Hello,
I created a scroll area and called setWidget() to set the "inner" widget. The inner widget has a layout that I want to clear from time to time. In the documentation for QLayout::takeAt() I found this:

http://doc.trolltech.com/4.5/qlayout.html#takeAt

Unfortunately, it does not work (it looks like a redraw problem). What works is keeping a separate list of added widgets, and deleting them manually. I can't understand what's going on. I'm posting a complete test class showing the problem:

Qt Code: 
  1. #include <QWidget>
  2. #include <QVBoxLayout>
  3. #include <QPushButton>
  4. #include <QScrollArea>
  5. #include <QLabel>
  6. #include <QList>
  7.  
  8. class ScrollAreaTest : public QWidget
  9. {
  10.   Q_OBJECT
  11.  
  12. public:
  13. 	ScrollAreaTest(QWidget* parent = 0):
  14. 		QWidget(parent)
  15. 	{
  16. 		// buttons
  17. 		QPushButton* btnAdd = new QPushButton("Add label");
  18. 		connect(btnAdd, SIGNAL(clicked()), this, SLOT(onBtnAdd()));
  19.  
  20. 		QPushButton* btnClear1 = new QPushButton("Clear Layout (mode 1)");
  21. 		connect(btnClear1, SIGNAL(clicked()), this, SLOT(onBtnClear1()));
  22.  
  23. 		QPushButton* btnClear2 = new QPushButton("Clear Layout (mode 2)");
  24. 		connect(btnClear2, SIGNAL(clicked()), this, SLOT(onBtnClear2()));
  25.  
  26. 		// scroll area
  27. 		QScrollArea* myScrollArea = new QScrollArea();
  28. 		myScrollArea->setWidgetResizable(true);
  29. 		myScrollArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
  30. 		myScrollArea->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
  31.  
  32. 		// scroll area "inner" widget
  33. 		QWidget* innerWidget = new QWidget();
  34. 		innerWidgetLayout = new QVBoxLayout();
  35. 		innerWidget->setLayout(innerWidgetLayout);
  36.  
  37. 		// set scroll area inner widget
  38. 		myScrollArea->setWidget(innerWidget);
  39.  
  40. 		// main layout
  41. 		QVBoxLayout* layout = new QVBoxLayout();
  42. 		layout->addWidget(btnAdd);
  43. 		layout->addWidget(btnClear1);
  44. 		layout->addWidget(btnClear2);
  45. 		layout->addWidget(myScrollArea);
  46. 		setLayout(layout);
  47. 	}
  48.  
  49. private:
  50. 	QVBoxLayout* innerWidgetLayout;
  51. 	QList<QLabel*> addedLabels;
  52.  
  53. private slots:
  54.  
  55. 	void onBtnAdd()
  56. 	{
  57. 		QLabel* l = new QLabel("Hello there!");
  58. 		innerWidgetLayout->addWidget(l);
  59.  
  60. 		addedLabels.push_back(l);  // I'm keeping a list of added labels (see onBtnClear2)
  61. 	}
  62.  
  63. 	void onBtnClear1() // this is from the docs and doesn't work
  64. 	{
  65. 		QLayoutItem *child;
  66.  
  67. 		while ((child = innerWidgetLayout->takeAt(0)) != 0)
  68. 			delete child;
  69.  
  70. 		/*
  71. 		innerWidgetLayout->activate();
  72. 		innerWidgetLayout->update();
  73. 		update();
  74. 		*/
  75. 	}
  76.  
  77. 	void onBtnClear2() // this works
  78. 	{
  79. 		for (QList<QLabel*>::iterator it = addedLabels.begin(); it != addedLabels.end(); ++it)
  80. 			delete *it;
  81.  
  82. 		addedLabels.clear();
  83. 	}
  84. };
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Thank you