QTableView: how to edit non-editable cells in the program? - qt

How should this be done by using the model->setData() method call?
I have derived a class called "MyStandardItemModel" from QStandardItemModel. I have made my third and fourth columns non-editable by overriding the protected virtual flags method. This is how it goes:
#define TX_PACKET_COLUMN (4u)
#define RX_PACKET_COLUMN (5u)
Qt::ItemFlags MyStandardItemModel::flags(const QModelIndex& index) const
{
if (index.column() == TX_PACKET_COLUMN || index.column() == RX_PACKET_COLUMN)
{
return (QStandardItemModel::flags(index) & ~Qt::ItemIsEditable);
}
else
{
return QStandardItemModel::flags(index);
}
}
...
//Set model
ui->testCaseTableView->setModel(model);
Having this done, I am not able to edit the cells in the third and fourth column.
Now, I want that when I double click on these cells, a pop-up dialog comes up. I will modify some data in the editable field of that dialog, and then copy it back to the non editable cells inside the code.
I tried to just write a doubleclick() handler for the QTreeView and just copy some data to the cells just to see if it is possible to copy data to the non-editable cells.
This operation is failing, and the data is not written into the non-editable cells.
Here you can find the double click handler:
void MainWindow::on_testCaseTableView_doubleClicked(const QModelIndex &index)
{
QVariant variant;
variant.toString() = "AA";
if((index.column() == TX_PACKET_COLUMN)||(index.column() == RX_PACKET_COLUMN))
{
model->setData(index, variant); // set new value
}
}
The setData(..) operation is clearing the already written data in the cells, but string "AA" is not getting written. Please suggest how to copy some data to non-editable cells inside the code.

QVariant set is empty. Nothing needs to be wrong in your model. Error is on this line:
variant.toString() = "AA";
change to:
QVariant variant("AA"); // just for testing anyway

As I indicated in my comment, you have to fix this first issue:
instead of:
QVariant variant;
variant.toString() = "AA";
you should write
QVariant variant = QLatin1String("AA");
In general, you would look into the setData(...) implementation for such cases whether you emit the data changed signal properly and so forth, but here you are entering a prior issue which can lead to problems, so let us fix that.
Note, you should use QLatin1String to avoid the unnecessary explicit conversion from raw char* to QString. This is a good practice in general, and this is available with Qt 4 as well as Qt 5.
Although, you could also use the QStringLiteral macro for creating a QString very efficiently with template magic out of your raw literal, but that requires C++11.

Related

QTextLayout / QTextLine support grouping of several-characters so it acts as one character for the cursor

Is it possible for QTextLayout to render several characters, but to process/handle it as one character. For example rendering a code point like: [U+202e], and when moving the caret/calculating positions, it is treated as one character.
Edited:
Please check this following issue, were I explain what I'm trying to do. It for the edbee Qt component. It's using QTextLayout for line rendering.
https://github.com/edbee/edbee-lib/issues/127
Possibly it isn't possible with QTextLayout, the documentation is quite limited.
According to Qt docs:
"The class has a rather low level API and unless you intend to implement your own text rendering for some specialized widget, you probably won't need to use it directly." - https://doc.qt.io/qt-5/qtextlayout.html#details
You should probably use a QLineEdit or a QTextEdit (each has a method called setReadOnly(bool)).
Before answering the question, I will point out that the CursorMode enum (https://doc.qt.io/qt-5/qtextlayout.html#CursorMode-enum) seems very promising for this problem, but to me, the documentation isn't clear on how to use it or set it.
Now to answer your question in regards to QLineEdit or QTextEdit, it's a bit complicated, but it's the same for QLineEdit and QTextEdit, so lets look at QTextEdit.
Firstly, mouse clicks: QTextEdit has a signal called cursorPositionChanged(), which will be helpful here. You'll want to connect that to a custom slot, which can make use of the function moveCursor(QTextCursor::MoveOperation operation, QTextCursor::MoveMode mode = QTextCursor::MoveAnchor) (https://doc.qt.io/qt-5/qtextedit.html#moveCursor). Notice that there are very helpful enumeration values for you here in QTextCursor::MoveOperation regarding word hopping (https://doc.qt.io/qt-5/qtextcursor.html#MoveOperation-enum). How do we put all of this together? Well, probably the right way to do it is to determine the width of the chars to the left of the cursor's position and the width of the chars to the right of the cursor's position when the cursorPositionChanged() signal is emitted and go to the side of the word that has less width. However, I'm not sure how to do that. At this point I'd settle with checking the number of chars to the left and right and going to the side with less.
Secondly, keyboard presses: This goes a bit out of my knowledge, but almost everything drawable and iteractable inherits from QWidget. Take a look at https://doc.qt.io/qt-5/qwidget.html#keyPressEvent and it's possible that overriding that in your own implementation of QTextEdit is necessary to get the left arrow and right arrow keypresses to jump words (once you get that part it's pretty easy, just use the same function as last section for moving the cursor, or in the case of QLineEdit, cursorWordForward()/cursorWordBackward()).
All this being said, I've so far been assuming that you're not deleting anything or selecting anything. Selection can be a real pain depending on if you allow multiple selections, but the functions are all there in the documentation to implement those things.
Example of mouse click impl:
myclass.hpp
#include <QTextEdit>
#include <QTextCursor>
#include <QObject>
#include <QString>
int distance_to_word_beginning_or_end(const QString &str, int index, bool beginning);
class MyClass {
MyClass();
~MyClass();
private:
QTextEdit *text_edit;
public slots:
void text_edit_changed_cursor_location();
};
myclass.cpp
#include "myclass.hpp"
int distance_to_word_beginning_or_end(const QString &str, int index, bool beginning)
{
// return the distance from the beginning or end of the word from the index given
int inc_or_dec = (beginning) ? -1 : 1;
int distance = 0;
while (index >= 0 && index < str.length())
{
if (str.at(index) == ' ' || str.at(index) == '\n' || str.at(index) == '\t')
{
return distance;
}
distance++;
index += inc_or_dec;
}
return --distance;
}
MyClass::MyClass()
{
text_edit = new QTextEdit();
QObject::connect(text_edit, &QTextEdit::cursorPositionChanged, this, &MyClass::text_edit_changed_cursor_location);
}
MyClass::~MyClass()
{
delete text_edit;
}
void MyClass::text_edit_changed_cursor_location()
{
QString text_edit_string = text_edit->text();
QTextCursor text_edit_cursor = text_edit->textCursor();
auto current_position = text_edit_cursor.position();
QTextCursor new_text_cursor;
int distance_to_beginning = distance_to_word_beginning_or_end(text_edit_string, current_position, true);
int distance_to_end = distance_to_word_beginning_or_end(text_edit_string, current_position, false);
auto movement_type;
if (distance_to_beginning > distance_to_end)
{
new_text_cursor.setPosition(current_position + distance_to_end);
} else {
new_text_cursor.setPosition(current_position - distance_to_beginning);
}
text_edit->setTextCursor(new_text_cursor);
}

Qt QMap<int, MyClass> ignores insert command

I've a question that couldn't find anywhere. I have a QMap that's ignoring the QMap.insert(Key, Value) command. Here's the code:
//gets the selected problem index on the ProblemList
int selProblem = ui->tree_projects->currentItem()->data(0, Qt::UserRole).toInt();
//creates a new problem, sets its values and then replaces the old one on the ProblemsList variable
ProblemSets nProblem;
if(!problemsList.isEmpty()) //problemsList is an attribute of MainWindow
nProblem = problemsList.value(selProblem);
// some data collection that has been omitted because isn't important
// temporary maps that will carry the modifications
QMap<int, QString> nResName, nResType;
//data insertion into the maps
//these are fine
nResName.insert(fIdx, results_model->data(results_model->index(fIdx, 0)).toString());
nResType.insert(fIdx, results_model->data(results_model->index(fIdx, 1)).toString());
//replaces the old maps with the new ones
nProblem.SetProbResultsNames(nResName);
nProblem.SetProbResultsTypes(nResType);
//replaces the old problem with the new one
problemsList.insert(selProblem, nProblem); //this is the line that's doing nothing
}
That last line appears to be doing nothing! I've even tried to use
problemsList.remove(selProblem);
problemList.insert(selProblem, nProblem);
but got a similar result: the map not being inserted at the index selProblem. It got inserted, but with an outdated value - the same one of the deleted index -. I've checked on Debug and all the indexes and variables are correct, but when the .insert hits, nothing happens.
The most awkward thing is that this code is a copy/paste that I made from another method that I'm using that does similar thing, just changing the variable names, but that one works.
EDIT 1: This is the contents of nProblem, selProb and problemsList.value(selProblem)
Just before the Line:
problemsList.insert(selProblem, nProblem);
selProb: 0
nProblem:
ProbResultsNames: "NewRow0"
ProbResultsType: "Real"
problemsList.value(selProblem):
ProbResultsNames: non-existent
ProbResultsType: non-existent
After the line
problemsList.insert(selProblem, nProblem);
selProb: 0
nProblem:
ProbResultsNames: "NewRow0"
ProbResultsType: "Real"
problemsList.value(selProblem):
ProbResultsNames: non-existent
ProbResultsType: non-existent
EDIT 2:
class ProblemSets
{
public:
ProblemSets();
virtual ~ProblemSets();
ProblemSets(const ProblemSets& other);
ProblemSets& operator=(const ProblemSets& other);
//I hid getters and setters to avoid pollution on the post
private:
int index;
bool usingBenchmark;
QString functionSelected;
QString info;
QMap<int, QString> probVars_name, probVars_type, probResultsNames, probResultsTypes;
QMap<int, float> probVars_min, probVars_max;
QMap<int, int> probVars_stpSize, probVars_stp;
int varsNumber; // holds how many vars has been created, just for display purposes
int resNumber; // holds how many results has been created, just for display purposes
};
A simple test proves that QMap works as expected:
QMap<int, QString> mm;
mm.insert(1, "Test1");
qDebug() << mm[1]; // "Test1"
mm.remove(1);
qDebug() << mm[1]; // "" (default constructed value)
mm.insert(1, "Test2");
qDebug() << mm[1]; // "Test2"
Which means that the problem lies in your code.
This statement itself is highly suspicious:
That last line appears to be doing nothing!
Because then you go on to say that the map still contains the "old value". But you removed that key, so if the insert() method didn't work, you shouldn't be getting the old value, but a default constructed value.
Which means that the problem is most likely that nProblem has the same value as the one that is previously associated to that key in the map. The map works, you values are likely wrong.
Found the issue! I didn't have both the variables declared on the copy method of the ProblemSets class.
Solved simply adding them to the copy method
MainWindow::ProblemSets::ProblemSets(const ProblemSets& other)
{
// copy
index = other.index;
usingBenchmark = other.usingBenchmark;
functionSelected = other.functionSelected;
info = other.info;
probVars_name = other.probVars_name;
probVars_type = other.probVars_type;
probVars_min = other.probVars_min;
probVars_max = other.probVars_max;
probVars_stpSize = other.probVars_stpSize;
probVars_stp = other.probVars_stp;
//here
probResultsNames = other.probResultsNames;
probResultsTypes = other.probResultsTypes;
//
varsNumber = other.varsNumber;
resNumber = other.resNumber;
}
I had this issue before with the std::vector class, and that's why I suspected that could be that. Thanks to everyone that helped!

How to update a TableView with progress data for multiple ProgressBars?

I've started to extend the qGet DownloadManager to emit the progress of a TransferItem, so that i can connect to it. I'm inserting the progress data into a cell of a TableView model for display with an Delegate, finally the delegate paints the progress bar. That works in theory, but i'm running into the following
Problem: when there are multiple downloads in parallel, then i get progress updates from both signals into both cells!
Both progress bars show progress data, but the signal is kind of mixed and not unique to the current index (QModelIndex index / index.row()).
(Please ignore the small transitioning problem between UserRoles (after clicking the download button "ActionCell" is displayed and then "Install", before the "ProgressBar" shows up.). That is not the main problem here. My question is about the index problem.) The text "112" and "113" is the int index.row.
Questions:
How to update a TableView with progress data for multiple ProgressBars?
What must i change to render a progress bar for each download?
Source
Emit progress of a download
I've added the following things to re-emit the signal through the classes, until it bubbles up to the top, where it becomes connectable from the GUI.
a connection from QNetworkReply - downloadProgress(qint64,qint64) to TransferItem - updateDownloadProgress(qint64,qint64)
void TransferItem::startRequest()
{
reply = nam.get(request);
connect(reply, SIGNAL(readyRead()), this, SLOT(readyRead()));
connect(reply, SIGNAL(downloadProgress(qint64,qint64)),
this, SLOT(updateDownloadProgress(qint64,qint64)));
connect(reply, SIGNAL(finished()), this, SLOT(finished()));
timer.start();
}
the SLOT function TransferItem - updateDownloadProgress(qint64,qint64) as receiver calculates the progress and stores it in progress (QMap<QString, QVariant>).
After the calculation the downloadProgress(this) signal is emitted.
// SLOT
void TransferItem::updateDownloadProgress(qint64 bytesReceived, qint64 bytesTotal)
{
progress["bytesReceived"] = QString::number(bytesReceived);
progress["bytesTotal"] = QString::number(bytesTotal);
progress["size"] = getSizeHumanReadable(outputFile->size());
progress["speed"] = QString::number((double)outputFile->size()/timer.elapsed(),'f',0).append(" KB/s");
progress["time"] = QString::number((double)timer.elapsed()/1000,'f',2).append("s");
progress["percentage"] = (bytesTotal > 0) ? QString::number(bytesReceived*100/bytesTotal).append("%") : "0 %";
emit downloadProgress(this);
}
QString TransferItem::getSizeHumanReadable(qint64 bytes)
{
float num = bytes; QStringList list;
list << "KB" << "MB" << "GB" << "TB";
QStringListIterator i(list); QString unit("bytes");
while(num >= 1024.0 && i.hasNext()) {
unit = i.next(); num /= 1024.0;
}
return QString::fromLatin1("%1 %2").arg(num, 3, 'f', 1).arg(unit);
}
When a new download is enqueued, i'm connecting the emitted downloadProgress(this) to the Slot DownloadManager - downloadProgress(TransferItem*). (dl is DownloadItem which extends TransferItem).
void DownloadManager::get(const QNetworkRequest &request)
{
DownloadItem *dl = new DownloadItem(request, nam);
transfers.append(dl);
FilesToDownloadCounter = transfers.count();
connect(dl, SIGNAL(downloadProgress(TransferItem*)),
SLOT(downloadProgress(TransferItem*)));
connect(dl, SIGNAL(downloadFinished(TransferItem*)),
SLOT(downloadFinished(TransferItem*)));
}
Finally, i'm re-emitting the download progress one more time:
void DownloadManager::downloadProgress(TransferItem *item)
{
emit signalProgress(item->progress);
}
Now the TableView with Delegate, doDownload(index) and ProgressBarUpdater
QTableView
with added QSortFilterProxyModel (for case-insensitivity)
with added ColumnDelegate, which renders DownloadButton and ProgressBar based on custom UserRoles. The delegate handles the button click: the SIGNAL downloadButtonClicked(index) is emited from the editorEvent(event, model, option, index) method.
actionDelegate = new Updater::ActionColumnItemDelegate;
ui->tableView->setItemDelegateForColumn(Columns::Action, actionDelegate);
connect(actionDelegate, SIGNAL(downloadButtonClicked(QModelIndex)), this, SLOT(doDownload(QModelIndex)));
The doDownload method receives the index and fetches the download URL from the model. Then the URL is added to the DownloadManager
and i'm setting up a ProgressBarUpdater object to set the progress data to the model at the given index. Finally i'm, connecting downloadManager::signalProgress to progressBar::updateProgress and invoke the downloadManager::checkForAllDone to start the download processing.
void UpdaterDialog::doDownload(const QModelIndex &index)
{
QUrl downloadURL = getDownloadUrl(index);
if (!validateURL(downloadURL)) return;
QNetworkRequest request(downloadURL);
downloadManager.get(request); // QueueMode is Parallel by default
ProgressBarUpdater *progressBar = new ProgressBarUpdater(this, index.row());
progressBar->setObjectName("ProgressBar_in_Row_" + QString::number(index.row()) );
connect(&downloadManager, SIGNAL(signalProgress(QMap<QString, QVariant>)),
progressBar, SLOT(updateProgress(QMap<QString, QVariant>)));
QMetaObject::invokeMethod(&downloadManager, "checkForAllDone", Qt::QueuedConnection);
}
The model update part: the ProgressBarUpdater takes the index and the progress and should update the model at the given index.
ProgressBarUpdater::ProgressBarUpdater(UpdaterDialog *parent, int currentIndexRow) :
QObject(parent), currentIndexRow(currentIndexRow)
{
model = parent->ui->tableView_1->model();
}
void ProgressBarUpdater::updateProgress(QMap<QString, QVariant> progress)
{
QModelIndex actionIndex = model->index(currentIndexRow, UpdaterDialog::Columns::Action);
// set progress to model
model->setData(actionIndex, progress, ActionColumnItemDelegate::DownloadProgressBarRole);
model->dataChanged(actionIndex, actionIndex);
}
The rendering part: i'm rendering the fake ProgressBar from the delegate; fetching the progress data with index.model()->data(index, DownloadProgressBarRole).
void ActionColumnItemDelegate::drawDownloadProgressBar(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
QStyleOptionProgressBarV2 opt;
opt.initFrom(bar);
opt.rect = option.rect;
opt.rect.adjust(3,3,-3,-3);
opt.textVisible = true;
opt.textAlignment = Qt::AlignCenter;
opt.state = QStyle::State_Enabled | QStyle::State_Active;
// get progress from model
QMap<QString, QVariant> progress =
index.model()->data(index, DownloadProgressBarRole).toMap();
QString text = QString::fromLatin1(" %1 %2 %3 %4 %5 ")
.arg(QString::number(index.row()))
.arg(progress["percentage"].toString())
.arg(progress["size"].toString())
.arg(progress["speed"].toString())
.arg(progress["time"].toString());
opt.minimum = 0;
opt.maximum = progress["bytesTotal"].toFloat();
opt.progress = progress["bytesReceived"].toFloat();
opt.text = text;
bar->style()->drawControl(QStyle::CE_ProgressBar,&opt,painter,bar);
}
I've added QString::number(index.row() to the progress bar text, so that each ProgressBar gets its row number rendered. In other words: the rendering is unique to the row, but the incoming progress data is somehow mixed.
I'm stuck on the index problem for a while now. Thank you in advance for your help.
Update: The issue is resolved!
Thank you very much ddriver!! I followed your suggestions and fixed it:
The DownloadManager tracks the progress for all transfers, and you keep each transfer item's data in the respective TransferItem.
The logical thing IMO would be to have a connection from each TransferItem to the corresponding ProgressBarUpdater, and emit from the transfer item.
However, in your case, you are reporting progress not from each individual transfer item, but from the download manager. So each time you are emitting a progress, you are emitting the progress for a particular transfer item to all progress bars.
connect(&downloadManager, SIGNAL(signalProgress(QMap<QString, QVariant>)),
progressBar, SLOT(updateProgress(QMap<QString, QVariant>)));
So instead of a
TransferItem --progress--> CorrespondingUI
you have a:
TransferItem --transferItem--> DownloadManager --progress--> AllUIs
This leads to having one single and varying progress for all progress bars, which corresponds to the last download that happen to report progress before the UI updated. Which is why you get no more variation after the first download is completed, as the manager only updates the progress for the second.
Finally, i'm re-emitting the download progress one more time:
void DownloadManager::downloadProgress(TransferItem *item)
{
emit signalProgress(item->progress);
}
And who exactly needs an anonymous progress, containing no information whatsoever to which transfer it applies? Aside from the bug of course.
Would you be so nice to explain, how to simplify it?
I was at the end of my mental rope yesterday when I commented, on a clear head it doesn't look all that overdone, but still I'd probably go for something more streamlined, involving 3 key components only:
DownloadsManager -> DownloadController -> UI
-> DownloadController -> UI
It just seems redundant to have a DownloadItem and then also a TransferItem, considering that a download is a transfer.
The model and view are totally unnecessary as well, as is storing the progress in the model rather than just having it as a member of the progress bar. You could go with just a regular widget for each download, and place them in a vertical layout.
Update:
The excessive, unnecessary compartmentalization has led to a level of fragmentation which makes it hard to get to the data, needed to make it work once you put everything together. The main issue is you have no way to tie a transfer item to the right progress bar updater, and since you still haven't posted all of the relevant code, the simplest possible solution I can offer involves the following minor changes:
// in DownloadManager
void signalProgress(QMap<QString, QVariant>); // this signal is unnecessary, remove
void DownloadManager::downloadProgress(TransferItem *item) // change this
{
registry[item->request.url()]->updateProgress(item->progress);
}
QMap<QUrl, ProgressBarUpdater *> registry; // add this
// in UpdaterDialog
void UpdaterDialog::doDownload(const QModelIndex &index)
{
QUrl downloadURL = getDownloadUrl(index);
if (!validateURL(downloadURL)) return;
QNetworkRequest request(downloadURL);
downloadManager.get(request); // QueueMode is Parallel by default
ProgressBarUpdater *progressBar = new ProgressBarUpdater(this, index.row());
progressBar->setObjectName("ProgressBar_in_Row_" + QString::number(index.row()) );
// remove the connection - source of the bug, instead register the updater
downloadManager.registry[downloadURL] = progressBar;
QMetaObject::invokeMethod(&downloadManager, "checkForAllDone", Qt::QueuedConnection);
}
That's pretty much it, the progress updater is associated with the URL, and in DownloadManager::downloadProgress instead of emitting the progress to all progress updaters, you simply lookup the one which actually corresponds to the particular download, and only update its progress. It is somewhat clumsy, but as I said, if your design is proper, it would not be needed and you wouldn't have the problem in the first place.
There are other solutions as well:
change the DownloadManager's signal to void signalProgress(TransferItem *), and the body of downloadProgress toemit signalProgress(item); , change to void ProgressBarUpdater::updateProgress(TransferItem *), and in the body compare the transfer item's request's url to the one in the model at the currentIndexRow, and only model-setData() if it is the same. This solution is not very efficient, since it will emit to all progress updaters just to modify one.
cut out the middleman, what I've been suggesting from the start, make DownloadManager ::get() return a pointer to the DownloadItem/TransferItem created in its body, then in UpdaterDialog::doDownload() you can connect the transfer item directly to the appropriate progress updater, so you will no longer need DownloadManager::downloadProgress() and the signalProgress signal, you only need to change the signature of the signal in TransferItem to void downloadProgress(QMap<QString, QVariant>); and emit the progress rather than the item. This is actually the most efficient solution, as it involves nothing extra, jsut the removal of unnecessary stuff.

Should QAbstractItemModel::index(row, column, parent) check for invalid inputs?

Subclassing QAbstractItemModel, I have implemented my own index() method as required. I currently check for valid inputs, but I'm wondering if that's correct. I'm wondering if it's ever valid to create an index for a non-existent piece of data? Perhaps while inserting a row or column?
Code:
QModelIndex LicenseDataModel::index(int row, int column, const QModelIndex & /*parent*/) const
{
/// TODO: Is this necessary? Should we avoid creating invalid indexes? Or could this
/// be a bug?
if (validRowColumn(row, column))
return createIndex(row, column);
return QModelIndex();
}
[ I have a better answer. :-) ]
Although I merely repeat what Giuseppe D'Angelo from KDAB has to say about this...
You must distinguish between an invalid and an ill-formed QModelIndex:
About invalid indices (from Navigation and model index creation in Qt's Model/View Programming guide):
QAbstractItemModel::parent(): Provides a model index corresponding to the parent of any given child item. If the model index specified corresponds to a top-level item in the model, or if there is no valid parent item in the model, the function must return an invalid model index, created with the empty QModelIndex() constructor.
This explains the meaning of index.isValid():
A valid index refers to an existing item, the invalid index refers to the root of all items.
Giuseppe D'Angelo first notes that an invalid index (with .isValid() returning false) is still a valid input to functions like rowCount(), hasChildren() etc.
But a QModelIndex can also be ill-formed. It can have a non-existing row or column index, and it can even be from a different model. And QModelIndex::isValid() does not check that.
Giuseppe D'Angelo says:
I personally maintain quite a strong point of view about this issue: passing such indices is a violation of the API contract. A model should never be assumed to be able to handle illegal indices. In other words, in my (not so humble) opinion, the QAbstractItemModel API has a narrow contract.
But since All Programmers Make Mistakes (TM), it facilitates the debugging process to check indices for being well-formed. For this purpose, Giuseppe D'Angelo introduced QAbstractItemModel::checkIndex() into Qt 5.11.
If you're still using a lower Qt version, you can simply write that function yourself.
[ If anyone has a better answer, I'll gladly accept it. ]
Looking at the source for QListWidget, it seems that checking the inputs is what Qt does itself:
QModelIndex QListModel::index(int row, int column, const QModelIndex &parent) const
{
if (hasIndex(row, column, parent))
return createIndex(row, column, items.at(row));
return QModelIndex();
}
It also appears that I didn't know about hasIndex() which will do what my validRowColumn() method does.
bool QAbstractItemModel::hasIndex(int row, int column, const QModelIndex &parent) const
{
if (row < 0 || column < 0)
return false;
return row < rowCount(parent) && column < columnCount(parent);
}
For that matter, I'm not sure why the documentation uses index.isValid() everywhere when hasIndex(index.row(), index.column(), index.parent()) would be more appropriate. Then, I'm sure a hasIndex(QModelIndex &) method would be added. hasIndex() does the same check as QModelIndex::isValid() and more:
inline bool isValid() const { return (r >= 0) && (c >= 0) && (m != 0); }

Why doesn't QTableView row count update?

I created a QAbstractTableModel called PresetTableModel, and connected it to a QTableView. I implemented the rowCount, columnCount, and data functions. Everything works if I have rowCount return a fixed number, but as soon as I get it to return a variable value, the list view doesn't show any rows. The debug statement in the code below shows the size value starting at 0, but changing to 9 once the list gets populated.
int PresetTableModel::rowCount(const QModelIndex & /*parent*/) const
{
qDebug() << preset_list.count();
return preset_list.size();
}
Is there something else I need to do to force it to update the number of rows?
When modifying the underlying data, you must use the model's notification mechanism to notify the views. E.g, when appending data:
beginInsertRows(QModelIndex(), preset_list.size(), preset_list.size()+1); //notify that two rows will be appended (rows size() and size() + 1)
preset_list.append(something);
preset_list.append(somethingelse);
endInsertRows(); //notify views that you're done with modifying the underlying data
Accordingly, you have to call beginRemoveRows() and endRemoveRows() when removing rows, and emit dataChanged() when existing entries are updated.
On a side note, your rowCount() method should read
if (!parent.isValid())
return preset_list.size(); //top-level: return list size
else
return 0; //list item: no further children (flat list)
to limit the depth. Otherwise each item in the list has again preset_list.size() entries.
i use:
void refresh() {
emit dataChanged(index(0, 0),
index(rowCount(), columnCount())); // update whole view
emit layoutChanged();
}

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