How to add Item to ListView with C++?

[BBFAG3]

I tried to write follow the example,but I have a factastic error here...

#include "father.h"
#include"QDebug"
#include"QVariant"
father::father(QObject *parent) :
QObject(parent)
{
ctxt=viewer.rootContext();
msgList.append("asdf");
msgList.append("asdf");
msgList.append("asdf");//add item to QStringList
}

void father::run()
{
ctxt->setContextProperty("msglist",QVariant::fromValue(msgList));//It works, 4*"asdf" display in ListView
viewer.rootContext()->setContextProperty("sendMsg",new father);
viewer.setMainQmlFile(QStringLiteral("qml/KnightLegend/main.qml"));
viewer.showFullScreen();
}

void father::addmsg()
{
msgList.append("asd");
ctxt->setContextProperty("msglist",QVariant::fromValue(msgList));//But This doesn't work,I'm sure is function has been called.
return;
}

My QML:
ListView
{
id:chat
y:0
width: (fwidth/3)*2
height: cw.height-50

    model:msglist
    delegate: Text { text: modelData }

    Image//Background
    {
        anchors.fill:parent
        source:"qrc:Penguins.jpg"
        z:-2
    }
    MouseArea
    {
        anchors.fill: parent
    }
}

Thanks a lot! :)