer.MAX_VALUE)) {
if (serviceClass.getName().equals(service.service.getClassName())) {
return true;
}
}
return false;
}
And I call it using:
isMyServiceRunning(MyService.class)
This works reliably, because it is based on the information about running services provided by the Android operating system through ActivityManager#getRunningServices.
All the approaches using onDestroy or onSometing events or Binders or static variables will not work reliably because as a developer you never know, when Android decides to kill your process or which of the mentioned callbacks are called or not. Please note the "killable" column in the lifecycle events table in the Android documentation.
Best Answer
Run
apksigner verify -v <apk>
and look forVerified using v2 scheme (APK Signature Scheme v2): true
in the output. apksigner can be found in Android SDK build tools 24.0.3. apksigner's source code is here: https://android.googlesource.com/platform/tools/apksig/.For an already installed package on Android Nougat:
adb shell pm dump <package name> | grep apkSigningVersion
.1
means conventional JAR signing scheme,2
means APK Signature Scheme v2.You can also run
grep 'APK Sig Block 42' app.apk
but this may have false positives. Only if there is no match is it certain that the APK is not signed using APK Signature Scheme v2.EDIT: Added information about apksigner which wasn't yet available when the original answer was written.