I build a widget has a qlabel, below is its constructor
Qt Code: 
  1. #ifndef VIEWER_H
  2. #define VIEWER_H
  3.  
  4. #include <iostream>
  5.  
  6. #include <QWidget>
  7. #include <QPixmap>
  8. #include <QLabel>
  9. #include <QImage>
  10. #include <QVBoxLayout>
  11.  
  12.  
  13. using namespace std;
  14.  
  15. class Viewer : public QWidget
  16. {
  17. 	Q_OBJECT
  18.  
  19. 	public:
  20. 		Viewer(QWidget *parent=0);
  21.     public slots:
  22. 		void setIplImage();
  23.  
  24.  
  25. 	private:
  26.  
  27. 		QVBoxLayout *mainLayout;
  28. 		QLabel *movieLabel;
  29.  
  30.  
  31. };
  32.  
  33. #endif
  34.  
  35. Viewer::Viewer(QWidget* parent)
  36.     : QWidget(parent)
  37. {
  38.  movieLabel = new QLabel(tr("No movie loaded"));
  39.     movieLabel->setAlignment(Qt::AlignCenter);
  40.     movieLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
  41.     movieLabel->setBackgroundRole(QPalette::Dark);
  42.     movieLabel->setAutoFillBackground(true);
  43.     movieLabel->setScaledContents(true);
  44.  
  45.  
  46.  
  47. 	mainLayout = new QVBoxLayout;
  48.     mainLayout->addWidget(movieLabel);
  49. 	setLayout(mainLayout);
  50.  
  51. }
  52.  
  53.  
  54. void
  55. Viewer::setIplImage()
  56. {
  57.  
  58.     QImage image("test.jpg");
  59.     //image.save("test2.jpg"); //it works
  60.  
  61.    movieLabel->setPixmap(QPixmap::fromImage(image)); //compile success but runtime error with access violation.
  62.  
  63.  }
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and if i use it in constructor, the setPixmap() can run.
Thanks for any comments