Disable TextInput update during editing

[Mark81]

My TextInput is bound to a C++ function, like this:

TextInput {
    text: MyApp.foo()
}

of course, I need to disable updates when editing. I tried something like this:

Item {
    property bool _dirty: false
    property bool _cancel: false
    property string _oldText

    TextInput {
        color: _dirty ? "red" : "forestgreen"
        text: {
            var value = MyApp.foo()
            if (_dirty) {
                if (parseFloat(value) === parseFloat(text)) _dirty = false
                return text

            } else return value === undefined ? "-" : parseFloat(value).toFixed(2)
        }

        Keys.onEscapePressed: {
            _cancel = true
            focus = false
        }

        onEditingFinished: {
            if (_cancel) {
                text = _oldText
                _oldText = ""
                _dirty = false
                _cancel = false

            } else {
                MyApp.write(text)
                focus = false
            }
        }

        onActiveFocusChanged: {
            if (activeFocus) {
                _oldText = text
                selectAll()
                _dirty = true
            }
        }
    }
}

The expected behavior is the following:

1. normally the text is given by the foo() value, green color
2. when the user enter in the fields, the color turns red and you can edit the text
3. if you press 'esc' it ends restoring the previous value and set the green color
4. if you press 'enter' it calls a C++ functions and waits until the foo() value is equal to the inserted one. When this happens it turns green and binds again with the foo value

The problem is it complains about a binding loop for property "text".
It doesn't say the exact line but I might guess is:

return text

I thought to keep the current value it would be enough to return the actual one. Is it wrong?

[Shrinidhi Upadhyaya]

Hi @Mark81 , here is the sample code:-

Rectangle {
        id: root

        height: 100
        width: 100
        color: "transparent"
        border.color: "red"

        property string oldTxt: 'Hello World'

        TextInput {
            id: inpTxt

            color: activeFocus ? "red" : "forestgreen"
            anchors.fill: parent

            Keys.onEscapePressed: {
                focus = false
                root.foo('')
            }

            Keys.onReturnPressed: {
                root.oldTxt = inpTxt.text
                focus = false
                root.foo(text)
            }
        }

        function foo(newText) {
            if(newText === '')
                inpTxt.text = root.oldTxt
            else
                inpTxt.text = newText
        }

        Component.onCompleted: {
            root.foo('')
        }
    }

Note:- as its just a sample code, i have called the javascript function, you need to call the c++ function as you are doing it now.

[Mark81]

@Shrinidhi-Upadhyaya thanks for your hints! Out of curiosity, what should be the return value of a property to maintain the current value?

[Shrinidhi Upadhyaya]

@Mark81 , you mean the current text right?It should be a string :-)

[Mark81]

@Shrinidhi-Upadhyaya said in Disable TextInput update during editing:

@Mark81 , you mean the current text right?It should be a string :-)

I mean, if you have a Text object you can set its text property to any value in two ways:

text: myTextVar

or

text: { return myTextVar }

the second way allows you do to more complex things, i.e.:

text: {
    if (myFooVar === 1) return "blabla"
    else if (myFoo2Var === 10) return myTextVar1
    else return myTextVar2
}

but sometime you might need to leave the value unchanged, I mean keeping the last value. I'm aware I can do it using another variable but it become clumsy:

text: {
    var currText
    if (myFooVar === 1) currText = "blabla"
    else if (myFoo2Var === 10) currText = myTextVar1
    else currText = oldText // keep the current content

    oldText = currText
    return currText
}

I though it was fine and more readable to return the actual value:

text: return text

but it creates a binding-loop error (I hoped this case was handled as an exception in order to keep the current value).
So I wonder if Qt developer provided a way to keep the current value or we need to use another variable like the example above.

[Shrinidhi Upadhyaya]

Hi @Mark81 ,yeah it depends upon how complex things you need to handle, for example if you just need to handle only 2 scenarios like if the value of "myFooVar" is "1", you want to display "Hello" else "Bye" then, you can do like

 text: myFooVar === 1 ? "Hello" : "Bye"

I dont think there is a predefined property or a function to retrieve or store the last value.