上一篇文章已经介绍了qt键鼠热插拔经历的曲折之路，这篇就具体解决热插拔问题。
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如上一篇文章所述，在源码中搜索了键鼠热插拔时的调试信息， qt.qpa.input: Found mouse at "/dev/input/event0"
qt.qpa.input: Found matching devices ("/dev/input/event0")
qt.qpa.input: Adding mouse at "/dev/input/event0"
qt.qpa.input: create mouse handler for "/dev/input/event0" ""
qt.qpa.input: evdevtouch: Using device discovery
在QT_ROOT/qtbase/src源码目录下搜索上述信息，在中断键入【grep -rn "Adding mouse at"】，结果如下

发现在QT_ROOT/qtbase/src/platformsupport/input/evdevmouse/qevdevmousemanager.cpp文件中存在相应语句。从命名上就可以猜到该文件是用来管理mouse的，后续验证确实是。将相应的函数贴出来： void QEvdevMouseManager::addMouse(const QString &deviceNode) { qCDebug(qLcEvdevMouse) << "Adding mouse at" << deviceNode; QEvdevMouseHandler *handler; handler = QEvdevMouseHandler::create(deviceNode, m_spec); if (handler) { connect(handler, SIGNAL(handleMouseEvent(int,int,bool,Qt::MouseButtons)), this, SLOT(handleMouseEvent(int,int,bool,Qt::MouseButtons))); connect(handler, SIGNAL(handleWheelEvent(int,Qt::Orientation)), this, SLOT(handleWheelEvent(int,Qt::Orientation))); m_mice.insert(deviceNode, handler); QInputDeviceManagerPrivate::get(QGuiApplicationPrivate::inputDeviceManager())->setDeviceCount( QInputDeviceManager::DeviceTypePointer, m_mice.count()); } else { qWarning("evdevmouse: Failed to open mouse device %s", qPrintable(deviceNode)); } }
在同一个文件中的类函数中（贴出部分，如下）可以看出该函数是用于接收信号的槽，且信号为deviceDetected
。。。。 qCDebug(qLcEvdevMouse) << "evdevmouse: Using device discovery"; m_deviceDiscovery = QDeviceDiscovery::create(QDeviceDiscovery::Device_Mouse | QDeviceDiscovery::Device_Touchpad, this); if (m_deviceDiscovery) { // scan and add already connected keyboards QStringList devices = m_deviceDiscovery->scanConnectedDevices(); foreach (const QString &device, devices) { addMouse(device); } connect(m_deviceDiscovery, SIGNAL(deviceDetected(QString)), this, SLOT(addMouse(QString))); connect(m_deviceDiscovery, SIGNAL(deviceRemoved(QString)), this, SLOT(removeMouse(QString))); }  。。。。
同理还存在另外一对信号与槽，全部列举出来： SIGNAL(deviceDetected(QString)) —— SLOT(addMouse(QString))
SIGNAL(deviceRemoved(QString))—— SLOT(removeMouse(QString)) 这两对函数正如猜测的那样，是udev管理热插拔时发出的，具体的发出位置可以搜索【grep -rn "deviceDetected"】 ，结果如下：

发现在名为qdevicediscovery_udev.cpp的文件中进行的信号发送工作：emit deviceDetected(devNode);
打开qdevicediscovery_udev.cpp所在路径的devicediscovery.pri文件，内容如下： HEADERS += $$PWD/qdevicediscovery_p.h linux { contains(QT_CONFIG, libudev) { SOURCES += $$PWD/qdevicediscovery_udev.cpp HEADERS += $$PWD/qdevicediscovery_udev_p.h INCLUDEPATH += $$QMAKE_INCDIR_LIBUDEV LIBS_PRIVATE += $$QMAKE_LIBS_LIBUDEV } else: contains(QT_CONFIG, evdev) { SOURCES += $$PWD/qdevicediscovery_static.cpp HEADERS += $$PWD/qdevicediscovery_static_p.h } else { SOURCES += $$PWD/qdevicediscovery_dummy.cpp HEADERS += $$PWD/qdevicediscovery_dummy_p.h } } else { SOURCES += $$PWD/qdevicediscovery_dummy.cpp }移植过Linux的应该很眼熟，很明显是根据配置单进行选择编译的文件，由于没有配置libudev而默认配置了evdev，因此自动编译的文件名称为qdevicediscovery_static.cpp/.h。
思路与目标已经明确：
1.在qdevicediscovery_static.cpp文件中实现检测键鼠插入与移除，并发送相应的信号deviceDetected/deviceRemoved即可。
2.检测键鼠的插入与移除可以检测文件系统中/dev/input/目录下设备节点的变化，具体的监听采用QFileSystemWatcher类的路径监听（directoryChanged）。

一、添加监听代码
1.为了方便恢复，复制qdevicediscovery_static.cpp和头文件为qdevicediscovery_hotplug.cpp和qdevicediscovery_hotplug_p.h，修改文件中的static关键字为hotplug（强迫症，可不修改）。
2.由于需要保持监听长时存在，因此监听的实例声明要放在头文件中，并添加相应头文件，由于需要记住上一次添加的设备，因此仿造.cpp文件实现添加一个QStringList变量。
添加头文件：#include                      #include
声明监听实例：QFileSystemWatcher *m_fileWatcher; 声明上一次添加设备的列表：QStringList m_devices;
声明信号函数：
private slots: void handleHotPlugWatch(const QString &path);
3.初始化监听变量与信号监听函数实现 // 初始化文件监听器 m_fileWatcher = new QFileSystemWatcher(this); m_fileWatcher->addPath(QString::fromLatin1(QT_EVDEV_DEVICE_PATH));// "dev/input/" connect(m_fileWatcher, SIGNAL(directoryChanged(QString)), this, SLOT(handleHotPlugWatch(QString)));
信号监听函数实现
void QDeviceDiscoveryHotPlug::handleHotPlugWatch(const QString &path) { if(path.compare(QString::fromLatin1(QT_EVDEV_DEVICE_PATH))) { return; } QStringList devices; // 先移除原来的设备 foreach (const QString &device, m_devices) deviceRemoved(device); // 获取现在的设备 // 注，这里获取的设备已经经过过滤，原因是在对该类进行实例化的时候 // 已经传进了筛选参数，如：QDeviceDiscovery::Device_Keyboard devices = this->scanConnectedDevices(); // 重新添加设备 foreach (const QString &device, devices) deviceDetected(device); }
4.修改QStringList QDeviceDiscoveryHotPlug::scanConnectedDevices()函数，保存添加设备的列表 将QStringList devices;改成m_devices.clear();，用以清除上一次的值 将该函数中的devices全部改成m_devices，用以保存新的值。

二、修改devicediscovery.pri文件中的编译选项 如下：
。。。 } else: contains(QT_CONFIG, evdev) { SOURCES += $$PWD/qdevicediscovery_hotplug.cpp HEADERS += $$PWD/qdevicediscovery_hotplug_p.h } 。。。

修改文件完成后，重新make/make install，将安装后的qt文件移植到开发板上即可。现在QT5.5.1已经支持热插拔了～～～～





附录：修改后的qdevicediscovery_hotplug.cpp和qdevicediscovery_hotplug_p.h文件如下 1.qdevicediscovery_hotplug.cpp文件具体代码如下： /**************************************************************************** ** ** usb input device hot plug function ** by sn02241 ** ****************************************************************************/ #include "qdevicediscovery_hotplug_p.h" #include #include #include #include #include #include #include #include /* android (and perhaps some other linux-derived stuff) don't define everything * in linux/input.h, so we'll need to do that ourselves. */ #ifndef KEY_CNT #define KEY_CNT (KEY_MAX+1) #endif #ifndef REL_CNT #define REL_CNT (REL_MAX+1) #endif #ifndef ABS_CNT #define ABS_CNT (ABS_MAX+1) #endif #define LONG_BITS (sizeof(long) * 8 ) #define LONG_FIELD_SIZE(bits) ((bits / LONG_BITS) + 1) static bool testBit(long bit, const long *field) { return (field[bit / LONG_BITS] >> bit % LONG_BITS) & 1; } QT_BEGIN_NAMESPACE Q_LOGGING_CATEGORY(lcDD, "qt.qpa.input") QDeviceDiscovery *QDeviceDiscovery::create(QDeviceTypes types, QObject *parent) { return new QDeviceDiscoveryHotPlug(types, parent); } QDeviceDiscoveryHotPlug::QDeviceDiscoveryHotPlug(QDeviceTypes types, QObject *parent) : QDeviceDiscovery(types, parent),m_fileWatcher(0) { // 初始化文件监听器 m_fileWatcher = new QFileSystemWatcher(this); m_fileWatcher->addPath(QString::fromLatin1(QT_EVDEV_DEVICE_PATH));// "dev/input/" connect(m_fileWatcher, SIGNAL(directoryChanged(QString)), this, SLOT(handleHotPlugWatch(QString))); qCDebug(lcDD) << "hotplug device discovery for type" << types; } QStringList QDeviceDiscoveryHotPlug::scanConnectedDevices() { m_devices.clear(); QDir dir; dir.setFilter(QDir::System); // check for input devices if (m_types & Device_InputMask) { dir.setPath(QString::fromLatin1(QT_EVDEV_DEVICE_PATH)); foreach (const QString &deviceFile, dir.entryList()) { QString absoluteFilePath = dir.absolutePath() + QString::fromLatin1("/") + deviceFile; if (checkDeviceType(absoluteFilePath)) m_devices << absoluteFilePath; } } // check for drm devices if (m_types & Device_VideoMask) { dir.setPath(QString::fromLatin1(QT_DRM_DEVICE_PATH)); foreach (const QString &deviceFile, dir.entryList()) { QString absoluteFilePath = dir.absolutePath() + QString::fromLatin1("/") + deviceFile; if (checkDeviceType(absoluteFilePath)) m_devices << absoluteFilePath; } } qCDebug(lcDD) << "Found matching devices" << m_devices; return m_devices; } bool QDeviceDiscoveryHotPlug::checkDeviceType(const QString &device) { bool ret = false; int fd = QT_OPEN(device.toLocal8Bit().constData(), O_RDONLY | O_NDELAY, 0); if (!fd) { qWarning() << "Device discovery cannot open device" << device; return false; } long bitsKey[LONG_FIELD_SIZE(KEY_CNT)]; if (ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(bitsKey)), bitsKey) >= 0 ) { if (!ret && (m_types & Device_Keyboard)) { if (testBit(KEY_Q, bitsKey)) { qCDebug(lcDD) << "Found keyboard at" << device; ret = true; } } if (!ret && (m_types & Device_Mouse)) { long bitsRel[LONG_FIELD_SIZE(REL_CNT)]; if (ioctl(fd, EVIOCGBIT(EV_REL, sizeof(bitsRel)), bitsRel) >= 0 ) { if (testBit(REL_X, bitsRel) && testBit(REL_Y, bitsRel) && testBit(BTN_MOUSE, bitsKey)) { qCDebug(lcDD) << "Found mouse at" << device; ret = true; } } } if (!ret && (m_types & (Device_Touchpad | Device_Touchscreen))) { long bitsAbs[LONG_FIELD_SIZE(ABS_CNT)]; if (ioctl(fd, EVIOCGBIT(EV_ABS, sizeof(bitsAbs)), bitsAbs) >= 0 ) { if (testBit(ABS_X, bitsAbs) && testBit(ABS_Y, bitsAbs)) { if ((m_types & Device_Touchpad) && testBit(BTN_TOOL_FINGER, bitsKey)) { qCDebug(lcDD) << "Found touchpad at" << device; ret = true; } else if ((m_types & Device_Touchscreen) && testBit(BTN_TOUCH, bitsKey)) { qCDebug(lcDD) << "Found touchscreen at" << device; ret = true; } else if ((m_types & Device_Tablet) && (testBit(BTN_STYLUS, bitsKey) || testBit(BTN_TOOL_PEN, bitsKey))) { qCDebug(lcDD) << "Found tablet at" << device; ret = true; } } } } if (!ret && (m_types & Device_Joystick)) { long bitsAbs[LONG_FIELD_SIZE(ABS_CNT)]; if (ioctl(fd, EVIOCGBIT(EV_ABS, sizeof(bitsAbs)), bitsAbs) >= 0 ) { if ((m_types & Device_Joystick) && (testBit(BTN_A, bitsKey) || testBit(BTN_TRIGGER, bitsKey) || testBit(ABS_RX, bitsAbs))) { qCDebug(lcDD) << "Found joystick/gamepad at" << device; ret = true; } } } } if (!ret && (m_types & Device_DRM) && device.contains(QString::fromLatin1(QT_DRM_DEVICE_PREFIX))) ret = true; QT_CLOSE(fd); return ret; } void QDeviceDiscoveryHotPlug::handleHotPlugWatch(const QString &path) { if(path.compare(QString::fromLatin1(QT_EVDEV_DEVICE_PATH))) { return; } QStringList devices; // 先移除原来的设备 foreach (const QString &device, m_devices) deviceRemoved(device); // 获取现在的设备 // 注，这里获取的设备已经经过过滤，原因是在对该类进行实例化的时候 // 已经传进了筛选参数，如：QDeviceDiscovery::Device_Keyboard devices = this->scanConnectedDevices(); // 重新添加设备 foreach (const QString &device, devices) deviceDetected(device); } QT_END_NAMESPACE
2.qdevicediscovery_hotplug_p.h文件具体代码如下：
/**************************************************************************** ** ** usb input device hot plug function ** by sn02241 ** ****************************************************************************/ #ifndef QDEVICEDISCOVERY_HOTPLUG_H #define QDEVICEDISCOVERY_HOTPLUG_H // // W A R N I N G // ------------- // // This file is not part of the Qt API. It exists purely as an // implementation detail. This header file may change from version to // version without notice, or even be removed. // // We mean it. // #include "qdevicediscovery_p.h" #include #include QT_BEGIN_NAMESPACE class QDeviceDiscoveryHotPlug : public QDeviceDiscovery { Q_OBJECT public: QDeviceDiscoveryHotPlug(QDeviceTypes types, QObject *parent = 0); QStringList scanConnectedDevices() Q_DECL_OVERRIDE; private slots: void handleHotPlugWatch(const QString &path); private: bool checkDeviceType(const QString &device); // 用于检测鼠标键盘热插拔 QFileSystemWatcher *m_fileWatcher; // 原有的设备列表 QStringList m_devices; }; QT_END_NAMESPACE #endif // QDEVICEDISCOVERY_HOTPLUG_H