I am trying to use a QTextEdit widget inside of a form containing several QT widgets. The form itself sits inside a QScrollArea that is the central widget for a window. My intent is that any necessary scrolling will take place in the main QScrollArea (rather than inside any widgets), and any widgets inside will automatically resize their height to hold their contents.
I have tried to implement the automatic resizing of height with a QTextEdit, but have run into an odd issue. I created a sub-class of QTextEdit and reimplemented sizeHint() like this:
QSize OperationEditor::sizeHint() const {
QSize sizehint = QTextBrowser::sizeHint();
sizehint.setHeight(this->fitted_height);
return sizehint;
}
this->fitted_height is kept up-to-date via this slot that is wired to the QTextEdit's "contentsChanged()" signal:
void OperationEditor::fitHeightToDocument() {
this->document()->setTextWidth(this->viewport()->width());
QSize document_size(this->document()->size().toSize());
this->fitted_height = document_size.height();
this->updateGeometry();
}
The size policy of the QTextEdit sub-class is:
this->setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::Preferred);
I took this approach after reading this post.
Here is my problem:
As the QTextEdit gradually resizes to fill the window, it stops getting larger and starts scrolling within the QTextEdit, no matter what height is returned from sizeHint(). If I initially have sizeHint() return some large constant number, then the QTextEdit is very big and is contained nicely within the outer QScrollArea, as one would expect. However, if sizeHint gradually adjusts the size of the QTextEdit rather than just making it really big to start, then it tops out when it fills the current window and starts scrolling instead of growing.
I have traced this problem to be that, no matter what my sizeHint() returns, it will never resize the QTextEdit larger than the value returned from maximumViewportSize(), which is inherited from QAbstractScrollArea. Note that this is not the same number as viewport()->maximumSize(). I am unable to figure out how to set that value.
Looking at QT's source code, maximumViewportSize() is returning "the size of the viewport as if the scroll bars had no valid scrolling range." This value is basically computed as the current size of the widget minus (2 * frameWidth + margins) plus any scrollbar widths/heights. This does not make a lot of sense to me, and it's not clear to me why that number would be used anywhere in a way that supercede's the sub-class's sizeHint() implementation. Also, it does seem odd that the single "frameWidth" integer is used in computing both the width and the height.
Can anyone please shed some light on this? I suspect that my poor understanding of QT's layout engine is to blame here.
Edit: after initially posting this, I had the idea to reimplement maximumViewportSize() to return the same thing as sizeHint(). Unfortunately, this did not work as I still have the same problem.
I have solved this issue. There were 2 things that I had to do to get it to work:
Walk up the widget hierarchy and make sure all the size policies made sense to ensure that if any child widget wanted to be big/small, then the parent widget would want to be the same thing.
This is the main source of the fix. It turns out that since the QTextEdit is inside a QFrame that is the main widget in a QScrollArea, the QScrollArea has a constraint that it will not resize the internal widget unless the "widgetResizable" property is true. The documentation for that is here: http://doc.qt.io/qt-4.8/qscrollarea.html#widgetResizable-prop. The documentation was not clear to me until I played around with this setting and got it to work. From the docs, it seems that this property only deals with times where the main scroll area wants to resize a widget (i.e. from parent to child). It actually means that if the main widget in the scroll area wants to ever resize (i.e. child to parent), then this setting has to be set to true.
So, the moral of the story is that the QTextEdit code was correct in overriding sizeHint, but the QScrollArea was ignoring the value returned from the main frame's sizeHint.
Yay! It Works!
You may try setting minimumSize property of the QTextEdit to see if that force the layout to grow.
I don't understand most of Qt's layout scheme but setting minimum and maximum size pretty much does what I want it to do. Well, most of the time anyways.
Related
just like the title described, when i redraw the scrollbar in QTreeView which has a header(QHeaderView), but the scrollbar's height is the entire height of QTreeView, and i want to let the scrollbar's height equals the QTreeView's height minus the header's height.just like the pic below:
A solution for your problem might be setting the location of the vertical scrollbar to a constant_offset value acquired from the QHeaderView (on the y axis).
This could be done by subclassing the QTreeView like so:
class MyTreeView : public QTreeView
{
public:
MyTreeView(QWidget* parent = nullptr): QTreeView(parent){}
void updateVertScrollBar()
{
auto* ptr = verticalScrollBar();
QRect rect = ptr->geometry();
rect.setTop(header()->height());
ptr->setGeometry(rect);
}
void resizeEvent(QResizeEvent* ev) override
{
QTreeView::resizeEvent(ev);
updateVertScrollBar();
}
};
Depending on the sizePolicy the updateVertScrollBar method could be called just after data is filled or as presented in the sample implementation the update can occur for each resizeEvent - which should cover various resizing performed to the widget.
EDIT
Additionally removing the blank space left from the shrunk scrollbar would be tricky. First denote that the QTreeView is built from a viewport widget and scrollbars (among others). The issue you now see comes from the fact that viewport plus vertical scrollbar widths (if visible) should match and this is calculated internally.
I stated that it's tricky since there is a load of stuff happening when you try to force the size of these components. Some updates are called in-place some are called through the event loop. You can check this to get more detaile info about the concept. Similar approach is probably applied to QTreeView.
Basically what you would need to do is to stretch the viewport width. This should be probably done during the resizeEvent but calling from there methods like viewport()->setGeometry() might not end well - you might get caught into a loop. You might try blockSignals but I'm not sure this would help. In general if you want to mess with the internals of a given Qt widget you should go through it's implementation at least briefly.
Here is a screenshot of my Qt application. I have blurred everything which isn't important. Look at the bottom-right.
That "Comment" bit is a QGroupBox containing a QTextEdit, it is being cropped because some containing QWidget is not expanding to fit it.
So far I have seen widgets expand by default to fit their contents (as long as child widgets are added to layouts before they become visible, which is what's happening here) but suddenly this is no longer happening. If I manually expand the window, the "Comment" box is laid out as expected.
The innermost QTextEdit has setMinimumHeight called and I have verified that every widget in the hierarchy has QSizePolicy::GrowFlag set in its sizePolicy. I have grepped the source to check that I am not setting maximum sizes anywhere in the application. And, yes, the QTextEdit is in the layout of the QGroupBox.
It seems like Qt is saying "I'll automatically expand the main window to fit the contents, but only up to a limit."
Why is this happening and how do I stop it? Or rather, how do I make it continue the helpful auto-resizing behaviour regardless of the size/depth of child widgets?
I have been now two years working deeply with Qt layout system. After this time i encountered thosand of problems with SizePolicies and Layouts. I normally found out solutions, but never really understood what i was doing.
Now i was taking some time to try to understand correctly and build a 101 GUIDE for them and never fail. I found out this piece of information in the documentation about QSizePolicy of a QWidget:
This property holds the default layout behavior of the widget
If there is a QLayout that manages this widget's children, the size
policy specified by that layout is used. If there is no such QLayout,
the result of this function is used.
I thought that if you had a QLabel, for example, and you set the policies to Horizontal Expanding, Vertical Fixed, THE LABEL itself changed that way.
But it doesn't, at all.
When reading that i see that it talks about ITS CHILDREN inside the LAYOUT. So what does it mean, then?. Nothing is inside the label, is that why it does not work?.
WHat about inserting a label inside a QFrame, and telling the frame to be Expanding... Will the QFrame expand or stretch (depending on the rest of brother widgets in the same Layout) or will the label expand or stretch, not the QFrame?
What a mess...
What about Stretching?. If you set stretching 10 when you add the widget:
layout->addwidget(label, 10, Qt::AlignHCenter);
It doesn't work either.
Stretch 0 when you add the widget means : Take the policies i told you. Default, depends on the type of widget. Button-like widgets have expanding-fixed. Box-like Expanding-Expanding...
Stretch 10 means: grow maximum.
Am i right? Well. When having a QFrame and a QLabel inside, setting Expanding, and 10 to strech to the label DOES NOT WORK.
I don't understand all of your questions, so I will only answer to those that I think i do.
I thought that if you had a QLabel, for example, and you set the policies to Horizontal Expanding, Vertical Fixed, THE LABEL itself
changed that way. But it doesn't, at all.
I don't know what that means. What is the exact behavior you're expecting and what is actually happening? Is this label in a layout? Are there any other widgets in this layout?
WHat about inserting a label inside a QFrame, and telling the frame to be Expanding...
If you set a QSizePolicy to your QFrame object and set a layout to it, this size policy might be ignored. Docs: If there is a QLayout that manages this widget's children, the size policy specified by that layout is used. If there is no such QLayout, the result of this function is used. This means that the widget's layout should manage the size of the widget. Note that it will still respect the minimum/maximum width/height values.
Stretch 10 means: grow maximum.
What makes you think that?. The stretch factor is dependent on other widgets inside the layout. Docs: Stretch factors are used to change how much space widgets are given in proportion to one another.
When having a QFrame and a QLabel inside, setting Expanding, and 10 to strech to the label DOES NOT WORK.
Does not work how? If you set stretch for QFrame to 1 and for QLabel to 10, your QLabel object should always be 10 times as wide/high(depending of your layout type) as your QFrame object. If your QFrame has a layout and it contains children, then this might not work as it would depend on the childrens size policies.
it's not the first time that I want a scroll area which behaves like the following (imagine a log or chat window, but too complex to use a simple QTextBrowser):
I want to add multiple widgets, which appear one below the other (like when placed in a QVBoxLayout)
Each widget within this layout should have a fixed size or a height-for-width (like a simple label)
The scroll area should auto-scroll to the most recently added one
(optional) When there is space left (scroll bar not yet enabled), the contents should be aligned to bottom
Using QScrollArea:
My attempt in the past was using a QScrollArea using a QVBoxLayout inside. But this seems to be not as simple as I thought: Whenever I add a widget to the layout, the layout doesn't resize the scroll area content widget immediately, resulting in a delayed adjustment of the contents. For one short moment, the widgets contained in the layout are resized so that the total size equals the total size before the add operation, resulting in a too small size per widget. Also, scrolling to the newly added widget is thus not possible until the layout corrected its size to the new total size of widgets, so even a QTimer::singleShot(0, ...) doesn't help here. Even with a timeout of 20 or so, there are situations in which the layout needs more time to resize. It's not deterministic, and thus far away from a nice solution.
In order to get the bottom alignment behaviour, I initially place a spacer item in the layout. It won't require any space as soon as there is no space left and scrolling gets enabled.
Using QListView:
As my items are too complex, they need to be QWidgets. They can't have the focus, aren't selectable, so an item-based solution seems to be just "the wrong way". Also, this solution sounds too "heavy".
I just can't believe that there is no easy way, so I think I just haven't seen it yet!
QListView should be fine. You claim that your items are static, there's no interaction with them: no focus, no selection. It'd seem that a QWidget is an overkill for such items. You only need something that has a fixed size and can draw itself. That is precisely what delegates in the Qt's model-view system are for. Just implement one or more QAbstractItemDelegates for your items, and provide an implementation of a model for the data they will be rendering. The QAbstractItemView is is already a QAbstractScrollArea!
If you want to paint HTML within a delegate, it's easy to do -- again, QWidget is an overkill for a static display! There is a very food reason why it's "hard" to use QWidget for this -- the API guides you to the correct solution. Assuming your model contains html for each item, here's how you can paint it. You can go fancy with the sizeHint, of course, and should be caching the text document, ideally storing it in the model I'd think.
void MyDelegate::paint(QPainter* p, const QStyleOptionViewItem & opt, const QModelIndex & index) const
{
QTextDocument doc;
doc.setHtml(index.data().toString());
doc.drawContents(p, QRect(QPoint(0,0), sizeHint(opt, index)));
}
QSize MyDelegate::sizeHint(const QStyleOptionViewItem &, const QModelIndex &) const
{
return QSize(100, 200);
}
I am writting a QStyle Here I am changing the QProgressBar to a Slim single line, no text. So Height will also be reduced to 5px. However Widget Width will be determined by layout. what should I do in My Style's drawControl to change widget height ?
I've never actually written a QStyle but I would consider it odd if you were supposed to resize anything inside drawControl. I could be wrong on this by a quick review of the documentation would seem to suggest that you would override subElementRect and return a rect based on current width and your preferred height. I assume this would be called by layout activities and would be sorted out by the time drawControl gets called.
Do you need the height for the widget to be fixed? Or just the drawn height to never go past 5 pixels? For the first, set the height and resize policy on the polish function. For the second, override the drawing in the QStyle to only use 5 pixels. The functions that do the drawing generally take rects; you can call the base class's draw with a modified rect if you properly override the appropriate functions. Unfortunately, it's been years since I've done any QStyle work, so I'm not sure exactly what those functions are.