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QT——绘图事件、鼠标事件、QPainter、键盘事件、光标样式、登录框密码回显模式、移除字符串前后的空白、对话框accept()

2014-05-24 12:47 561 查看

1、void QWidget::paintEvent(QPaintEvent * event) [virtual protected]

A paint event is a request to repaint all or part of a widget.

It can happen for one of the following reasons:

1.repaint() orupdate() was invoked(调用)

2.the widget was obscured(遮挡) and has now been uncovered(露出), or many other reasons.

------------------------------------------------------------------------------------------------------

Many widgets can simply repaint their entire surface when asked to, but some slow widgets need to optimize by painting only the requested region/*通过绘制被请求的区域来优化*/:QPaintEvent::region().

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Qt also tries to speed up painting by merging multiple paint events into one/*合并多个绘制事件*/.
When update() is called several times or the window system sends several paint events, Qt merges these events into one event with a larger region (seeQRegion::united()).
Therepaint() function does not permit this optimization, so we suggest usingupdate()whenever possible./*如果有可能，应尽量使用update()*/

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When the paint event occurs, the update region has normally been erased, so you are painting on the widget's background./*在背景上进行绘制*/The
background can be set using setBackgroundRole() andsetPalette().

Since Qt 4.0, QWidget automatically double-buffers its painting/*自动双缓存*/, so there is no need to write double-buffering code inpaintEvent()to
avoid flicker/*避免闪烁*/.

========================================================

2、鼠标事件及相关

void QWidget::mousePressEvent(QMouseEvent * event) [virtual protected]

void QWidget::mouseDoubleClickEvent(QMouseEvent * event) [virtual protected]

void QWidget::mouseReleaseEvent(QMouseEvent * event) [virtual protected]

void QWidget::mouseMoveEvent(QMouseEvent * event) [virtual protected]

void
setMouseTracking(bool enable) /* 鼠标跟随 */

Qt::MouseButtons QMouseEvent::buttons() const /*发生事件时，哪些按钮还处于按下状态 */

Returns the button state when the event was generated/*触发*/. The button state is a combination/*组合*/ ofQt::LeftButton,Qt::RightButton,Qt::MidButtonusing
theOR operator.

For mouse move events, this is all buttons that are pressed down./*对于移动事件，所有的按钮都是按下状态 */

For mouse press and double click events this includes the button that caused the event.

For mouse release events this excludes the button that caused the event./*对于鼠标释放事件，不包含导致事件发生的按钮 */

Qt::MouseButton QMouseEvent::button() const /*哪个按钮发生了此事件。返回事件的按钮，但是对于鼠标移动事件，总是返回Qt::NoButton */

QPoint QMouseEvent::pos() const

QPoint QMouseEvent::globalPos() const

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void Dialog::mousePressEvent(QMouseEvent *event)

    if(event->button()==Qt::LeftButton) //鼠标左键按下

        qDebug() << event->pos();

void Dialog::mouseMoveEvent(QMouseEvent *event)

    if(event->buttons()&Qt::LeftButton) //鼠标左键按下的同时移动鼠标 (判断状态)

void Dialog::mouseReleaseEvent(QMouseEvent *event)

    if(event->button() == Qt::LeftButton) //鼠标左键释放

========================================================

3、QPainter

1.画图工具主要有3部分组成：QPainter QPaintDevice QPaintEngine

2.QPainter类提供了画图操作的各种接口；QPaintDevice类提供了画图的空间，由QPainter在上面进行绘制；QPaintEngine提供了画笔QPainter在不同的设备上进行绘制的统一接口。QPainter和QPaintDevice之间使用QPaintEngine进行通讯。

3.QPainter类提供了丰富的操作窗口，可以很方便地绘制各种各样的图形（直线、方形、圆形、文字、图片），与QPainterPath类结合，可以绘制出任意复杂的图形。

4.QPaintDevice类是所有可用QPainter类进行绘制的类的基类，常用的画图容器：QImage、QPixmap、QPicture、QWidget。

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5.绘制工具QPainter的典型用法：
★构造一个绘图工具：QPainterpainter(this);
★设置画笔和画刷等：painter.setPen(Qt::blue);
★绘制：painter.drawText(rect(), Qt::AlignCenter, "Qt");
★销毁绘图工具
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6.常用绘图函数：
voiddrawPath(const QPainterPath & path)

voiddrawPixmap(int x, int y, const QPixmap & pixmap)
========================================================

4、键盘事件

void QWidget::keyPressEvent(QKeyEvent * event) [virtual protected]

void MainWindow::keyPressEvent(QKeyEvent *k)

    if(k->key() == Qt::Key_A) //判断是否是A键按下

        ui->label->setPixmap(QPixmap("://1.png"));

========================================================

5、光标样式

QCursor(const
QPixmap & pixmap, int hotX = -1, int hotY = -1) /* 构造光标 */

void QGuiApplication::setOverrideCursor(const
QCursor & cursor) [static] /* 设置光标 */

QCursor myCursor(QPixmap("://2.png"));

QApplication::setOverrideCursor(myCursor);

========================================================

6、密码回显：

void
setEchoMode(EchoMode)

enum QLineEdit::EchoMode —— ... QLineEdit::Password...

========================================================

7、QString QString::trimmed() const

Returns a string that has whitespace removed from the start and the end./*移除字符串前后的whitespace
*/

Whitespace means any character for which QChar::isSpace() returns true. This includes the ASCII characters'\t', '\n', '\v', '\f', '\r',
and' '.

Example:

QString str = "  lots\t of\nwhitespace\r\n ";

str = str.trimmed();

// str == "lots\t of\nwhitespace"

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8、void QDialog::accept() [virtual slot]

Hides the modal dialog and sets the result code to Accepted./*隐藏模式对话框，并且设置代码的执行结果为 Accepted */

...... ......

accept();

..... ......

Widget w;

loginDlg login;

if(login.exec()==QDialog::Accepted)

  w.show();

  return a.exec();

========================================================

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