Practical Model View Programming

P R A C T IC A L M O D EL V IEW
PR O GR A M M IN G
C O D E LESS . V I EW M O R E.

Marius Bugge Monsen,
MSc (N TN U),
Software D eveloper

C ontents

● An O verview of the Q t Model View Architecture
● An Introduction to The Model Interface
● Advanced Model View Techniques (Q t 4.1+)

A n O verview of the Q t M odel V iew A rchitecture

I tem S elections

U ser I nput I tem Selection State

U ser I nput
V iew I tem D elegate

C hange N otif cations
i D ata C hanges

M odel

Item B ased V iews (Q t 3 and 4)

Table W idget T ree W idget List W idget

I tem S elections

V iew V iew

M odel

int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QDirModel model;
QTableView view1;
QTreeView view2;

view1.setModel(&model);
view2.setModel(&model);

view1.setRootIndex(model.index(0, 0));
view1.show();
view2.show();
app.exec();
}

W hat do you get ?

Eff ciency
i
Flexibility
Maintainability

A n I ntroduction To T he M odel Interface

class ListModel : public QAbstractListModel
{
Q_OBJECT
public:
ListModel(QObject *parent = 0);
~ListModel();

int rowCount(const QModelIndex &parent) const;
QVariant data(const QModelIndex &index, int role) const;
};

ListModel::ListModel(QObject *parent)
: QAbstractListModel(parent) {}
ListModel::~ListModel() {}

int ListModel::rowCount(const QModelIndex &) const
{
return 10000;
}

QVariant ListModel::data(const QModelIndex &index,
int role) const
{
if (role == Qt::DisplayRole)
return index.row();
return QVariant();
}

0 0 1 2

0 0

1 1

2 2

int main(int, char *[])
{
ListModel model;

QModelIndex index = model.index(2);
QVariant data = model.data(index, Qt::DisplayRole);

qDebug() << data;
}

D ecoration R ole
Type:Image File
Size: 1.2 Mb

ToolT ip R ole

M y W orld

D isplay R ole

QVariant ListModel::data(const QModelIndex &index,
int role) const
{
if (role == Qt::DisplayRole)
return index.row();

if (role == Qt::DecorationRole)
return QColor(Qt::green);

return QVariant();
}

class ColorDelegate : public QItemDelegate
{
Q_OBJECT
public:
ColorDelegate(QObject *parent = 0);
protected:
void paint(QPainter *painter,
const QStyleOptionViewItem &option,
const QModelIndex &index) const;
};

void ColorDelegate::paint(QPainter *painter,
const QStyleOptionViewItem &option,
const QModelIndex &index) const
{
const QAbstractItemModel *model = index.model();
QVariant decoration = model->data(index, Qt::DecorationRole);
if (decoration.type() == QVariant::Color) {
QLinearGradient gradient(option.rect.left(), 0,
option.rect.width(), 0);
QColor left = option.palette.color(QPalette::Background);
gradient.setColorAt(0, left);
QColor right = qvariant_cast<QColor>(decoration);
gradient.setColorAt(1, right);
painter->fillRect(option.rect, gradient);
}
QItemDelegate::paint(painter, option, index);
}

One 100 -300 500
Two 599 300 233
Three 33 -34 -55
Four 200 502 200

class TableModel : public QAbstractTableModel
{
Q_OBJECT
public:
TableModel(QObject *parent = 0);
~TableModel();
int rowCount(const QModelIndex &parent) const;
int columnCount(const QModelIndex &parent) const;
QVariant data(const QModelIndex &index, int role) const;
bool setData(const QModelIndex &index,
const QVariant &value, int role);
Qt::ItemFlags flags(const QModelIndex &index) const;
// not part of the model interface
bool load(const QString &fileName);
bool save(const QString &fileName) const;
private:
int rows, columns;
QVector<QVariant> table;
};

QVariant TableModel::data(const QModelIndex &index,
int role) const
{
int i = index.row() * columns + index.column();
QVariant value = table.at(i);

if (role == Qt::EditRole || role == Qt::DisplayRole)
return value;

if (role == Qt::TextColorRole
&& value.type() == QVariant::Int) {
if (value.toInt() < 0)
return QColor(Qt::red);
return QColor(Qt::blue);
}
return QVariant();
}

bool TableModel::setData(const QModelIndex &index,
const QVariant &value, int role)
{
int i = index.row() * columns + index.column();
if (role == Qt::EditRole) {
table[i] = value;
QModelIndex topLeft = index;
QModelIndex bottomRight = index;
emit dataChanged(topLeft, bottomRight);// <<< important!
return true;
}
return false;
}
Qt::ItemFlags TableModel::flags(const QModelIndex &index) const
{
return QAbstractTableModel::flags(index)|Qt::ItemIsEditable;
}

bool TableModel::load(const QString &fileName)
{
QFile file(fileName);
if (!file.open(QIODevice::ReadOnly|QIODevice::Text))
return false;
rows = columns = 0;
table.clear();
QTextStream in(&file);
bool result = parse(in);

reset();// <<< important!

return result;
}

A dvanced M odel V iew Techniques (Q t 4.1+)

{
TableModel model;
model.load("table.data");

QSortingProxyModel sorter;
sorter.setSourceModel(&model);
QTreeView treeview;
treeview.setModel(&sorter);

treeview.header()->setClickable(true);
treeview.header()->setSortIndicatorShown(true);
treeview.show();
return app.exec();
}

{
QWidget widget;
QBoxLayout *layout = new QBoxLayout(QBoxLayout::TopToBottom,
&widget);
QLineEdit *lineedit = new QLineEdit;
layout->addWidget(lineedit);
TableModel model;
model.load("table.data");
QStringFilterModel filter;
filter.setSourceModel(&model);
QObject::connect(lineedit,SIGNAL(textChanged(const QString&)),
&filter,SLOT(setPattern(const QString&)));
QTableView *tableview = new QTableView;
tableview->setModel(&filter);
layout->addWidget(tableview);
widget.show();
return app.exec();
}

M odel
1

A gg regating V iew
M odel
2

{
QTreeView treeview;
QStringListModel model_1(QStringList()
<< "ALPHA" << "BRAVO"
<< "CHARLIE" << "DELTA");
QDirModel model_2;
QAggregatingProxyModel aggregator;
aggregator.appendSourceModel(&model_1);
aggregator.appendSourceModel(&model_2);
treeview.setModel(&aggregator);
treeview.show();
return app.exec();
}

W hat we have covered

● Q t Model View Architecture O verview
● The Model Interface Introduction
● Advanced Techniques Using the Model Interface

M ore Inform ation

http://doc.trolltech.com/4.0/model-view-programming.html
http://doc.trolltech.com/4.0/model-view.html

Practical Model View Programming

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