QPainter::begin: Widget painting can only begin as a result of a paintEvent

[uytgh7458]

想把摄像头采集的数据放到QT上面显示！摄像头可以显示，但是总会出现这个错误，网上说要增加Qwidget的属性，但是不知道怎么加！！代码如下，希望大神指教一下

#include <QtGui>
#include "processImage.h"
#include "videodevice.h"
extern "C"
{
#include <stdio.h>
#include <stdlib.h>
}
ProcessImage::ProcessImage(QWidget *parent):QWidget(parent)
{
//this->setAttribute(Qt::WA_PaintOutsidePaintEvent);
pp = (unsigned char *)malloc(320 * 240/*QWidget::width()*QWidget::height()*/* 3 * sizeof(char));
painter = new QPainter(this);
frame = new QImage(pp,320,240,QImage::Format_RGB888);
//frame = new QPixmap(640,240);
label = new QLabel();
vd = new VideoDevice(tr("/dev/video0"));

connect(vd, SIGNAL(display_error(QString)), this,SLOT(display_error(QString)));
rs = vd->open_device();
if(-1==rs)
{
QMessageBox::warning(this,tr("error"),tr("open /dev/dsp error"),QMessageBox::Yes);
vd->close_device();
}

rs = vd->init_device();
if(-1==rs)
{
QMessageBox::warning(this,tr("error"),tr("init failed"),QMessageBox::Yes);
vd->close_device();
}

rs = vd->start_capturing();
if(-1==rs)
{
QMessageBox::warning(this,tr("error"),tr("start capture failed"),QMessageBox::Yes);
vd->close_device();
}

if(-1==rs)
{
QMessageBox::warning(this,tr("error"),tr("get frame failed"),QMessageBox::Yes);
vd->stop_capturing();
}

timer = new QTimer(this);
connect(timer,SIGNAL(timeout()),this,SLOT(update()));
timer->start(30);

QHBoxLayout *hLayout = new QHBoxLayout();
hLayout->addWidget(label);
setLayout(hLayout);
setWindowTitle(tr("Capture"));
}

ProcessImage::~ProcessImage()
{
rs = vd->stop_capturing();
rs = vd->uninit_device();
rs = vd->close_device();
}

void ProcessImage::paintEvent(QPaintEvent *)
{
rs = vd->get_frame((void **)&p,&len);
convert_yuv_to_rgb_buffer(p,pp,320,240/*QWidget::width(),QWidget::height()*/);
frame->loadFromData((uchar *)p,/*len*/320 * 240 * 3 * sizeof(char));

// painter->begin(this);
// painter->drawImage(0,0,*frame);
// painter->end();
// rs = vd->unget_frame();
// frame->load("./img3.jpg");
// label->setAttribute(Qt::WA_PaintOutsidePaintEvent);
label->setPixmap(QPixmap::fromImage(*frame,Qt::AutoColor));
// label->show();
rs = vd->unget_frame();
// label->drawFrame();
}

void ProcessImage::display_error(QString err)
{
QMessageBox::warning(this,tr("error"), err,QMessageBox::Yes);
}

/*yuv格式转换为rgb格式*/
int ProcessImage::convert_yuv_to_rgb_buffer(unsigned char *yuv, unsigned char *rgb, unsigned int width, unsigned int height)
{
unsigned int in, out = 0;
unsigned int pixel_16;
unsigned char pixel_24[3];
unsigned int pixel32;
int y0, u, y1, v;
for(in = 0; in < width * height * 2; in += 4) {
pixel_16 =
yuv[in + 3] << 24 |
yuv[in + 2] << 16 |
yuv[in + 1] << 8 |
yuv[in + 0];
y0 = (pixel_16 & 0x000000ff);
u = (pixel_16 & 0x0000ff00) >> 8;
y1 = (pixel_16 & 0x00ff0000) >> 16;
v = (pixel_16 & 0xff000000) >> 24;
pixel32 = convert_yuv_to_rgb_pixel(y0, u, v);
pixel_24[0] = (pixel32 & 0x000000ff);
pixel_24[1] = (pixel32 & 0x0000ff00) >> 8;
pixel_24[2] = (pixel32 & 0x00ff0000) >> 16;
rgb[out++] = pixel_24[0];
rgb[out++] = pixel_24[1];
rgb[out++] = pixel_24[2];
pixel32 = convert_yuv_to_rgb_pixel(y1, u, v);
pixel_24[0] = (pixel32 & 0x000000ff);
pixel_24[1] = (pixel32 & 0x0000ff00) >> 8;
pixel_24[2] = (pixel32 & 0x00ff0000) >> 16;
rgb[out++] = pixel_24[0];
rgb[out++] = pixel_24[1];
rgb[out++] = pixel_24[2];
}
return 0;
}

int ProcessImage::convert_yuv_to_rgb_pixel(int y, int u, int v)
{
unsigned int pixel32 = 0;
unsigned char *pixel = (unsigned char *)&pixel32;
int r, g, b;
r = y + (1.370705 * (v-128));
g = y - (0.698001 * (v-128)) - (0.337633 * (u-128));
b = y + (1.732446 * (u-128));
if(r > 255) r = 255;
if(g > 255) g = 255;
if(b > 255) b = 255;
if(r < 0) r = 0;
if(g < 0) g = 0;
if(b < 0) b = 0;
pixel[0] = r * 220 / 256;
pixel[1] = g * 220 / 256;
pixel[2] = b * 220 / 256;
return pixel32;
}
/*yu

[kael_9527]

默认情况下要使用QPainter画图必须在在paintEvent()函数里，如果在其它地方的话，运行时会提示如下错误 QPainter::begin: Widget painting can only begin as a result of a paintEvent 要避免这个问题可以设置你要画图的那个widget的一个属性，加上类似这样的代码this->setAttribute(Qt::WA_PaintOutsidePaintEvent);就可以了。 painter = new QPainter(this); 你的这一句有什么用?去掉也可以吧

[jdwx]

setAttribute(Qt::WA_PaintOutsidePaintEvent)这个属性是有限制的，下面是帮助原文。 Makes it possible to use QPainter to paint on the widget outside paintEvent(). This flag is not supported on Windows, Mac OS X or Embedded Linux. We recommend that you use it only when porting Qt 3 code to Qt 4.

[667778]

你好，我在网上下载了你这个程序，也出现和你一样的错误，请问你解决了吗？