casting complex widget pointers

[TheKedge]

Hello,

I've got a class facading two classes, each with its own UI. I don't know at compile time which of these UIs will be shown.

How can I make a function that returns a pointer to on of the UIs:

QWidget* facade::widget()
{
if (suchAndSuc)
return new class1UI; 
else
return class2UI;
}

QWidget* facade::widget()
{
if (suchAndSuc)
return new class1UI; 
else
return class2UI;
}

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or is this the wrong approach?

I'm trying to keep everything as modular as possible - each class should bring its own UI with it - but I don't know which classes will be used. So how do I build a form with widgets without knowing their type?
Could just make sure that all the UIs have a common type as parent and pass this as a pointer? i.e. CommonUI* widget(){return new class1UI;}

thanks
K

[wysota]

If you'll just be passing QWidget pointers, you should be safe (that's what Designer does). Then you can use qobject_cast to cast the result to more complex types if you need them.

[TheKedge]

well, I've got something like:

class UI_one : public QWidget
{
private:
QLabel* l;
QTextEdit* txt;
QPushButton* btn;
//some signals and slots
}
 
class UI_two : public QWidget
{
QPushButton* btn1;
QPushButton* btn2;
//...
}
 
//facade implementation
QWidget* facadeUI::showUI
{
if(condition)
//need to pass pointer to class UI_one
return (QWidget*)new UI_one;//is cast like this ok?
else
//need to pass pointer to class UI_two
return (QWidget*)new UI_one;//???
}
 
//building the user interface
CompleteUI::show()
{
QWidget* someWidget = facade->showUI()
someWidget ->show();//shows on its own
//or
someLayout->addWidget(someWidget );//how it as part of something else
}

class UI_one : public QWidget
{
private:
QLabel* l;
QTextEdit* txt;
QPushButton* btn;
//some signals and slots
}

class UI_two : public QWidget
{
QPushButton* btn1;
QPushButton* btn2;
//...
}

//facade implementation
QWidget* facadeUI::showUI
{
if(condition)
//need to pass pointer to class UI_one
return (QWidget*)new UI_one;//is cast like this ok?
else
//need to pass pointer to class UI_two
return (QWidget*)new UI_one;//???
}

//building the user interface
CompleteUI::show()
{
QWidget* someWidget = facade->showUI()
someWidget ->show();//shows on its own
//or
someLayout->addWidget(someWidget );//how it as part of something else
}

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is that what you mean? - can I down-cast for the pass and still use them properly?
thanks
K

[TheKedge]

ok, I've done it, and it works fine.
I didn't find it obvious that casting a a pointer to something derived from a widget to a widget pointer would work.

thanks for the help,
K

[Chicken Blood Machine]

You don't need those casts either.

QWidget* facadeUI::showUI
{
  if(condition)
    //need to pass pointer to class UI_one
    return new UI_one;
  else
    //need to pass pointer to class UI_two
    return new UI_two;
 
}

QWidget* facadeUI::showUI
{
  if(condition)
    //need to pass pointer to class UI_one
    return new UI_one;
  else
    //need to pass pointer to class UI_two
    return new UI_two;

}

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Also make sure you have a guard so that you don't create new objects everytime showUI is called (unless that is what you intended).