Question

I have a C++ project that is using QT4. I’ve used QT Designer to build my form, and in the top bar I have "File -> Open Image". The “Open Image” piece is designated by the QT Designer as a QObject with objectName: actionOpen_Image.

How do I go from a user pressing this QObject, to selecting an image and getting its path so I can load it?

Answer 1

Generally, menu items are QAction objects – if you can get your object to be an action, that would be a good first step.

QActions have a signal triggered which is emitted when selected by a user. This signal can be connected to a slot which can be part of an existing QObject or custom-defined.

To create and object with a slot, the following example may be helpful:

class MyClass : QObject{
Q_OBJECT //<---macro which flags the class for the Meta-Object Compiler(moc) tool
public:
  MyClass(QObject* parent=):QObject(parent){}
public slots: //<--- also for the moc tool to handle
  void mySlot(){
    //custom behavior
    QString fileName = QFileDialog::getOpenFileName(/*args*/);
  }
};

Here, the QFileDialog class is used (via a static method) to get the name of a file. You can set filters for file types and other useful properties, and the dialog will use the native file-dialog of whatever operating system you’re working with.

Use the connect(QObject* sender, SIGNAL, QObject* receiver, SLOT) method to connect the QAction::triggered signal to the slot you wish to be activated.

Actual implementation is up to you of course, hope this can get you started.