1.16 入门实例：从文件中加载与保存到文件.txt

qt的源代码

void saveToFile();
     void loadFromFile();
     ...
     QPushButton *loadButton;
     QPushButton *saveButton; 
loadButton->setToolTip(tr("Load contacts from a file"));
     ...
     saveButton->setToolTip(tr("Save contacts to a file"));
void AddressBook::saveToFile()
 {
     QString fileName = QFileDialog::getSaveFileName(this,
         tr("Save Address Book"), "",
         tr("Address Book (*.abk);;All Files (*)"));
if (fileName.isEmpty())
         return;
     else {
         QFile file(fileName);
         if (!file.open(QIODevice::WriteOnly)) {
             QMessageBox::information(this, tr("Unable to open file"),
                 file.errorString());
             return;
         }
QDataStream out(&file);
         out.setVersion(QDataStream::Qt_4_3);
         out << contacts;
     }
 }
void AddressBook::loadFromFile()
 {
     QString fileName = QFileDialog::getOpenFileName(this,
         tr("Open Address Book"), "",
         tr("Address Book (*.abk);;All Files (*)"));
if (fileName.isEmpty())
         return;
     else {
         QFile file(fileName);
         if (!file.open(QIODevice::ReadOnly)) {
             QMessageBox::information(this, tr("Unable to open file"),
                 file.errorString());
             return;
         }
         QDataStream in(&file);
         in.setVersion(QDataStream::Qt_4_3);
         contacts.empty();   
         in >> contacts;
if (contacts.isEmpty()) {
             QMessageBox::information(this, tr("No contacts in file"),
                 tr("The file you are attempting to open contains no contacts."));
         } else {
             QMap<QString, QString>::iterator i = contacts.begin();
             nameLine->setText(i.key());
             addressText->setText(i.value());
}
     }
     updateInterface(NavigationMode);
 }