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The QMessageBox class provides a modal dialog with a short message, an icon, and buttons laid out depending on the current style. More...
#include <QMessageBox>
Inherits QDialog.
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The QMessageBox class provides a modal dialog with a short message, an icon, and buttons laid out depending on the current style.
Message boxes are used to provide informative messages and to ask simple questions.
The easiest way to pop up a message box in Qt is to call one of the static functions QMessageBox::information(), QMessageBox::question(), QMessageBox::critical(), and QMessageBox::warning(). For example:
int ret = QMessageBox::warning(this, tr("My Application"),
tr("The document has been modified.\n"
"Do you want to save your changes?"),
QMessageBox::Save | QMessageBox::Discard
| QMessageBox::Cancel,
QMessageBox::Save);
Buttons are specified by combining StandardButtons using the bitwise OR operator. The order of the buttons on screen is platform-dependent. For example, on Windows, Save is displayed to the left of Cancel, whereas on Mac OS, the order is reversed.
The text part of all message box messages can be either rich text or plain text. 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 Qt::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 recommend using the application name as the window's title.
The Standard Dialogs example shows how to use QMessageBox as well as other built-in Qt dialogs.
QMessageBox supports four severity levels, indicated by an icon:
| Question | For message boxes that ask a question as part of normal operation. Some style guides recommend using Information for this purpose. |
| 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. |
If the convenience static functions, such as QMessageBox::information() and QMessageBox::warning(), are not flexible enough for your needs, you can instantiate a QMessageBox on the stack. You can then use addButton() to add buttons with standard or arbitrary text.
When using an instance of QMessageBox with standard buttons, you can test the return value of exec() to determine which button was clicked. For example,
QMessageBox msgBox;
msgBox.setStandardButtons(QMessageBox::Yes | QMessageBox::No);
switch (msgBox.exec()) {
case QMessageBox::Yes:
// yes was clicked
break;
case QMessageBox::No:
// no was clicked
break;
default:
// should never be reached
break;
}
When using an instance of QMessageBox with custom buttons, you can test the value of clickedButton() after calling exec(). For example,
QMessageBox msgBox;
QPushButton *connectButton = msgBox.addButton(tr("Connect"), QMessageBox::ActionRole);
QPushButton *abortButton = msgBox.addButton(QMessageBox::Abort);
msgBox.exec();
if (msgBox.clickedButton() == connectButton) {
// connect
} else if (msgBox.clickedButton() == abortButton) {
// abort
}
In the example above, the Connect button is created using the addButton() overload that takes a text and a ButtonRole. The ButtonRole is used by QMessageBox to determine the ordering of the buttons on screen (which varies according to the platform).
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.
The default button (i.e., the button that is activated when the user presses Enter) can be specified using setDefaultButton(). If none is specified, QMessageBox will try to find one automatically based on the ButtonRoles of the buttons in the dialog.
Similarly, the escape button (the button that is activated when the user presses Esc) is specified using setEscapeButton(). If no escape button is specified, QMessageBox attempts to automatically detect an escape button as follows:
When an escape button could not be automatically detected, pressing Esc has no effect.
See also QDialogButtonBox, GUI Design Handbook: Message Box, Standard Dialogs Example, and Application Example.
This enum describes the roles that can be used to describe buttons in the button box. Combinations of these roles are as flags used to describe different aspects of their behavior.
| Constant | Value | Description |
|---|---|---|
| QMessageBox::InvalidRole | -1 | The button is invalid. |
| QMessageBox::AcceptRole | 0 | Clicking the button causes the dialog to be accepted (e.g. OK). |
| QMessageBox::RejectRole | 1 | Clicking the button causes the dialog to be rejected (e.g. Cancel). |
| QMessageBox::DestructiveRole | 2 | Clicking the button causes a destructive change (e.g. for Discarding Changes) and closes the dialog. |
| QMessageBox::ActionRole | 3 | Clicking the button causes changes to the elements within the dialog, without closing the dialog. |
| QMessageBox::HelpRole | 4 | The button can be clicked to request help. |
| QMessageBox::YesRole | 5 | The button is a "Yes"-like button. |
| QMessageBox::NoRole | 6 | The button is a "No"-like button. |
| QMessageBox::ApplyRole | 8 | The button applies current changes. |
| QMessageBox::ResetRole | 7 | The button resets the dialog's fields to default values. |
See also StandardButton.
This enum has the following values:
| Constant | Value | Description |
|---|---|---|
| QMessageBox::NoIcon | 0 | the message box does not have any icon. |
| QMessageBox::Question | 4 | an icon indicating that the message is asking a question. |
| QMessageBox::Information | 1 | an icon indicating that the message is nothing out of the ordinary. |
| QMessageBox::Warning | 2 | an icon indicating that the message is a warning, but can be dealt with. |
| QMessageBox::Critical | 3 | an icon indicating that the message represents a critical problem. |
These enums describe flags for standard buttons. Each button has a defined ButtonRole.
| Constant | Value | Description |
|---|---|---|
| QMessageBox::Ok | 0x00000400 | An "OK" button defined with the AcceptRole. |
| QMessageBox::Open | 0x00002000 | A "Open" button defined with the AcceptRole. |
| QMessageBox::Save | 0x00000800 | A "Save" button defined with the AcceptRole. |
| QMessageBox::Cancel | 0x00400000 | A "Cancel" button defined with the RejectRole. |
| QMessageBox::Close | 0x00200000 | A "Close" button defined with the RejectRole. |
| QMessageBox::Discard | 0x00800000 | A "Discard" or "Don't Save" button, depending on the platform, defined with the DestructiveRole. |
| QMessageBox::Apply | 0x02000000 | An "Apply" button defined with the ApplyRole. |
| QMessageBox::Reset | 0x04000000 | A "Reset" button defined with the ResetRole. |
| QMessageBox::RestoreDefaults | 0x08000000 | A "Restore Defaults" button defined with the ResetRole. |
| QMessageBox::Help | 0x01000000 | A "Help" button defined with the HelpRole. |
| QMessageBox::SaveAll | 0x00001000 | A "Save All" button defined with the AcceptRole. |
| QMessageBox::Yes | 0x00004000 | A "Yes" button defined with the YesRole. |
| QMessageBox::YesToAll | 0x00008000 | A "Yes to All" button defined with the YesRole. |
| QMessageBox::No | 0x00010000 | A "No" button defined with the NoRole. |
| QMessageBox::NoToAll | 0x00020000 | A "No to All" button defined with the NoRole. |
| QMessageBox::Abort | 0x00040000 | An "Abort" button defined with the RejectRole. |
| QMessageBox::Retry | 0x00080000 | A "Retry" button defined with the AcceptRole. |
| QMessageBox::Ignore | 0x00100000 | An "Ignore" button defined with the AcceptRole. |
| QMessageBox::NoButton | 0x00000000 | An invalid button. |
The following values are obsolete:
| Constant | Value | Description |
|---|---|---|
| QMessageBox::YesAll | YesToAll | Use YesToAll instead. |
| QMessageBox::NoAll | NoToAll | Use NoToAll instead. |
| QMessageBox::Default | 0x00000100 | Use the defaultButton argument of information(), warning(), etc. instead, or call setDefaultButton(). |
| QMessageBox::Escape | 0x00000200 | Call setEscapeButton() instead. |
| QMessageBox::FlagMask | 0x00000300 | |
| QMessageBox::ButtonMask | ~FlagMask |
This enum was introduced in Qt 4.2.
The StandardButtons type is a typedef for QFlags<StandardButton>. It stores an OR combination of StandardButton values.
See also ButtonRole and standardButtons.
This property holds the text to be displayed in the details area.
The text will be interpreted as a plain text. The default value of this property is an empty string.
This property was introduced in Qt 4.2.
Access functions:
This property holds the message box's icon.
The icon of the message box can be one of the following predefined icons:
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.
Access functions:
See also 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 all GUI styles; you may want to supply a different pixmap for each platform.
Access functions:
See also icon.
This property holds the informative text that provides a fuller description for the message.
Infromative text can be used to expand upon the text() to give more information to the user. On the Mac, this text appears in small system font below the text(). On other platforms, it is simply appended to the existing text.
This property was introduced in Qt 4.2.
Access functions:
This property holds collection of standard buttons in the message box.
This property controls which standard buttons are used by the message box.
This property was introduced in Qt 4.2.
Access functions:
See also addButton().
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 Qt::AutoText, i.e. the message box will try to auto-detect the format of the text.
The default value of this property is an empty string.
Access functions:
See also 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 Qt::AutoText.
Access functions:
See also setText().
Constructs a message box with no text and no buttons.
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 argument is passed to the QDialog constructor.
Constructs a message box with the given icon, title, text, and standard buttons. (Buttons can also be added at any time using addButton().)
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 f arguments are passed to the QDialog constructor.
See also setWindowTitle(), setText(), setIcon(), and setStandardButtons().
Destroys the message box.
Displays a simple about box with title title and text text. The about box's parent is parent.
about() looks for a suitable icon in four locations:
The about box has a single button labelled "OK".
See also QWidget::windowIcon() and QApplication::activeWindow().
Displays a simple message box about Qt, with the given title and centered over parent (if parent is not 0). The message includes the version number of Qt being used by the application.
This is useful for inclusion in the Help menu of an application, as shown in the Menus example.
QApplication provides this functionality as a slot.
See also QApplication::aboutQt().
Adds the given button to the message box with the specified role.
This function was introduced in Qt 4.2.
See also removeButton(), button(), and setStandardButtons().
This is an overloaded member function, provided for convenience.
Creates a button with the given text, adds it to the message box for the specified role, and returns it.
This function was introduced in Qt 4.2.
This is an overloaded member function, provided for convenience.
Adds a standard button to the message box if it is valid to do so, and returns the push button.
This function was introduced in Qt 4.2.
See also setStandardButtons().
Returns a pointer corresponding to the standard button which, or 0 if the standard button doesn't exist in this message box.
This function was introduced in Qt 4.2.
See also standardButtons and standardButton().
Returns the button that was clicked by the user, or 0 if the user hit the Esc key and no escape button was set.
If exec() hasn't been called yet, returns 0.
Example:
QMessageBox messageBox(this);
QAbstractButton *disconnectButton =
messageBox.addButton(tr("Disconnect"), QMessageBox::ActionRole);
...
messageBox.exec();
if (messageBox.clickedButton() == disconnectButton) {
...
}
This function was introduced in Qt 4.2.
See also standardButton() and button().
Opens a critical message box with the title title and the text text. The standard buttons buttons is added to the message box. defaultButton specifies the button be used as the defaultButton. If the defaultButton is set to QMessageBox::NoButton, QMessageBox picks a suitable default automatically.
Returns the identity of the standard button that was activated. If Esc was pressed, returns the escape button (if any).
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.
This function was introduced in Qt 4.2.
See also question(), warning(), and information().
Returns the button that should be the message box's default button. Returns 0 if no default button was set.
This function was introduced in Qt 4.2.
See also setDefaultButton(), addButton(), and QPushButton::setDefault().
Returns the button that is activated when escape is pressed.
By default, QMessageBox attempts to automatically detect an escape button as follows:
When an escape button could not be automatically detected, pressing Esc has no effect.
This function was introduced in Qt 4.2.
See also setEscapeButton() and addButton().
Shows the message box as a modal dialog, blocking until the user closes it.
When using a QMessageBox with standard buttons, this functions returns a StandardButton value indicating the standard button that was clicked. When using QMessageBox with custom buttons, this function returns an opaque value; use clickedButton() to determine which button was clicked.
Users cannot interact with any other window in the same application until they close the dialog, either by clicking a button or by using a mechanism provided by the window system.
Opens an information message box with the title title and the text text. The standard buttons buttons is added to the message box. defaultButton specifies the button be used as the defaultButton. If the defaultButton is set to QMessageBox::NoButton, QMessageBox picks a suitable default automatically.
Returns the identity of the standard button that was activated. If Esc was pressed, returns the escape button (if any).
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.
This function was introduced in Qt 4.2.
See also question(), warning(), and critical().
Opens a question message box with the title title and the text text. The standard buttons buttons is added to the message box. defaultButton specifies the button be used as the defaultButton. If the defaultButton is set to QMessageBox::NoButton, QMessageBox picks a suitable default automatically.
Returns the identity of the standard button that was activated. If Esc was pressed, returns the escape button (if any).
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.
This function was introduced in Qt 4.2.
See also information(), warning(), and critical().
Removes button from the button box without deleting it.
This function was introduced in Qt 4.2.
See also addButton() and setStandardButtons().
Sets the message box's default button to button.
This function was introduced in Qt 4.2.
See also defaultButton(), addButton(), and QPushButton::setDefault().
This is an overloaded member function, provided for convenience.
Sets the message box's default button to button.
This function was introduced in Qt 4.3.
See also addButton() and QPushButton::setDefault().
Sets the button that gets activated when the Escape key is pressed to button.
This function was introduced in Qt 4.2.
See also escapeButton(), addButton(), and clickedButton().
This is an overloaded member function, provided for convenience.
Sets the buttons that gets activated when the Escape key is pressed to button.
This function was introduced in Qt 4.3.
See also addButton() and clickedButton().
This function shadows QWidget::setWindowModality().
Sets the modality of the message box to windowModality.
On Mac OS X, if the modality is set to Qt::WindowModal and the message box has a parent, then the message box will be a Qt::Sheet, otherwise the message box will be a standard dialog.
This function was introduced in Qt 4.2.
This function shadows QWidget::setWindowTitle().
Sets the title of the message box to title. On Mac OS X, the window title is ignored (as required by the Mac OS X Guidelines).
This function was introduced in Qt 4.2.
Returns the standard button enum value corresponding to the given button, or NoButton if the given button isn't a standard button.
This function was introduced in Qt 4.2.
See also button() and standardButtons().
Opens a warning message box with the title title and the text text. The standard buttons buttons is added to the message box. defaultButton specifies the button be used as the defaultButton. If the defaultButton is set to QMessageBox::NoButton, QMessageBox picks a suitable default automatically.
Returns the identity of the standard button that was activated. If Esc was pressed, returns the escape button (if any).
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.
This function was introduced in Qt 4.2.
See also question(), information(), and critical().
This macro can be used to ensure that the application is run against a recent enough version of Qt. This is especially useful if your application depends on a specific bug fix introduced in a bug-fix release (e.g., 4.0.2).
The argc and argv parameters are the main() function's argc and argv parameters. The version parameter is a string literal that specifies which version of Qt the application requires (e.g., "4.0.2").
Example:
#include <QApplication>
#include <QMessageBox>
int main(int argc, char *argv[])
{
QT_REQUIRE_VERSION(argc, argv, "4.0.2")
QApplication app(argc, argv);
...
return app.exec();
}
| Copyright © 2008 Trolltech | Trademarks | Qt 4.3.5 |