c++ GUI programming with QT4

最新推荐文章于 2018-01-23 17:08:24 发布

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最新推荐文章于 2018-01-23 17:08:24 发布

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分类专栏： qt 文章标签： qt c++ application localization object initialization

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QT是一个跨平台的C++框架，用于使用一次编写、到处编译的方法开发GUI应用。本文介绍了QApplication和QLabel的用法，QApplication负责管理GUI应用的控制流程和主要设置，而QLabel则提供文本或图像显示功能。通过QApplication的event loop，程序等待用户操作并响应。QLabel可以设置为其他交互控件的标签，并支持快捷键设置。

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Qt is a comprehensive(综合) c++ framework for devleoping cross-platform GUI applications using a "write once,compile anywhere" approach. Qt lets programmers use a single source tree for applicaion

Hello Qt :

#include <QAppliction> #include <QLabel> int main(int argc,char **argv) { QApplication app(argc,argv); QLabel label = new QLabel("hello qt!"); label->show(); return app.exe(); }

1. QApplication :[QtGui module] : this class manage the GUI application' control flow and main settrings. contains the main event loop,where all events form the window system and other sources are processed and dispatched(委派). it also handles the application's initialization,finalization,and provids session management; In addition, QApplication handles most of the system-wide and application-wide settings.

For any GUI application using Qt, there is precisely one QApplication object, no matter whether the application has 0, 1, 2 or more windows at any given time. For non-GUI Qt applications, use QCoreApplication instead, as it does not depend on the QtGui library.

The QApplication object is accessible through the instance() function that returns a pointer equivalent to the global qApp pointer

(1) It initializes the application with the user's desktop settings such as palette(), font() and doubleClickInterval(). (2) It performs event handling, meaning that it receives events from the underlying(底层) window system and dispatches them to the relevant(相关的) widgets. (3) It parses common command line arguments and sets its internal state accordingly (4) It defines the application's look and feel, which is encapsulated in a QStyle object (5) It specifies how the application is to allocate(分配) colors. See setColorSpec() for details. (6) It provides localization(定位) of strings that are visible to the user via translate(). (7) It provides some magical objects like the desktop() and the clipboard(). (8) It knows about the application's windows. You can ask which widget is at a certain position using widgetAt(), get a list of topLevelWidgets() and closeAllWindows(), etc. (9) It manages the application's mouse cursor handling, see setOverrideCursor() (10) It provides support for sophisticated session management. This makes it possible for applications to terminate gracefully when the user logs out, to cancel a shutdown process if termination isn't possible and even to preserve the entire application's state for a future session. See isSessionRestored(), sessionId() and commitData() and saveState() for details.

2 QLabel[QtGui module] The QLabel widget provides a text or image display.A QLabel is often used as a label for an interactive widget. For this use QLabel provides a useful mechanism for adding an mnemonic (see QKeySequence) that will set the keyboard focus to the other widget (called the QLabel's "buddy").

3 Qt is so flexible(灵活) that any widget can be a window. this label is application window;

4 app.exec(), the programe enters the event loop.this is kind of stand-by(备用) mode where the program waits for user action such as mouse clicks and key presses.

we don't bother calling delete on the QLabel object and the end .this memory will be reclaimed(回收) where the programe terminateds;

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