格式化文件异常被 try catch 块忽略

我必须通过使用Windows资源管理器选择文件来从XML文件加载数据。如果我选择其他格式，而不是 XML，则 catch 块应该会出现异常。但它没有，应用程序失败。这是我到目前为止编写的代码。我错过了什么？我将表达式从 xml 方法扔到readVehicles(QString fileName)中。

    QList<Vehicle> VehicleHelper::readVehicles(QString fileName){
     QList<Vehicle> vehicles;
     Vehicle newVehicle;
     QFile file(fileName);
     QDomDocument document;
     if(!file.open(QIODevice::ReadOnly | QIODevice::Text)){
        throw FileCannotBeOpenException();
     }
     else{
        if(!document.setContent(&file)){
            throw InvalidXMLContentException();
        }
        file.close();
    }
    QDomElement root = document.firstChildElement();
    QDomNodeList carElements = root.elementsByTagName("Car");
    for(int i = 0; i < carElements.size(); i++){
        QDomNode carNode = carElements.at(i);
        QDomElement carElement = carNode.toElement();
        QString carID = carElement.attribute("ID");
       //if the idNumber is null, generate one
       if(carID.isEmpty()){
            QUuid newId = Vehicle::generateID();
            newVehicle.setVehicleId(newId);
       }
       else {
            QUuid id;
            try{
               id = QUuid::QUuid(carID);
            } catch(QException &ex){
               continue;
        }
        newVehicle.setVehicleId(id);
    }
    //Owner
    //****************************************************************
    QDomElement ownerElement = carNode.firstChildElement("Owner");
    //FirstName
    QDomElement fNameElement = ownerElement.firstChildElement("FirstName");
    QString fName = fNameElement.text();

    //LastName
    QDomElement lNameElement = fNameElement.nextSiblingElement("LastName");
    QString lName = lNameElement.text();

    //Address
    QDomElement addressElement = lNameElement.nextSiblingElement("Address");
    QString address = addressElement.text();
    //append vehicle to the list
    vehicles.append(newVehicle);
  }
}

并且 try-catch 块在 on_actionOpen_triggered() 方法中

    void MainWindow::on_actionOpen_triggered()
{
    if(isModified){
        QMessageBox msgBox;
        QString message = "There are unsaved changes! Do you proceed? ";
        msgBox.setWindowTitle("Save Changes");
        msgBox.setText(message);
        msgBox.addButton("Don't save",QMessageBox::NoRole);
        msgBox.addButton(QMessageBox::Save);
        msgBox.addButton(QMessageBox::Cancel);
        msgBox.setIcon(QMessageBox::Question);
        int result = msgBox.exec();
        if(result == QMessageBox::Save){
            VehicleHelper::writeVehicles(cars,filename);
            msgBox.close();
        } else {
            QString fileName = QFileDialog::getOpenFileName(this,"Open file");
            if(!fileName.isEmpty()){
                setFileName(fileName);
                QFile file(fileName);
                try {
                    cars = VehicleHelper::readVehicles(fileName);
                } catch(FileCannotBeOpenException &ex) {
                    QMessageBox msgBox;
                    msgBox.setIcon(QMessageBox::Critical);
                    msgBox.setWindowTitle("Message!");
                    msgBox.setText("Failed to open file");
                    msgBox.setDefaultButton(QMessageBox::Ok);
                    msgBox.exec();
                    return;
                } catch(InvalidXMLContentException &ex){
                    QMessageBox msgBox;
                    msgBox.setIcon(QMessageBox::Critical);
                    msgBox.setWindowTitle("Message!");
                    msgBox.setText("Failed to load data!");
                    msgBox.setDefaultButton(QMessageBox::Ok);
                    msgBox.exec();
                    return;
                }
                setTakenNumbersList(cars);
                //set data to the table view
                populate(cars);
           }
        }
    } else {
        QString fileName = QFileDialog::getOpenFileName(this,"Open file");
        if(!fileName.isEmpty()){
            setFileName(fileName);
            QFile file(fileName);
            if(file.open(QFile::ReadOnly | QFile::Text)){
                cars = VehicleHelper::readVehicles(fileName);
                setTakenNumbersList(cars);
                file.close();
                //set data to the table view
                populate(cars);
                ui->actionAdd->setEnabled(true);
                ui->actionBy_name->setEnabled(true);
                ui->actionBy_registration_date->setEnabled(true);
                ui->actionBy_registration_number->setEnabled(true);
                ui->actionBy_revision_date->setEnabled(true);
                ui->actionBy_type->setEnabled(true);
                ui->actionClear_Search->setEnabled(true);
                ui->actionDelete->setEnabled(true);
                ui->actionEdit->setEnabled(true);
                ui->actionSave->setEnabled(true);
                ui->actionSave_As->setEnabled(true);
            }
        }
    }
}