Looking for suggestions or hints on best way to...

[SPlatten]

I'm implementing classes which are derived from Qt controls and I need to implement a way of saving an original state of say for example QCheckBox or QComboBox etc.

The checkbox is easy enough I could just save a boolean value and compare if later, but I'm looking for something more generic.

I would like to have a function that saves the a copy of the control state and then later I can compare the current state with the original for change. I realise that using memcpy isn't going to be a workable solution for comparing classes, can I rely on the '=' operator to compare a copy against the current version?

If anyone can suggest a portable and generic way that I can use for Qt controls, very much appreciated.

[SGaist]

Hi,

You can do some meta system programming and store the value of the property that is marked as USER.

See the property system documentation for more information.

[SPlatten]

@SGaist , I'm looking at this now, I would imagine that implementing this method would require a specific implementation for each control, I was hoping to add something that would require minimal differences between different controls. I started with a base class that has a couple of pure virtual functions such as:

virtual bool blnChanged() = 0; // Returns true if control has changed from original
virtual void saveOriginal() = 0; // Saves the current state as the original

[SGaist]

That's why I am suggesting using meta system programming. Inspect the objects QMetaObject to get the right property and store that one.

[SPlatten]

@SGaist , I'll read up.

[SPlatten]

Doesn't look like a simple solution, I need to take a break and come back fresh another day. Need to think about this.

[SPlatten]

@SGaist , can properties be added at run-time?

I want to store the original data for each GUI object, I was thinking of doing this in properties the comparing the original data with the current data and returning true if there is a difference.

Just found this:
https://doc.qt.io/qt-5/properties.html#dynamic-properties

Looking into it.

[JoeCFD]

Try to use QStateMachine.

[SimonSchroeder]

@SGaist said in Looking for suggestions or hints on best way to...:

That's why I am suggesting using meta system programming. Inspect the objects QMetaObject to get the right property and store that one.

Having a quick look shows that QMetaObject even has a userProperty() member functions. The link @SGaist already provided says the following about the USER property:

The USER attribute indicates whether the property is designated as the user-facing or user-editable property for the class. Normally, there is only one USER property per class (default false). e.g., QAbstractButton::checked is the user editable property for (checkable) buttons.

So, I would suggest trying something like this:

const char *propertyName = widget->metaObject()->userProperty()->name();
QVariant value = widget->property(name);
...
widget->setProperty(name, value);

You need to figure out, though, what happens if there is no USER property. Maybe propertyName would be an empty string or nullptr?

[SPlatten]

I've made some progress in this area, not all widgets have USER property, but its pretty simple to figure out.