android - adapter.getBluetoothLeScanner() 在某些 Android 6.0 设备上返回 null

Question

我的应用程序适用于 BLE 设备并按以下方式搜索它们 (API 21+):

adapter.getBluetoothLeScanner().startScan(filters, scanSettings, this);

它适用于大多数设备(例如三星)，但在某些 LGE 和 HTC 设备(使用 Android 6.0)上返回 null 并崩溃:

Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.startScan(java.util.List, android.bluetooth.le.ScanSettings, android.bluetooth.le.ScanCallback)' on a null object reference

该应用程序针对棉花糖之前的 android，因此(应该)授予权限。

Answer 1

我认为您可以在 adapter.enable() 之后立即调用 startScan。 因为 BluetoothAdapter.enable() 是一个异步调用，所以你可能会得到 NullPointer 异常，你可以尝试注册广播接收器来接收 BluetoothAdapter 状态，如下所示。

    private BroadcastReceiver receiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        final String action = intent.getAction();
        if (action.equals(BluetoothAdapter.ACTION_STATE_CHANGED)) {
            final int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE,
                    BluetoothAdapter.ERROR);
            switch (state) {
                case BluetoothAdapter.STATE_OFF:
                    break;
                case BluetoothAdapter.STATE_TURNING_OFF:
                    break;
                case BluetoothAdapter.STATE_ON:
                    //to check if BluetoothAdapter is enable by your code
                    if(enableFlag){
                      adapter.getBluetoothLeScanner().startScan(filters, scanSettings, callBack);
                    }
                    break;
                case BluetoothAdapter.STATE_TURNING_ON:
                    break;
            }
        }
    }
};