QStackedWidget, widget gets overlap after few to and fro switches

**newbie2201** · 2011-01-13, 17:20

Hi,

I am utilizing the QStackedWidget to implement the multiview application in QT . On application init I am creating 5 widgets and adding to stack. During execution I am switching to and fro from one widget to other using the setCurrentWidget (I am not destroying the widget as I want to keep their state maintained for next visit).

To my surprise widget starts overlapping each other after few runs. I am not able to get the cause of problem. I searched in the forum and no such issue is reported so may I am doing something wrong.

Is there some one who can guide me to prevent this problem?

Regards,

**Jon Heron** · 2011-01-14, 01:48

Can we see your code?
I have not had any such issues after extensive use of the QStackedWidget (well extensive for my limited experience

).
Cheers,
Jon

**danhicksbyron** · 2011-01-14, 03:46

What do you mean by "overlapping"? Do they slide side-to-side such that the edge of the widget below is visible, or do parts of one widget "stick" on the screen when a new widget is pushed or popped?

**newbie2201** · 2011-01-14, 14:42

HI,

Overlapping means one widget over the widget.

For much of the time when I keep activating on widget, I can see the controls(buttton, table, image etc) of active wd only. But after many switches, when I activate widget, the controls of previous widget also remains on the screen underneath.

I think I need to make the widget opaque or not sure what the cause of problem is.

Regards,

**dahiya.vinod** · 2011-01-14, 14:44

You are running ur code on device or emulator?

**newbie2201** · 2011-01-14, 14:56

I am running the code on Nokia N8. On emulator there is no overlapping. Is there way to make the background opaque. Though it does nto make sense as when one widget is active the other gets hidden I think.

**danhicksbyron** · 2011-01-14, 17:22

Do a lot of your widgets have images for backgrounds? Are you running out of heap? Are you setting any WA_... attributes with QWidget::setAttributes()?

**newbie2201** · 2011-01-14, 18:50

Hey,

I have logged the heap memory stats. And realize that the problem start happenign when the heap memory reaches 30 000 000 (30 MB). I am using multiple widgest having web view. So whn i start using the stress testing on widgets having web view the memory rises incredibily and hwne I leave the widget memory does not goes down. Problem of memory keep on increasing is in wdigets having QWebView.

I think there is memory leak with the QWebView. If i do not browse any of widget havign webview application keeps working fine. Heap stats remains constant.

I have already set enough heap memory for application which is

TARGET.EPOCHEAPSIZE = 0x20000 0x4000000

which states max 67 MB but when the heap stats reaches near to 30 MB application widget starts overlapping

This behaviour is disgusting. QWebView is eating a memory as he is hungry from year or so.

**sevdotcom** · 2011-01-14, 19:36

Hey newbie2201,

I am having the same overlapping problem with stacked or tab widget and QWebView. I noticed that the overlapping start to happen when changing the device (N8) orientation with the QWebView being visible. Here is some simple code that would reproduce the problem:

QTabWidget* tab = new QTabWidget(this);
tab->setGeometry(0, 0, 200, 300);

QListWidget* list = new QListWidget();
list->addItem("Item 1");
tab->addTab(list, "List");

QWebView* web = new QWebView();
web->setHtml("<html><body>Hi</body></html>");
tab->addTab(web, "Web");

If anybody has any ideas please us let know.

Thanks

**danhicksbyron** · 2011-01-14, 19:42

WebView has some unsavory characteristics, but it is should do fine in 64MB. I suspect you have some leaks.

There is a documented leak in 4.6.x in QAbstractScrollArea, and often WebViews are embedded in QScrollAreas. The circumvention is to do this prior to destroying the scroll area:

scrollAreaPtr ->viewport() ->ungrabGesture(Qt::PanGesture);

This is supposed to be fixed in 4.7.x, but I don't know that it has been.

**sevdotcom** · 2011-01-14, 20:06

I can repro this problem consistently. Using the code I mentioned earlier, here are the steps:
1) Run the app
2) With the first tab visible go from portrait to landscape and then back to portrait.
3) Click on the second tab and go from portrait to landscape and then back to portrait again.
4) Click on the first tab and you can see the widgets overlapped. It looks really ugly.

I tried:
-using different layout managers
-building my own stacked/tab widget
-setting the resize policy to fixed
-increase heap size

Please throw at me any ideas you can think of.

Thanks

**newbie2201** · 2011-01-14, 20:24

Hey Thanks for the info,

How can i get the scrollAreaPtr ?

Also earlier I was delete QWebView objects on application. But now I have decided to delete on widget switch so that the heap memory cna be released. Is there any other way to release the heap memory. And I notice still its not freeing up the memory on switchign from widget.

This behaviour is screwing me.

Regards,

**sevdotcom** · 2011-01-14, 20:43

I just found this thread. It may or may not be related to our problem.

**newbie2201** · 2011-01-14, 21:07

Hi Sev,

It is not relevant to our problem. As the QWebView is working fine the overlapping starts happen only when the heap memory reached near to 30 MB, after navigating and rotating the device many a times. And the controls of views remain at their position but the widget do start overlapping each other.

Regards,

**sevdotcom** · 2011-01-14, 21:19

Yeah, it did not fix my problem either. Nokia folks, please help.

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