QT4: How to get access to an object what is on mainwidow from an other class?

If Im in mainwindow.cpp then i can get every obj开发者_StackOverflow中文版ect on it with:

this->ui->textBox ...

What if there is another class (myclass2.cpp) and I would like to get the value of one the textBoxes. But they are on my mainwindow. I cant use this->ui->textBox

Whats the way to get access to the objects?

Thank You

In general, this is not a problem specific to Qt. There are several ways you can do this:

1. Provide a method on mainwindow that encapsulates what you want, and call that from myclass2.

   // In mainwindow.cpp:
   QString mainwindow::valueOfTheTextEditYouAreInterestedIn() const
   {
        return ui->textBox->toPlainText();
   }
   

   This has lots of benefits: clean design, easy to change later, and highly self-documenting, just to name a few. For this to work, your myclass2 object will still need a pointer to the main window, though. Then you would call it like this:

   // In myclass2.cpp:
   {
       // we're in some function of myclass2
       QString value = theMainWindow->valueOfTheTextEditYouAreInterestedIn();
   
       // Use the value...
   }
   

2. Provide an accessor for the text edit. This is not such a good idea, because then myclass2 can alter the text edit without mainwindow knowing about it. However, it would look like:

   QTextEdit *getTheInterestingTextEdit()
   {
        return ui->textBox;
   }
   

   This can be made more acceptable by returning a constant pointer, so that myclass2 will be able to read, but not modify, the values of the text edit:

   const QTextEdit *getTheInterestingTextEdit() const
   {
        return ui->textBox;
   }
   

   Qt provides yet another way to do the same thing, but you don't have to write your own method for it:

   // In myclass2.cpp:
   QTextEdit *textBox = theMainWindow->findChild<QTextEdit *>("textBox");
   

   where mainwindow is a pointer to the main window object that myclass2 will need to obtain somehow, and "textBox" is the Qt object name you gave the interesting text box in Designer. And it will only work if the text edit object is a child widget of the main window object, which it should be in this case. You may run into trouble if you rely on this technique in general, though.

3. You could always make myclass2 a friend of mainwindow. This is so much not recommended, that I'm not going to post some code, though. :-)