Use QSaveFile in MainWindow examples

QSaveFile should preferably be used by editor applications to catch
write errors.

Task-number: QTBUG-60635
Change-Id: Ia609435871b56b45714c3dd3d32bbc85b5cb4dd5
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

examples/widgets/doc/src/application.qdoc

@@ -327,9 +327,12 @@
     \snippet mainwindows/application/mainwindow.cpp 44
     \snippet mainwindows/application/mainwindow.cpp 45
 
-    Saving a file is very similar to loading one. Here, the
+    Saving a file is similar to loading one. We use QSaveFile to ensure
-    QFile::Text flag ensures that on Windows, "\\n" is converted into
+    all data are safely written and existing files are not damaged
-    "\\r\\n" to conform to the Windows convension.
+    should writing fail.
+    We use the QFile::Text flag to make sure that on Windows, "\\n"
+    is converted into "\\r\\n" to conform to the Windows convention.
+
 
     \snippet mainwindows/application/mainwindow.cpp 46
     \snippet mainwindows/application/mainwindow.cpp 47

examples/widgets/mainwindows/application/mainwindow.cpp

@@ -353,24 +353,28 @@ void MainWindow::loadFile(const QString &fileName)
 bool MainWindow::saveFile(const QString &fileName)
 //! [44] //! [45]
 {
-    QFile file(fileName);
+    QString errorMessage;
-    if (!file.open(QFile::WriteOnly | QFile::Text)) {
+
-        QMessageBox::warning(this, tr("Application"),
+    QGuiApplication::setOverrideCursor(Qt::WaitCursor);
-                             tr("Cannot write file %1:\n%2.")
+    QSaveFile file(fileName);
-                             .arg(QDir::toNativeSeparators(fileName),
+    if (file.open(QFile::WriteOnly | QFile::Text)) {
-                                  file.errorString()));
+        QTextStream out(&file);
+        out << textEdit->toPlainText();
+        if (!file.commit()) {
+            errorMessage = tr("Cannot write file %1:\n%2.")
+                           .arg(QDir::toNativeSeparators(fileName), file.errorString());
+        }
+    } else {
+        errorMessage = tr("Cannot open file %1 for writing:\n%2.")
+                       .arg(QDir::toNativeSeparators(fileName), file.errorString());
+    }
+    QGuiApplication::restoreOverrideCursor();
+
+    if (!errorMessage.isEmpty()) {
+        QMessageBox::warning(this, tr("Application"), errorMessage);
         return false;
     }
 
-    QTextStream out(&file);
-#ifndef QT_NO_CURSOR
-    QGuiApplication::setOverrideCursor(Qt::WaitCursor);
-#endif
-    out << textEdit->toPlainText();
-#ifndef QT_NO_CURSOR
-    QGuiApplication::restoreOverrideCursor();
-#endif
-
     setCurrentFile(fileName);
     statusBar()->showMessage(tr("File saved"), 2000);
     return true;

examples/widgets/mainwindows/mdi/mdichild.cpp

@@ -115,19 +115,28 @@ bool MdiChild::saveAs()
 
 bool MdiChild::saveFile(const QString &fileName)
 {
-    QFile file(fileName);
+    QString errorMessage;
-    if (!file.open(QFile::WriteOnly | QFile::Text)) {
+
-        QMessageBox::warning(this, tr("MDI"),
+    QGuiApplication::setOverrideCursor(Qt::WaitCursor);
-                             tr("Cannot write file %1:\n%2.")
+    QSaveFile file(fileName);
-                             .arg(QDir::toNativeSeparators(fileName), file.errorString()));
+    if (file.open(QFile::WriteOnly | QFile::Text)) {
+        QTextStream out(&file);
+        out << toPlainText();
+        if (!file.commit()) {
+            errorMessage = tr("Cannot write file %1:\n%2.")
+                           .arg(QDir::toNativeSeparators(fileName), file.errorString());
+        }
+    } else {
+        errorMessage = tr("Cannot open file %1 for writing:\n%2.")
+                       .arg(QDir::toNativeSeparators(fileName), file.errorString());
+    }
+    QGuiApplication::restoreOverrideCursor();
+
+    if (!errorMessage.isEmpty()) {
+        QMessageBox::warning(this, tr("MDI"), errorMessage);
         return false;
     }
 
-    QTextStream out(&file);
-    QGuiApplication::setOverrideCursor(Qt::WaitCursor);
-    out << toPlainText();
-    QGuiApplication::restoreOverrideCursor();
-
     setCurrentFile(fileName);
     return true;
 }

examples/widgets/mainwindows/sdi/mainwindow.cpp

@@ -425,19 +425,28 @@ void MainWindow::openRecentFile()
 
 bool MainWindow::saveFile(const QString &fileName)
 {
-    QFile file(fileName);
+    QString errorMessage;
-    if (!file.open(QFile::WriteOnly | QFile::Text)) {
+
-        QMessageBox::warning(this, tr("SDI"),
+    QGuiApplication::setOverrideCursor(Qt::WaitCursor);
-                             tr("Cannot write file %1:\n%2.")
+    QSaveFile file(fileName);
-                             .arg(QDir::toNativeSeparators(fileName), file.errorString()));
+    if (file.open(QFile::WriteOnly | QFile::Text)) {
+        QTextStream out(&file);
+        out << textEdit->toPlainText();
+        if (!file.commit()) {
+            errorMessage = tr("Cannot write file %1:\n%2.")
+                           .arg(QDir::toNativeSeparators(fileName), file.errorString());
+        }
+    } else {
+        errorMessage = tr("Cannot open file %1 for writing:\n%2.")
+                       .arg(QDir::toNativeSeparators(fileName), file.errorString());
+    }
+    QGuiApplication::restoreOverrideCursor();
+
+    if (!errorMessage.isEmpty()) {
+        QMessageBox::warning(this, tr("SDI"), errorMessage);
         return false;
     }
 
-    QTextStream out(&file);
-    QGuiApplication::setOverrideCursor(Qt::WaitCursor);
-    out << textEdit->toPlainText();
-    QGuiApplication::restoreOverrideCursor();
-
     setCurrentFile(fileName);
     statusBar()->showMessage(tr("File saved"), 2000);
     return true;