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我正在通过 BLE 将图像从 Android 应用程序发送到 iOS 应用程序。根据一些文章，通过 BLE 发送的最大大小为 1 KB，因此我将图像拆分为 1 KB 的块，并以 40 毫秒的延迟将其发送到 Swift 应用程序。

但是，块大小似乎太大了。调试后，我注意到我从 Swift 中读取的特征值最多只能是 187 字节。因此，当我将 Android 中的块大小减少到该数字或更小时，传输成功，否则由于数据被切断，传输不会成功。

有谁知道为什么它限制在这个大小，尽管它应该是 1 KB？或者，如果可配置，我如何增加大小？

这是我的安卓代码：

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.");
}

这是读取它的 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。

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