How to link from ComboBox to another ComboBox - qt

Question

I try to make a converter app depending on two ComboBoxes using Controls 2.
For example:
// First combobox is input unit:
ComboBox {
id: res_combo1
width: res_comborect1.width
currentIndex: 0
model: ListModel {
id: model1
ListItem { text: qsTr("meter") }
ListItem { text: qsTr("mile") }
ListItem { text: qsTr("km") }
}
}
}
// Second combobox is output unit:
ComboBox {
id: res_combo2
width: res_comborect1.width
currentIndex: 0
model: ListModel {
id: model2
ListItem { text: qsTr("meter") }
ListItem { text: qsTr("mile") }
ListItem { text: qsTr("km") }
}
}
}
When current index is selected from first combobox, second combobox should remove the current index. When another index is selected from first, second should restore previous index and it should remove current index dynamically. For example if meter is selected, second combobox should be {"mile", "km"}
I only know a very long way that can be performed with combination of a few index, but my combobox data includes 20 item so I cannot apply this way. Long way:
function visible1(){
if(res_combo1.currentIndex==0){
return true
}
else{
return false
}
}
function visible2(){
if(res_combo1.currentIndex==1){
return true
}
else{
return false
}
}
function visible3(){
if(res_combo1.currentIndex==2){
return true
}
else{
return false
}
}
// if meter is selected from first combobox, second combobox:
RowLayout{
visible: parent.visible1()
ComboBox {
id: outcombo1
currentIndex: 0
model: ListModel {
id: model_o1
ListElement { text: qsTr("mile") }
ListElement { text: qsTr("km") }
}
}
}
// if mile is selected from first combobox:
RowLayout{
visible: parent.visible2()
ComboBox {
id: outcombo1
currentIndex: 0
model: ListModel {
id: model_o2
ListElement { text: qsTr("meter") }
ListElement { text: qsTr("km") }
}
}
}
// if km is selected from first combobox:
RowLayout{
visible: parent.visible3()
ComboBox {
id: outcombo1
currentIndex: 0
model: ListModel {
id: model_o3
ListElement { text: qsTr("meter") }
ListElement { text: qsTr("mile") }
}
}
}
I think we cannot change ListItem dynamically, so JavaScript with JSON list model is required by finding the current index via:
function find(model, criteria) {
for(var i = 0; i < model.count; ++i) if (criteria(model.get(i))) return i
return null
}
But I couldn't do this in QML. Is there any solution? Thanks

Answer 1

You cannot change a ListItem, but you CAN change the ListModel itself.
ListModel {
id: fromModel
ListElement {text: "m" }
ListElement {text: "mile" }
ListElement {text: "km" }
}
ListModel {
id: toModel
function updateModel()
{
// Update model Here
}
}
RowLayout
{
anchors.centerIn: parent
ComboBox
{
id: fromCombobox
model: fromModel
onCurrentIndexChanged: toModel.updateModel()
}
ComboBox
{
id: toComboBox
model: toModel
}
}
This way, every time the first combo changes, the second combo's model will be updated.
Before you update the model 2, check if the previously selected item in combo 2 will still be available after the update, in order to restore it once the model2 is rebuilt.
function updateModel()
{
// Save old selection
var selectedFrom = fromModel.get(fromCombobox.currentIndex).text
if(toComboBox.currentText != selectedFrom)
var valueToRestore = toComboBox.currentText
else
valueToRestore = ""
// Update model
clear()
for(var i=0; i<fromModel.count; i++)
{
if(i == fromCombobox.currentIndex)
continue
append(fromModel.get(i))
}
//Restore selection
for(var i=0; i<toModel.count; i++)
{
// If no value to restore, select first available
if(valueToRestore == "")
{
if(toModel.get(i).text != selectedFrom)
{
toComboBox.currentIndex = i
break
}
}
// Else, restore previously selected item
else
{
if(toModel.get(i).text == valueToRestore)
{
toComboBox.currentIndex = i
break
}
}
}
}