Documentation: Fix "Using Model Indexes" in Model View Programming guide to work

The code introduced by 54d5ca0c2766e915c960fa437cee6c20a324c1a7
did not work since the variables parentIndex/numRows
were local to the lambda and the outer code would not wait.
Move the widgets population into the lambda to fix this.

Modernize the remaining code a bit.

Change-Id: I2a09878987df9edb9ff04f0ac4ad82af1a8b52c8
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
(cherry picked from commit c49bf9fe27e0632aa8da393ff007cf4577a1c9cd)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/doc/snippets/simplemodel-use/main.cpp

@@ -7,55 +7,61 @@
   A simple example of how to access items from an existing model.
 */
 
-#include <QtGui>
+#include <QApplication>
+#include <QLabel>
+#include <QVBoxLayout>
+#include <QWidget>
+
+#include <QFileSystemModel>
+#include <QPalette>
+
+#include <QDir>
+#include <QModelIndex>
 
 /*!
     Create a default directory model and, using the index-based interface to
     the model and some QLabel widgets, populate the window's layout with the
     names of objects in the directory.
-
-    Note that we only want to read the filenames in the highest level of the
-    directory, so we supply a default (invalid) QModelIndex to the model in
-    order to indicate that we want top-level items.
 */
 
 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
 
-    QWidget *window = new QWidget;
+    QWidget window;
-    QVBoxLayout *layout = new QVBoxLayout(window);
+    auto *layout = new QVBoxLayout(&window);
-    QLabel *title = new QLabel("Some items from the directory model", window);
+    auto *title = new QLabel("Some items from the directory model", &window);
     title->setBackgroundRole(QPalette::Base);
     title->setMargin(8);
     layout->addWidget(title);
 
 //! [0]
-    QFileSystemModel *model = new QFileSystemModel;
+    auto *model = new QFileSystemModel;
-    connect(model, &QFileSystemModel::directoryLoaded, [model](const QString &directory) {
+
+    auto onDirectoryLoaded = [model, layout, &window](const QString &directory) {
         QModelIndex parentIndex = model->index(directory);
-        int numRows = model->rowCount(parentIndex);
+        const int numRows = model->rowCount(parentIndex);
-    });
+//! [1]
-    model->setRootPath(QDir::currentPath);
+        for (int row = 0; row < numRows; ++row) {
+            QModelIndex index = model->index(row, 0, parentIndex);
+//! [1]
+
+//! [2]
+            QString text = model->data(index, Qt::DisplayRole).toString();
+//! [2]
+            // Display the text in a widget.
+            auto *label = new QLabel(text, &window);
+            layout->addWidget(label);
+//! [3]
+        }
+//! [3]
+    };
+
+    QObject::connect(model, &QFileSystemModel::directoryLoaded, onDirectoryLoaded);
+    model->setRootPath(QDir::currentPath());
 //! [0]
 
-//! [1]
+    window.setWindowTitle("A simple model example");
-    for (int row = 0; row < numRows; ++row) {
+    window.show();
-        QModelIndex index = model->index(row, 0, parentIndex);
-//! [1]
-
-//! [2]
-        QString text = model->data(index, Qt::DisplayRole).toString();
-        // Display the text in a widget.
-//! [2]
-
-        QLabel *label = new QLabel(text, window);
-        layout->addWidget(label);
-//! [3]
-    }
-//! [3]
-
-    window->setWindowTitle("A simple model example");
-    window->show();
     return app.exec();
 }

src/widgets/doc/src/model-view-programming.qdoc

@@ -449,11 +449,13 @@
     \snippet simplemodel-use/main.cpp 0
 
     In this case, we start by setting up a default QFileSystemModel. We connect
-    it to a lambda, in which we will obtain a parent index using a specific
+    its signal \c directoryLoaded(QString) to a lambda, in which we will
+    obtain a parent index for the directory using a specific
     implementation of \l{QFileSystemModel::}{index()} provided by that model.
-    In the lambda, we count the number of rows in the model using the
+
-     \l{QFileSystemModel::}{rowCount()} function. Finally, we set the root path
+    In the lambda, we determine the number of rows in the model using the
-    of the QFileSystemModel so it starts loading data and triggers the lambda.
+     \l{QFileSystemModel::}{rowCount()} function.
+
 
     For simplicity, we are only interested in the items in the first column
     of the model. We examine each row in turn, obtaining a model index for
@@ -474,6 +476,9 @@
     \codeline
     \snippet simplemodel-use/main.cpp 3
 
+    Finally, we set the root path of the QFileSystemModel so it starts
+    loading data and triggers the lambda.
+
     The above example demonstrates the basic principles used to retrieve
     data from a model: