The property doesn't exist on the Qt Quick input items. You can vote for the feature here.
In the meantime, you can use TextArea
from Qt Quick Controls 2.
If you would rather use pure Qt Quick, you can do something similar to what the Controls do and add a Text
item above the field:
import QtQuick 2.5
import QtQuick.Window 2.2
Window {
width: 300
height: 300
visible: true
TextEdit {
id: textEdit
width: 200
height: 50
property string placeholderText: "Enter text here..."
Text {
text: textEdit.placeholderText
color: "#aaa"
visible: !textEdit.text
}
}
}