Joining together a QComboBox, QStringList, and enum

[Phlucious]

I've done multiple searches (Google and otherwise) to see if there's an elegant Qt way to join together a QString and an enum for a QComboBox without having to manage two separate objects (a const QStringList and an enum), often defined in two separate places, and without hardcoding the link. Having not found anything, I thought I'd post something I came across today.

This centers on QComboBox's little-discussed ability to store "UserData" fields in its associated data model. To associate the QString with an enum simply use the third field of QComboBox::insertItem.

For example:

enum Fruit
{
	APPLE,
	ORANGE,
	TANGERINE,
	STARFRUIT
}
 
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
	ui(new Ui::MainWindow)
{
	/* Set up the GUI */
	ui->setupUi(this);
 
	/* generate the default options with associated values */
	myComboBox->insertItem(myComboBox->count(), "Star Fruit", STARFRUIT);
	myComboBox->insertItem(myComboBox->count(), "Granny Smith", APPLE);
	myComboBox->insertItem(myComboBox->count(), "Navel Orange", ORANGE);
	myComboBox->insertItem(myComboBox->count(), "Fancy Orange", TANGERINE);
	//etc
 
	/* add another few */
	int nextCode = 84;
	myComboBox->insertItem(myComboBox->count(), "user-entered text", nextCode++);
	myComboBox->insertItem(myComboBox->count(), "more text", nextCode++);
	myComboBox->insertItem(0, "at the beginning", nextCode++);
}
 
/* data retrieval */
int MainWindow::getCode(QString label)
{
	return myComboBox->findText(label)->toInt();
}
QString MainWindow::getLabel(int code = APPLE)
{
	return myComboBox->itemText(myComboBox->findData(code)->toInt());
}

enum Fruit
{
	APPLE,
	ORANGE,
	TANGERINE,
	STARFRUIT
}


MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
	ui(new Ui::MainWindow)
{
	/* Set up the GUI */
	ui->setupUi(this);

	/* generate the default options with associated values */
	myComboBox->insertItem(myComboBox->count(), "Star Fruit", STARFRUIT);
	myComboBox->insertItem(myComboBox->count(), "Granny Smith", APPLE);
	myComboBox->insertItem(myComboBox->count(), "Navel Orange", ORANGE);
	myComboBox->insertItem(myComboBox->count(), "Fancy Orange", TANGERINE);
	//etc

	/* add another few */
	int nextCode = 84;
	myComboBox->insertItem(myComboBox->count(), "user-entered text", nextCode++);
	myComboBox->insertItem(myComboBox->count(), "more text", nextCode++);
	myComboBox->insertItem(0, "at the beginning", nextCode++);
}

/* data retrieval */
int MainWindow::getCode(QString label)
{
	return myComboBox->findText(label)->toInt();
}
QString MainWindow::getLabel(int code = APPLE)
{
	return myComboBox->itemText(myComboBox->findData(code)->toInt());
}

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Note that a big advantage here is that order suddenly doesn't matter any more since the "code" has been divorced from the QComboBox::currentIndex, allowing you to sort the QComboBox by code or by label, to insert at arbitrary locations (perhaps with user-entered data), and to still switch-case using the enum without error-prone hard-coding of fixed values. Plus, you only have to enter the strings once, in a single location, significantly reducing mistakes whenever you need to change the label of a particular item.

Re-use is a piece of cake, too. If you use the same list frequently, you can easily sub-class QComboBox and insert the list into the constructor:

class FruitComboBox : public QComboBox
{
	Q_OBJECT
public:
	explicit ClassComboBox(QWidget *parent = 0);
	QStringList fruitList() const;
	int currentFruit() const;
 
	enum Fruits
	{
		APPLE,
		PEAR,
		ORANGE
	};
signals:
	void currentFruitChanged(QString);
	void currentFruitChanged(int);
public slots:
	void insertFruit(const QString& newlabel);
	void setCurrentFruit(const QString& fruit);
	void setCurrentFruit(int fruitcode);
protected:
	int m_nextFruitCode;
}
 
FruitComboBox::FruitComboBox(QWidget *parent) :
	QComboBox(parent), m_nextFruitCode(-1)
{
	/* generate the default list */
	insertItem(count(), "I love apples!", APPLE);
	insertItem(count(), "I love pears!", PEAR);
	insertItem(count(), "ZOMG oranges!", ORANGE);
}
 
void FruitComboBox::insertFruit(const QString& newlabel)
{
	insertItem(0, newlabel, m_nextFruitCode--);
}

class FruitComboBox : public QComboBox
{
	Q_OBJECT
public:
	explicit ClassComboBox(QWidget *parent = 0);
	QStringList fruitList() const;
	int currentFruit() const;

	enum Fruits
	{
		APPLE,
		PEAR,
		ORANGE
	};
signals:
	void currentFruitChanged(QString);
	void currentFruitChanged(int);
public slots:
	void insertFruit(const QString& newlabel);
	void setCurrentFruit(const QString& fruit);
	void setCurrentFruit(int fruitcode);
protected:
	int m_nextFruitCode;
}

FruitComboBox::FruitComboBox(QWidget *parent) :
	QComboBox(parent), m_nextFruitCode(-1)
{
	/* generate the default list */
	insertItem(count(), "I love apples!", APPLE);
	insertItem(count(), "I love pears!", PEAR);
	insertItem(count(), "ZOMG oranges!", ORANGE);
}

void FruitComboBox::insertFruit(const QString& newlabel)
{
	insertItem(0, newlabel, m_nextFruitCode--);
}

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Personally, I like to decrement the "nextCode" field so that it's easy to tell the difference between the enum values (>= 0) and the user-entered fields (<0).

Hope that helps the next person trying to do something like this. Comments?


PS—I've accomplished similar functionality using a QMap<QString, int> of label-enum pairs and then using QMap::keys() to populate the QComboBox, but the proposed method is more flexible.

[Spitfire]

I was using that approach for quite some time, but it never occured to me that it's may not be that common knowledge.
Thanks for taking the effort to post it