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Thread: QAbstractProxyModel , mapToSource() and mapFromSource()

  1. #1
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    Default QAbstractProxyModel , mapToSource() and mapFromSource()

    Hi forum,


    I would like to browse through an example where QAbstractProxyModel is sub-classed and the above mentioned functions are over-ridden.

    If any one aware of any open source examples , please refer them to me.


    I really like to have some idea of this concept.


    Regards
    Sajjad

  2. #2
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    Default Re: QAbstractProxyModel , mapToSource() and mapFromSource()

    Here is one: [wiki]Transpose proxy model[/wiki]

    There are others in Qt docs too. Some more are available on this forum in different threads.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  3. The following user says thank you to wysota for this useful post:

    d_stranz (28th March 2012)

  4. #3
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    Default Re: QAbstractProxyModel , mapToSource() and mapFromSource()

    Hi forum,

    The transpose roxy model example mantains the information hiding while the other example at Qt site didi not do that at all. They customized a tree view with proxy model and while doing that they have used many global variables as follows:

    Qt Code:
    1. #include <QtGui>
    2.  
    3. QList<QStandardItem *> list;
    4.  
    5. class SortProxy : public QAbstractProxyModel
    6. {
    7. Q_OBJECT
    8.  
    9. public:
    10. SortProxy(QObject *parent = 0) : QAbstractProxyModel(parent), hideThem(false)
    11. {
    12. fixModel();
    13. }
    14.  
    15. int rowCount(const QModelIndex &parent) const
    16. {
    17. QModelIndex sourceParent;
    18. if (parent.isValid())
    19. sourceParent = mapToSource(parent);
    20. int count = 0;
    21. QMapIterator<QPersistentModelIndex, QPersistentModelIndex> it(proxySourceParent);
    22. while (it.hasNext()) {
    23. it.next();
    24. if (it.value() == sourceParent)
    25. count++;
    26. }
    27. return count;
    28. }
    29.  
    30. int columnCount(const QModelIndex &) const
    31. {
    32. return 1;
    33. }
    34.  
    35. QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const
    36. {
    37. QModelIndex sourceParent;
    38. if (parent.isValid())
    39. sourceParent = mapToSource(parent);
    40. QMapIterator<QPersistentModelIndex, QPersistentModelIndex> it(proxySourceParent);
    41. while (it.hasNext()) {
    42. it.next();
    43. if (it.value() == sourceParent && it.key().row() == row &&
    44. it.key().column() == column)
    45. return it.key();
    46. }
    47. return QModelIndex();
    48. }
    49.  
    50. QModelIndex parent(const QModelIndex &child) const
    51. {
    52. QModelIndex mi = proxySourceParent.value(child);
    53. if (mi.isValid())
    54. return mapFromSource(mi);
    55. return QModelIndex();
    56. }
    57.  
    58. QModelIndex mapToSource(const QModelIndex &proxyIndex) const
    59. {
    60. if (!proxyIndex.isValid())
    61. return QModelIndex();
    62. return mapping.key(proxyIndex);
    63. }
    64.  
    65. QModelIndex mapFromSource(const QModelIndex &sourceIndex) const
    66. {
    67. if (!sourceIndex.isValid())
    68. return QModelIndex();
    69. return mapping.value(sourceIndex);
    70. }
    71.  
    72. public slots:
    73. void hideEverythingButA1AndChildren()
    74. {
    75. hideThem = !hideThem;
    76. // Now we set up the proxy <-> source mappings
    77. emit layoutAboutToBeChanged();
    78. fixModel();
    79. emit layoutChanged();
    80. }
    81.  
    82. private:
    83. void fixModel()
    84. {
    85. mapping.clear();
    86. proxySourceParent.clear();
    87.  
    88. //the following list is already populated
    89. //in the tree view and we shall browse and
    90. //customize it here
    91. for (int i=0;i<list.size();i++)
    92. {
    93. //pull out a standard item
    94. QStandardItem *si = list.at(i);
    95.  
    96. if (hideThem)
    97. {
    98. //if the hide item flag is true
    99.  
    100. //check if the standard item's text start with 'A'
    101. //of the item is not parent
    102. if (!si->text().startsWith("A") || !si->parent())
    103. continue;
    104.  
    105.  
    106. //means that we have encountered item that does not start with 'A'
    107. //or the item is not the parent
    108.  
    109. //we pull out the model index by creating the model index with the source items
    110. //row , column
    111. QModelIndex proxy = createIndex(si->row(), si->column(), si->index().internalPointer());
    112.  
    113. //insert the source model's index and the proxy index into the map
    114. mapping.insert(QPersistentModelIndex(si->index()), proxy);
    115. QModelIndex sourceParent;
    116.  
    117. if (si->parent()->parent())
    118. sourceParent = si->parent()->index();
    119. proxySourceParent.insert(proxy, sourceParent);
    120. }
    121. else
    122. {
    123. QModelIndex proxy = createIndex(si->row(), si->column(), si->index().internalPointer());
    124. mapping.insert(QPersistentModelIndex(si->index()), proxy);
    125. QModelIndex sourceParent;
    126. if (si->parent())
    127. sourceParent = si->parent()->index();
    128. proxySourceParent.insert(proxy, sourceParent);
    129. }
    130. }
    131. }
    132.  
    133. QMap<QPersistentModelIndex, QPersistentModelIndex> mapping;
    134. QMap<QPersistentModelIndex, QPersistentModelIndex> proxySourceParent;
    135. bool hideThem;
    136. };
    137.  
    138. SortProxy *proxyModel = 0;
    139.  
    140. class Tree : public QTreeView
    141. {
    142. Q_OBJECT
    143.  
    144. public:
    145. Tree(QWidget *parent = 0) : QTreeView(parent)
    146. {
    147. QStandardItemModel *sourceModel = new QStandardItemModel(this);
    148.  
    149. QStandardItem *parentA = sourceModel->invisibleRootItem();
    150. for (int i = 0; i < 2; ++i) {
    151. itemA = new QStandardItem(QString("A %0").arg(i));
    152. parentA->appendRow(itemA);
    153. parentA = itemA;
    154. list.append(itemA);
    155. }
    156. itemA = new QStandardItem(QString("A 2"));
    157. parentA->appendRow(itemA);
    158. list.append(itemA);
    159. itemA3 = new QStandardItem(QString("A 3"));
    160. list.append(itemA3);
    161. parentA->appendRow(itemA3);
    162. itemA4 = new QStandardItem(QString("A 4"));
    163. list.append(itemA4);
    164. parentA->appendRow(itemA4);
    165. itemNonA = new QStandardItem(QString("Non A"));
    166. list.append(itemNonA);
    167. parentA->appendRow(itemNonA);
    168.  
    169. QStandardItem *parentB = sourceModel->invisibleRootItem();
    170. for (int i = 0; i < 3; ++i) {
    171. itemB = new QStandardItem(QString("B %0").arg(i));
    172. parentB->appendRow(itemB);
    173. parentB = itemB;
    174. list.append(itemB);
    175. }
    176.  
    177. QStandardItem *parentC = sourceModel->invisibleRootItem();
    178. for (int i = 0; i < 3; ++i) {
    179. itemC = new QStandardItem(QString("C %0").arg(i));
    180. parentC->appendRow(itemC);
    181. parentC = itemC;
    182. list.append(itemC);
    183.  
    184. }
    185.  
    186. proxyModel = new SortProxy(this);
    187. proxyModel->setSourceModel(sourceModel);
    188. setModel(proxyModel);
    189. expandAll();
    190. }
    191. QStandardItem *itemA;
    192. QStandardItem *itemA3;
    193. QStandardItem *itemA4;
    194. QStandardItem *itemNonA;
    195. QStandardItem *itemB;
    196. QStandardItem *itemC;
    197. };
    198.  
    199.  
    200. #include "main.moc"
    201.  
    202. int main(int argc, char **argv)
    203. {
    204. QApplication app(argc, argv);
    205. QWidget widget;
    206. QPushButton *button = new QPushButton("Make only A1 + 'A' children visible", &widget);
    207. Tree *tree = new Tree(&widget);
    208. QVBoxLayout *lay = new QVBoxLayout(&widget);
    209. lay->addWidget(button);
    210. QObject::connect(button, SIGNAL(clicked()), proxyModel, SLOT(hideEverythingButA1AndChildren()));
    211. lay->addWidget(tree);
    212. widget.show();
    213. return app.exec();
    214. }
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    How do i access to those data if i want to remove the global variables that they have declared. In my own project i do not have any global variable that let the proxy model and main source model to interact with.


    Need your suggestion.


    Regards
    Sajjad

  5. #4
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    Default Re: QAbstractProxyModel , mapToSource() and mapFromSource()

    The proxy has access to the source model data using QAbstractProxyModel::sourceModel(). There is no need for any global variables and I can't see any relevant global variables in the code you posted.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  6. #5
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    Default Re: QAbstractProxyModel , mapToSource() and mapFromSource()

    At the beginning of the code snippet :

    Qt Code:
    1. QList<QStandardItem *> list;
    To copy to clipboard, switch view to plain text mode 

    Both the view and the model is accessing this , the source model is populating it and the proxy model is customizing it. Wouldnt you consider is global. I should be residing only inside the Source Model's scope, isnt it ?

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    Default Re: QAbstractProxyModel , mapToSource() and mapFromSource()

    Quote Originally Posted by sajis997 View Post
    At the beginning of the code snippet :

    Qt Code:
    1. QList<QStandardItem *> list;
    To copy to clipboard, switch view to plain text mode 

    Both the view and the model is accessing this ,
    Not really. The view indeed is accessing it however creating the model in the view's constructor is a silly approach by itself and besides doing that the view doesn't access the variable anymore. If you move model creation outside the view class and discard the global variable in favour of a local variable, the program will work exactly the same way. I'm not commenting bad C++ practices here

    the source model is populating it and the proxy model is customizing it.
    The proxy doesn't access the "list" variable anywhere.
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.


  8. #7
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    Default Re: QAbstractProxyModel , mapToSource() and mapFromSource()

    SortProxy does access the list variable inside the private function called fixModel()

  9. #8
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    Default Re: QAbstractProxyModel , mapToSource() and mapFromSource()

    Ahh... indeed it does. In that case don't look at this code anymore since it's inherently broken. Find a better example
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

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