* Electron version: 1.6.10
* Operating system: macOS Sierra 10.12.4 (16E195)

# Improve Handoff API support

Hi!

Today the API of Handoff provides the methods: `setUserActivity`, `getCurrentActivityType` and dispatch the event `continue-activity`

I'm using Handoff and noticed that in some circumstances the broadcast takes a long time to update its userInfo which does not happen on the native iOS client

1. To invalidate or resign the current activity we currently need to create a non-existing activity type and set it as the current activity. There's no way to handle the activity life cycle through electron.
2. When we need to update a given user activity userInfo frequently (i.e in response to a search bar's text changes), we have no efficient way. Setting a new userActivity with the updated information takes several seconds to bridge, whereas doing this on iOS native app is instantaneous.

I believe that exposing a bit more of the NSUserActivity API to Electron would help, namely `becomeCurrent`, `resignCurrent` and `invalidate` which would address point 1, and `needsSave` and a new event to allow updating an activity when needed to address point 2.
These are described in more detail in https://developer.apple.com/reference/foundation/nsuseractivity.

I'm are open to help in any way i can such as explaining how the native API work, providing sample code or testing possible implementations

Thank you!
atom/browser/api/atom_api_app.cc
if (command_line->HasSwitch(service_manager::switches::kNoSandbox)) {
    const base::CommandLine::CharType* noSandboxArg =
        FILE_PATH_LITERAL("--no-sandbox");
    base::CommandLine::StringVector modified_command_line;
    for (auto& arg : command_line->argv()) {
      if (arg.compare(noSandboxArg) != 0) {
        modified_command_line.push_back(arg);
      }
    }
    command_line->InitFromArgv(modified_command_line);
  }
}
void App::EnableSandbox(mate::Arguments* args) {
  if (Browser::Get()->is_ready()) {
    args->ThrowError(
        "app.enableSandbox() can only be called "
        "before app is ready");
    return;
  }
  auto* command_line = base::CommandLine::ForCurrentProcess();
  RemoveNoSandboxSwitch(command_line);
  command_line->AppendSwitch(switches::kEnableSandbox);
}
void App::SetUserAgentFallback(const std::string& user_agent) {