Qt Quick Demo - Calqlatr

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 import QtQuick
 import QtQuick.Window

 Item {
     id: display
     property real fontSize: Math.floor(Screen.pixelDensity * 5.0)
     property bool enteringDigits: false
     property int maxDigits: (width / fontSize) + 1
     property string displayedOperand
     property string errorString: qsTr("ERROR")
     property bool isError: displayedOperand === errorString

     function displayOperator(operator)
     {
         listView.model.append({ "operator": operator, "operand": "" })
         enteringDigits = true
         listView.positionViewAtEnd()
     }

     function newLine(operator, operand)
     {
         displayedOperand = displayNumber(operand)
         listView.model.append({ "operator": operator, "operand": displayedOperand })
         enteringDigits = false
         listView.positionViewAtEnd()
     }

     function appendDigit(digit)
     {
         if (!enteringDigits)
             listView.model.append({ "operator": "", "operand": "" })
         var i = listView.model.count - 1;
         listView.model.get(i).operand = listView.model.get(i).operand + digit;
         enteringDigits = true
         listView.positionViewAtEnd()
     }

     function setDigit(digit)
     {
         var i = listView.model.count - 1;
         listView.model.get(i).operand = digit;
         listView.positionViewAtEnd()
     }

     function clear()
     {
         displayedOperand = ""
         if (enteringDigits) {
             var i = listView.model.count - 1
             if (i >= 0)
                 listView.model.remove(i)
             enteringDigits = false
         }
     }

     // Returns a string representation of a number that fits in
     // display.maxDigits characters, trying to keep as much precision
     // as possible. If the number cannot be displayed, returns an
     // error string.
     function displayNumber(num) {
         if (typeof(num) != "number")
             return errorString;

         var intNum = parseInt(num);
         var intLen = intNum.toString().length;

         // Do not count the minus sign as a digit
         var maxLen = num < 0 ? maxDigits + 1 : maxDigits;

         if (num.toString().length <= maxLen) {
             if (isFinite(num))
                 return num.toString();
             return errorString;
         }

         // Integer part of the number is too long - try
         // an exponential notation
         if (intNum == num || intLen > maxLen - 3) {
             var expVal = num.toExponential(maxDigits - 6).toString();
             if (expVal.length <= maxLen)
                 return expVal;
         }

         // Try a float presentation with fixed number of digits
         var floatStr = parseFloat(num).toFixed(maxDigits - intLen - 1).toString();
         if (floatStr.length <= maxLen)
             return floatStr;

         return errorString;
     }

     Item {
         id: theItem
         width: parent.width + 32
         height: parent.height

         Rectangle {
             id: rect
             x: 16
             color: "white"
             height: parent.height
             width: display.width - 16
         }
         Image {
             anchors.right: rect.left
             source: "images/paper-edge-left.png"
             height: parent.height
             fillMode: Image.TileVertically
         }
         Image {
             anchors.left: rect.right
             source: "images/paper-edge-right.png"
             height: parent.height
             fillMode: Image.TileVertically
         }

         Image {
             id: grip
             source: "images/paper-grip.png"
             anchors.horizontalCenter: parent.horizontalCenter
             anchors.bottom: parent.bottom
             anchors.bottomMargin: 20
         }

         ListView {
             id: listView
             x: 16; y: 30
             width: display.width
             height: display.height - 50 - y
             delegate: Item {
                 height: display.fontSize * 1.1
                 width: parent.width
                 Text {
                     id: operator
                     x: 6
                     font.pixelSize: display.fontSize
                     color: "#6da43d"
                     text: model.operator
                 }
                 Text {
                     id: operand
                     font.pixelSize: display.fontSize
                     anchors.right: parent.right
                     anchors.rightMargin: 22
                     text: model.operand
                 }
             }
             model: ListModel { }
         }

     }

 }