React-native在指定的时间长度内运行函数

Question

I am writing a react native app that scans for bluetooth low energy devices.

I have a function, scan , which searches for devices, and a function stopScan , which stops the search. When the user presses the 'scan' button, I want this function to run for five seconds, and then stop and present the results. Effectively I want something like this:

foo = () => {
    this.scan()
    //WAIT FIVE SECONDS
    this.stopScan()
}

I've looked at setTimeout etc, but I don't see how they solve the problem. I'm also anxious to do this correctly, as I know that blocking the event loop can be problematic.

Edit:

  findDevices = () => {
      this.setState({ scannerStatus: "scanning" });
      this.scanAndConnect();
      setTimeout(this.manager.stopDeviceScan, 5000);
      this.setState({ scannerStatus: "scanned" });
  };

  scanAndConnect() {
    this.manager.startDeviceScan(null, null, (error, device) => {
      this.info("Scanning...");

      if (error) {
        console.log(error);
        this.manager.stopDeviceScan();
        this.error(error.message);
        return;
      }

      if (device.name === "foo") {
        this.info("Connecting to device");
        device
          .connect()
          .then(device => {
            this.info("Discovering services and characteristics");
            return device.discoverAllServicesAndCharacteristics();
          })
          .then(device => {
            this.info("Setting notifications");
            return this.setupNotifications(device);
          })
          .then(
            () => {
              this.info("Listening...");
            },
            error => {
              this.error(error.message);
            }
          );
      }
    });
  }

Answer 1

If you need to call the scan function in repetition for 5seconds you can do like this:

 foo = () => {
      const scanInterval = setInterval(this.scan, 250) // It will call the scan function every 250ms

      setTimeout(() => {
        clearInterval(scanInterval)
        this.stopScan()
      }, 5000) // Stop the interval after 5s

    }

If you just need to call the stopScan() function after 5s, you can use a simple timeout:

foo = () => {
  this.scan()
  setTimeout(this.stopScan, 5000)
}

Which one you need to use depends on the actual implementation of scan() and stopScan()

EDIT: I have seen your code. The main issue is that setTimeout is NOT a blocking function. It will NOT block the execution until the time has passed (ie 5second), but it will only execute the function you pass as first parameter after the delay. So your code:

setTimeout(this.manager.stopDeviceScan, 5000);
this.setState({ scannerStatus: "scanned" });

will immediately set the scannerStatus to scanned, without waiting 5s. You need to set the call inside the timeout callback:

setTimeout(() => {
   this.manager.stopDeviceScan();
   this.setState({ scannerStatus: "scanned" });
}, 5000);