Understanding QML attributes

Circuits

I am stuck on a problem, I will try to explain it. We have a GUI which was put together by another entity. They gave us a great shell but some alterations need to be made. Currently, I am working on the alphanumeric number pad and here is how it is being instantiated in a script called WizardSectionDisplay.qml:

onShowKeyboard: {
                var comp = Qt.createComponent("qrc:/Source//UiControls/WizardPopupKeyboard.qml");
                comp.createObject(application, {
                                      "title": mod_data.label
                                      ,"objectName":"systemDialog"
                                      , "hint": qsTr("Enter a value between %1 and %2").arg(Math.round(mod_data.minValue)).arg(Math.round(mod_data.maxValue))
                                      , "modelButtons": [qsTr("Cancel"), qsTr("Finished")]
                                      , "primaryIndex": 1
                                      , "controlTarget": minMaxSplitBtn
                                      , "settingValue": mod_data
                                  })
            }

so in other words I am adding some functionality to the WizzardPopupKeyboard.qml file. One of the problems I am addressing has to do with the units being displayed. Here, where the object is being created, they are accessing units like so:

mod_data.unit

I am trying to do something similar inside of WizzardPopupKeyboard.qml:

if(mod_Data.unit === "s")
           {
               entryDisplay.text = settingValue.value
           }

this does work, I am getting the functionality I need but for some reason an error is being reported:

ReferenceError: mod_Data is not defined

this seems odd to me because its working despite mod_Data not being defined. Here is how mod_Data is being defined inside of the WizardSectionDisplay.qml:

Loader{
                    id:contentContainer
                    height: parent.height
                    anchors.left: delegateLabel.right
                    anchors.right: parent.right
                    //this is required due to a qml *bug* that will eat the modelData property from the listmodel parent.
                    property variant mod_data: modelData
                    sourceComponent: numberEntry
                }

As you can see it's based off of modelData but modelData is not defined inside of WizardSectionDisplay.qml, in fact, I can't seem to figure out where its being defined. So my question is how can I go about using mod_data in the WizardPopupKeyboard.qml without getting the error?

sierdzio

modelData is a property of all models in QML. See the docs. So I guess that your loader is used as a delegate in some view.

That might explain why mod_data is not always defined - maybe your onShowKeyboard is called before the model is ready, or before the delegate is created etc. Views can create / destroy delegates at any point in time, too, so it might be unreliable depending on them like that. Hard to say for sure as I don't know how your system works in detail - but maybe these hints will help.

Circuits

So that's why modelData is used all over the place. So modelData is only ever used in WizardSectionDisplay.qml after the keyboard is created but mod_data is used throughout the script. One thing I can't seem to understand. During the creation of the keyboard object mod_data is passed as settingValue:

, "settingValue": mod_data

however; I can't seem to use it's unit attribute, for instance if I try:

if(presentationManager.guiSettingsPresenter.model.useUSUnits)
                                {
                                    if(settingValue.unit === "s")
                                    {
                                        true
                                    }

                                    false
                                }

in WizardPopupKeyboard.qml the above code throws no errors but doesn't work. However, if I import the UiControls then, as I showed in the code from my previous post, I can simply call mod_data.unit directly and the it works but throws the error. I would think that they should both work and that they should both throw an error. I even tried passing the units directly:

,  "unit": mod_data.unit

and then calling:

if(presentationManager.guiSettingsPresenter.model.useUSUnits)
                                {
                                    if(unit === "s")
                                    {
                                        true
                                    }

                                    false
                                }

however, that did not work either. I dont understand how I can use settingValue.value, or settingValue.label in WizardPopupKeyboard.qml without any errors but I can't use settingValue.unit... seems odd. In my previous code you can see the comment they left behind during the creation of the mod_data property:

//this is required due to a qml *bug* that will eat the modelData property from the listmodel parent.

perhaps my problem is related?

EDIT: A bit more confused now. Turns out I can access the settingValue.unit but I can't use it in an if statement like I want? To test and see if I have access to .unit I decided to change the text of the . button to:

settingValue.unit

and voila it worked:

PushButton
                        {
                            width: 75
                            height: width
                            text: settingValue.unit //"."
                            enabled:
                            {
                                if(presentationManager.guiSettingsPresenter.model.useUSUnits)
                                {
                                    if(settingValue.unit === "s")
                                    {
                                        true
                                    }

                                    false
                                }
                            }
                            onClicked:
                            {
                                outValue+=".";
                            }
                        }

the keyboard is now showing an s where the period use to be but for some reason the s is still being grayed out... as thought the condition can't be met...

Circuits

Alright, perhaps someone can explain to me why the previous code did not work but this code does:

PushButton
                       {
                           width: 75
                           height: width
                           text: "."
                           enabled:
                           {
                               if(presentationManager.guiSettingsPresenter.model.useUSUnits)
                               {
                                   if(settingValue.unit === "s")
                                   {
                                       true
                                   }
                                   else
                                   {
                                       false
                                   }
                               }
                               else
                               {
                                   true
                               }

                           }
                           onClicked:
                           {
                               outValue+=".";
                           }
                       }

the logic seems to be the same to me but adding these brackets and a few else clauses has fixed the issue. I was under the impression that as long as my logic was only one line then I didn't need the brackets.

fcarney

@Circuits said in Understanding QML attributes:

if(mod_Data.unit === "s")

ReferenceError: mod_Data is not defined

Is this a copy and paste of actual code and is the error code a copy and paste?

Because the code you pasted before has:

"settingValue": mod_data

While the if statement has:

if(mod_Data.unit === "s")

You are mixing variable cases "mod_data" != "mod_Data"

Circuits

@fcarney Yes that was an error on my part. The error message when using mod_data was supposed to be slightly different but I can't remember now what it was.