Request MTU is not working in Nougat

Question

I am working on App which is communicate with BLE device.I can write 20 bytes easily on characteristics but when it is more than 20 bytes it's create problem.I am using

mBluetoothGatt.requestMtu(512);

write charateristics after getting success.

 @Override
                    public void onMtuChanged(BluetoothGatt gatt, int mtu, int status) {
                        super.onMtuChanged(gatt, mtu, status);

                        if (status == BluetoothGatt.GATT_SUCCESS) {
                            System.out.print("Mtu Granted");
//                            this.supportedMTU = mtu;
                        }
                    }

which is working fine in marshmallow and lolipop.But it is not working in Nougat(Samsung galaxy s6).

Answer 1

I was having this exact same issue, so I put the mtu request in a loop and it seems to work after 2 attempts regularly.

            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (!mtuConfirmed) {
                        mBluetoothGatt.requestMtu(512);
                        mtuRequestCounter++;
                        try {
                            Thread.sleep(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    Log.d(TAG, "MTU change reply received after " + mtuRequestCounter + " attempts");
                }
            }).start();

Answer 2

I had the same problem. It was because I had multiple requests from the Gatt object at the same time. I called GATT.discoverServices() and GATT.requestMtu(512) at the same time. And always, only the first call worked. Gatt object has several callbacks, so for example, you can first request changing the MTU. Then when onMtuChanged is called, you call to ask for the other request. In my case, GATT.discoverServices()