qvariant.3qt

Linux 下的图形编程环境。

'\" t
.TH QVariant 3qt "5 March 2001" "Trolltech AS" \" -*- nroff -*-
.\" Copyright 1992-2001 Trolltech AS.  All rights reserved.  See the
.\" license file included in the distribution for a complete license
.\" statement.
.\"
.ad l
.nh
.SH NAME
QVariant \- Acts like a union for the most common Qt data types
.br
.PP
\fC#include <qvariant.h>\fR
.PP
.SS "Public Members"
.in +1c
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.BI "enum \fBType\fR { Invalid, Map, List, String, StringList, Font, Pixmap, Brush, Rect, Size, Color, Palette, ColorGroup, IconSet, Point, Image, Int, UInt, Bool, Double, CString, PointArray, Region, Bitmap, Cursor, SizePolicy }"
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.BI "\fBQVariant\fR () "
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.BI "\fB~QVariant\fR () "
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.BI "\fBQVariant\fR ( const QVariant & ) "
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.BI "\fBQVariant\fR ( QDataStream & s ) "
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.BI "\fBQVariant\fR ( const QString & ) "
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.BI "\fBQVariant\fR ( const QCString & ) "
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.BI "\fBQVariant\fR ( const char * ) "
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.BI "\fBQVariant\fR ( const QStringList & ) "
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.BI "\fBQVariant\fR ( const QFont & ) "
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.BI "\fBQVariant\fR ( const QPixmap & ) "
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.BI "\fBQVariant\fR ( const QImage & ) "
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.BI "\fBQVariant\fR ( const QBrush & ) "
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.BI "\fBQVariant\fR ( const QPoint & ) "
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.BI "\fBQVariant\fR ( const QRect & ) "
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.BI "\fBQVariant\fR ( const QSize & ) "
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.BI "\fBQVariant\fR ( const QColor & ) "
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.BI "\fBQVariant\fR ( const QPalette & ) "
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.BI "\fBQVariant\fR ( const QColorGroup & ) "
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.BI "\fBQVariant\fR ( const QIconSet & ) "
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.BI "\fBQVariant\fR ( const QPointArray & ) "
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.BI "\fBQVariant\fR ( const QRegion & ) "
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.BI "\fBQVariant\fR ( const QBitmap & ) "
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.BI "\fBQVariant\fR ( const QCursor & ) "
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.BI "\fBQVariant\fR ( const QValueList<QVariant> & ) "
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.BI "\fBQVariant\fR ( const QMap<QString, QVariant> & ) "
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.BI "\fBQVariant\fR ( int ) "
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.BI "\fBQVariant\fR ( uint ) "
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.BI "\fBQVariant\fR ( bool, int ) "
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.BI "\fBQVariant\fR ( double ) "
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.BI "\fBQVariant\fR ( QSizePolicy ) "
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.BI "QVariant& \fBoperator=\fR ( const QVariant & ) "
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.BI "bool \fBoperator==\fR ( const QVariant & ) const"
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.BI "bool \fBoperator!=\fR ( const QVariant & ) const"
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.BI "Type \fBtype\fR () const"
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.BI "const char* \fBtypeName\fR () const"
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.BI "bool \fBcanCast\fR ( Type ) const"
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.BI "bool \fBisValid\fR () const"
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.BI "void \fBclear\fR () "
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.BI "const QString \fBtoString\fR () const"
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.BI "const QCString \fBtoCString\fR () const"
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.BI "const QStringList \fBtoStringList\fR () const"
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.BI "const QFont \fBtoFont\fR () const"
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.BI "const QPixmap \fBtoPixmap\fR () const"
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.BI "const QImage \fBtoImage\fR () const"
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.BI "const QBrush \fBtoBrush\fR () const"
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.BI "const QPoint \fBtoPoint\fR () const"
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.BI "const QRect \fBtoRect\fR () const"
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.BI "const QSize \fBtoSize\fR () const"
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.BI "const QColor \fBtoColor\fR () const"
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.BI "const QPalette \fBtoPalette\fR () const"
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.BI "const QColorGroup \fBtoColorGroup\fR () const"
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.BI "const QIconSet \fBtoIconSet\fR () const"
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.BI "const QPointArray \fBtoPointArray\fR () const"
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.BI "const QBitmap \fBtoBitmap\fR () const"
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.BI "const QRegion \fBtoRegion\fR () const"
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.BI "const QCursor \fBtoCursor\fR () const"
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.BI "int \fBtoInt\fR () const"
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.BI "uint \fBtoUInt\fR () const"
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.BI "bool \fBtoBool\fR () const"
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.BI "double \fBtoDouble\fR () const"
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.BI "const QValueList<QVariant> \fBtoList\fR () const"
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.BI "const QMap<QString, QVariant> \fBtoMap\fR () const"
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.BI "QSizePolicy \fBtoSizePolicy\fR () const"
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.BI "QValueListConstIterator<QVariant> \fBlistBegin\fR () const"
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.BI "QValueListConstIterator<QVariant> \fBlistEnd\fR () const"
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.BI "QValueListConstIterator<QString> \fBstringListBegin\fR () const"
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.BI "QValueListConstIterator<QString> \fBstringListEnd\fR () const"
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.BI "QMapConstIterator<QString, QVariant> \fBmapBegin\fR () const"
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.BI "QMapConstIterator<QString, QVariant> \fBmapEnd\fR () const"
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.BI "QMapConstIterator<QString, QVariant> \fBmapFind\fR ( const QString & ) const"
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.BI "QString& \fBasString\fR () "
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.BI "QCString& \fBasCString\fR () "
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.BI "QStringList& \fBasStringList\fR () "
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.BI "QFont& \fBasFont\fR () "
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.BI "QPixmap& \fBasPixmap\fR () "
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.BI "QImage& \fBasImage\fR () "
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.BI "QBrush& \fBasBrush\fR () "
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.BI "QPoint& \fBasPoint\fR () "
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.BI "QRect& \fBasRect\fR () "
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.BI "QSize& \fBasSize\fR () "
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.BI "QColor& \fBasColor\fR () "
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.BI "QPalette& \fBasPalette\fR () "
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.BI "QColorGroup& \fBasColorGroup\fR () "
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.BI "QIconSet& \fBasIconSet\fR () "
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.BI "QPointArray& \fBasPointArray\fR () "
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.BI "QBitmap& \fBasBitmap\fR () "
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.BI "QRegion& \fBasRegion\fR () "
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.BI "QCursor& \fBasCursor\fR () "
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.BI "int& \fBasInt\fR () "
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.BI "uint& \fBasUInt\fR () "
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.BI "bool& \fBasBool\fR () "
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.BI "double& \fBasDouble\fR () "
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.BI "QValueList<QVariant>& \fBasList\fR () "
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.BI "QMap<QString, QVariant>& \fBasMap\fR () "
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.BI "QSizePolicy& \fBasSizePolicy\fR () "
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.BI "void \fBload\fR ( QDataStream & ) "
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.BI "void \fBsave\fR ( QDataStream & ) const"
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.SS "Static Public Members"
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.BI "const char* \fBtypeToName\fR ( Type typ ) "
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.BI "Type \fBnameToType\fR ( const char * name ) "
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.in -1c
.SH DESCRIPTION
Acts like a union for the most common Qt data types.
.PP
Since C++ forbids unions from including types that have non-default constructors or destructors, most interesting Qt classes cannot be used in unions. This is a problem when using QObject::property(), among other things.
.PP
This class provides union functionality for property() and most other needs that might be solved by a union including e.g. QWidget.
.PP
A QVariant object can hold any one type() at a time, and you can find out what type it holds, convert it to a different type using e.g. asSize(), get its value using e.g. toSize(), and check whether the type can be converted to e.g. QSize using canCast().
.PP
The methods named toT() (for any supported T, see the Type documentation for a list) are const. If you ask for the stored type, they return a copy of the stored object. If you ask for a type which can be generated from the stored type, toT() copies and converts, and leaves the object itself unchanged. If you ask for a type that cannot be generated from the stored type, the result depends on the type, see the function documentation for details.
.PP
Note that three data types supported by QVariant are explicitly shared, namely QImage, QPointArray, and QCString, and in these cases the toT() methods return a shallow copy. In almost all cases, you must make a deep copy of the returned values before modifying them.
.PP
The methods named asT() are not const. They do conversion like toT() methods, set the variant to hold the converted value, and return a reference to the new contents of the variant.
.PP
Here is some example code to demonstrate use of QVariant:
.PP
.nf
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    QDataStream out(...);
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    QVariant v(123);          // The variant now contains an int
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    int x = v.toInt();        // x = 123
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    out << v;                 // Writes a type tag and an int to out
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    v = QVariant("hello");    // The variant now contains a QCString
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    v = QVariant(tr("hello"));// The variant now contains a QString
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    int y = v.toInt();        // y = 0 since v cannot be converted to an int
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    QString s = v.toString(); // s = tr("hello")  (see QObject::tr())
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    out << v;                 // Writes a type tag and a QString to out
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    ...
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    QDataStream in(...);      // (opening the previously written stream)
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    in >> v;                  // Reads an Int variant
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    int z = v.toInt();        // z = 123
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    qDebug("Type is %s",      // prints "Type is int"
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      v.typeName());
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    v.asInt() += 100;         // The variant now hold the value 223.
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    v = QVariant( QStringList() );
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    v.asStringList().append( "Hallo" );
.fi
.PP
You can even have a QValueList<QVariant> stored in the variant - giving arbitrarily complex data values with lists of variants, some of which are strings while others are integers and other still are lists of lists of lists of variants. This is very powerful, and you can easily shoot yourself in the foot with all this power. Caveat programmor.
.SS "Member Type Documentation"
.SH "QVariant::Type"
This enum type defines the types of variable that a QVariant can contain. The supported enum values and the associated types are: 
.TP
\fCInvalid\fR - no type
.TP
\fCList\fR - a QValueList<QVariant>
.TP
\fCMap\fR - a QMap<QString,QVariant>
.TP
\fCString\fR - a QString
.TP
\fCStringList\fR - a QStringList
.TP
\fCFont\fR - a QFont
.TP
\fCPixmap\fR - a QPixmap
.TP
\fCBrush\fR - a QBrush
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\fCRect\fR - a QRect
.TP
\fCSize\fR - a QSize
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\fCColor\fR - a QColor
.TP
\fCPalette\fR - a QPalette