Qml: ScrollView containing a ListView does not adjust ScrollBar handle - qt

Question

I am trying to add vertical scrollbar, as needed, to a ListView. I have been told that the best approach is to place the ListView inside a ScrollView, instead of inserting a scrollbar into the ListView (like in this question), because that would make it more efficient for the GPU.
I inserted it, as in the example below - but no matter what I tried, if the scroll bar shows, its handle always takes the entire height and of course doesn't move.
I hope you can take a look at my sample and give me a suggestion, why the scroll bar is not showing up properly.
There are comments inside the code explaining what I did and why.
import QtQuick 2.0
import QtQuick.Controls 1.4
import QtQuick.Controls.Styles 1.4
Item
{
readonly property int parentWidth: 280
readonly property int parentMaxHeight: 400
// Main reason for doing this - the items are custom objects and
// their width does not automatically adjust for having the scroll bar or not
// But also, to set scroll bars because Qt.ScrollBarAsNeeded makes them not show
property bool scrollBarVisible: myListView.contentHeight > myListView.height
width: parentWidth
height: parentMaxHeight
Rectangle
{
id: myMenuRect
anchors.rightMargin: 2
anchors.leftMargin: 2
anchors.bottomMargin: 4
anchors.topMargin: 4
width: parentWidth
height: myListView.height
radius: 10
z: 2
color: "red" // Adding this to show why the height of the rectangle must match the listview
}
ScrollView
{
id: myScrollView
parent: myMenuRect
anchors.fill: parent
anchors.topMargin: 5
anchors.bottomMargin: 5
anchors.rightMargin: 5
frameVisible: false
// I have tried to set implicitHeight in many different ways,
// no matter what I do the scroll bar handle occupies the enire bar and doesn't move
// The Qt.ScrollBarAsNeeded didn't work... so I did this
verticalScrollBarPolicy: scrollBarVisible ? Qt.ScrollBarAlwaysOn : Qt.ScrollBarAlwaysOff
// Adding colors on scrollbar to show which part is showing
style: ScrollViewStyle
{
handle: Rectangle
{
implicitWidth: 10
implicitHeight: 2
radius: 10
anchors.leftMargin: 1
anchors.left: parent.left
color: "yellow"
}
scrollBarBackground: Rectangle
{
implicitWidth: 12
anchors.right: parent.right
color: "green"
}
}
ListView
{
id: myListView
parent: myScrollView
model: wifiComboListModel
focus: true
clip: true
interactive: false
width: parent.width
// I am trying to tell my view to take the minimum space it needs that is below
// a certain height. Ignore the "myListView." prefixes here, I know they are not needed but
// make it easier to move this outside if needed
height: (myListView.contentHeight > 0 ?
(myListView.contentHeight < parentMaxHeight ?
myListView.contentHeight : parentMaxHeight) : 0)
// I made this as simple as possible, without affecting "quality"
delegate: Text
{
text: _comboBoxText
height: 70
width: parent.width - 20
}
}
ListModel
{
id: wifiComboListModel
}
// I want to populate my model from outside, not be static. Not sure if this affects the bars
function populateComboBoxListModel()
{
wifiComboListModel.clear();
for (var itemIndex = 0; itemIndex < listItems.length; itemIndex++)
{
wifiComboListModel.append
({
_id: itemIndex,
_comboBoxText: listItems[itemIndex]
});
}
}
Component.onCompleted:
{
populateComboBoxListModel();
}
property var listItems: [
"This",
"annoying",
"list",
"view",
"does",
"not behave the way",
"I expect.",
"I",
"tried many",
"things,",
"now I am",
"begging for your",
"help",
"."
]
}

Answer 1

you have a binding loop for height in myMenuRect. This occurs because myMenuRect depends on height of the list view and vice versa. After fixing it seems to be working:
import QtQuick 2.0
import QtQuick.Controls 1.4
ApplicationWindow
{
readonly property int parentWidth: 280
readonly property int parentMaxHeight: 400
visible: true
// Main reason for doing this - the items are custom objects and
// their width does not automatically adjust for having the scroll bar or not
// But also, to set scroll bars because Qt.ScrollBarAsNeeded makes them not show
property bool scrollBarVisible: myListView.contentHeight > myListView.height
width: parentWidth
height: parentMaxHeight
Rectangle
{
id: myMenuRect
anchors.rightMargin: 2
anchors.leftMargin: 2
anchors.bottomMargin: 4
anchors.topMargin: 4
width: parentWidth
height: parentMaxHeight
radius: 10
z: 2
}
ScrollView
{
id: myScrollView
parent: myMenuRect
anchors.fill: parent
anchors.topMargin: 5
anchors.bottomMargin: 5
anchors.rightMargin: 5
frameVisible: false
// I have tried to set implicitHeight in many different ways,
// no matter what I do the scroll bar handle occupies the enire bar and doesn't move
// The Qt.ScrollBarAsNeeded didn't work... so I did this
verticalScrollBarPolicy: scrollBarVisible ? Qt.ScrollBarAlwaysOn : Qt.ScrollBarAlwaysOff
ListView
{
id: myListView
model: wifiComboListModel
focus: true
clip: true
interactive: false
width: parent.width
// I am trying to tell my view to take the minimum space it needs that is below
// a certain height. Ignore the "myListView." prefixes here, I know they are not needed but
// make it easier to move this outside if needed
height: (myListView.contentHeight > 0 ?
(myListView.contentHeight < parentMaxHeight ?
myListView.contentHeight : parentMaxHeight) : 0)
// I made this as simple as possible, without affecting "quality"
delegate: Text
{
text: _comboBoxText
height: 70
width: parent.width - 20
}
}
}
ListModel
{
id: wifiComboListModel
}
// I want to populate my model from outside, not be static. Not sure if this affects the bars
function populateComboBoxListModel()
{
wifiComboListModel.clear();
for (var itemIndex = 0; itemIndex < listItems.length; itemIndex++)
{
wifiComboListModel.append
({
_id: itemIndex,
_comboBoxText: listItems[itemIndex]
});
}
}
Component.onCompleted:
{
populateComboBoxListModel();
}
property var listItems: [
"This",
"annoying",
"list",
"view",
"does",
"not behave the way",
"I expect.",
"I",
"tried many",
"things,",
"now I am",
"begging for your",
"help",
"."
]
}

Answer 2

The reason why my ScrollView did not behave was parenthood :)
The issue: even though I set the parent in the ListView, it seems it did not take:
ListView
{
parent: myScrollView
What I had to do to make it work was actually nest the ListView inside the ScrollView.
ScrollView
{
id: myScrollView
parent: myMenuRect
anchors.fill: parent
ListView
{
id: myListView
model: wifiComboListModel
I think the "parent" property may not work well for all controls, and will remember that in the future.