QAbstractListModel 崩溃 [英] QAbstractListModel crashes

问题描述

我正在使用 QAbstractListModel 向 QML ListView 公开数据.除此之外使用 QML SectionScroller，它使用 get 和 data 函数.

I'm using QAbstractListModel to expose data to QML ListView. QML SectionScroller is used beside this, which uses get and data functions.

滚动一段时间后，出现崩溃.回溯是:

After some time of scrolling, a crash is experienced. The backtrace is:

Program received signal SIGILL, Illegal instruction.
0x0000cdcc in QBasicAtomicInt::ref (
    this=0x35)
    at /usr/include/QtCore/qatomic_armv6.h:119
119 /usr/include/QtCore/qatomic_armv6.h: No such file or directory.
    in /usr/include/QtCore/qatomic_armv6.h
(gdb) bt
#0  0x0000cdcc in QBasicAtomicInt::ref (
    this=0x35)
    at /usr/include/QtCore/qatomic_armv6.h:119
#1  0x0000f4e8 in QString (
    this=0xbebf1a5c, other=...)
    at /usr/include/QtCore/qstring.h:729
#2  [address] in IrregularVerb::getForm0
    (this=0x92e428) at IrregularVerb.h:16
#3  0x0000e29c in IrregularListWrapper::data (this=0x92dd20, index=..., role=33)
    at IrregularListWrapper.cpp:37
#4  0x4010e9c6 in ?? ()
   from /usr/lib/libQtDeclarative.so.4
#5  0x4010e9c6 in ?? ()
   from /usr/lib/libQtDeclarative.so.4
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

在其他设备上(第一个是 N900，第二个是 N950)回溯是类似的.它是 SIGSEGV 而不是 SIGILL，但除此之外，回溯是相同的.我注意到曾经有过一些字段在崩溃时变得空白的情况.(使用getForm0和getForm1的)

On other device (first is N900, the second N950) the backtrace is similar. It's SIGSEGV instead of SIGILL, but the backtrace is identical beside this. I noticed once a situtation where some of the fields have gotten blank at the moment on crash. (the ones using getForm0 and getForm1)

当我向返回的值添加额外的赋值时，在赋值时发生了崩溃.

When I added an extra assignement, to the returned value, the crash happened at the assignment.

一些重要的代码:

元素:

class IrregularVerb : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString form0 READ getForm0 CONSTANT)
    Q_PROPERTY(QString form1 READ getForm1 CONSTANT)
    Q_PROPERTY(QString form2 READ getForm2 CONSTANT)
public:
    QString forms[3];
    QString getForm0() const { return forms[0]; }
    QString getForm1() const { return forms[1]; }
    QString getForm2() const { return forms[2]; }
    IrregularVerb(QString a, QString b, QString c) { forms[0] = a; forms[1] = b; forms[2] = c; }
};

型号:

class IrregularListWrapper : public QAbstractListModel
{
    Q_OBJECT
    Q_PROPERTY(QString langName READ getLangName NOTIFY langChanged)
    Q_PROPERTY(int count READ rowCount NOTIFY langChanged)
    Q_ENUMS(Language)
public:

    Q_INVOKABLE int rowCount(const QModelIndex& = QModelIndex()) const { return db->count(); }
    Q_INVOKABLE QObject* get(int index) const {return db->at(index);}
    QVariant data(const QModelIndex &index, int role) const;

    enum Language
    {
        English = 0,
        German = 1
    };

    enum IrregularVerbRoles
    {
        Form0Role = Qt::UserRole + 1,
        Form1Role,
        Form2Role
    };

    IrregularListWrapper();

    QString getLangName() const { return langName; }
    Q_INVOKABLE void changeLang(Language l) { beginResetModel(); db = 0; setLang(l); endResetModel(); }

    static QMap<Language, QString> plugins;

signals:
    void langChanged();
protected:
    void setLang(Language);
    QString langName;
    AbstractIrregularList * db;

};


QVariant IrregularListWrapper::data(const QModelIndex &index, int role) const
{
    if (!index.isValid()) return QVariant();

    int rowno = index.row();

    qDebug() << "Row is " << index.row() << flush;

    const IrregularVerb* verb = db->at(index.row());

    switch (role)
    {
    case Form0Role:
        return verb->getForm0();
        break;
    case Form1Role:
        return verb->getForm1();
        break;
    case Form2Role:
        return verb->getForm2();
        break;
    }
    return QVariant();
}

AbstractIrregularList:

AbstractIrregularList:

class AbstractIrregularList : public QObject, public QList<IrregularVerb*>
{
    Q_OBJECT
public:
    void IV(const char* a, const char* b, const char* c) { append (new IrregularVerb(a, b, c)); }
    void IV(const char *a, const char *b) { IV(a, b, b); }
    void IV(const char *a) { IV(a,a,a); }
};

Q_DECLARE_INTERFACE(AbstractIrregularList, "com.marmistrz.Plugin.AbstractIrregularList/1.0");

你知道为什么会这样吗?谢谢！

Do you have an idea why it's happening? Thanks!

/edit1:感谢您的回复.这样可以吗?

/edit1: Thanks for your reply. Would this be ok?

Q_INVOKABLE QObject* get(int index)
{
    QObject* item = db->at(index);
    QDeclarativeEngine::setObjectOwnership(item, QDeclarativeEngine::CppOwnership);
    item->setParent(this); // do I need to do this? An QList<QObject*>-child would clean it, right? 
    return item;
}

谢谢

推荐答案

看起来你在 QML 端使用 QAbstractListModel 有一个经典"问题.您的 IrregularListWrapper 具有 get 方法，该方法返回具有 JS 所有权的对象(这种所有权是 Q_INVOKABLE 方法的默认值)，它们将被垃圾收集QML 端的 JS 引擎.为防止这种情况，您应该在将对象返回到 QML 之前更改对象的所有权 <代码>QDeclarativeEngine::setObjectOwnership.请参阅我的答案中的示例此处.

It looks like you have a "classic" problem using QAbstractListModel on QML side. Your IrregularListWrapper has get method which returns objects with JS ownership (that kind of ownership is default for Q_INVOKABLE methods) and they will be garbage collected with JS engine on QML side. To prevent this you should change objects' ownership before returning them to QML with QDeclarativeEngine::setObjectOwnership. See example in my answer here.

这篇关于QAbstractListModel 崩溃的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！