Android 低功耗蓝牙 - 读取浮点特性

Question

我正在尝试读取已连接的低功耗蓝牙设备 (Genuino 101) 的浮点特性。出于测试目的，设备提供了一个硬编码值为“55.3”的 FloatCharacteristic。虽然我能够接收到某种类似于浮点数的字符串，但我无法读取实际的浮点值。
这是处理字符串的代码片段：

// For all other profiles, writes the data formatted in HEX.
        final byte[] data = characteristic.getValue();
        if (data != null && data.length > 0) {
            final StringBuilder stringBuilder = new StringBuilder(data.length);
            for(byte byteChar : data)
                stringBuilder.append(String.format("%02X ", byteChar));
            intent.putExtra(EXTRA_DATA, new String(data) + "\n" + stringBuilder.toString());
        }

这是直接从 android 开发者主页的 https://developer.android.com/samples/BluetoothLeGatt/index.html BLE 演示项目复制而来的。然后由以下代码段处理意图：

private final BroadcastReceiver mGattUpdateReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("Broadcast received");
        final String action = intent.getAction();
        if (BluetoothLeService.ACTION_GATT_CONNECTED.equals(action)) {

        } else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {

        } else if (BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED.equals(action)) {

        } else if (BluetoothLeService.ACTION_DATA_AVAILABLE.equals(action)) {
           displayData(intent.getStringExtra(BluetoothLeService.EXTRA_DATA));
        }
    }
};

private void displayData(String data) {
    if (data != null) {
        System.out.println("Data Received: " + data);
    }
}

这导致输出

I/System.out: Data Received: 33]B 
I/System.out: 33 33 5D 42

因此，抛开交换的字节序，这是 55.3f 的正确十六进制值。
但是，如果我尝试使用 characteristic.getFloatValue()，我只会得到垃圾。以下是我尝试弄清楚如何接收实际浮点数的方法：

final byte[] data = characteristic.getValue();
        if (data != null && data.length > 0) {
            for (int i = 0; i< 333; i++) {
                try {
                    final float fData = characteristic.getFloatValue(BluetoothGattCharacteristic.FORMAT_FLOAT, i);
                    System.out.println("Offset = "+ i + ". Data that gets sent: " + fData + "/Data that we would expect: " + 55.3f);
                } catch (Exception e) {
                    System.out.println("Exception at offset " + i);
                }
            }
        }

输出总是

I/System.out: Offset = 0. Data that gets sent: Infinity/Data that we would expect: 55.3
I/System.out: Exception at offset 1
I/System.out: Exception at offset 2
...

我这里的错误是什么？另外，我不确定应该如何理解 Offset 参数。它是以位为单位，以字节为单位的偏移量吗？从 MSB 计数，从 LSB 计数？ getFloatValue() 的文档也声称 "returns float - Cached value of the characteristic at a given offset or null if the requested offset exceeds the value size. "。但是上面的代码片段严重超过了任何 gatt 特征的最大大小，但方法调用没有返回 'null'，而是抛出异常。那么这里获得浮动的正确方法是什么？

Answer 1

目前，我通过

格式化数据来帮助自己

 float f1 = ByteBuffer.wrap(data).order(ByteOrder.LITTLE_ENDIAN).getFloa‌t();

.

Android 低功耗蓝牙 - 读取浮点特性

Android Bluetooth LE - Read float characteristic

android

bluetooth-lowenergy

android-bluetooth

gatt