java - 停止正在进行的可运行 Android

Question

我正在创建一个 BLE 应用程序，需要按照预定义的时间间隔连续启动和停止扫描。我实现它的方式是使用两个相互调用的可运行对象，如下所示:

private Runnable scan = new Runnable() {
    @Override
    public void run() {
        scanHandler.postDelayed(stopScan, SCAN_PERIOD);
        mLEScanner.startScan(filters, settings, mScanCallback);
        Log.e("BLE_Scanner", "Start Scan");
    }
};

private Runnable stopScan = new Runnable() {
    @Override
    public void run() {
        mLEScanner.stopScan(mScanCallback);
        scanHandler.postDelayed(scan, STOP_PERIOD);
        Log.e("BLE_Scanner", "Stop Scan");
    }
};

我正在尝试开始连续扫描并在单击按钮时暂停。开始按钮可以正常启动该过程，但我在停止扫描时遇到问题。

    //scan button functionality
    scanButton=(Button)findViewById(R.id.scan_button);
    scanButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            spinner.setVisibility(View.VISIBLE);
            scan.run();
        }
    });

    //stop scan button functionality
    stopButton=(Button)findViewById(R.id.stop_button);
    stopButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            spinner.setVisibility(View.INVISIBLE);
            scanHandler.removeCallbacks(scan);
            scanHandler.removeCallbacks(stopScan);
        }
    });

如果我在停止间隔期间按下停止按钮，扫描将停止。但是，如果我在扫描可运行程序运行时按下停止按钮，则似乎会删除 stopScan 可运行程序的回调，同时使扫描可运行程序持续运行。我需要的是两个可运行程序在按下按钮时停止。为了提供更多详细信息，下面提供了我的整个代码。感谢您的帮助。

public class MainActivity extends Activity {
private BluetoothAdapter mBluetoothAdapter;
private int REQUEST_ENABLE_BT = 1;
private static final long SCAN_PERIOD = 5000;
private static final long STOP_PERIOD = 1000;
private BluetoothLeScanner mLEScanner;
private ScanSettings settings;
private List<ScanFilter> filters;
private BluetoothGatt mGatt;
private Button scanButton;
private Button stopButton;
//private String proximityUUID = "0000180f-0000-1000-8000-00805f9b34fb";
private ProgressBar spinner;
private Handler scanHandler;

private String[] filterList = {
        "D9:ED:5F:FA:0E:02",
        "FF:37:3A:25:56:C7",
        "F4:57:89:69:93:91"
};

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    scanHandler = new Handler();
    //determine if device supports BLE
    if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
        Toast.makeText(this, "BLE Not Supported",
                Toast.LENGTH_SHORT).show();
        finish();
    }
    //set up bluetooth manager
    final BluetoothManager bluetoothManager =
            (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
    mBluetoothAdapter = bluetoothManager.getAdapter();

    //scan progress bar
    spinner=(ProgressBar)findViewById(R.id.progressBar);
    spinner.setVisibility(View.GONE);

    //scan button functionality
    scanButton=(Button)findViewById(R.id.scan_button);
    scanButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            spinner.setVisibility(View.VISIBLE);
            scan.run();
        }
    });

    //stop scan button functionality
    stopButton=(Button)findViewById(R.id.stop_button);
    stopButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            spinner.setVisibility(View.INVISIBLE);
            scanHandler.removeCallbacks(scan);
            scanHandler.removeCallbacks(stopScan);
        }
    });
}

@Override
protected void onResume() {
    super.onResume();
    if (mBluetoothAdapter == null || !mBluetoothAdapter.isEnabled()) {
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
    } else {
        mLEScanner = mBluetoothAdapter.getBluetoothLeScanner();
        //scan settings
        settings = new ScanSettings.Builder()
                .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
                .build();

        //scan filter
        //populate the filter list
        filters = new ArrayList<ScanFilter>();
        for (int i=0; i< filterList.length ; i++) {
            ScanFilter filter = new ScanFilter.Builder().setDeviceAddress(filterList[i]).build();
            filters.add(filter);

        }
    }
}

@Override
protected void onPause() {
    super.onPause();
    if (mBluetoothAdapter != null && mBluetoothAdapter.isEnabled()) {
    }
}

@Override
protected void onDestroy() {
    if (mGatt == null) {
        return;
    }
    mGatt.close();
    mGatt = null;
    super.onDestroy();
}

//start scan
private Runnable scan = new Runnable() {
    @Override
    public void run() {
        scanHandler.postDelayed(stopScan, SCAN_PERIOD);
        mLEScanner.startScan(filters, settings, mScanCallback);
        Log.e("BLE_Scanner", "Start Scan");
    }
};

private ScanCallback mScanCallback = new ScanCallback() {
    @Override
    public void onScanResult(int callbackType, ScanResult result) {
        Log.i("callbackType", String.valueOf(callbackType));
        Log.i("result", result.toString());
        BluetoothDevice device = result.getDevice();
        int mRSSI = result.getRssi();
    }

    @Override
    public void onBatchScanResults(List<ScanResult> results) {
        for (ScanResult sr : results) {
            Log.i("ScanResult - Results", sr.toString());
        }
    }

    @Override
    public void onScanFailed(int errorCode) {
        Log.e("Scan Failed", "Error Code: " + errorCode);
    }
};

//stop scan
private Runnable stopScan = new Runnable() {
    @Override
    public void run() {
        mLEScanner.stopScan(mScanCallback);
        scanHandler.postDelayed(scan, STOP_PERIOD);
        Log.e("BLE_Scanner", "Stop Scan");
    }
};

private static double calculateAccuracy(int txPower, double rssi) {
    if (rssi == 0) {
        return -1.0; // if we cannot determine accuracy, return -1.
    }

    double ratio = -rssi*1.0/txPower;
    if (ratio < 1.0) {
        return Math.pow(ratio,10);
    }
    else {
        double accuracy =  (0.89976)*Math.pow(ratio,7.7095) + 0.111;
        return accuracy;
    }
}

}

Answer 1

我想您只想在按下开始按钮时立即调用 startScan (不是在 Runnable 中，也不是通过处理程序调度)。该调用是异步的，因此不会阻塞，Android 将在另一个线程中完成所有扫描。如果您想安排一个调用在将来停止，那么您可以使用处理程序来发布一个 Runnable，该 Runnable 在您需要的延迟时调用 stopScan。

如果知道之前正在进行扫描，则停止扫描的按钮也可以直接调用 stopScan() 。仅当之前调用过 startScan() 时，您可能才需要使用 boolean 值来控制对 stopScan 的调用。