TableModel: add roleDataProvider callback

As an alternative to trying to write smarter C++ in the data() accessor, we
give the user full control of data conversion by calling an external JS
function if defined, to map role to the value that data() should return.
This enables extracting arbitrary values, converting the data in arbitrary
ways, or even doing calculations in case the EditRole stores a formula and the
DisplayRole should provide the result, or something like that.

This callback is implemented somewhat like TableView.columnWidthProvider, but
the arguments are more complex: function(row, column, role, rawData)

Change-Id: Ifaf5807f4809e0b5ad1d1c403f65c0707b902f10
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

2 files changed, 46 insertions, 0 deletions

diff --git a/src/qml/types/qqmltablemodel.cpp b/src/qml/types/qqmltablemodel.cpp
index cf3fc0298a..9bf8c7f562 100644
--- a/src/qml/types/qqmltablemodel.cpp
+++ b/src/qml/types/qqmltablemodel.cpp
@@ -548,6 +548,38 @@ void QQmlTableModel::setRow(int rowIndex, const QVariant &row)
     }
 }
 
+/*!
+    \qmlproperty var TableModel::roleDataProvider
+
+    This property can hold a function that will map roles to values.
+
+    When assigned, it will be called each time data() is called, to enable
+    extracting arbitrary values, converting the data in arbitrary ways, or even
+    doing calculations. It takes 4 arguments: \c row, \c column, \c role (as a
+    string), and \c cellData, which is the complete data that is stored in the
+    given cell. (If the cell contains a JS object with multiple named values,
+    the entire object will be given in cellData.) The function that you define
+    must return the value to be used; for example a typical delegate will
+    display the value returned for the \c display role, so you can check
+    whether that is the role and return data in a form that is suitable for the
+    delegate to show:
+
+    \snippet qml/tablemodel/roleDataProvider.qml 0
+*/
+QJSValue QQmlTableModel::roleDataProvider() const
+{
+    return mRoleDataProvider;
+}
+
+void QQmlTableModel::setRoleDataProvider(QJSValue roleDataProvider)
+{
+    if (roleDataProvider.strictlyEquals(mRoleDataProvider))
+        return;
+
+    mRoleDataProvider = roleDataProvider;
+    emit roleDataProviderChanged();
+}
+
 QModelIndex QQmlTableModel::index(int row, int column, const QModelIndex &parent) const
 {
     return row >= 0 && row < rowCount() && column >= 0 && column < columnCount() && !parent.isValid()
@@ -603,6 +635,14 @@ QVariant QQmlTableModel::data(const QModelIndex &index, int role) const
         return QVariant();
 
     const QVariantList rowData = mRows.at(row).toList();
+
+    if (mRoleDataProvider.isCallable()) {
+        const auto args = QJSValueList() << row << column <<
+                                            QString::fromUtf8(mRoleNames.value(role)) <<
+                                            qmlEngine(this)->toScriptValue(rowData.at(column));
+        return const_cast<QQmlTableModel*>(this)->mRoleDataProvider.call(args).toVariant();
+    }
+
     const QVariantMap columnData = rowData.at(column).toMap();
 
     int effectiveRole = role;
diff --git a/src/qml/types/qqmltablemodel_p.h b/src/qml/types/qqmltablemodel_p.h
index 8da930872d..863c592678 100644
--- a/src/qml/types/qqmltablemodel_p.h
+++ b/src/qml/types/qqmltablemodel_p.h
@@ -65,6 +65,7 @@ class Q_QML_PRIVATE_EXPORT QQmlTableModel : public QAbstractTableModel
     Q_PROPERTY(int columnCount READ columnCount NOTIFY columnCountChanged FINAL)
     Q_PROPERTY(int rowCount READ rowCount NOTIFY rowCountChanged FINAL)
     Q_PROPERTY(QVariant rows READ rows WRITE setRows NOTIFY rowsChanged FINAL)
+    Q_PROPERTY(QJSValue roleDataProvider READ roleDataProvider WRITE setRoleDataProvider NOTIFY roleDataProviderChanged)
 
 public:
     QQmlTableModel(QObject *parent = nullptr);
@@ -81,6 +82,9 @@ public:
     Q_INVOKABLE void removeRow(int rowIndex, int rows = 1);
     Q_INVOKABLE void setRow(int rowIndex, const QVariant &row);
 
+    QJSValue roleDataProvider() const;
+    void setRoleDataProvider(QJSValue roleDataProvider);
+
     QModelIndex index(int row, int column, const QModelIndex &parent) const override;
     int rowCount(const QModelIndex &parent = QModelIndex()) const override;
     int columnCount(const QModelIndex &parent = QModelIndex()) const override;
@@ -92,6 +96,7 @@ Q_SIGNALS:
     void columnCountChanged();
     void rowCountChanged();
     void rowsChanged();
+    void roleDataProviderChanged();
 
 private:
     class ColumnPropertyInfo
@@ -136,6 +141,7 @@ private:
     // key = column index
     // value = index (key) into mRoleNames
     QHash<int, int> mDefaultDisplayRoles;
+    QJSValue mRoleDataProvider;
 };
 
 QT_END_NAMESPACE