A few queries about Model View Programming

[wysota]

We need to migrate from text file to CSS but it would most probably be in the next version of the application.

You can read settings from a text file and apply them using stylesheets.

Please go thru my queries and if you know answer to any of them, it would be of great help to me.

From what I see you are doing it the wrong way. You can't modify the rect you paint on. This is the rect that Qt gives you to draw the check on and it supplies the option object to read and apply parameters of the check drawn. If you want something different then provide a full-blown delegate derived from QAbstractItemDelegate. Currently you are strained by the classes you use and instead of getting rid of those constraints you try to work around them, this is not the way.

[montylee]

You can read settings from a text file and apply them using stylesheets.

hmmm maybe. i'll explore about this. So, if i use CSS can i customize everything i have mentioned in my queries?

From what I see you are doing it the wrong way. You can't modify the rect you paint on. This is the rect that Qt gives you to draw the check on and it supplies the option object to read and apply parameters of the check drawn. If you want something different then provide a full-blown delegate derived from QAbstractItemDelegate. Currently you are strained by the classes you use and instead of getting rid of those constraints you try to work around them, this is not the way.

okie, so i should not modify the rect argument in the drawCheck() function.
I suppose, if i subclass QAbstractItemDelegate then i can fully customize the checkbox look.

One query:
I have basically no idea about QPainter yet, so does the QPainter code i shared earlier (in void CheckboxDelegate::drawCheck) look ok (except modifying the rect offcourse)? I mean if i subclass QAbstractItemDelegate and rewrite the paint function. In the paint function, i'll just display a checkbox pixmap. In the paint() function, i'll get the information about the current model index too:

virtual void paint ( QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index ) const = 0

so i can display different images when a row is highlighted.

Now, in this case, can i specify my own rect and draw the checkbox image as i like? You said that in QItemDelegate:drawCheck(), i can't modify the rect but here i am not getting any rect as argument, so is it ok to specify my own desired rect and display the pixmap within that rect?

[wysota]

hmmm maybe. i'll explore about this. So, if i use CSS can i customize everything i have mentioned in my queries?

Well... so far we were basically tallking about a custom checkbox, so yes.

okie, so i should not modify the rect argument in the drawCheck() function.

Correct.

I suppose, if i subclass QAbstractItemDelegate then i can fully customize the checkbox look.

Yes, but then you also have to handle clicking on the checkbox yourself (detecting the hit area, modifying the model and handle drawing).

One query:
I have basically no idea about QPainter yet, so does the QPainter code i shared earlier (in void CheckboxDelegate::drawCheck) look ok (except modifying the rect offcourse)?

Yeah, it looks fine although it doesn't do much - you force a fill of a rect with a specified colour and then render a pixmap on top of it. I don't see the point of neither making the fill nor filling with that colour and not some other, but the code itself is ok.

I mean if i subclass QAbstractItemDelegate and rewrite the paint function. In the paint function, i'll just display a checkbox pixmap. In the paint() function, i'll get the information about the current model index too:

so i can display different images when a row is highlighted.

Basically you have to look inside the QStyleOptionViewItem object and fetch all the necessary info from it (like the palette, areas to paint, current state of the item, etc.).

Now, in this case, can i specify my own rect and draw the checkbox image as i like?

Yes, you get the area for the whole item and its current state and you can draw as many checks or other things as you like.

You said that in QItemDelegate:drawCheck(), i can't modify the rect but here i am not getting any rect as argument, so is it ok to specify my own desired rect and display the pixmap within that rect?

Yes, provided the rect is within the item's rect which you receive inside the option argument. The painter is clipped anyway, so you wouldn't be able to draw outside of the rectangle even if you wanted to.

[montylee]

wow, thanks for the reply
things seem a bit clear now, i hope i am able to implement it properly.

BTW, i downloaded ur new article which was in the Qt quarterly newsletter. You really are a Qt guru

Thanks for your help! I might bug you later on again

[montylee]

hey, i tried using style sheets in my application. They seem to be so simple and i am able to set most of the things. But i have a problem.

I am using QWidget::setStyleSheet to set the style for widgets especially my QTableView. I am able to set the background color, highlight color etc...

Now the problem is how to set background color or image for the checkbox? Since the checkbox is displayed through the delegate automatically, i am not able to modify it.

I tried using QWidget::setStyleSheet in the QItemDelegate::drawCheck() method but it gives a compilation error since setStyleSheet method can be used only for QApplication and QWidget classes.

Now, you said that using Style sheets i would be able to custom display the checkbox, but i am not able to find any info about using style sheets in delegate drawing. Please help me.

[montylee]

I was able to display a checkbox icon in the entire table view cell. I subclassed QStyledItemDelegate class and rewrote the paint function. Here's the code for reference:

void CheckboxDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const 
{
	if (index.column() == 3) {
		QVariant state = index.model()->data(index, Qt::CheckStateRole);
		if (state == Qt::Checked) {
			// Calculate rectangle to draw the checkbox icon
			QRect rect = option.rect.adjusted(20, 5, -25, -10);
			if (option.state & QStyle::State_Selected) {
				// Fill the highlight rectangle
				painter->fillRect(option.rect, option.palette.highlight());
				// Draw "ALL" icon in the first row and checkbox icons in other rows
				if (index.row() == 0)
					painter->drawPixmap(option.rect, QPixmap("all-on.png"));
				else
					painter->drawPixmap(rect, QPixmap("check-icon-hl.png"));
			} else {
				if (index.row() == 0)
					painter->drawPixmap(option.rect, QPixmap("all-on.png"));
				else
					painter->drawPixmap(rect, QPixmap("check-icon.png"));
			}
		} else {
			if (option.state & QStyle::State_Selected)
				painter->fillRect(option.rect, option.palette.highlight());
			if (index.row() == 0)
					painter->drawPixmap(option.rect, QPixmap("all-off.png"));
		}
	} else {
		QStyledItemDelegate::paint(painter, option, index);	
	}
}

void CheckboxDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const 
{
	if (index.column() == 3) {
		QVariant state = index.model()->data(index, Qt::CheckStateRole);
		if (state == Qt::Checked) {
			// Calculate rectangle to draw the checkbox icon
			QRect rect = option.rect.adjusted(20, 5, -25, -10);
			if (option.state & QStyle::State_Selected) {
				// Fill the highlight rectangle
				painter->fillRect(option.rect, option.palette.highlight());
				// Draw "ALL" icon in the first row and checkbox icons in other rows
				if (index.row() == 0)
					painter->drawPixmap(option.rect, QPixmap("all-on.png"));
				else
					painter->drawPixmap(rect, QPixmap("check-icon-hl.png"));
			} else {
				if (index.row() == 0)
					painter->drawPixmap(option.rect, QPixmap("all-on.png"));
				else
					painter->drawPixmap(rect, QPixmap("check-icon.png"));
			}
		} else {
			if (option.state & QStyle::State_Selected)
				painter->fillRect(option.rect, option.palette.highlight());
			if (index.row() == 0)
					painter->drawPixmap(option.rect, QPixmap("all-off.png"));
		}
	} else {
		QStyledItemDelegate::paint(painter, option, index);	
	}
}

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