如何判断BLE扫描是否正在进行？解决扫描失败重启前的检查问题

Hey there! Let's work through how to check if your BLE scan is running before starting a new one—super important for avoiding conflicts, especially since you're using a state machine to manage the flow. Here's what you need to know for the two main mobile platforms:

Android Platform #

Android doesn't have a built-in API to directly query if a BLE scan is active, so the most reliable approach is to track the scan state with a member variable and sync it with your scan callbacks. This keeps your state machine aligned with the actual system scan status.

• First, declare a boolean variable to track scanning status:

  private boolean isScanning = false;
  

• Update this variable whenever you start or stop a scan, and in failure callbacks to catch unexpected stops:

  private BluetoothLeScanner bleScanner;
  private ScanCallback scanCallback = new ScanCallback() {
      @Override
      public void onScanResult(int callbackType, ScanResult result) {
          // Process your BLE broadcast data here
      }
  
      @Override
      public void onScanFailed(int errorCode) {
          // Mark scan as stopped when it fails unexpectedly
          isScanning = false;
          // Trigger your restart logic from here if needed
      }
  };
  
  // Your restart scan method
  private void restartBleScan() {
      // Check if scan is currently running
      if (isScanning) {
          // Stop the existing scan first to avoid conflicts
          bleScanner.stopScan(scanCallback);
          isScanning = false;
      }
  
      // Configure scan settings/filters as needed
      ScanSettings scanSettings = new ScanSettings.Builder()
              .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
              .build();
      List<ScanFilter> scanFilters = new ArrayList<>(); // Add filters if required
  
      // Start the new scan and update state
      bleScanner.startScan(scanFilters, scanSettings, scanCallback);
      isScanning = true;
  }
  

• Pro tip: If you're using the older BluetoothAdapter.startLeScan() API, use the same variable-tracking pattern—set isScanning = true when starting, and false when calling stopLeScan() or if the scan fails.

iOS Platform #

iOS makes this way easier with CoreBluetooth's built-in property. The CBCentralManager has an isScanning boolean you can check directly to see if a scan is in progress.

• Here's how to implement the restart logic:

  import CoreBluetooth
  
  class BleScanner: NSObject, CBCentralManagerDelegate {
      private let centralManager = CBCentralManager(delegate: self, queue: nil)
  
      func restartBleScan() {
          // Check if a scan is already running
          if centralManager.isScanning {
              centralManager.stopScan()
          }
  
          // Configure scan options (e.g., allow duplicate results)
          let scanOptions: [String: Any] = [
              CBCentralManagerScanOptionAllowDuplicatesKey: true
          ]
  
          // Start scanning (pass service UUIDs if you want to filter)
          centralManager.scanForPeripherals(withServices: nil, options: scanOptions)
      }
  
      // Implement CBCentralManagerDelegate methods as needed
      func centralManagerDidUpdateState(_ central: CBCentralManager) {
          // Handle Bluetooth state changes here
      }
  }
  

Integrating with Your State Machine #

To keep everything in sync with your state machine:

• Map the isScanning (Android) or centralManager.isScanning (iOS) state to your state machine's "Scanning" state.
• When your state machine triggers a restart scan event, first transition to a "Stopping Scan" state (if active), then move to "Starting Scan" once the old scan is stopped.
• Update your state machine whenever the scan starts/fails/stops to ensure alignment with the actual system state.

内容的提问来源于stack exchange，提问作者tbfp