QQuickTableView: add isColumnLoaded() and isRowLoaded()

TableView needs an API that lets you check if the
delegate items inside a row or column is available
for iteration from within the columnWidth/rowHeightProvider.

This is especially needed since we call the providers
several times when loading a new row or column - once
to figure out if it's visible, and another time later,
to get the width to use for layout when the items
are loaded.

[ChangeLog][QtQuick][TableView] Added API to query if a
row or column is loaded and available for iteration:
isRowLoaded(row) and isColumnLoaded(column).

Fixes: QTBUG-92151
Change-Id: Iad0c9953a794bb6464b973f79e18826b4727fb47
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

2 files changed, 124 insertions, 0 deletions

diff --git a/tests/auto/quick/qquicktableview/data/iscolumnloaded.qml b/tests/auto/quick/qquicktableview/data/iscolumnloaded.qml
new file mode 100644
index 0000000000..1cae7aad75
--- /dev/null
+++ b/tests/auto/quick/qquicktableview/data/iscolumnloaded.qml
@@ -0,0 +1,103 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtQuick module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick
+import QtQuick.Window
+
+Item {
+    width: 640
+    height: 450
+
+    property alias tableView: tableView
+    property int itemsInColumnAfterLoaded: 0
+    property int itemsInRowAfterLoaded: 0
+
+    TableView {
+        id: tableView
+        width: 600
+        height: 400
+        anchors.margins: 1
+        clip: true
+        delegate: tableViewDelegate
+        columnSpacing: 1
+        rowSpacing: 1
+        columnWidthProvider: function(column) {
+            if (isColumnLoaded(column)) {
+                var count = 0;
+                for (var row = topRow; row <= bottomRow; ++row) {
+                    var item = itemAtCell(Qt.point(column, row))
+                    if (item)
+                        count++;
+                }
+                itemsInColumnAfterLoaded = count;
+            }
+
+            return -1
+        }
+        rowHeightProvider: function(row) {
+            if (isRowLoaded(row)) {
+                var count = 0;
+                for (var column = leftColumn; column <= rightColumn; ++column) {
+                    var item = itemAtCell(Qt.point(column, row))
+                    if (item)
+                        count++;
+                }
+                itemsInRowAfterLoaded = count;
+            }
+
+            return -1
+        }
+    }
+
+    Component {
+        id: tableViewDelegate
+        Rectangle {
+            objectName: "tableViewDelegate"
+            implicitWidth: 20
+            implicitHeight: 20
+            color: "lightgray"
+            border.width: 1
+            Text {
+                anchors.centerIn: parent
+                text: modelData
+            }
+        }
+    }
+
+}
diff --git a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
index 005aae0639..069e424d44 100644
--- a/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
+++ b/tests/auto/quick/qquicktableview/tst_qquicktableview.cpp
@@ -118,6 +118,7 @@ private slots:
     void checkRowHeightProviderInvalidReturnValues();
     void checkRowHeightProviderNegativeReturnValue();
     void checkRowHeightProviderNotCallable();
+    void isColumnLoadedAndIsRowLoaded();
     void checkForceLayoutFunction();
     void checkForceLayoutEndUpDoingALayout();
     void checkForceLayoutDuringModelChange();
@@ -553,6 +554,26 @@ void tst_QQuickTableView::checkRowHeightProviderNotCallable()
         QCOMPARE(fxItem->item->height(), kDefaultRowHeight);
 }
 
+void tst_QQuickTableView::isColumnLoadedAndIsRowLoaded()
+{
+    // Check that all the delegate items are loaded and available from
+    // the columnWidthProvider/rowHeightProvider when 'isColumnLoaded()'
+    // and 'isRowLoaded()' returns true.
+    LOAD_TABLEVIEW("iscolumnloaded.qml");
+
+    auto model = TestModelAsVariant(4, 5);
+
+    tableView->setModel(model);
+
+    WAIT_UNTIL_POLISHED;
+
+    const int itemsInColumnAfterLoaded = view->rootObject()->property("itemsInColumnAfterLoaded").toInt();
+    const int itemsInRowAfterLoaded = view->rootObject()->property("itemsInRowAfterLoaded").toInt();
+
+    QCOMPARE(itemsInColumnAfterLoaded, tableView->rows());
+    QCOMPARE(itemsInRowAfterLoaded, tableView->columns());
+}
+
 void tst_QQuickTableView::checkForceLayoutFunction()
 {
     // When we set the 'columnWidths' property in the test file, the