Question

我正在通过BLE将Android应用中的图像发送到iOS应用。根据一些文章，通过BLE发送的最大大小是1 KB，因此我将我的图像分成1 KB块并将其发送到Swift应用程序，延迟时间为40毫秒。

然而，块大小似乎太大了。调试之后，我注意到我在Swift中读取的特征值只能达到187个字节。因此，当我将Android中的块大小减少到该数量或更小时，传输成功，否则它不会因为数据被切断。

有人知道它为什么限制在那个大小，尽管它应该是1 KB吗？或者，如果可配置我如何增加尺寸？

这是我的Android代码：

private void writeImageToCharacteristic() {
    // determine number of chunks and checksum
    final int chunkSize = 1000; // fails with 1000, succeeds with 180
    int numberOfChunks = imageInByte.length / chunkSize;
    numberOfChunks = imageInByte.length == numberOfChunks * chunkSize ? numberOfChunks : numberOfChunks + 1;

    // get the characteristic
    BluetoothGattCharacteristic imgCharacteristic = mBluetoothGattServer
            .getService(SERVICE_UUID)
            .getCharacteristic(IMAGE_CHARACTERISTIC_UUID);

    Log.d(TAG, "Image size in byte: " + imageInByte.length);
    Log.d(TAG, "Number of chunks: " + numberOfChunks);
    Log.d(TAG, "Start sending...");
    updateStateLabel("State: sending image data...");

    // first message contains information about the image
    final String msg = String.valueOf(numberOfChunks);
    imgCharacteristic.setValue(msg.getBytes());
    mBluetoothGattServer.notifyCharacteristicChanged(mConnectedDevice, imgCharacteristic, false);

    // create the chunks (and checksums if configured)
    List<byte[]> messages = new ArrayList<>();
    for(int i = 0; i < numberOfChunks; ++i) {
        final int start = i * chunkSize;
        final int end = start + chunkSize > imageInByte.length ? imageInByte.length : start + chunkSize;
        final byte[] chunk = Arrays.copyOfRange(imageInByte, start, end);
        messages.add(chunk);

        if(includeChecksums) {
            final String chunkCheckSum = calculateCheckSum(chunk);
            messages.add(chunkCheckSum.getBytes());
        }
    }

    // send the data to the device by writing
    // it to the characteristic with a delay of 40 ms
    for(byte[] aMsg : messages) {
        SystemClock.sleep(40);
        imgCharacteristic.setValue(aMsg);
        mBluetoothGattServer.notifyCharacteristicChanged(mConnectedDevice, imgCharacteristic, false);
    }

    Log.d(TAG, "Finished sending");
    updateStateLabel("State: finished sending.");
}

以下是读取它的Swift代码：

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
    switch characteristic.uuid {
        case Constants.ImageCharacteristicUUID:
            let imgData = characteristic.value!
            // here, the characteristic.value seems to be limited to 187 bytes - why?
            processImageData(data: imgData!)
        default:
            print("Unhandled Characteristic UUID: \(characteristic.uuid)")
    }
}

感谢任何帮助。

iOS - Swift蓝牙 - 收到的特征值太小

0 个答案: