problem of CheckBox in ListView

[Mr Pang]

I am writing a simple file manager. I want to realize multi-select.
Suppose that there is three files a,b,c in current path. If I check file a, a selection menu will apper.
Then I uncheck file a, and choose "Select All". file b and c will be checked as expected,but file a not.
What is the problem?
Here is my code:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QtQml>
#include <QQmlContext>
#include "mainclass.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;
    qmlRegisterType<MainClass>("per.pqy.mc", 1, 0, "MainClass");
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    return app.exec();
}

#ifndef MAINCLASS_H
#define MAINCLASS_H
#include <QObject>
#include <QDir>
#include <QFile>

class MyModelItem :public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString name READ name CONSTANT)
    Q_PROPERTY(bool checked READ checked WRITE setChecked NOTIFY checkedChanged)

public:
    MyModelItem(const QString &name, QObject *parent=0):_name(name), _checked(false){}
    QString name() const{ return _name; }
    bool checked() const {return _checked; }

signals:
    void checkedChanged();

public slots:
    void setChecked(bool c){ _checked = c; emit checkedChanged();}

private:
    QString _name, _info;
    bool _checked;
};

class MainClass : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString currentPath READ currentPath CONSTANT)
    Q_PROPERTY(QList<QObject*>  myModel READ myModel  NOTIFY myModelChanged)

    public:
        explicit MainClass(QObject *parent = 0, QString root = "/");
        QString currentPath(){return _currentPath;}
        QStringList filesInfoList();
        QList<QObject*> myModel(){ return fList; }

        inline QDir::Filters currentFilter(){
            if(QDir(_currentPath).isRoot())
                    return QDir::NoDotAndDotDot|QDir::AllEntries;
            else
                    return QDir::NoDot|QDir::AllEntries;
        }

signals:
        void myModelChanged();
        void clickFile(QString type);

public slots:
        void setCurrentPath(int index);
        void selectAll();
        void reverseSelect();

private:
    QString _currentPath;
    QList<QObject*> fList;
};

#endif // MAINCLASS_H

#include "mainclass.h"

MainClass::MainClass(QObject *parent,QString root) : QObject(parent),_currentPath(root)
{
    QStringList currentFilesList = QDir(_currentPath).entryList(currentFilter(),QDir::DirsFirst);
    for(int i=0;i<currentFilesList.count();i++)
        fList.append(new MyModelItem(currentFilesList[i]));
    emit myModelChanged();
}

void MainClass::setCurrentPath(int index)
{
    QStringList currentFilesList = QDir(_currentPath).entryList(currentFilter(),QDir::DirsFirst);
  QFileInfo finfo(_currentPath,currentFilesList[index]);
  QString cp = _currentPath;
  if(!finfo.isReadable()){
      //todo
  }
  else if(finfo.isDir()&&finfo.isExecutable()){
      cp += "/";
      cp += currentFilesList[index];
            _currentPath = QDir(cp).absolutePath();
            _currentPath = QDir(_currentPath).path();
            currentFilesList = QDir(_currentPath).entryList(currentFilter(),QDir::DirsFirst);
            qDeleteAll(fList);
            fList.clear();
            for(int i=0;i<currentFilesList.count();i++)
                fList.append(new MyModelItem(currentFilesList[i]));
            emit myModelChanged();

  }
  else if(finfo.isFile()){
      if(finfo.suffix()=="apk")
          emit clickFile("ApkMenu.qml");
      else
          emit clickFile("NormalMenu.qml");
  }
}

void MainClass::selectAll()
{
    for(int i=0;i<fList.count();i++){
        MyModelItem *item = qobject_cast<MyModelItem *>(fList[i]);
        item->setChecked(true);
    }
}

void MainClass::reverseSelect()
{
    for(int i=0;i<fList.count();i++){
        MyModelItem *item = qobject_cast<MyModelItem *>(fList[i]);
        item->setChecked(!item->checked());
    }
}

import QtQuick 2.5
import QtQuick.Controls 1.4
import per.pqy.mc 1.0

ApplicationWindow {
    visible: true
    width: 480
    height: 800
    title: qsTr("Hello World")

    function showselectMenu(){
            selectMenu.y = 0;
        }

    function hideselectMenu(){
            selectMenu.y = -selectMenu.height;
        }

    MainClass {
            id:mc
    }

    Rectangle {
            id: root
            anchors.fill: parent
            color: "#000000"

            ListView {
                id: list
               anchors.fill: parent
               flickDeceleration: 3000
               maximumFlickVelocity: 8000
               spacing: 1
               clip: true

               model:mc.myModel
               delegate: Rectangle {
                    id: listItem
                    height: root.height/15
                    width: root.width
                    property alias checked: checkItem.checked
                    MouseArea {
                        id:mouseArea
                      anchors.fill: parent
                      onClicked:  mc.setCurrentPath(index)
                    }
                     color: mouseArea.pressed?"#ff999999":"#aa505050"

                     CheckBox {
                         id: checkItem
                         anchors.right: parent.right
                         anchors.top: parent.top
                         anchors.bottom: parent.bottom
                         anchors.margins: root.height/150
                         width: height
                         checked: model.modelData.checked
                         onClicked: {
                             model.modelData.setChecked(checked);
                             showselectMenu();
                         }
                     }

                     Text {
                         id: t1
                         text: model.modelData.name
                         color: "white"
                         height: parent.height*2/3
                         font.pixelSize: height*4/7
                         anchors.left: parent.left
                     }

                }
            }
        }
    Rectangle {
        id: selectMenu
        width: root.width/2
        height: root.height/5+2
        anchors.horizontalCenter: parent.horizontalCenter
        opacity: 0.8
        y: -height
        Behavior on y {
            NumberAnimation {
                duration: 500
                easing.type: Easing.OutExpo
            }
        }
        Column {
            anchors.fill: parent
            spacing: 1
            property real btnWid: parent.width
            property real btnHei: (parent.height-2)/3
            Button {
                id: button1
                text: qsTr("Select All")
                width: parent.btnWid
                height: parent.btnHei
                onClicked: mc.selectAll()
            }

            Button {
                id: button2
                text: qsTr("Reverse Selection")
                width: parent.btnWid
                height: parent.btnHei
                onClicked: mc.reverseSelect()
            }

            Button {
                id: button3
                text: qsTr("Done Selection")
                width: parent.btnWid
                height: parent.btnHei
                onClicked: hideselectMenu()
            }
        }
    }

}