Having trouble interpreting an error message. Is my C++ that bad?

[johnny_sparx]

I have a class where I defined the following:

const QModelIndex *Current_Model_Index;

The class has a slot that defines the value of Current_Model_Index (a slot):


void AcquisitionBrowserWidget::Display_File_Path(QStrin g *File_Path_Clicked, const QModelIndex *index)
{
Acquisition_Browser->MainFilePathDisplay->setText(*File_Path_Clicked);
// Update the internal target file path.
Target_File_Path = *File_Path_Clicked;
Current_Model_Index = index;
Update_All_Browser_Information();
//Acquisition_Browser->Transfer_Progress_Bar->setValue(0);
}

The following bit of code results in an error that I can't seem to interpret:

Current_Model_Index->model()->setData(*Current_Model_Index,Qt::blue,Qt::TextColo rRole);

The error:

roetgen 1121% make
g++ -c -pipe -g -Wall -W -D_REENTRANT -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/export/data/jsalik/local/Qt-4.1.1/mkspecs/linux-g++ -I. -I/export/data/jsalik/local/Qt-4.1.1/include/QtCore -I/export/data/jsalik/local/Qt-4.1.1/include/QtGui -I/export/data/jsalik/local/Qt-4.1.1/include -I. -I. -I. -o AcquisitionBrowserWidget.o AcquisitionBrowserWidget.cpp
AcquisitionBrowserWidget.cpp: In member function `void
AcquisitionBrowserWidget::DICOM_Tree_Changed(QTree WidgetItem*, int)':
AcquisitionBrowserWidget.cpp:225: error: passing `const QAbstractItemModel' as
`this' argument of `virtual bool QAbstractItemModel::setData(const
QModelIndex&, const QVariant&, int)' discards qualifiers
AcquisitionBrowserWidget.cpp:202: warning: unused parameter `int column'
AcquisitionBrowserWidget.cpp: In member function `void
AcquisitionBrowserWidget::DICOM_Tree_Item_Double_C licked(QTreeWidgetItem*,
int)':
AcquisitionBrowserWidget.cpp:708: warning: unused parameter `int column'
AcquisitionBrowserWidget.cpp: In member function `int
AcquisitionBrowserWidget::Move_Files(QString, QString)':
AcquisitionBrowserWidget.cpp:799: warning: unused variable `
QClipboard*clipboard'
make: *** [AcquisitionBrowserWidget.o] Error 1
roetgen 1122%

The function where the error occurs is:

void AcquisitionBrowserWidget::DICOM_Tree_Changed(QTree WidgetItem * item, int column )
{
if(Target_File_Path!="" || Acquisition_Browser->Read_Only_Checkbox->checkState()==Qt::Unchecked)
{
Acquisition_Browser->Update_Header_Button->setIcon(QIcon("blueball.png"));
DICOM_Tree_Data_Changed = true;
DICOM_Tree_Data_Updated = false;
}
else
{
Acquisition_Browser->Update_Header_Button->setIcon(QIcon("greenball.png"));
DICOM_Tree_Data_Changed = false;
DICOM_Tree_Data_Updated = false;
}


if(item==DICOM_Information__Patient_Information__N ame)
{
QString Patient_Name = item->text(1);
//Acquisition_Browser->Transfer_Message->setText(item->text(1));
if(Patient_Name_Valid(Patient_Name))
{
Current_Flag_Database_Update(PATIENT_NAME_FIELD_IN VALID,false);
Acquisition_Browser->Transfer_Message->setText("Patient name is \nVALID.");
Current_Model_Index->model()->setData(*Current_Model_Index,Qt::blue,Qt::TextColo rRole);
//DICOM_Information__Patient_Information__Name->setTextColor(1,Qt::black);
}
else
{
Current_Flag_Database_Update(PATIENT_NAME_FIELD_IN VALID,true);
Acquisition_Browser->Transfer_Message->setText("Patient name is \nINVALID.");
//Current_Model_Index->setData(Current_Model_Index,Qt::blue,Qt::TextColor Role);
//item->setTextColor(0,Qt::red);
}
emit Flags_Updated();
}
}

Can anyone tell me what I am doing wrong? I feel this is something simple and I am just stressed out... either that, or my brain has a C++ memory leak.

Thanks.

[jacek]

QModelIndex::model() returns a pointer to a const QAbstractItemModel, so you can't invoke QAbstractItemModel::setData() (which isn't marked as const).

http://www.parashift.com/c++-faq-lite/const-correctness.html

[johnny_sparx]

Ahh. The link you posted is very good.

Despite glancing over it, as well as playing around with my code, I do not see how to get around this programatically. Do you have any suggestions? Reading my initial post, and the modification I made below (lines 25 and 26):


void AcquisitionBrowserWidget::DICOM_Tree_Changed(QTree WidgetItem * item, int column )
{
if(Target_File_Path!="" || Acquisition_Browser->Read_Only_Checkbox->checkState()==Qt::Unchecked)
{
Acquisition_Browser->Update_Header_Button->setIcon(QIcon("blueball.png"));
DICOM_Tree_Data_Changed = true;
DICOM_Tree_Data_Updated = false;
}
else
{
Acquisition_Browser->Update_Header_Button->setIcon(QIcon("greenball.png"));
DICOM_Tree_Data_Changed = false;
DICOM_Tree_Data_Updated = false;
}


if(item==DICOM_Information__Patient_Information__N ame)
{
QString Patient_Name = item->text(1);
//Acquisition_Browser->Transfer_Message->setText(item->text(1));
if(Patient_Name_Valid(Patient_Name))
{
Current_Flag_Database_Update(PATIENT_NAME_FIELD_IN VALID,false);
Acquisition_Browser->Transfer_Message->setText("Patient name is \nVALID.");
const QAbstractItemModel *Model = Current_Model_Index->model();
Model->setData(*Current_Model_Index,Qt::blue,Qt::TextColo rRole);
//DICOM_Information__Patient_Information__Name->setTextColor(1,Qt::black);
}
else
{
Current_Flag_Database_Update(PATIENT_NAME_FIELD_IN VALID,true);
Acquisition_Browser->Transfer_Message->setText("Patient name is \nINVALID.");
//Current_Model_Index->setData(Current_Model_Index,Qt::blue,Qt::TextColor Role);
//item->setTextColor(0,Qt::red);
}
emit Flags_Updated();
}
}

I need to call setData to change the color. :confused: The error I get is the same as before.

[wysota]

You can use const_cast<>() to cast a const pointer to a non-const one.


QAbstractItemModel *Model = const_cast<QAbstractItemModel*>(Current_Model_Index->model());

Just remember you are breaking the rule of not modifying const objects. But if you know what you're doing, feel free to do it.

EDIT: maybe in your case it'll be enough to remove the "const" keyword for the index variable?

[jpn]

What's that "current model index" laying around, anyway?
Are you aware that:

Model indexes can become invalid over time so they should be used immediately and then discarded. If you need to keep a model index over time use a QPersistentModelIndex.
In my opinion, you should rather consider storing a non-const pointer to the model as a member variable or something..
One option could also be to store a a pointer to the view's selection model, which contains always an up-to-date "current index".
And why not even store a pointer to the view, from which you can access both (non-const)..

[johnny_sparx]

Good point about the model indexes, in fact that is what I did without knowing.

wysota's suggestion for removing the "const" ness of the model index not only works, but is sufficient. When I remove the "const" ness of the member Current_Model_Index. const_cast Was the not-so elegant solution I was looking for.

The elegant solution was - again as wysota suggested, to remove the const keyword from the index. I am in a rush now, but will try that later on today if I have the chance.

Thank you both.

By the way, in this forum, when I click on "thanks" does that close the thread? Does it change the rating of the person receiving the thanks?

J.

[wysota]

By the way, in this forum, when I click on "thanks" does that close the thread?
No.

Does it change the rating of the person receiving the thanks?

Currently only the amount of "Thanks" and "Thanked" increases.

[jacek]

By the way, in this forum, when I click on "thanks" does that close the thread? Does it change the rating of the person receiving the thanks?
It's just a method of saying "Thank you" without interfering with ad rem discussion.

[adrianoleal]

You can use const_cast<>() to cast a const pointer to a non-const one.


QAbstractItemModel *Model = const_cast<QAbstractItemModel*>(Current_Model_Index->model());

Just remember you are breaking the rule of not modifying const objects. But if you know what you're doing, feel free to do it.

EDIT: maybe in your case it'll be enough to remove the "const" keyword for the index variable?

I'm with a similar problem, but in my case, i want do:


Model->setData(*Current_Model_Index,"Item shows this string?",Qt::DisplayRole);

And not:


Model->setData(*Current_Model_Index,Qt::blue,Qt::TextColo rRole);

I used your suggestion to remove the "const" keyword and now i can to call setData(), but it ever return me FALSE. Someone knows why?

[moviemax]

Hi Johnny,
at the first glance I don`t like



void AcquisitionBrowserWidget::Display_File_Path(QStrin g *File_Path_Clicked, const QModelIndex *index)

why don`t you use

void AcquisitionBrowserWidget::displayFilePath(const QString &filePath , const QModelIndex &index)
??
The const Problem is your design. Why don`t you let the objects doing there own buissnes. It`s C++ not C ;)
So the const is right and leading you to the right way
myModel->setData( ... ) should called by some delegate for instance, or

void AcquisitionBrowserWidget::updateFilePath(const QString &filePath, QModelIndex &index)

regards