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| author | Tarja Sundqvist <tarja.sundqvist@qt.io> | 2025-12-15 16:14:22 +0200 |
|---|---|---|
| committer | Tarja Sundqvist <tarja.sundqvist@qt.io> | 2025-12-15 16:14:22 +0200 |
| commit | b58ec3b086518da5aa573f99426235854c23e35f (patch) | |
| tree | 861a9935d8f1cdba2fdca546836a351736dbddbf /src/quick/items/qquicklistview.cpp | |
| parent | 4826f86e274f1b29bd769e6790824f9e62a40f62 (diff) | |
| parent | 22032227d16c39211e2ebceef97d21f4d89c7c87 (diff) | |
Merge tag 'v6.5.8-lts-lgpl' into 6.56.5
Qt 6.5.8-lts-lgpl release
Diffstat (limited to 'src/quick/items/qquicklistview.cpp')
| -rw-r--r-- | src/quick/items/qquicklistview.cpp | 46 |
1 files changed, 43 insertions, 3 deletions
diff --git a/src/quick/items/qquicklistview.cpp b/src/quick/items/qquicklistview.cpp index 92b66ca5ed..063c48260a 100644 --- a/src/quick/items/qquicklistview.cpp +++ b/src/quick/items/qquicklistview.cpp @@ -2077,7 +2077,7 @@ QQuickItemViewAttached *QQuickListViewPrivate::getAttachedObject(const QObject * The list view itself is a focus scope (see \l{Keyboard Focus in Qt Quick} for more details). Delegates are instantiated as needed and may be destroyed at any time. - As such, state should \e never be stored in a delegate. + As such, \l {Avoid Storing State in Delegates}{state should \e never be stored in a delegate}. Delegates are usually parented to ListView's \l {Flickable::contentItem}{contentItem}, but typically depending on whether it's visible in the view or not, the \e parent can change, and sometimes be \c null. Because of that, binding to @@ -2215,8 +2215,9 @@ QQuickItemViewAttached *QQuickListViewPrivate::getAttachedObject(const QObject * item is reused. This includes \c index and \c row, but also any model roles. - \note Avoid storing any state inside a delegate. If you do, reset it - manually on receiving the \l ListView::reused signal. + \note \l {Avoid Storing State in Delegates}{Avoid storing any state inside + a delegate}. If you do, reset it manually on receiving the + \l ListView::reused signal. If an item has timers or animations, consider pausing them on receiving the \l ListView::pooled signal. That way you avoid using the CPU resources @@ -2248,6 +2249,45 @@ QQuickItemViewAttached *QQuickListViewPrivate::getAttachedObject(const QObject * items, at the expense of additional memory usage. \l{ListView::section}{Sections} have the same effect because they attach and elongate the section label to the first item within the section. + + \section1 Avoid Storing State in Delegates + + ListView's delegates are instantiated as needed and may be destroyed when + out of view. For an illustration of this, run the following example: + + \snippet qml/listview/stateInDelegate.qml ListView + + When an item is clicked, \c channelActivated is set to \c true. However, + because delegates can be \l {Reusing Items}{reused} and destroyed, all + state is lost when the view is moved far enough. When the delegate becomes + visible again, it will have its default, unmodified state (or, in the case + of an item that was reused, old state from a previous item). + + To avoid this, state should be stored in the model: + + \snippet qml/listview/stateInModel.qml ListView + + \section1 Hiding Delegates + + Setting a delegate's \l {Item::}{visible} property to \c false will hide + that item, but the space it occupied in the view will remain. It is + possible to set the item's \l {Item::}{height} to \c 0 (for a \l + {ListView::orientation}{vertical} ListView): + + \snippet qml/listview/hideDelegate.qml ListView + + Note that the hidden state is stored in the model, following the advice of + the \l {Avoid Storing State in Delegates} section. + + However, if \l spacing is non-zero, there will be uneven gaps between + delegates. + + A better option is to filter your model so that items that should not be + visible are not loaded by the view at all. This can be achieved with + \l QSortFilterProxyModel. + + Another option is to \l {Item::enabled}{disable} the delegate instead of + hiding it. */ QQuickListView::QQuickListView(QQuickItem *parent) : QQuickItemView(*(new QQuickListViewPrivate), parent) |