用qt做画图板的问题

[lzhpopo_hoho]

菜鸟一个，比着网上的代码敲的，敲完之后不显示画板，真心求教
#ifndef PAINTAREA_H
#define PAINTAREA_H

#include <QWidget>
#include<QPixmap>
class paintarea : public QWidget
{
Q_OBJECT

public:
explicit paintarea(QWidget *parent = 0);
//paintarea(QPixmap& pixmap2);
//~paintarea();
void paint(QPixmap& pximap1);

protected:
void mousePressEvent(QMouseEvent*);
void mouseMoveEvent(QMouseEvent*);
void mouseReleaseEvent(QMouseEvent*);
void paintEvent(QPaintEvent*);

private:
QPixmap pixmap;
QPoint beginpoint,endpoint;
QRgb backcolor;

signals:

public slots:

};

#endif // PAINTAREA_H

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include<QtGui>
#include<QtCore>
#include<QMessageBox>
#include<paintarea.h>
paintarea* area;
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
area=new paintarea;
}

MainWindow::~MainWindow()
{
delete ui;
}

#include "paintarea.h"
#include <QMouseEvent>
#include<QPoint>
#include<QPainter>
#include<QPixmap>
paintarea::paintarea(QWidget *parent) :
QWidget(parent)
{
pixmap=QPixmap(400,300);
backcolor=qRgb(255,255,255);
pixmap.fill(backcolor);
}

/*void paintarea::paintarea(QPixmap& pixmap2)
{
pixmap=QPixmap(400,300);
}*/

void paintarea::paint(QPixmap& pixmap1)
{
QPainter pt(&pixmap1);
pt.drawLine(beginpoint,endpoint);
beginpoint=endpoint;
}

void paintarea::paintEvent(QPaintEvent *)
{
QPainter pp(this);
pp.drawPixmap(0,0,pixmap);
}

void paintarea::mousePressEvent(QMouseEvent* event)
{
if(event->button() == Qt::LeftButton)
beginpoint=event->pos();

}

void paintarea::mouseMoveEvent(QMouseEvent*event)
{
if(event->button()&Qt::LeftButton)
endpoint=event->pos();
paint(pixmap);
}

void paintarea::mouseReleaseEvent(QMouseEvent*event)
{
if(event->button()==Qt::LeftButton)
endpoint=event->pos();
paint(pixmap);
}

哎确实不怎么会QT的GUI啊%>_<%

[fly_dragon_fly]

area=new paintarea;
改为 area=new paintarea(this);

[lzhpopo_hoho]

非常感谢 方便的话能给我说下为什么吗？

[fly_dragon_fly]

QT有些可能记得不是很清楚了，新建widget没大小看不见，mainwindow内部有layoUT，作为子控件会得到大小

[cnyfk]

你new paintarea的时候要传入父窗口的指针 new paintarea(this)

[小修凌云]

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    area = new PaintArea;

    setCentralWidget(area);
}

[小修凌云]

加上this比较好

new PaintArea(this);

另外，你的应该还不能显示线条，要update()一下，最好搭配QTimer