I'm trying to use a delegate to customize the way data from a model is displayed when using a QDataWidgetMapper.
I have two different versions of a widget, one is view-only (the data is displayed in QLabels) and the other is used to edit the data (the data is displayed in appropriate editors).
The latter one works perfectly with the delegate, everything is fine.
As you may have guessed the problem arises with the first one... When mapping the sections of my model to QLabels using the QDataWidgetMapper, the delegate is never called and the data is displayed correctly for the sections with regular data (strings, ints,...) but no data is displayed for the sections of my model with a custom data type (a kind of list) which I would like to format as a string using the delegate.
I've already performed this operation successfully when the same data is displayed in a QTableView (the method paint() of the delegate is called when the data is displayed).
After having looked at it a little bit closer, I've been able to see that, when using QLabels to display the data, the delegate is never called though I've explicitly associated a delegate to the QDataWidgetMapper using its method setItemDelegate().
So in synthesis, assume a class CustomItemDelegate which inherits QStyledItemDelegate with virtual methods:
void CustomItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const {
qDebug() << "DELEGATE: PAINT" << index.column();
QStyledItemDelegate::paint(painter, option, index);
}
void CustomItemDelegate::setEditorData(QWidget *editor, const QModelIndex &index) const {
qDebug() << "DELEGATE: SET EDITOR DATA" << index.column();
QStyledItemDelegate::setEditorData(editor, index);
}
and a widget with following in it:
QDataWidgetMapper* mapper = new QDataWidgetMapper();
CustomItemDelegate* delegate = new CustomItemDelegate();
mapper->setModel(model);
mapper->setItemDelegate(delegate);
mapper->addMapping(editorWidget, 1);
mapper->addMapping(label, 2, "text");
mapper->toFirst();
QTableView* view = new QTableView();
CustomItemDelegate* delegate2 = new CustomItemDelegate();
view->setModel(model);
view->setItemDelegate(delegate2);
the code outputs:
DELEGATE: SET EDITOR DATA 1
// NOTHING ?!
DELEGATE: PAINT 1
DELEGATE: PAINT 2
and as a result I got
my editorWidget with the correct data in it (whatever data type the section contains: regular or custom, as long as the editor handles the type of course),
my label only displays the data if the section contains a regular type of the data as the delegate is not called
my view would display everything fine as the delegate is called for each section
So my questions are:
why isn't the delegate called when the mapped widget is a QLabel?
in this case, how come the data is even displayed when the data type is regular? Magic?
Thanks very much and I apologize in advance if the answer is obvious (but even then, thank you for pointing it out :P),
ixM
This is the code from QT that populates widgets
void QDataWidgetMapperPrivate::populate(WidgetMapper &m)
{
if (m.widget.isNull())
return;
m.currentIndex = indexAt(m.section);
if (m.property.isEmpty())
delegate->setEditorData(m.widget, m.currentIndex);
else
m.widget->setProperty(m.property, m.currentIndex.data(Qt::EditRole));
}
In the first case when you do not specify a property delegate is used whereas in the second case the data is set to widget directly by passing your delegate.
I don't know why it was designed this way but this is how it works currently !
Related
I'm new with Qt , so please bear with me .
I've successfully managed to populate a ListView from a StringList and a QList of Object*
What I'm struggling now with is to populate a ListView in QML using a class defined in C++ that derives QAbstractListModel.
Here's the prototype of my CPP class :
class MessageListEntryModel : public QAbstractListModel
{
Q_OBJECT
public:
enum eMLERoleTypes
{
MLERT_MSG = Qt::UserRole+1,
MLERT_COLOR
};
MessageListEntryModel(QObject* parent=0);
virtual ~MessageListEntryModel();
void AddEntry(QString aMessage, QColor aColor);
// pure virtuals implementations
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
int rowCount(const QModelIndex &parent = QModelIndex()) const ;
int columnCount(const QModelIndex &parent = QModelIndex()) const ;
QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const;
QModelIndex parent(const QModelIndex &child) const ;
QHash<int,QByteArray> roleNames();
private:
QList<MessageEntry*> m_vpMessages;
MessageEntry is a simple class that contains 2 memebers , a QColor and a QString (the class doesn't extend QObject).
I had to implement all the above functions since they're pure virtual in an underlying class (is this normal? so far in tutorials/samples people mentioned only about roleNames and data).
The implementation of roleNames and data are as following :
QHash<int,QByteArray> MessageListEntryModel::roleNames()
{
QHash<int,QByteArray> rez;
rez[MLERT_MSG]="message";
rez[MLERT_COLOR]="messagecolor";
return rez;
}
QVariant MessageListEntryModel::data(const QModelIndex &index, int role) const
{
qDebug()<<" Data asked for "<<index.row()<<" and role "<<role;
if (index.row()<0 || index.row()>=m_vpMessages.size())
{
return QVariant();
}
MessageEntry* entry = m_vpMessages[index.row()];
if (role == MLERT_MSG)
{
return QVariant::fromValue(entry->message);
} else if (role == MLERT_COLOR)
{
return QVariant::fromValue(entry->messageColor);
}
// should be unreachable code
return QVariant();
}
The QML portion of the List View is something like this :
ListView {
id: quickMessageListdata
model: quickListModel
delegate: Rectangle {
width: 400
height: 25
color:"#000000"
Text{
text: model.message
color: model.messagecolor
}
}
So far this is my understanding on how to implement things in CPP and QML.
For linking these two, I use the following code :
MessageListEntryModel* model =new MessageListEntryModel();
// Add various entries
...
// assign model in QML
m_pViewRef->rootContext()->setContextProperty("quickListModel",model);
With the code above, when running nothing is displayed in the ListView and I'm getting the following errors :
Unable to assign [undefined] to QString
Unable to assign [undefined] to QColor
I'm also registering the model class to be exported to QML (don't know if this is necessary) :
qmlRegisterType<MessageListEntryModel> ("dlti.exported",1,0,"MessageListEntryModel");
So it's quite obvious that either I missuderstood the proper use of a QAbstractListItem derived class OR I miss a simple vital key information.
I would appreciate some pointers to some relevant samples / tutorials (one that also shows you how to properly access data from the model in QML, since I've noticed that in CPP it never passes through the data function).
Also please notice that I'm using qt5 , so qt4.8 samples won't do the trick.
EDIT
After long hours of frustrations, I finally managed what was wrong with the damn thing :
My roleNames function signature was wrong !
The correct signature for overload is :
protected :
QHash<int,QByteArray> roleNames() const;
Please notice the protected and the const modifiers.
After declaring the function the correct way , it all worked fine.
For further notice, implementing data and rowCount was sufficient :).
Thanks for the help.
I will accept BaCaRoZzo's answer since I only manged to figure this out after looking over the code from the example.
As a side note, it works well with both message and model.message.
How do you implement the addition method? You should use a method like in the example provided in my comment.
From the docs:
An insertRows() implementation must call beginInsertRows() before
inserting new rows into the data structure, and it must call
endInsertRows() immediately afterwards.
You should have something like:
void MessageListEntryModel::add(params...)
{
beginInsertRows(QModelIndex(), rowCount(), rowCount()); // kindly provided by superclass
// object creation based on params...
m_vpMessages << objectCreated;
endInsertRows(); // kindly provided by superclass
}
with
int MessageListEntryModel::rowCount(const QModelIndex & parent) const {
Q_UNUSED(parent);
return m_vpMessages.count();
}
Also, #Jonathan Mee comment is correct: use just the role names inside the delegate as you defined them in the model. If everything else is correct that is the way to access data.
One of the best documentation piece to understand C++ models implementation and usage is the Model subclassing reference. In this document is clearly depicted which are the most important methods to subclass and for what purposes.
As for the methods to implement, it really depends on the needs. Depending on the possible actions on the model, different methods should be implemented (refer to the above link for full details). A model for a ListView in which items can be added/removed can inherit from QAbstractListModel and just rely on the default implementations for most of the functions. You just need data(), roleNames() and rowCount(), as you already saw in most examples.
If instead you also need to edit data not just adding/removing it, then you also need other functions, particularly setData(). It is also your duty to notify the attached view(s) with any modification of the model occurred in setData(), via the signal dataChanged(). Refer again to the above provide subclassing reference.
Note also that, if the add method is modified with the Q_INVOKABLE modifier, i.e. it is declared as
Q_INVOKABLE void add(params...);
in the model header, you can also call it from QML (since the model is set as a context property) and you can write, for instance:
ListView {
id: quickMessageListdata
model: quickListModel
delegate: Rectangle {
width: 400
height: 25
color:"#000000"
Text{
text: model.message
color: model.messagecolor
}
}
Component.onCompleted: {
quickListModel.add(params)
quickListModel.add(params)
}
}
to insert items in the view as soon as the view is created. Clearly the same approach can be applied to other QML signals so that you can react to QML events and trigger addition/removal behaviours.
Finally, you don't need to register the model with qmlRegisterType. For your current requirement it is superfluous.
Hmmm... I'm not super familiar with QML but I believe that this is your problem: http://qt-project.org/doc/qt-5/qtquick-modelviewsdata-cppmodels.html#qabstractitemmodel
According to the link it looks like you need to change your Text block to:
Text{
text: message
color: messagecolor
}
Further reading: http://qt-project.org/forums/viewthread/5491
I've also experienced hard times before when creating own list models with Qt C++. To avoid the development overhead for a C++ model, I started to use QSyncable (a existing QAbstractListModel implementation by Ben Lau). You can find it on GitHub here.
The best part of the project is the JsonListModel QML type. It can transform any variant JSON list that you create or fetch in QML to a full-featured QML ListModel. This saves a lot of time and effort for applications that e.g. work with JSON or REST services. You can find a detailed guide how it works here.
My QTableView doesn't show strings from a QStringList.
In QTableWidget I have QTableWidgetItems. Must I set the strings manually or will the view show them automatically? In all the tutorials I don't see a "->setItem", they appear automatically.
I have 2 QLineEdits that give the QStrings to my Model :
void View::pushButtonClicked() {
meinModel->setData(txtname->text(), txtvalue->text());
}
In setData I push the Strings in two QLists.
names.push_back(name);
values.push_back(value);
I emit a dataChanged signal with the index from topleft and bottomright.
QModelIndex topLeft = createIndex(names.size()+1,0);
QModelIndex bottomRights = createIndex(names.size()-1,1);
emit dataChanged(topLeft, bottomRights);
I have a QAbstractTableModel and so i override the columnCount, rowCount and data Method.
In my data() Method I return my value and name:
QString returnValue;
if(0 == index.column()) { returnValue = names.at(index.row()); }
All of this compiles without warnings, but doesn't work correctly :( Is there something I'm doing obviously wrong?
One obvious problem is that you didn't get the semantics of dataChanged correctly. dataChanged means that an existing item has changed its value. When you change the structure of the model by adding/removing rows or columns, you have to enclose the modification in beginXxx and endXxx calls - see this answer for details.
For example:
void MyModel::setData(const QString & name, const QString & value) {
beginInsertRows(QModelIndex(), names.size(), names.size());
names.push_back(name);
values.push_back(value);
endInsertRows();
}
I have a QTableView that obtains the data from a custom model and it's edited using a custom delegate.
//...
view->setModel(stockModel);
view->setItemDelegateForColumn(0, nameDelegate);
When the user edits a specific cell it types some text (name for an object) and this text could be accepted by the program or not (the program doesn't want to have repeated names).
My solution for this was to the custom delegate to have a signal: notValidText(QModelIndex) and use the signal/slot mechanism to connect the signal to the tableview edit(QModelIndex) slot. This, from what i know, should reedit the cell in question:
//implementation of the delegate
void NameDelegate::setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index)
{
QLineEdit *line = static_cast<QLineEdit*>(editor);
if(!model->setData(index, line->text(), Qt::EditRole))
{
emit notValidData(index);
}
}
//connection of the view with the delegate
connect(nameDelegate, SIGNAL(notValidData(QModelIndex)), view, SLOT(edit(QModelIndex)));
Unfortunately this is not what happens, so i'm doing something wrong. If someone could give me a tip i would really appreciate.
I just put here some code to show what i did, ask if you need me to post anymore.
Thanks in advance
I'm developing an application using QT5.0 and new to QT. Badly, i have not too much time for a long learning curve.
I have derived my own TableModel and set it to a editable TableView. TableView shows model's data, it works. But when i activate a cell on the tableview, the data disappears. I looked at the documentation and saw that QTableView is derived from QAbstractItemView class which have a signal called 'activated' and a slot called 'edit'. So, i think 'activated' signal is connected to 'edit' slot. But 'edit' is not virtual, so i can not override it. I may connect my child class to parents 'activated' signal but actually i do not know how to handle this signal in order to save the current data of the TableView object.
There is no problem if the code uses SqlTableModel. I think it handles the 'activated' signal but I'm not sure about these, just speculating..
What is the right way to do this?
Check your the data function:
QVariant TableModel::data(const QModelIndex &index, int role) const
if( !index.isValid() )
return QVariant();
if( role == Qt::DisplayRole || role == Qt::EditRole) {
return <your data>
}
return QVariant();
}
Ensure that you process the EditRole role.
Good luck!
I am undertaking a game using a combination of c++ in visual studios 2010 and Qt 4.7 (both windows). The game is a clone of battleship and is console input based. I have created my gui how I want it to look, and on the Qt side in Qt designer, my gui consists of a grid layout 10x10, using labels to hold pixmaps of game cells:
I have painstakingly named each label to represent its position in the 2d array (ie. fleet map => F_00 => F[0,0] => F[i],[j]). I can manually choose what pixmap I would like to display using the properties editor, but I would like something dynamic.
I use an update mapboard class to redraw the game board after a player fires, which keeps storing over a char array. I would like to update my pixmaps for each, using a generic getupdatearray type function. As we traverse the array it will update the pixmap currently associated with individual labels to match their cousins from the array. (say F[5][6] = 'X' for hit, then when the loops got to that position in the array it would update the grid of pixmaps at F_56 to equal hit.png, replacing the empty.png.
I have an idea how to make the loop that would accomplish this, but unsure how i would go about getting the pixmap for each label to be more along the lines of a runtime feature versus the now compile time (static) feature. I have read about QPainter and another Qt class that deals with images, but still having a hard go at it.
Question to any of you, how do I update these pixmaps based on a 2d array?
loop structure - i can figure out
condition statements - i can figure out
qt specific syntax dealing with labels- newbie so no idea atm.
Here's some pseudocode of the kind of thing I am trying to do with map.h:
#include <QtCore>
#include <QtGui>
// WARNING: PSEUDOCODE, DOES NOT COMPILE
// AT A LOSS ON HOW TO SELECT THE CORRECT LABEL
// MAYBE A CHILD CLASS FOR THAT?
class map {
public:
char updateboard(char mapname, char b[][10]){
for(int i=0;i<10;i++){
for(int j=0;j<10;j++){
char C = b[i][j];
if (C == 'M'){//miss
Qlabel mapname_[i][j](<img src='images/missspace.png'/>);
mapname_[i][j].show();
}
else if(C == 'X'){//hit
Qlabel mapname_[i][j](<img src='images/hitspace.png'/>);
mapname_[i][j].show();
}
else if(C == ' '){//undiscovered space
Qlabel mapname_[i][j](<img src='image/emptyspace.png'/>);
mapname_[i][j].show();
}
}
}
}
};
Then in my mainwindow.cpp, I include map.h and say:
// calls class function update board
// takes updated array values and replaces old pixmap with new
map.updateboard(T,b[][10]); // target map update
map.updateboard(F,v[][10]); // fleet map update
Thanks in Advance
UPDATE:
I've gotten to the point where I can swap pixmaps with buttons presses, but I would like to create something more dynamic. I wanted to use a Qstring in which I place the name of the label I want to change using by appending x y values using:
TR_position.append(QString::number(xvalue));
When I try to call it using:
ui->TR_position->setPixmap(QPixmap(":/images/missspace.png"));
...it obviously doesnt work. Is there a way to type case it, or use the contents of the string as the Qlabel name?
You manually entered and named 200 label widgets? Let no one call you lazy. :)
Per your update, you now know how to use QLabel::setPixmap(). What you think you need is getting a QLabel pointer from a name, which would be a combination of two things:
QWidget::findChild to get a QWidget* from a QString
qobject_cast to get a QLabel* from a QWidget
If you go down this path, what you'd wind up with is something like:
QWidget* cellWidget = ui->findChild(TR_position);
QLabel* cellLabel = qobject_cast<QLabel*>(cellWidget);
cellLabel->setPixmap(QPixmap(":/images/missspace.png"));
But BEWARE! There are many things wrong with this approach.
It's brittle: What if there doesn't happen to be any widget with that name (mysterious crash)? Or even worse, what if there are multiple widgets with that name and this code marches along blissfully ignorant of that odd condition that is likely a bug?
It's poor OOP: While there are some decent cases to use dynamic casting (or "downcasting"), it usually indicates a flaw in a design. You know that all QLabels are QWidgets, but not all QWidgets are QLabels...so that qobject_cast call might return NULL. It's just one more point of failure. Sometimes you can't avoid this, but really there is no reason your program needs to be structured in such a way.
It's terribly slow: Searching for a widget by its name is essentially a naive recursive search. If you've set aside a separate widget frame for each grid and only search that, Qt will have to do 100 string compares to find the last element (so 50 in the average case). Imagine clearing the grid with a loop...now you're talking about 100*50 string compares!
All these things are avoidable. Just as it's possible to use loops to set the images on the controls by name, it's possible to use loops to create the widgets in the first place. You basically would leave the area for the game board blank in the design tool, and then dynamically create the controls with code...attach them to the layout with code...and save pointers to them in 2D array. (You wouldn't access them by label name at that point, you'd index them just as you are indexing your board.)
You could create your own class derived from QLabel (such as a GameCell class) which contained the information for your board cell and methods related to it. Then you wouldn't need an array of label widgets in parallel to an array representing your board. You'd simply have one array of objects that took care of both aspects of the implementation.
UPDATE: Since you asked in the comments for specifics, here's a GameCell class:
class GameCell : public QLabel
{
Q_OBJECT
public:
enum State { Undiscovered, Hit, Miss };
GameCell (QWidget *parent = 0) : QLabel (parent),
currentState (Undiscovered)
{
syncBitmap();
}
State getState() const { return currentState; }
void setState(State newState) {
if (currentState != newState) {
currentState = newState;
syncBitmap();
}
}
private:
void syncBitmap() { // you'd use setPixmap instead of setText
switch (currentState) {
case Undiscovered: setText("U"); break;
case Hit: setText("H"); break;
case Miss: setText("M"); break;
}
}
State currentState;
};
This does double duty by behaving like a QWidget as well as maintaining a piece of internal state. Then a GameMap widget can use a QGridLayout of these GameCells:
class GameMap : public QWidget {
Q_OBJECT
public:
static const int Rows = 10;
static const int Columns = 10;
GameMap (QWidget* parent = 0) :
QWidget (parent)
{
layout = new QGridLayout (this);
for (int column = 0; column < Columns; column++) {
for (int row = 0; row < Rows; row++) {
GameCell* cell = new GameCell (this);
cells[column][row] = cell;
layout->addWidget(cell, row, column);
}
}
}
private:
GameCell* cells[Columns][Rows];
QGridLayout* layout;
};
If you wanted to, you could just leave spaces in your layout in the designer you wanted to fill in with the GameMap widget. Or you can push on and do the whole thing programmatically. For the sake of simplicity I'll just put two boards next to each other with a vertical separator on the surface of a dialog:
class Game : public QDialog
{
Q_OBJECT
public:
Game (QWidget *parent = 0)
: QDialog(parent)
{
targetMap = new GameMap (this);
fleetMap = new GameMap (this);
verticalSeparator = new QFrame (this);
verticalSeparator->setFrameShape(QFrame::VLine);
verticalSeparator->setFrameShadow(QFrame::Sunken);
layout = new QHBoxLayout (this);
layout->addWidget(targetMap);
layout->addWidget(verticalSeparator);
layout->addWidget(fleetMap);
setLayout(layout);
setWindowTitle(tr("Battleship"));
}
private:
GameMap* targetMap;
QFrame* verticalSeparator;
GameMap* fleetMap;
QHBoxLayout* layout;
};
I'm not going to write a whole game here or make it look fancy. That's just the gist, showing how to get 200 labels up in a programmatic fashion:
With my code, getting a GameCell from an (x,y) coordinate doesn't require an average of 50 string compares. Due to the formalized and predictable nature of 2D arrays, indexing into cells[x][y] only requires a single multiply operation and a single addition operation. There's no downcasting, and you can simply write:
cells[x][y].setState(GameCell::Miss);
ADDENDUM: Creating a QWidget for each grid cell isn't necessarily the way to go in the first place. Some might consider that "heavyweight". If your game were being played out on a large virtual space of tiles then it could be much too slow. You might find it useful to look into QGraphicsGridLayout, which could be a more appropriate approach in the long run:
http://doc.qt.io/qt-5/qtwidgets-graphicsview-basicgraphicslayouts-example.html
Using QWidgets won't be much of an issue with a 10x10 grid, however, so if you want to just stick with that then you can. If you're going to do it that way, then at least you shouldn't be placing them all by hand!