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39 | |
40 | #include "qqmlparserstatus.h" |
41 | |
42 | QT_BEGIN_NAMESPACE |
43 | |
44 | /*! |
45 | \class QQmlParserStatus |
46 | \since 5.0 |
47 | \inmodule QtQml |
48 | \brief The QQmlParserStatus class provides updates on the QML parser state. |
49 | |
50 | QQmlParserStatus provides a mechanism for classes instantiated by |
51 | a QQmlEngine to receive notification at key points in their creation. |
52 | |
53 | This class is often used for optimization purposes, as it allows you to defer an |
54 | expensive operation until after all the properties have been set on an |
55 | object. For example, QML's \l {Text} element uses the parser status |
56 | to defer text layout until all of its properties have been set (we |
57 | don't want to layout when the \c text is assigned, and then relayout |
58 | when the \c font is assigned, and relayout again when the \c width is assigned, |
59 | and so on). |
60 | |
61 | Be aware that QQmlParserStatus methods are only called when a class is instantiated |
62 | by a QQmlEngine. If you create the same class directly from C++, these methods will |
63 | not be called automatically. To avoid this problem, it is recommended that you start |
64 | deferring operations from classBegin instead of from the initial creation of your class. |
65 | This will still prevent multiple revaluations during initial binding assignment in QML, |
66 | but will not defer operations invoked from C++. |
67 | |
68 | To use QQmlParserStatus, you must inherit both a QObject-derived class |
69 | and QQmlParserStatus, and use the Q_INTERFACES() macro. |
70 | |
71 | \code |
72 | class MyObject : public QObject, public QQmlParserStatus |
73 | { |
74 | Q_OBJECT |
75 | Q_INTERFACES(QQmlParserStatus) |
76 | |
77 | public: |
78 | MyObject(QObject *parent = 0); |
79 | ... |
80 | void classBegin(); |
81 | void componentComplete(); |
82 | } |
83 | \endcode |
84 | */ |
85 | |
86 | /*! \internal */ |
87 | QQmlParserStatus::QQmlParserStatus() |
88 | : d(nullptr) |
89 | { |
90 | } |
91 | |
92 | /*! \internal */ |
93 | QQmlParserStatus::~QQmlParserStatus() |
94 | { |
95 | if(d) |
96 | (*d) = nullptr; |
97 | } |
98 | |
99 | /*! |
100 | \fn void QQmlParserStatus::classBegin() |
101 | |
102 | Invoked after class creation, but before any properties have been set. |
103 | */ |
104 | |
105 | /*! |
106 | \fn void QQmlParserStatus::componentComplete() |
107 | |
108 | Invoked after the root component that caused this instantiation has |
109 | completed construction. At this point all static values and binding values |
110 | have been assigned to the class. |
111 | */ |
112 | |
113 | QT_END_NAMESPACE |
114 | |