QMLエンジンの内部。 パート2：バインディング

import QtQuick 2.0 Rectangle { width: 300 height: 300 color: "lightsteelblue" Text { anchors.centerIn: parent text: "Window Area: " + (parent.width * parent.height) } } 

1. C ++クラスQQuickRectangleのRectangle要素のwidthプロパティに値300を割り当てるなどの単純なプロパティ割り当てこの場合、VMEはこのコンポーネントを作成するときにSTORE_DOUBLEバイトコード命令を実行するだけです。 VMEは関数QMetaObject :: metacall（QMetaObject :: WriteProperty、...）を呼び出すだけで、最終的にはQQuickRectangle :: SetWidth（）の呼び出しで終了します。 この割り当ての後。 QMLエンジンはこの割り当てを忘れています。
2. 上記の例のように、 テキストプロパティへの「ウィンドウ領域：」+（parent.width * parent.height）またはcenterInプロパティへの親のバインディング割り当て。 バインディングの魔法のおかげで、Rectangle要素の高さまたは幅が変更されるたびに、 テキストプロパティが自動的に更新されます。 どのように機能しますか？ 魔法はまったくありません。答えを見つけるために読み進めてください。

バインディングを作成

 ... 9 STORE_COMPILED_BINDING 43 1 0 10 FETCH 19 11 STORE_COMPILED_BINDING 17 0 1 ... 

 function $text() { return “Window Area: ” + (parent.width * parent.height) } 

バインド

 #0 QQuickItem::width (this=0x6d8580) at items/qquickitem.cpp:4711 #1 0x00007ffff78e592d in QQuickItem::qt_metacall (this=0x6d8580, _c=QMetaObject::ReadProperty, _id=8, _a=0x7fffffffc270) at .moc/debug-shared/moc_qquickitem.cpp:675 #2 0x00007ffff7a61689 in QQuickRectangle::qt_metacall (this=0x6d8580, _c=QMetaObject::ReadProperty, _id=9, _a=0x7fffffffc270) at .moc/debug-shared/moc_qquickrectangle_p.cpp:526 #3 0x00007ffff7406dc3 in ReadAccessor::Direct (object=0x6d8580, property=..., output=0x7fffffffc2c8, n=0x0) at qml/v8/qv8qobjectwrapper.cpp:243 #4 0x00007ffff7406330 in GenericValueGetter (info=...) at qml/v8/qv8qobjectwrapper.cpp:296 #5 0x00007ffff49bf16a in v8::internal::JSObject::GetPropertyWithCallback (this=0x363c64f4ccb1, receiver=0x363c64f4ccb1, structure=0x1311a45651a9, name=0x3c3c6811b7f9) at ../3rdparty/v8/src/objects.cc:198 #6 0x00007ffff49c11c3 in v8::internal::Object::GetProperty (this=0x363c64f4ccb1, receiver=0x363c64f4ccb1, result=0x7fffffffc570, name=0x3c3c6811b7f9, attributes=0x7fffffffc5e8) at ../3rdparty/v8/src/objects.cc:627 #7 0x00007ffff495c0f1 in v8::internal::LoadIC::Load (this=0x7fffffffc660, state=v8::internal::UNINITIALIZED, object=..., name=...) at ../3rdparty/v8/src/ic.cc:933 #8 0x00007ffff4960ff5 in v8::internal::LoadIC_Miss (args=..., isolate=0x603070) at ../3rdparty/v8/src/ic.cc:2001 #9 0x000034b88ae0618e in ?? () ... [more ?? frames from the JIT'ed v8::Function code] ... #1 0x00007ffff481c3ef in v8::Function::Call (this=0x694fe0, recv=..., argc=0, argv=0x0) at ../3rdparty/v8/src/api.cc:3709 #2 0x00007ffff7379afd in QQmlJavaScriptExpression::evaluate (this=0x6d7430, context=0x6d8440, function=..., isUndefined=0x7fffffffcd23) at qml/qqmljavascriptexpression.cpp:171 #3 0x00007ffff72b7b85 in QQmlBinding::update (this=0x6d7410, flags=...) at qml/qqmlbinding.cpp:285 #4 0x00007ffff72b8237 in QQmlBinding::setEnabled (this=0x6d7410, e=true, flags=...) at qml/qqmlbinding.cpp:389 #5 0x00007ffff72b8173 in QQmlBinding::setEnabled (This=0x6d7448, e=true, f=...) at qml/qqmlbinding.cpp:370 #6 0x00007ffff72c15fb in QQmlAbstractBinding::setEnabled (this=0x6d7448, e=true, f=...) a /../../qtbase/include/QtQml/5.0.0/QtQml/private/../../../../../../qtdeclarative/src/qml/qml/qqmlabstractbinding_p.h:98 #7 0x00007ffff72dcb14 in QQmlVME::complete (this=0x698930, interrupt=...) at qml/qqmlvme.cpp:1292 #8 0x00007ffff72c72ae in QQmlComponentPrivate::complete (enginePriv=0x650560, state=0x698930) at qml/qqmlcomponent.cpp:919 #9 0x00007ffff72c739b in QQmlComponentPrivate::completeCreate (this=0x698890) at qml/qqmlcomponent.cpp:954 #10 0x00007ffff72c734c in QQmlComponent::completeCreate (this=0x698750) at qml/qqmlcomponent.cpp:947 #11 0x00007ffff72c6b2f in QQmlComponent::create (this=0x698750, context=0x68ea30) at qml/qqmlcomponent.cpp:781 #12 0x00007ffff79d4dce in QQuickView::continueExecute (this=0x7fffffffd2f0) at items/qquickview.cpp:445 #13 0x00007ffff79d3fca in QQuickViewPrivate::execute (this=0x64dc10) at items/qquickview.cpp:106 #14 0x00007ffff79d4400 in QQuickView::setSource (this=0x7fffffffd2f0 at items/qquickview.cpp:243 #15 0x0000000000400d70 in main () 

バインディング更新

 Q_PROPERTY(qreal width READ width WRITE setWidth NOTIFY widthChanged) 

おわりに