c++ - 尝试从 QFile 读取时出错

Question

我想用 QT 从文件中读取一些数据，然后通过 QComboBox 在 QTableWidget 中显示数据。

void DemoDataView::on_comboBox_activated(const QString &arg1)
{
    ui->tableWidget->setColumnCount(5);
    ui->tableWidget->setRowCount(21);
    ui->tableWidget->verticalHeader()->setVisible(false);
    ui->tableWidget->setHorizontalHeaderLabels(QString("Age Range ; Male Population ; Male Percentage ; Female Population ; Female Percentage").split(";"));
    ui->tableWidget->resizeColumnsToContents();
    ui->tableWidget->resizeRowsToContents();

QFile inputFile("./data.txt");

if(!inputFile.open(QIODevice::ReadOnly))
{
    QMessageBox::information(0, "Error", inputFile.errorString());
}

QTextStream in(&inputFile);
int rows = 0;

while(!in.atEnd()) {

    QString mLine = in.readLine();
    QStringList fields = mLine.split(" ");
    QStringList::iterator it = fields.begin();
    QString regName = *it;

    ui->label->setText(arg1);

    if(regName != "<END>" && QString::compare(regName, arg1) == 0) {
        ui->label->setText(regName);
        it++;
        QString ageRange = *it;
        it++;
        QString nMale = *it;
        double male = nMale.toDouble();
        it++;
        QString nFemale = *it;
        double female = nFemale.toDouble();
        ui->tableWidget->setItem(rows, 0, new QTableWidgetItem(ageRange));
        ui->tableWidget->setItem(rows, 1, new QTableWidgetItem(nMale));
        ui->tableWidget->setItem(rows, 3, new QTableWidgetItem(nFemale));
        ui->tableWidget->setItem(rows, 2, new QTableWidgetItem(malePercCalc(male, female)));
        ui->tableWidget->setItem(rows, 4, new QTableWidgetItem(femalePercCalc(male, female)));

        rows++;

    }

inputFile.close();

    }
}

该文件在项目文件夹和构建项目文件夹中。当我运行该应用程序时，一切正常，但在“应用程序输出”选项卡中出现此错误消息:

“QIODevice::read (QFile, "./data.txt"): 设备未打开”

每次我点击 QComboBox 项目时。

如果有用的话，这是QComboBox的填充代码:

void DemoDataView::setComboBoxRegion() {

QFile inputFile("./data.txt");

if(!inputFile.open(QIODevice::ReadOnly))
{
    QMessageBox::information(0, "Error", inputFile.errorString());
}

QTextStream in(&inputFile);

while(!in.atEnd()) {

    QString mLine = in.readLine();
    QStringList fields = mLine.split(" ");


    QStringList::iterator it = fields.begin();
    QString regName = *it;

    if(regName != "<END>") {
        if(ui->comboBox->findText(regName) == -1){
            ui->comboBox->addItem(regName);
        }
    }
}

inputFile.close();
}

Answer 1

您的问题是您正在调用:

inputFile.close();

循环的内部，这意味着它在第一个循环中关闭。我真的想不出有任何情况会希望发生这种情况；

要解决这个问题，您应该将它移到循环的外部。