Qt检测U盘插入拔出Demo

要做这个，要先知道Qt的QAbstractNativeEventFilter类，虚函数nativeEventFilter。这个类的主要作用是捕获全局windows消息。

先看一下效果：

基本注意以下两点：

1、新建的类要继承

QAbstractNativeEventFilter

2、新建的类要被安装事件过滤，比如：

qApp->installNativeEventFilter(QAbstractNativeEventFilter *filterObj);

这里我封装了一个简单的类uDisk：

①头文件

#ifndef UDISK_H
#define UDISK_H
#include <QWidget>
#include <windows.h>
#include <QAbstractNativeEventFilter>
#include <dbt.h>
class uDisk : public QWidget, public QAbstractNativeEventFilter
{
    Q_OBJECT
protected:
    bool nativeEventFilter(const QByteArray &eventType, void *message, long *result);
signals:
    void sigUDiskCome(QString uDiskName);
    void sigUDiskRemove();
private:
    char FirstDriveFromMask(ULONG unitmask);
};
#endif // UDISK_H

②源文件

#include "uDisk.h"
#include <QApplication>
#include <QDebug>
char uDisk::FirstDriveFromMask(ULONG unitmask)
{
    char i;
    for (i = 0; i < 26; ++i) {
        if (unitmask & 0x1) {
            break;
        }
        unitmask = unitmask >> 1;
    }
    return (i + 'A');
}
bool uDisk::nativeEventFilter(const QByteArray &eventType, void *message, long *result)
{
    MSG* msg = reinterpret_cast<MSG*>(message);
    int msgType = msg->message;
    if(msgType == WM_DEVICECHANGE) {
        PDEV_BROADCAST_HDR lpdb = (PDEV_BROADCAST_HDR)msg->lParam;
        switch (msg->wParam) {
        case DBT_DEVICEARRIVAL:
            if(lpdb->dbch_devicetype == DBT_DEVTYP_VOLUME) {
                PDEV_BROADCAST_VOLUME lpdbv = (PDEV_BROADCAST_VOLUME)lpdb;
                if(lpdbv->dbcv_flags ==0) {
                    QString USBDisk = QString(this->FirstDriveFromMask(lpdbv ->dbcv_unitmask));
                    emit sigUDiskCome(USBDisk);
                }
            }
            break;
        case DBT_DEVICEREMOVECOMPLETE:
            if(lpdb->dbch_devicetype == DBT_DEVTYP_VOLUME) {
                PDEV_BROADCAST_VOLUME lpdbv = (PDEV_BROADCAST_VOLUME)lpdb;
                if(lpdbv->dbcv_flags == 0) {
                    emit sigUDiskRemove();
                }
            }
            break;
        case DBT_DEVNODES_CHANGED:
            break;
        default:
            break;
        }
    }
    return QWidget::nativeEvent(eventType, message, result);
}

如何使用：

1、引用头文件#include "uDisk.h"

2、声明uDisk *m_uDisk = Q_NULLPTR;

3、调用：    

m_uDisk = new uDisk;
    qApp->installNativeEventFilter(m_uDisk);
    connect(m_uDisk, &uDisk::sigUDiskCome, [=](QString uDiskName){
        ui->label->setText(tr("U Disk Come!").append(tr("The Disk is ") + uDiskName));
    });
    connect(m_uDisk, &uDisk::sigUDiskRemove, [=](){
        ui->label->setText(tr("U Disk Remove!"));
    });

4、在调用类析构时记得析构掉：    

if(m_uDisk) {
        delete m_uDisk;
        m_uDisk = Q_NULLPTR;
    }