How to compute the height of a QTreeWidget content?

Question

I want a QTreeWidget that has a preferred height that shows all its contents without scrollbar. Use case for this is twofold: 1) trees in a QVBoxLayout taking space proportional to their content and 2) trees in a QScrollArea where there should be only one scrollbar for all trees instead of individual scrollbars.

I tried querying the tree and its viewport but they always return the same values no matter how much content they have:

size = PySide.QtCore.QSize(100, 30)
sizeHint = PySide.QtCore.QSize(256, 192)
minimumSize = PySide.QtCore.QSize(0, 0)
minimumSizeHint = PySide.QtCore.QSize(76, 76)
maximumSize = PySide.QtCore.QSize(16777215, 16777215)
baseSize = PySide.QtCore.QSize(0, 0)
frameSize = PySide.QtCore.QSize(100, 30)
viewport.size = PySide.QtCore.QSize(94, 5)
viewport.sizeHint = PySide.QtCore.QSize(-1, -1)
viewport.minimumSize = PySide.QtCore.QSize(0, 0)
viewport.minimumSizeHint = PySide.QtCore.QSize(-1, -1)
viewport.maximumSize = PySide.QtCore.QSize(16777215, 16777215)
viewport.baseSize = PySide.QtCore.QSize(0, 0)
viewport.frameSize = PySide.QtCore.QSize(94, 5)

Next I tried computing the size by adding up all the size hints for every item:

    size = super().sizeHint()
    height = self.horizontalScrollBar().sizeHint().height()
    rows = 0
    it = QtGui.QTreeWidgetItemIterator(self)
    while it.value() is not None:
        rows += 1
        size = it.value().sizeHint(0)
        height += size.height()
        it += 1
    size = QtCore.QSize(size.width(), height)

But all items return a size of (-1, -1). Even after the tree is displayed, not just during construction.

So how do I compute the height of the tree?

Answer 1

The trick seems to be to query the header for the width, the tree for individual row heights and add the frameWidth on all sides like this:

class TreeWidget(QtGui.QTreeWidget):
    def sizeHint(self):
        print("TreeWidget.sizeHint()")
        print("  frameWidth = {0}".format(self.frameWidth()))
        height = 2 * self.frameWidth() # border around tree
        if not self.isHeaderHidden():
            header = self.header()
            headerSizeHint = header.sizeHint()
            print("  headerSizeHint = {0}".format(headerSizeHint))
            height += headerSizeHint.height()
        rows = 0
        it = QtGui.QTreeWidgetItemIterator(self)
        while it.value() is not None:
            rows += 1
            index = self.indexFromItem(it.value())
            print("  rowHeight = {0}".format(self.rowHeight(index)))
            height += self.rowHeight(index)
            it += 1
        print("  computed height for {0} rows = {1}".format(rows, height))
        return QtCore.QSize(header.length() + 2 * self.frameWidth(), height)