WebEngineView + virtual keyboard - maintain scroll position after resizing (focused input) - qt

Question

I have a very simple browser app based on WebEngineView and virtual keyboard made in Qt Quick.
Everything works fine - the keyboard is shown perfectly each time I click on an input in the webview, but what bothers me is that if I click on an input that is at the bottom, the keyboard covers it after opening and I cannot see what I'm typing.
I tried solving it by resizing the WebEngineView element to accomodate for the keyboard height, like most mobile apps work. It works, I can scroll the page under the keyboard but the keyboard still covers the input and I need to scroll manually.
Is there any way I could adjust the web view scroll position so the keyboard doesn't cover the focused input from QML?
I cannot do it at a single website because I allow navigation to any website user wants, so I need some universal method.
Here is my qml code:
import QtQuick 2.12
import QtQuick.Window 2.12
import FreeVirtualKeyboard 1.0
import QtWebEngine 1.8
Window {
id: appContainer;
visible: true
width: 1280
height: 600
title: qsTr("WebEngineView")
property string pathUrl: "https://www.w3schools.com/html/html_forms.asp"
WebEngineView {
id: webview
width: appContainer.width
url: appContainer.pathUrl
height: appContainer.height
}
/*
Virtual keyboard
*/
InputPanel {
id: inputPanel
z: 99
y: appContainer.height
anchors.left: parent.left
anchors.right: parent.right
states: State {
name: "visible"
when: Qt.inputMethod.visible
PropertyChanges {
target: inputPanel
y: appContainer.height - inputPanel.height
}
}
transitions: Transition {
from: ""
to: "visible"
reversible: true
ParallelAnimation {
NumberAnimation {
properties: "y"
duration: 150
easing.type: Easing.InOutQuad
}
}
onRunningChanged: {
if(!running && inputPanel.state == "visible") {
// finished showing keyboard
webview.height = appContainer.height - inputPanel.height
console.log('Keyboard shown')
} else if(running && inputPanel.state != "visible") {
// begins to hide keyboard
webview.height = appContainer.height
console.log('Keyboard starts to hide');
}
}
}
}
}
So far the resizing part works okay - I do it in onRunningChanged so the webview resizes before the transition starts and after it ends - this prevents ugly empty space showing during transition.
Update
I have achieved the effect I wanted using webview.runJavaScript together with scrollIntoView after showing the keyboard:
webview.runJavaScript("document.activeElement.scrollIntoView({block: 'nearest', inline: 'nearest', behavior: 'smooth'})");
However I'm not sure if this is solution is the best, as I don't like the fact of involving javascript evaluation into the process. I'd like to know if there's any more "native" way of doing this.

Answer 1

Resize WebEngineView, scroll into view
The problem with resizing the WebEngineView is that HTML will see that your device screen suddenly shrunk and may decide to present a vastly different layout, for example move menu from top to side of the screen.
Even if this has not happened, layout has changed. The position on the new "screen" does not correspond to the position on the old one, there is no 1:1 relation, which is why it scrolls to a seemingly random spot in the first place.
We can tell webpage to scroll a focused element into view of new viewport:
If it was already onscreen than nothing happens.
If not, webpage scrolls so that the element fits on the screen if possible. scrollIntoView has parameters to scroll to the top/bottom of the screen as desired
So when onscreen keyboard is opened:
Save original scrollPosition
Resize WebEngineView
Optionally assign scrollPosition to saved value - although it probably won't do you any good
Use runJavaScript to determine activeElement and make it scrollIntoView
Repeat same steps when onscreen keyboard is dismissed.
Do not resize, scroll manually
Another approach would be to not resize the "screen" and just scroll the element into view if it got covered.
This would require Qt to change VisualViewport while leaving LayoutViewport intact (see this and this for more information) but it seems that Qt cannot do that, at least not through QML alone.
That leaves us with having to do it manually: determine position with getBoundingClientRect, calculate how much space does keyboard cover, and if it is not inside our calculated uncovered view area - scrollTo it.
(you will still need runJavaScript to get inside the webpage)
Perhaps this and this SO questions can help
Other options
#Hazelnutek reported some success with document.activeElement.scrollIntoViewIfNeeded()
Please see discussion in comments to this answer below: