c++ - How to Use Models with QML? -

i have gui written in qml , c++. there 2 comboboxes (qt control 5.1). second combobox has update @ runtime whenever value of first 1 changed.

maincontext->setcontextproperty("typemodel", qvariant::fromvalue(m_typemodel));  maincontext->setcontextproperty("unitmodel", qvariant::fromvalue(m_unitmodel)); 

these 2 models give qml c++.

combobox {     id: typebox      anchors.left: text1.right     anchors.leftmargin: 5     signal changed(string newtext)      width: 70     height: 23     anchors.top: parent.top     anchors.topmargin: 37     model: typemodel      oncurrenttextchanged: {          mainwin.unitgenerator(typebox.currenttext);      } 

this first combobox. see, c++ model of second combobox updated every time value of first changed (mainwin.unitgenerator(typebox.currenttext)). not seem update combobox's model.

how can update qml's model on runtime?

to begin address issue, we'd need see unitgenerator method does. if you're using custom model, it's you're not correctly implementing notifications. bet @ moment you're not signaling model reset.

below complete code example shows how can tie qstringlistmodel editable listview , comboboxes. second combobox's model regenerated based on selection first one. presumably approximates desired functionality.

note specific handling of roles done qstringlistmodel. model treats display , edit roles same: both mapped string value in list. yet when update particular role's data, datachanged signal carries only role you've changed. can used break binding loop might otherwise present in model editor item (textinput). when use custom model, may need implement similar functionality.

the display role used bind combo boxes model. edit role used pre-populate editor objects. editor's ontextchanged signal handler updating display role, , doesn't cause binding loop itself. if handler updating edit role, cause binding loop via text property.

on models in qml

there various kinds of "models" in qml. internally, qml wrap "anything" in model. internally not qobject yet can still model (say qvariant), won't notifying anything.

for example, "model" based on qvariant wraps int not issue notifications, because qvariant not qobject signal changes.

similarly, if "model" tied property value of class derived qobject, fail emit property change notification signal, won't work.

without knowing model types are, it's impossible tell.

main.qml

import qtquick 2.0 import qtquick.controls 1.0  applicationwindow {     width: 300; height: 300     listview {         id: view         width: parent.width         anchors.top: parent.top         anchors.bottom: column.top         model: model1         spacing: 2         delegate: component {             rectangle {                 width: view.width                 implicitheight: edit.implicitheight + 10                 color: "transparent"                 border.color: "red"                 border.width: 2                 radius: 5                 textinput {                     id: edit                     anchors.margins: 1.5 * parent.border.width                     anchors.fill: parent                     text: edit // "edit" role of model, break binding loop                     ontextchanged: model.display = text                 }             }         }     }     column {         id: column;         anchors.bottom: parent.bottom         text { text: "type";  }         combobox {             id: box1             model: model1             textrole: "display"             oncurrenttextchanged: generator.generate(currenttext)         }         text { text: "unit"; }         combobox {             id: box2             model: model2             textrole: "display"         }     } } 

main.cpp

#include <qguiapplication> #include <qqmlapplicationengine> #include <qquickwindow> #include <qstringlistmodel> #include <qqmlcontext>  class generator : public qobject {     q_object     qstringlistmodel * m_model; public:     generator(qstringlistmodel * model) : m_model(model) {}     q_invokable void generate(const qvariant & val) {         qstringlist list;         (int = 1; <= 3; ++i) {             list << qstring("%1:%2").arg(val.tostring()).arg(i);         }         m_model->setstringlist(list);     } };  int main(int argc, char *argv[]) {     qstringlistmodel model1, model2;     generator generator(&model2);     qguiapplication app(argc, argv);     qqmlapplicationengine engine;      qstringlist list;     list << "one" << "two" << "three" << "four";     model1.setstringlist(list);      engine.rootcontext()->setcontextproperty("model1", &model1);     engine.rootcontext()->setcontextproperty("model2", &model2);     engine.rootcontext()->setcontextproperty("generator", &generator);      engine.load(qurl("qrc:/main.qml"));     qobject *toplevel = engine.rootobjects().value(0);     qquickwindow *window = qobject_cast<qquickwindow *>(toplevel);     window->show();     return app.exec(); }  #include "main.moc"