load导致应用程序崩溃
QImage::load causes application to crash
我不知道为什么,但这段代码导致我的应用程序崩溃。当我在setPicture方法中使用一个指向QImage的全新指针时,它不会!什么会导致这种行为?
帆布类:
#include <QtGui>
class Canvas : public QWidget
{
Q_OBJECT
public:
QImage *p;
Canvas();
void setPicture(QString);
};
Canvas::Canvas()
{
}
void Canvas::setPicture(QString filename)
{
// This causes crash.
this->p = new QImage;
this->p->load(filename);
// This does not cause crash.Why?
//QImage *z = new QImage;
//z->load(filename);
}
这是窗口类:
#include <QtGui>
#include "Canvas.h"
class Window : public QWidget
{
Q_OBJECT
private:
Canvas *preview;
public:
Window();
public slots:
void browseFile();
};
Window::Window()
{
QGridLayout *layout = new QGridLayout;
Canvas *preview = new Canvas;
preview->setMinimumSize(400,200);
QSlider *slider = new QSlider;
slider->setOrientation(Qt::Horizontal);
QPushButton *browse = new QPushButton("Browse...");
layout->addWidget(preview, 1, 1);
//layout->addWidget(slider, 1, 2);
layout->addWidget(browse, 2, 2);
this->setLayout(layout);
this->resize(600,300);
QObject::connect(browse, SIGNAL(clicked()), SLOT(browseFile()));
}
void Window::browseFile()
{
QString filename;
filename = QFileDialog::getOpenFileName(this, "Open Picture", "", "Image Files (*.png *.jpg *.bmp)");
if(!filename.isEmpty())
{
qDebug() << "filename: "+filename;
preview->setPicture(filename);
//preview->repaint();
}
}
这是调用堆栈跟踪…
0 Canvas::setPicture Canvas.h 25 0x100003410
1 Window::browseFile Window.h 52 0x1000038c1
2 Window::qt_metacall moc_Window.cpp 72 0x1000025c8
3 QMetaObject::activate 0 0x100c93ac2
4 QAbstractButton::clicked 0 0x10063f2ed
5 QAbstractButtonPrivate::emitClicked 0 0x1003bc61e
6 QAbstractButtonPrivate::click 0 0x1003bd394
7 QAbstractButton::mouseReleaseEvent 0 0x1003bd556
8 QWidget::event 0 0x1000d2a52
9 QAbstractButton::event 0 0x1003bc5e6
10 QPushButton::event 0 0x100448ad2
11 QApplicationPrivate::notify_helper 0 0x100086e48
12 QApplication::notify 0 0x1000877a8
13 QCoreApplication::notifyInternal 0 0x100c805c6
14 qt_sendSpontaneousEvent 0 0x1000865da
15 qt_mac_handleMouseEvent 0 0x10004130a
16 -[QCocoaView mouseUp:] 0 0x100034be6
17 -[NSWindow sendEvent:] 0 0x7fff8ca74568
18 -[QCocoaWindow sendEvent:] 0 0x100039795
19 -[NSApplication sendEvent:] 0 0x7fff8ca0cd4d
20 -[QNSApplication sendEvent:] 0 0x10003cc1b
21 -[NSApplication run] 0 0x7fff8c9a325f
22 QEventDispatcherMac::processEvents 0 0x100044e7b
23 QEventLoop::exec 0 0x100c7dc55
24 QCoreApplication::exec 0 0x100c80bff
25 main main.cpp 12 0x100002cc0
指向Canvas类的指针是在Window类的构造函数中声明和实例化的,而不是使用私有声明的指针。
如果我没弄错的话,在调用browseFile方法时,窗口构造函数中指向Canvas的指针已经超出了作用域。
应该是:
class Window : public QWidget
{
Q_OBJECT
private:
Canvas *preview;
public:
Window();
public slots:
void browseFile();
};
Window::Window()
{
QGridLayout *layout = new QGridLayout;
preview = new Canvas;
....
虽然对我来说setPicture是如何被调用的是个谜!
经验教训:不要在构造函数中声明任何你打算以后使用的东西
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