why qt android bluetooth rfcomm always failed qt5.7

[dbskcnc]

android 4.4.2/qt 5.7 windows

i want to use qt to communicate with a bluetooth com, but qt always failed with log below:

D/libadPad.so( 2804): D:\yj\qt\adPad\adPad\src\tbluetoothmanager.cpp:75 (void TbluetoothManager::sl_deviceDiscovered(const QBluetoothDeviceInfo&)): one bluetooth device: "HC-05||98:D3:31:40:A8:F3||{00000000-0000-0000-0000-000000000000}"
D/libadPad.so( 2804): D:\yj\qt\adPad\adPad\src\tbluetoothmanager.cpp:114 (void TbluetoothManager::sl_serviceDiscovered(const QBluetoothServiceInfo&)): service addr: "98:D3:31:40:A8:F3" mcom addr: "98:D3:31:40:A8:F3" service uuid: "{00001101-0000-1000-8000-00805f9b34fb}"
D/libadPad.so( 2804): D:\yj\qt\adPad\adPad\src\tbluetoothmanager.cpp:120 (TbluetoothManager::sl_serviceDiscovered(const QBluetoothServiceInfo&)::<lambda()>): stop service disc
D/libadPad.so( 2804): D:\yj\qt\adPad\adPad\src\tbluetoothmanager.cpp:135 (void TbluetoothManager::sl_comConnectToService()): connect to addr: "98:D3:31:40:A8:F3" suuid: "{00001101-0000-1000-8000-00805f9b34fb}"
D/libadPad.so( 2804): D:\yj\qt\adPad\adPad\src\tbluetoothmanager.cpp:104 (void TbluetoothManager::sl_comStateChanged(QBluetoothSocket::SocketState)): comm state: QBluetoothSocket::ConnectingState
W/BluetoothAdapter( 2804): getBluetoothService() called with no BluetoothManagerCallback
D/BluetoothSocket( 2804): connect(), SocketState: INIT, mPfd: {ParcelFileDescriptor: FileDescriptor[74]}
W/System.err( 2804): java.io.IOException: read failed, socket might closed or timeout, read ret: -1
W/System.err( 2804): at android.bluetooth.BluetoothSocket.readAll(BluetoothSocket.java:505)
W/System.err( 2804): at android.bluetooth.BluetoothSocket.readInt(BluetoothSocket.java:516)
W/System.err( 2804): at android.bluetooth.BluetoothSocket.connect(BluetoothSocket.java:320)
W/System.err( 2804): at dalvik.system.NativeStart.run(Native Method)
W/libadPad.so( 2804): (null):0 ((null)): qt.bluetooth.android: Falling back to workaround.
W/libadPad.so( 2804): (null):0 ((null)): qt.bluetooth.android: Cannot determine RFCOMM service channel.
W/libadPad.so( 2804): (null):0 ((null)): qt.bluetooth.android: Workaround thread invoked.
W/BluetoothAdapter( 2804): getBluetoothService() called with no BluetoothManagerCallback
D/BluetoothSocket( 2804): connect(), SocketState: INIT, mPfd: {ParcelFileDescriptor: FileDescriptor[75]}
W/System.err( 2804): java.io.IOException: read failed, socket might closed or timeout, read ret: -1
W/System.err( 2804): at android.bluetooth.BluetoothSocket.readAll(BluetoothSocket.java:505)
W/System.err( 2804): at android.bluetooth.BluetoothSocket.waitSocketSignal(BluetoothSocket.java:482)
W/System.err( 2804): at android.bluetooth.BluetoothSocket.connect(BluetoothSocket.java:324)
W/System.err( 2804): at dalvik.system.NativeStart.run(Native Method)
W/libadPad.so( 2804): (null):0 ((null)): qt.bluetooth.android: Socket connect via workaround failed.
D/libadPad.so( 2804): D:\yj\qt\adPad\adPad\src\tbluetoothmanager.cpp:109 (void TbluetoothManager::sl_comError(QBluetoothSocket::SocketError)): com error: QBluetoothSocket::ServiceNotFoundError
D/libadPad.so( 2804): D:\yj\qt\adPad\adPad\src\tbluetoothmanager.cpp:104 (void TbluetoothManager::sl_comStateChanged(QBluetoothSocket::SocketState)): comm state: QBluetoothSocket::UnconnectedState
D/BluetoothAdapter( 2804): startLeScan(): null
D/BluetoothAdapter( 2804): onClientRegistered() - status=0 clientIf=5
D/dalvikvm( 2804): GC_CONCURRENT freed 770K, 15% free 4933K/5744K, paused 45ms+4ms, total 157ms
D/BluetoothAdapter( 2804): stopLeScan()

qt can scan the devices ,and discovry service is ok, but connectToService without any success.
i can use app bluetooth rfcomm pro, it just connect and function ok.

[dbskcnc]

the code

#ifndef TBLUETOOTHMANAGER_H
#define TBLUETOOTHMANAGER_H

#include <QObject>
#include<QTimer>
#include <qbluetoothaddress.h>
  #include <qbluetoothdevicediscoveryagent.h>
  #include <qbluetoothlocaldevice.h>

  #include <QBluetoothDeviceInfo>
#include<QBluetoothSocket>
#include<QBluetoothServiceDiscoveryAgent>

#define SPP_UUID QString("00001101-0000-1000-8000-00805F9B34FB")

class TbluetoothManager : public QObject
{
    Q_OBJECT

    Q_PROPERTY(bool comOk READ comOk WRITE setComOk NOTIFY comOkChanged)

    Q_PROPERTY(QList<QString> bluedevices READ bluedevices WRITE setBluedevices NOTIFY bluedevicesChanged)
    QList<QString> m_bluedevices;

    bool m_comOk;

public:
    explicit TbluetoothManager(QObject *parent = 0);

QList<QString> bluedevices() const;

bool comOk() const;

signals:
    void onComData(QByteArray data);

    void bluedevicesChanged(QList<QString> bluedevices);


    void deviceDiscovered(const QBluetoothDeviceInfo &info);

    void comOkChanged(bool     comOk);

public slots:
    void scanBluetoothDevices();

    void connectComDevices(QString device);

    void sl_deviceDiscovered(const QBluetoothDeviceInfo &info);

    void sl_comConnected();
    void sl_comDisconnected();
    void sl_comReadyRead();

    void sl_comStateChanged(QBluetoothSocket::SocketState state);

    void sl_comError(QBluetoothSocket::SocketError error);




    void sl_serviceDiscovered(const QBluetoothServiceInfo &info);
    void sl_comConnectToService();


    //auto gen

    void setBluedevices(QList<QString> bluedevices);

    void setComOk(bool     comOk);

protected:
    QBluetoothDeviceDiscoveryAgent * discoveryAgent;
    QBluetoothSocket* m_local_bluetooth_socket;
    QBluetoothServiceDiscoveryAgent* m_bluetooth_service_disc;

    QString m_com_device_addr;

    QBluetoothServiceInfo m_com_service_info;


};

#endif // TBLUETOOTHMANAGER_H

cpp:

#include "tbluetoothmanager.h"
#include<QBluetoothServiceInfo>
#include<QDebug>



TbluetoothManager::TbluetoothManager(QObject *parent) : QObject(parent)
{
    discoveryAgent= new QBluetoothDeviceDiscoveryAgent(this);
    connect(discoveryAgent, SIGNAL(deviceDiscovered(QBluetoothDeviceInfo)),
                  this, SLOT(sl_deviceDiscovered(QBluetoothDeviceInfo)));

    m_local_bluetooth_socket=0;

    m_bluetooth_service_disc= new QBluetoothServiceDiscoveryAgent(this);
    connect(m_bluetooth_service_disc,SIGNAL(serviceDiscovered(const  QBluetoothServiceInfo&)),SLOT(sl_serviceDiscovered(const QBluetoothServiceInfo&)));

}

QList<QString> TbluetoothManager::bluedevices() const
{
    return m_bluedevices;
}

bool TbluetoothManager::comOk() const
{
    return m_comOk;
}

void TbluetoothManager::scanBluetoothDevices()
{
    //qDebug()<<"start scan bluetooth";

    m_bluedevices.clear();
    emit bluedevicesChanged(m_bluedevices);

    discoveryAgent->start();
}

void TbluetoothManager::connectComDevices(QString device)
{
    int last_pos=device.lastIndexOf("||");
    if(last_pos<0){
        qDebug()<<"can not found sep in device string";
        return;
    }

    int last_second_pos=device.lastIndexOf("||",last_pos-1);
    if(last_second_pos<0){
        qDebug()<<"can not found second sep in device string";
        return;
    }

    m_com_device_addr=device.mid(last_second_pos+2,last_pos-last_second_pos-2);

    //qDebug()<< "device addr:"<<device_addr ;

    QString device_uuid=device.mid(last_pos+2,100);

    //qDebug()<< "device uuid:"<<device_uuid ;

    m_bluetooth_service_disc->setRemoteAddress(QBluetoothAddress(m_com_device_addr));
    m_bluetooth_service_disc->start();


}

void TbluetoothManager::sl_deviceDiscovered(const QBluetoothDeviceInfo &info)
{
    QString device=info.name()+"||"+info.address().toString()+"||"+ info.deviceUuid().toString();
    m_bluedevices.append(device);

    emit bluedevicesChanged(m_bluedevices);

    qDebug()<<"one bluetooth device:"<<device;

    connectComDevices(device);
}

void TbluetoothManager::sl_comConnected()
{
    qDebug()<< "com connected" ;

    setComOk(true);
}

void TbluetoothManager::sl_comDisconnected()
{
    qDebug()<< "com disconnected" ;

    setComOk(false);
}

void TbluetoothManager::sl_comReadyRead()
{
    QByteArray data=m_local_bluetooth_socket->readAll();

    qDebug()<< "com rev:" <<data;

}

void TbluetoothManager::sl_comStateChanged(QBluetoothSocket::SocketState state)
{
    qDebug()<< "comm state:" <<state;
}

void TbluetoothManager::sl_comError(QBluetoothSocket::SocketError error)
{
    qDebug()<< "com error:" <<error;
}

void TbluetoothManager::sl_serviceDiscovered(const QBluetoothServiceInfo &info)
{
    qDebug()<< "service addr:" <<info.device().address().toString()<<"mcom addr:"<<m_com_device_addr
            <<"service uuid:"<<info.serviceUuid().toString();

    if (info.device().address().toString()==m_com_device_addr) {

        QTimer::singleShot(10,[&]{
            qDebug()<< "stop service disc" ;
            m_bluetooth_service_disc->stop();;
        });

        m_com_service_info=info;

        QTimer::singleShot(1000,this,SLOT(sl_comConnectToService()));
        //m_local_bluetooth_socket->connectToService(info);
    }


}

void TbluetoothManager::sl_comConnectToService()
{
    qDebug()<< "connect to addr:"<<m_com_service_info.device().address().toString()<<"suuid:"<<m_com_service_info.serviceUuid().toString() ;

    if (m_local_bluetooth_socket) {
        m_local_bluetooth_socket->deleteLater();
    }

    m_local_bluetooth_socket=new QBluetoothSocket(QBluetoothServiceInfo::RfcommProtocol);
    m_local_bluetooth_socket->setPreferredSecurityFlags(QBluetooth::NoSecurity);

    connect(m_local_bluetooth_socket,SIGNAL(connected()), SLOT(sl_comConnected()));
    connect(m_local_bluetooth_socket,SIGNAL(disconnected()),SLOT(sl_comDisconnected()));
    connect(m_local_bluetooth_socket,SIGNAL(readyRead()),SLOT(sl_comReadyRead()));
    connect(m_local_bluetooth_socket,SIGNAL(stateChanged(QBluetoothSocket::SocketState)),SLOT(sl_comStateChanged(QBluetoothSocket::SocketState)));
    connect(m_local_bluetooth_socket,SIGNAL(error(QBluetoothSocket::SocketError)),SLOT(sl_comError(QBluetoothSocket::SocketError)));

    //m_local_bluetooth_socket->connectToService(m_com_service_info);
    m_local_bluetooth_socket->connectToService(m_com_service_info.device().address(),
                                               QBluetoothUuid(SPP_UUID));
}

void TbluetoothManager::setBluedevices(QList<QString> bluedevices)
{
    if (m_bluedevices == bluedevices)
        return;

    m_bluedevices = bluedevices;
    emit bluedevicesChanged(bluedevices);
}

void TbluetoothManager::setComOk(bool comOk)
{
    if (m_comOk == comOk)
        return;

    m_comOk = comOk;
    emit comOkChanged(comOk);
}