Qvariant equivalent to a consortium containing most QT data types (source interpretation)

Store the data as a member variable d of a private struct type:

<qvariant.cpp>

1 qvariant::qvariant (Type type) 2 {Create (type, 0);}

1 void qvariant::create (int type, const void *copy) 2 {3     d.type = type;4     handler->construct (&d, copy); 5}

static void Construct (qvariant::P rivate *x, const void *copy) {    x->is_shared = false;    Switch (x->type) {case    qvariant::string:        v_construct<qstring> (x, copy);        break;    ......    Default:        void *ptr = Qmetatype::construct (x->type, copy);        if (!ptr) {            x->type = qvariant::invalid;        } else {            x->is_shared = true;            x->data.shared = new qvariant::P rivateshared (PTR);        }        break;    }    X->is_null =!copy;}

1 qvariant::qvariant (int val) 2 {d.is_null = false; d.type = int; d.data.i = val;}

<qvariant.h>

Class Q_core_export qvariant{...   struct private    {        inline private (): Type (Invalid), is_shared (false), Is_null (true) {data.ptr = 0;}        Inline private (const private &other)            : Data (Other.data), type (other.type),              is_shared (other.is_shared), Is_null (Other.is_null)        {}        Union Data        {            char C;            int i;            UINT U;            BOOL B;            Double D;            float F;            Qreal Real;            Qlonglong ll;            Qulonglong ull;            Qobject *o;            void *ptr;            Privateshared *shared;        } data;        UINT Type:30;        UINT Is_shared:1;        UINT is_null:1;    };     ......    Private D;    ......}

Data types supported by Qvariant:

 1 enum Type {2 Invalid = 0, 3 4 Bool = 1, 5 Int = 2, 6 UInt = 3, 7 Longlong = 4 , 8 Ulonglong = 5, 9 Double = 6,10 Char = 7,11 Map = 8,12 List = 9,13 stri  ng = 10,14 Stringlist = 11,15 ByteArray = 12,16 BitArray = 13,17 Date = 14,18 time         = 15,19 DateTime = 16,20 Url = 17,21 Locale = 18,22 Rect = 19,23 RECTF = 20,24  Size = 21,25 SizeF = 22,26 line = 23,27 Linef = 24,28 point = 25,29 PointF =         26,30 REGEXP = 27,31 Hash = 28,32 Easingcurve = 29,33 Lastcoretype = easingcurve,34 35         Value internally reserved36 #ifdef qt3_support37 colorgroup = 63,38 #endif39 Font = 64,40 Pixmap = 65,41 Brush = 66,42 Color = 67,43 Palette = 68,44 Icon = 69,45 Ima GE = 70,46 PolygOn = 71,47 Region = 72,48 Bitmap = 73,49 Cursor = 74,50 Sizepolicy = 75,51 keysequ ence = 76,52 Pen = 77,53 TextLength = 78,54 TextFormat = 79,55 Matrix = 80,56 Tran         Sform = 81,57 matrix4x4 = 82,58 vector2d = 83,59 Vector3D = 84,60 vector4d = 85,61 quaternion = 86,62 Lastguitype = quaternion,63 usertype = 127,65 #ifdef qt3_support66 IconSet = icon,67 CString = bytearray,68 Pointarray = polygon,69 #endif70 Lasttype = 0xffffffff//need th is, so, GCC >= 3.4 allocates, bits for Type71};

Data type conversions:

The following data types can be automatically converted

The conversion of the specified data type can be determined by the member function bool Qvariant::canconvert (Type t) const

Custom Qvariant data types that can be stored:

Class Q_core_export qvariant{...   Template<typename t>    BOOL Canconvert () const    {return Canconvert (Type (qmetatypeid<t> ()));}    ......}

1 static inline Qvariant fromvalue (const T &value) 2     {return qvariantfromvalue (value);}

Template <typename t>inline qvariant qvariantfromvalue (const T &t) {    return qvariant (qmetatypeid<t > (reinterpret_cast<t *> (0)), &t, qtypeinfo<t>::ispointer);}

As you can see from the declaration of a class, to be a data type that qvariant can store, you must register the custom data type with a macro q_declare_metatype (type) into the Metatype system

<qmetatype.h>

 1 #define Q_DECLARE_METATYPE (TYPE) 2 qt_begin_namespace  3 Template <> 4 struct                                                                    qmetatypeid< TYPE > 5 {                                            6 enum {Defined = 1};                                                            7 static int qt_metatype_id () 8 { 9 static Qbasicatomicint metatype_id = Q_basic_atomic_initializer (0); if (!metatype_id) metatype_id = Qregisterm etatype< type > (#TYPE, reinterpret_cast< type *> (Quintptr (-1)));                         return metatype_id;            14} 15}; Qt_end_namespace

Example:

namespace mynamespace{    struct mystruct     {         int i;         ...     };} Q_declare_metatype (mynamespace::mystruct)

1 mystruct S; 2 qvariant var; 3 Var.setvalue (s); 4  5 ... 6  7 Qvariant var2 = Qvariant::fromvalue (s); 8 if (var2.canconvert<mystruct> ())  9 {ten     mystruct s2 = V Ar2.value<mystruct> (); 11}

Http://www.cnblogs.com/paullam/p/3706371.html

Qvariant equivalent to a consortium containing most QT data types (source interpretation)