How to check if an Activity is enabled?

If COMPONENT_ENABLED_STATE_DEFAULT is returned, how do I know if it's default as enabled or disabled?

You will need to load all the components using PackageManager and check the enabled state for the matching ComponentInfo. The following code should work:

java

public static boolean isComponentEnabled(PackageManager pm, String pkgName, String clsName) {
  ComponentName componentName = new ComponentName(pkgName, clsName);
  int componentEnabledSetting = pm.getComponentEnabledSetting(componentName);

  switch (componentEnabledSetting) {
    case PackageManager.COMPONENT_ENABLED_STATE_DISABLED:
      return false;
    case PackageManager.COMPONENT_ENABLED_STATE_ENABLED:
      return true;
    case PackageManager.COMPONENT_ENABLED_STATE_DEFAULT:
    default:
      // We need to get the application info to get the component's default state
      try {
        PackageInfo packageInfo = pm.getPackageInfo(pkgName, PackageManager.GET_ACTIVITIES
            | PackageManager.GET_RECEIVERS
            | PackageManager.GET_SERVICES
            | PackageManager.GET_PROVIDERS
            | PackageManager.GET_DISABLED_COMPONENTS);

        List<ComponentInfo> components = new ArrayList<>();
        if (packageInfo.activities != null) Collections.addAll(components, packageInfo.activities);
        if (packageInfo.services != null) Collections.addAll(components, packageInfo.services);
        if (packageInfo.providers != null) Collections.addAll(components, packageInfo.providers);

        for (ComponentInfo componentInfo : components) {
          if (componentInfo.name.equals(clsName)) {
            return componentInfo.isEnabled();
          }
        }

        // the component is not declared in the AndroidManifest
        return false;
      } catch (PackageManager.NameNotFoundException e) {
        // the package isn't installed on the device
        return false;
      }
  }
}

Testing the above code on my device:

java

System.out.println(isComponentEnabled(getPackageManager(),
    "com.android.systemui",
    "com.android.systemui.DessertCaseDream"));

System.out.println(isComponentEnabled(getPackageManager(),
    "com.android.settings",
    "com.android.settings.DevelopmentSettings"));

false

true