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Compose pointer to property of object

  • Hi

    I need to have multiple instances of an object, i.e. like:
    that I need to set properties from an external interface like:

    I get the ID# as an int value. Is there a way I can 'compose' these pointers in code like concatenate strings?
    Otherwise I don't see any other option as to store these object/property pointers in an array and load by the index if I don't want have huge (and fixed) iterations in code.

    Do I miss something or is there a better solution?

  • Lifetime Qt Champion

    Not sure what
    " pointers in code like concatenate strings?"
    would be, but you can easy make list with all such pointers

    QList<QPushButton *> allPButtons = parentWidget.findChildren<QPushButton *>();

    if you replace "QPushButton *" with the type of webGUI03
    (keep *) then you have a list of them.

  • Thanks.
    The idea is not to have something like this:

    char ShowGUIid(int ID) {
      case 01: ui->webGUI01->show();
      case 02: ui->webGUI02->show();
      case n: ui->webGUIn->show(); }

    but maybe something like (shown here as if it were strings - I know it doesn't work):

    char ShowGUIid(int ID) {
    'ui->webGUI' + ID + '->show()'; }

    Get the idea?
    I'd need this for setting various properties like url's, size, pos, visibility ...
    Second idea would make it easy to add additional webGUI's as needed, dynamically at runtime and is much less code.

    Maybe there is a much better way of doing this?!?

  • Lifetime Qt Champion

    but if you put in list u can do

    for (int dx=0; dx < allPButtons.size(); dx++ )


    and then u dont need the switch case. ?

  • @mrjj
    I'll try to implement your idea .. and get back with the result ( or more questions ;-)

  • @mrjj
    I got stock at some other place.
    What's the best way to create the webGUI's (qWebView) at run-time, only as needed?
    I mean, I always need one at least, but only sometimes more than one and was thinking of not using up the memory by preparing a defined number of copies.
    Any hint's, if possible at all?

  • Lifetime Qt Champion

    its always possible to NEW widgets on demand.
    How you will do it, mostly depends tón the GUI.
    How user will do it.

    At any time you can do
    QWebView *view = new QWebView(parent);

  • @mrjj
    Here's what I'm doing:

      QWebView *webGUI = new QWebView(this);
      webGUI->setGeometry(QRect(280, 190, 150, 120));
      webGUI->setStyleSheet(QString::fromUtf8("background-color: rgba(127, 127, 127, 0);"));
      webGUI->page()->mainFrame()->setScrollBarPolicy( Qt::Vertical, Qt::ScrollBarAlwaysOff );
      webGUI->page()->mainFrame()->setScrollBarPolicy( Qt::Horizontal, Qt::ScrollBarAlwaysOff );
      webGUI->setGeometry(0, 0, SCREEN_SIZE_X, SCREEN_SIZE_Y);

    This is in a separate function and does not yet have the code to make it create webGUI[01] .. webGUI[n]. I thought of trying with one first.
    I currently call this from the main constructor.

    Before, the concept used only one webGUI that I created in the Designer - everything worked as supposed.

    I'm accessing these webGUI's from various places in my code.

  • Lifetime Qt Champion

    If you make this into a fine function that returns a QWebView *, you
    can easy make more than one.

    I do wonder how the parent QWebView(this); << the "this" can
    show mutiple QWebView ?
    will you use a tab control or a stackedwidetget to allow user to flip between the
    WEbViews or ill the be in same page and just take a smaller share of it ?
    as in share the page/parent ?

  • 'This' might be one of my problems.
    While in Designer I had a centralWidget as parent for all my elements.
    The webGUI's are dynamically loaded with content from a local server and are shown/hidden as needed. They also are placed and sized as needed at run-time and cover all of the screen or or only parts, may overlap with transparency ...
    There is at least one, but should now be extendable on request.

    Am I correct that I will need to create webView01 from the constructor at startup and make it available in *.h. Otherwise all the references to it are not satisfied.

    All references/calls to any webGui need to make use pof the QList, right.

    As you may surely have noted, I never implemented such a logic/functionality before.
    Thanks a lot for your help and guidance!

  • Lifetime Qt Champion

    @McLion said:

    • 'This' might be one of my problems.
      Well "this" is just the parent. if no parent are giving, it will become a window.
      So often this will be mainwindow. There nothing wrong having mutiple
      WebViews in same parent but u might need to arrange them to not overlap.
      (use move or setGeometry) Since it sounds you will arrange them manually and not use a layout or tabs or something like that.

    • Am I correct that I will need to create webView01 from the constructor at startup and make it available in *.h. Otherwise all the references to it are not satisfied.
      Well you dont need that.
      You can have list
      QList< QWebView *> Webs;
      QWebView *webGUI = new QWebView(this);
      Webs.append(webGUI); // keep in list

    Then at any time
    QWebView *w = Webs[0]; // take from list
    or Webs[1] , 2,3,4 etc.

    So you dont need a named variable to access it.

    Also, handling signals. You a can use same slot for all webviews.
    the sender() function will tell you which webview
    QWebView * wv= qobject_cast<QWebView *>(sender());
    if (wv) ...
    inside the slot for a signal to know which of the webviews that send the signal.
    Not sure you will need it, so just a note :)

  • Getting forward :-)
    The hint with the sender in the signal was great too. As if you would know before, I really stumbled over this - thanks!

    I came across an issue with the list though.
    There are no absolute positions in the list. Saying if 3 entries are made (0,1,2) and the second list (1) is cancelled for instance because it's not needed anymore, former entry 2 becomes entry 1.
    QList seems to always fill from the 0 up and there are no absolute positions.

    I either did not get all of QList or I may need to switch to some other solution - unfortunately- because it otherwise works a treat.

  • Lifetime Qt Champion

    Im not sure what wrong with QList since its dynamic and
    we cant have invalid pointers around ?
    else use a map
    QMap<int,QWebView * > map;
    QWebView *webGUI = new QWebView(this);
    map[1] =webGUI ;
    map[2] =nextwebGUI ;
    QWebView *w=map[2]; // it will stay "2"

    They wont change position as 1,2 is a key
    like map["onekey"] =webGUI ;
    but we use int as no need for string.
    so even if we remove map[1] then
    map[2] is still there.

    So maybe it works better for you ?

  • Tried quickly ... and the Map is exactly what I need.
    Thanks a million! .... I'll be back ;-)

  • Lifetime Qt Champion

    notice if you reuse the key
    map[1] =webGUI ;
    map[1] =nextwebGUI ;
    It will replace the web *.

  • Thanks for the heads-up.
    I'll do some testing and experiment.

  • So far, everything related to this threads question and the QMap as solution seems to work.

    I stumbled over something else while relacing the QwebView from the Designer by my 'on-demand' created one:
    I can not load an url, it crashes with sig11.

    I get the following connect error on bootup:

    QMetaObject::connectSlotsByName: No matching signal for on_webGUI_loadFinished(bool)

    which I dont understand and may be the cause.
    I have connected:

    connect(webGUI, SIGNAL(loadFinished(bool)), this, SLOT(on_webGUI_loadFinished(bool)));

    and in *.h as private slot:

    void on_webGUI_loadFinished(bool arg1);

    This worked before, with the QWebView from the Designer.
    Any idea? Thanks.

  • Lifetime Qt Champion

    @McLion said:

    no matching signal for on_webGUI_loadFinished(bool)

    this warning comes as you name slot on_XXX
    This will trigger Qt auto connect feature so when you use
    a concrete connect you should rename it so it dont
    start with on__
    (right click it- refactor->rename)

    also please do
    qDebug() << "loadfin:" << connect(webGUI, SIGNAL(loadFinixxxx

    to see if it returns true; ( as in , it can connect)

  • I wasn't aware that using on_ in the name will trigger any functionality!
    Refactoring solved this problem - Thanks !

    However, the signal 11 crash when trying to load an url seems to have some other cause .... I'm searching ;-)

  • Lifetime Qt Champion

    You're most probably dereferencing a null pointer. Signal 11 means SIGSEGV (segmentation error).

  • @jsulm
    Yes - Thanks . Problem loacted, but not yet solved:

    void QTGUI_MainWindow::populateJavaScriptWindowObject()
      QWebView * webGUI = qobject_cast<QWebView *>(sender());
      webGUI->page()->mainFrame()->addToJavaScriptWindowObject("NativeBridge", this);

    The sender is the JS and not the QWebView and so I do not get the pointer to the QWebView that I need. Instead, the pointer is 0x0 and then - of course - the addToJ... crashes.

    Any idea how I get the pointer to the QWebView from which the JS is sending?

  • Lifetime Qt Champion

    What is JS?

  • @jsulm
    JavaScript (in/from QWebKit ... more precise page()->mainFrame().

  • I posted this as a separate question in the WebKit group.

  • Got it solved :-)

    QWebFrame * webGUIframe = qobject_cast<QWebFrame >(sender());
    QWebView * webGUI = (QWebView
    webGUI->page()->mainFrame()->addToJavaScriptWindowObject("NativeBridge", this);