Question

在使用Android 4.4的Nexus 7上运行时，onScanResult会抛出NullPointerExceptionas，如下面的日志中所示：

03-18 17:59:34.170: D/BluetoothAdapter(5092): onScanResult() - Device=78:4B:08:02:7C:91 RSSI=-77
03-18 17:59:34.170: W/BluetoothAdapter(5092): Unhandled exception: java.lang.NullPointerException

然而，其他设备没有这样的问题。

我在googlesource

上找到了这个

    public void onScanResult(String address, int rssi, byte[] advData) {
        if (DBG) Log.d(TAG, "onScanResult() - Device=" + address + " RSSI=" +rssi);

        // Check null in case the scan has been stopped
        synchronized(this) {
            if (mLeHandle <= 0) return;
        }
        try {
            BluetoothAdapter adapter = mBluetoothAdapter.get();
            if (adapter == null) {
                Log.d(TAG, "onScanResult, BluetoothAdapter null");
                return;
            }
            mLeScanCb.onLeScan(adapter.getRemoteDevice(address), rssi, advData);
        } catch (Exception ex) {
            Log.w(TAG, "Unhandled exception: " + ex);
        }
    }

其中有许多潜在的罪魁祸首，但当然我无法为这些变量设置值。

为什么这对Nexus 7失败而对其他设备失败？任何解决方法的想法？

Answer 1

Android 4.3, 4.4: BLE filtering in startLeScan(UUIDs, callback) doesn't work for 128-bit UUIDs

适用于三星s5，使用Android 4.4.2测试但由于某些原因，它在Nexus上失败了。等待来自Google堆栈的此修复程序。

如果您只想搜索特定地址，可以使用this解决方案。基本上，您必须使用scanRec []，需要额外的努力来解析它，然后将具有匹配地址的设备添加到列表适配器中。

[我知道，....希望简单的API能够运作！：P]

Answer 2

关闭WIFI：

我也可以确认，关闭WIFI会使蓝牙4.0更稳定，尤其是在谷歌Nexus上（我有一台Nexus 7）。问题

我正在开发的应用程序需要WIFI和连续蓝牙LE扫描。所以关闭WIFI对我来说是不可取的。

此外我已经意识到，持续蓝牙LE扫描实际上可以杀死WIFI连接并使WIFI适配器无法重新连接到任何WIFI网络，直到BLE扫描开启。（我不确定移动网络和移动互联网）。这肯定发生在以下设备上：

Nexus 7
Motorola Moto G

然而，使用WIFI进行BLE扫描似乎非常稳定：

Samsung S4
HTC One

我的解决方法

我在短时间内扫描BLE 3-4秒然后关闭扫描3-4秒。然后再次开启。

Obviously I always turn BLE scan OFF when I'm connecting to a BLE device.
When I disconnect from a device I restart BLE (turn adapter OFF and then ON) to reset the stack before starting scan again.
I also reset BLE when discovering services or characteristics fails.
When I get advertisement data from a device that the app should connect to (lets say 500 times without being able to connect - thats about 5-10 seconds of advertising) I reset BLE again.

在BluetoothAdapter的onScanResult上防止NPE

2 个答案: