QMessageBox Class Reference

Detailed Description

Message boxes are used to provide informative messages and to ask simple questions.

QMessageBox provides a range of different messages, arranged roughly along two axes: severity and complexity.

Severity is

	Information	for message boxes that are part of normal operation
	Warning	for message boxes that tell the user about unusual errors
	Critical	for message boxes that tell the user about critical errors

The message box has a different icon for each of the severity levels.

Complexity is one button (OK) for a simple messages, or two or even three buttons for questions.

There are static functions for common cases.

Examples:

If a program is unable to find a supporting file, but can do perfectly well without it:

QMessageBox::information( this, "Application name",
    "Unable to find the user preferences file.\n"
    "The factory default will be used instead." );

warning() can be used to tell the user about unusual errors, or errors which can't be easily fixed:

switch( QMessageBox::warning( this, "Application name",
        "Could not connect to the <mumble> server.\n"
        "This program can't function correctly "
        "without the server.\n\n",
        "Retry",
        "Quit", 0, 0, 1 ) )
    case 0: // The user clicked the Retry again button or pressed Enter
        // try again
        break;
    case 1: // The user clicked the Quit or pressed Escape
        // exit
        break;
}

The text part of all message box messages can be either rich text or plain text. If you specify a rich text formatted string, it will be rendered using the default stylesheet. See QStyleSheet::defaultSheet() for details. With certain strings that contain XML meta characters, the auto-rich text detection may fail, interpreting plain text incorrectly as rich text. In these rare cases, use QStyleSheet::convertFromPlainText() to convert your plain text string to a visually equivalent rich text string or set the text format explicitly with setTextFormat().

Note that the Microsoft Windows User Interface Guidelines strongly recommend using the application name as the window's caption.

Below are more examples of how to use the static member functions. After these examples you will find an overview of the non-static member functions.

Exiting a program is part of its normal operation. If there is unsaved data the user probably should be asked if they want to save the data. For example:

switch( QMessageBox::information( this, "Application name here",
        "The document contains unsaved changes\n"
        "Do you want to save the changes before exiting?",
        "&Save", "&Discard", "Cancel",
        0,      // Enter == button 0
        2 ) ) { // Escape == button 2
    case 0: // Save clicked or Alt+S pressed or Enter pressed.
        // save
        break;
    case 1: // Discard clicked or Alt+D pressed
        // don't save but exit
        break;
    case 2: // Cancel clicked or Alt+C pressed or Escape pressed
        // don't exit
        break;
}

The application name is used as the window caption in accordance with the Microsoft recommendation. The Escape button cancels the entire exit operation, and pressing Enter causes the changes to be saved before the exit occurs.

Disk full errors are unusual (in a perfect world, they are) and they certainly can be hard to correct. This example uses predefined buttons instead of hard-coded button texts:

switch( QMessageBox::warning( this, "Application name here",
        "Could not save the user preferences,\n"
        "because the disk is full.  You can delete\n"
        "some files and press Retry, or you can\n"
        "abort the Save Preferences operation.",
        QMessageBox::Retry | QMessageBox::Default,
        QMessageBox::Abort | QMessageBox::Escape )) {
    case QMessageBox::Retry: // Retry clicked or Enter pressed
        // try again
        break;
    case QMessageBox::Abort: // Abort clicked or Escape pressed
        // abort
        break;
}

The critical() function should be reserved for critical errors. In this example errorDetails is a QString or const char*, and QString is used to concatenate several strings:

QMessageBox::critical( 0, "Application name here",
        QString("An internal error occurred. Please ") +
        "call technical support at 123456789 and report\n"+
        "these numbers:\n\n" + errorDetails +
        "\n\n<Application> will now exit." );

In this example an OK button is displayed.

QMessageBox provides a very simple About box, which displays an appropriate icon and the string you provide:

QMessageBox::about( this, "About <Application>",
        "<Application> is a <one-paragraph blurb>\n\n"
        "Copyright 1951-2002 Such-and-such.  "
        "<License words here.>\n\n"
        "For technical support, call 123456789 or see\n"
        "http://www.such-and-such.com/Application/\n" );

See about() for more information.

If you want your users to know that the application is built using Qt (so that they know you use high quality tools:) you might like to add an "About Qt" menu option under the Help menu to invoke aboutQt().

If none of the standard message boxes is suitable, you can create a QMessageBox from scratch and with custom button texts:

QMessageBox mb( "Application name here",
        "Saving the file will overwrite the original file on the disk.\n"
        "Do you really want to save?",
        QMessageBox::Information,
        QMessageBox::Yes | QMessageBox::Default,
        QMessageBox::No,
        QMessageBox::Cancel | QMessageBox::Escape );
mb.setButtonText( QMessageBox::Yes, "Save" );
mb.setButtonText( QMessageBox::No, "Discard" );
switch( mb.exec() ) {
    case QMessageBox::Yes:
        // save and exit
        break;
    case QMessageBox::No:
        // exit without saving
        break;
    case QMessageBox::Cancel:
        // don't save and don't exit
        break;
}

QMessageBox defines two enum types: Icon and an unnamed button type. Icon defines the Information, Warning, and Critical icons for each GUI style. It is used by the constructor and by the static member functions information(), warning() and critical(). A function called standardIcon() gives you access to the various icons.

The button types are:

• Ok - the default for single-button message boxes
• Cancel - note that this is not automatically Escape
• Yes
• No
• Abort
• Retry
• Ignore

Button types can be combined with two modifiers by using OR, '|':

• Default - makes pressing Enter equivalent to clicking this button. Normally used with Ok, Yes or similar.
• Escape - makes pressing Escape equivalent to clicking this button. Normally used with Abort, Cancel or similar.

The text(), icon() and iconPixmap() functions provide access to the current text and pixmap of the message box. The setText(), setIcon() and setIconPixmap() let you change it. The difference between setIcon() and setIconPixmap() is that the former accepts a QMessageBox::Icon and can be used to set standard icons, whereas the latter accepts a QPixmap and can be used to set custom icons.

setButtonText() and buttonText() provide access to the buttons.

QMessageBox has no signals or slots.

See also QDialog, Isys on error messages, GUI Design Handbook: Message Box and Dialog Classes.

Member Type Documentation

QMessageBox::Icon

This enum includes provides the following values:

• QMessageBox::NoIcon - the message box does not have any icon.
• QMessageBox::Information - an icon indicating that the message is nothing out of the ordinary.
• QMessageBox::Warning - an icon indicating that the message is a warning, but can be dealt with.
• QMessageBox::Critical - an icon indicating that the message represents a critical problem.

Member Function Documentation

QMessageBox::QMessageBox ( QWidget * parent = 0, const char * name = 0 )

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

The parent and name arguments are passed to the QDialog constructor.

QMessageBox::QMessageBox ( const QString & caption, const QString & text, Icon icon, int button0, int button1, int button2, QWidget * parent = 0, const char * name = 0, bool modal = TRUE, WFlags f = WStyle_DialogBorder )

The icon must be one of the following:

• QMessageBox::NoIcon
• QMessageBox::Information
• QMessageBox::Warning
• QMessageBox::Critical

Each button, button0, button1 and button2, can have one of the following values:

• QMessageBox::NoButton
• QMessageBox::Ok
• QMessageBox::Cancel
• QMessageBox::Yes
• QMessageBox::No
• QMessageBox::Abort
• QMessageBox::Retry
• QMessageBox::Ignore

Use QMessageBox::NoButton for the later parameters to have fewer than three buttons in your message box.

One of the buttons can be OR-ed with the QMessageBox::Default flag to make it the default button (clicked when Enter is pressed).

One of the buttons can be OR-ed with the QMessageBox::Escape flag to make it the cancel or close button (clicked when Escape is pressed).

Example:

QMessageBox mb( "Application Name",
        "Hardware failure.\n\nDisk error detected\nDo you want to stop?",
        QMessageBox::NoIcon,
        QMessageBox::Yes | QMessageBox::Default,
        QMessageBox::No  | QMessageBox::Escape
        QMessageBox::NoButton );
if ( mb.exec() == QMessageBox::No )
    // try again

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

If modal is TRUE the message becomes modal; otherwise it becomes modeless.

The parent, name, modal, and f arguments are passed to the QDialog constructor.

See also caption, text and icon.

QMessageBox::~QMessageBox ()

void QMessageBox::about ( QWidget * parent, const QString & caption, const QString & text ) [static]

about() looks for a suitable icon in four locations:

1. It prefers parent->icon() if that exists.
2. If not, it tries the top-level widget containing parent.
3. If that fails, it tries the main widget.
4. As a last resort it uses the Information icon.

The about box has a single button labelled OK.

See also QWidget::icon and QApplication::mainWidget().

Examples: action/application.cpp, application/application.cpp, chart/chartform.cpp, helpviewer/helpwindow.cpp, mdi/application.cpp, menu/menu.cpp and themes/themes.cpp.

void QMessageBox::aboutQt ( QWidget * parent, const QString & caption = QString::null ) [static]

This is useful for inclusion in the Help menu. See the examples/menu/menu.cpp example.

Examples: action/application.cpp, application/application.cpp, chart/chartform.cpp, helpviewer/helpwindow.cpp, menu/menu.cpp, themes/themes.cpp and trivial/trivial.cpp.

void QMessageBox::adjustSize () [virtual]

This function will not be called if the message box has been explicitly resized before showing it.

Reimplemented from QWidget.

QString QMessageBox::buttonText ( int button ) const

See also setButtonText().

int QMessageBox::critical ( QWidget * parent, const QString & caption, const QString & text, int button0, int button1, int button2 = 0 ) [static]

• QMessageBox::NoButton
• QMessageBox::Ok
• QMessageBox::Cancel
• QMessageBox::Yes
• QMessageBox::No
• QMessageBox::Abort
• QMessageBox::Retry
• QMessageBox::Ignore

If you don't want all three buttons, set the last button, or last two buttons to QMessageBox::NoButton.

Returns the identity (QMessageBox::Ok, or QMessageBox::No, etc.) of the button that was clicked.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

See also information() and warning().

Examples: network/ftpclient/ftpmainwindow.cpp, process/process.cpp and xml/outliner/outlinetree.cpp.

int QMessageBox::critical ( QWidget * parent, const QString & caption, const QString & text, const QString & button0Text = QString::null, const QString & button1Text = QString::null, const QString & button2Text = QString::null, int defaultButtonNumber = 0, int escapeButtonNumber = -1 ) [static]

Displays a critical error message box with a caption, a text, and 1, 2 or 3 buttons. Returns the number of the button that was clicked (0, 1 or 2).

button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional, and button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1 (pressing Escape does nothing); supply 0, 1, or 2 to make pressing Escape equivalent to clicking the relevant button.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

See also information() and warning().

Icon QMessageBox::icon () const

Returns the message box's icon. See the "icon" property for details.

const QPixmap * QMessageBox::iconPixmap () const

Returns the current icon. See the "iconPixmap" property for details.

int QMessageBox::information ( QWidget * parent, const QString & caption, const QString & text, int button0, int button1 = 0, int button2 = 0 ) [static]

• QMessageBox::NoButton
• QMessageBox::Ok
• QMessageBox::Cancel
• QMessageBox::Yes
• QMessageBox::No
• QMessageBox::Abort
• QMessageBox::Retry
• QMessageBox::Ignore

If you don't want all three buttons, set the last button, or last two buttons to QMessageBox::NoButton.

Returns the identity (QMessageBox::Ok, or QMessageBox::No, etc.) of the button that was clicked.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

See also warning() and critical().

Examples: action/application.cpp, application/application.cpp, chart/chartform.cpp, dirview/dirview.cpp, fileiconview/qfileiconview.cpp, picture/picture.cpp and qwerty/qwerty.cpp.

int QMessageBox::information ( QWidget * parent, const QString & caption, const QString & text, const QString & button0Text = QString::null, const QString & button1Text = QString::null, const QString & button2Text = QString::null, int defaultButtonNumber = 0, int escapeButtonNumber = -1 ) [static]

Displays an information message box with caption caption, text text and one, two or three buttons. Returns the index of the button that was clicked (0, 1 or 2).

button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional. button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1 (pressing Escape does nothing); supply 0, 1 or 2 to make pressing Escape equivalent to clicking the relevant button.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

See also warning() and critical().

int QMessageBox::message ( const QString & caption, const QString & text, const QString & buttonText = QString::null, QWidget * parent = 0, const char * = 0 ) [static]

Opens a modal message box directly using the specified parameters.

Please use information(), warning() or critical() instead.

Example: grapher/grapher.cpp.

bool QMessageBox::query ( const QString & caption, const QString & text, const QString & yesButtonText = QString::null, const QString & noButtonText = QString::null, QWidget * parent = 0, const char * = 0 ) [static]

Queries the user using a modal message box with two buttons. Note that caption is not always shown, it depends on the window manager.

Please use information(), warning() or critical() instead.

void QMessageBox::setButtonText ( int button, const QString & text )

See also buttonText().

void QMessageBox::setIcon ( Icon )

Sets the message box's icon. See the "icon" property for details.

void QMessageBox::setIconPixmap ( const QPixmap & )

Sets the current icon. See the "iconPixmap" property for details.

void QMessageBox::setText ( const QString & )

Sets the message box text to be displayed. See the "text" property for details.

void QMessageBox::setTextFormat ( TextFormat )

Sets the format of the text displayed by the message box. See the "textFormat" property for details.

QPixmap QMessageBox::standardIcon ( Icon icon ) [static]

QPixmap QMessageBox::standardIcon ( Icon icon, GUIStyle style ) [static]

Returns the pixmap used for a standard icon. This allows the pixmaps to be used in more complex message boxes. icon specifies the required icon, e.g. QMessageBox::Information, QMessageBox::Warning or QMessageBox::Critical.

style is unused.

QString QMessageBox::text () const

Returns the message box text to be displayed. See the "text" property for details.

TextFormat QMessageBox::textFormat () const

Returns the format of the text displayed by the message box. See the "textFormat" property for details.

int QMessageBox::warning ( QWidget * parent, const QString & caption, const QString & text, int button0, int button1, int button2 = 0 ) [static]

• QMessageBox::NoButton
• QMessageBox::Ok
• QMessageBox::Cancel
• QMessageBox::Yes
• QMessageBox::No
• QMessageBox::Abort
• QMessageBox::Retry
• QMessageBox::Ignore

If you don't want all three buttons, set the last button, or last two buttons to QMessageBox::NoButton.

Returns the identity (QMessageBox::Ok, or QMessageBox::No, etc.) of the button that was clicked.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

See also information() and critical().

Examples: chart/chartform.cpp, i18n/main.cpp, network/mail/smtp.cpp, qwerty/qwerty.cpp, showimg/showimg.cpp and sound/sound.cpp.

int QMessageBox::warning ( QWidget * parent, const QString & caption, const QString & text, const QString & button0Text = QString::null, const QString & button1Text = QString::null, const QString & button2Text = QString::null, int defaultButtonNumber = 0, int escapeButtonNumber = -1 ) [static]

Displays a warning message box with a caption, a text, and 1, 2 or 3 buttons. Returns the number of the button that was clicked (0, 1, or 2).

button0Text is the text of the first button, and is optional. If button0Text is not supplied, "OK" (translated) will be used. button1Text is the text of the second button, and is optional, and button2Text is the text of the third button, and is optional. defaultButtonNumber (0, 1 or 2) is the index of the default button; pressing Return or Enter is the same as clicking the default button. It defaults to 0 (the first button). escapeButtonNumber is the index of the Escape button; pressing Escape is the same as clicking this button. It defaults to -1 (pressing Escape does nothing); supply 0, 1, or 2 to make pressing Escape equivalent to clicking the relevant button.

If parent is 0, the message box becomes an application-global modal dialog box. If parent is a widget, the message box becomes modal relative to parent.

See also information() and critical().

Property Documentation

Icon icon

This property holds the message box's icon.

The icon of the message box can be one of the following predefined icons:

• QMessageBox::NoIcon
• QMessageBox::Information
• QMessageBox::Warning
• QMessageBox::Critical

The actual pixmap used for displaying the icon depends on the current GUI style. You can also set a custom pixmap icon using the QMessageBox::iconPixmap property. The default icon is QMessageBox::NoIcon.

See also iconPixmap.

Set this property's value with setIcon() and get this property's value with icon().

QPixmap iconPixmap

This property holds the current icon.

The icon currently used by the message box. Note that it's often hard to draw one pixmap that looks appropriate in both Motif and Windows GUI styles; you may want to draw two pixmaps.

See also icon.

Set this property's value with setIconPixmap() and get this property's value with iconPixmap().

QString text

This property holds the message box text to be displayed.

The text will be interpreted either as a plain text or as rich text, depending on the text format setting (QMessageBox::textFormat). The default setting is AutoText, i.e. the message box will try to auto-detect the format of the text.

The default value of this property is QString::null.

See also textFormat.

Set this property's value with setText() and get this property's value with text().

TextFormat textFormat

This property holds the format of the text displayed by the message box.

The current text format used by the message box. See the Qt::TextFormat enum for an explanation of the possible options.

The default format is AutoText.

See also text.

Set this property's value with setTextFormat() and get this property's value with textFormat().

This file is part of the Qt toolkit. Copyright © 1995-2002 Trolltech. All Rights Reserved.