How to make a resizable rectangle in QML?

There are probably several ways to achieve the desired result. Since I've considered the implementation of a similar Component for a cropping tool software of mine, I'm going to share a toy example which uses part of that code.

Differently from the rubber band in the example, my Rectangle is resizable only on a single axis at a time. I'm confident that you can build on that and customise the code to meet your needs.

The basic idea of the code is to exploit the drag property of MouseArea. It can be used to move around the Rectangle and, combined with MouseX and MouseY properties, resize it.

Dragging is active inside the Rectangle whereas resizing is active on the knobs set on the sides of the Rectangle (no mouse cursor change is set for the sake of brevity).

import QtQuick 2.4
import QtQuick.Controls 1.3

ApplicationWindow {
    title: qsTr("Test Crop")
    width: 640
    height: 480
    visible: true
    property var selection: undefined

    Image {
        id: image1
        anchors.fill: parent
        source: "http://cdn.cutestpaw.com/wp-content/uploads/2013/01/l-Kitty-attack.jpg"

        MouseArea {
            anchors.fill: parent
            onClicked: {
                if(!selection)
                    selection = selectionComponent.createObject(parent, {"x": parent.width / 4, "y": parent.height / 4, "width": parent.width / 2, "height": parent.width / 2})
            }
        }
    }

    Component {
        id: selectionComponent

        Rectangle {
            id: selComp
            border {
                width: 2
                color: "steelblue"
            }
            color: "#354682B4"

            property int rulersSize: 18

            MouseArea {     // drag mouse area
                anchors.fill: parent
                drag{
                    target: parent
                    minimumX: 0
                    minimumY: 0
                    maximumX: parent.parent.width - parent.width
                    maximumY: parent.parent.height - parent.height
                    smoothed: true
                }

                onDoubleClicked: {
                    parent.destroy()        // destroy component
                }
            }

            Rectangle {
                width: rulersSize
                height: rulersSize
                radius: rulersSize
                color: "steelblue"
                anchors.horizontalCenter: parent.left
                anchors.verticalCenter: parent.verticalCenter

                MouseArea {
                    anchors.fill: parent
                    drag{ target: parent; axis: Drag.XAxis }
                    onMouseXChanged: {
                        if(drag.active){
                            selComp.width = selComp.width - mouseX
                            selComp.x = selComp.x + mouseX
                            if(selComp.width < 30)
                                selComp.width = 30
                        }
                    }
                }
            }

            Rectangle {
                width: rulersSize
                height: rulersSize
                radius: rulersSize
                color: "steelblue"
                anchors.horizontalCenter: parent.right
                anchors.verticalCenter: parent.verticalCenter

                MouseArea {
                    anchors.fill: parent
                    drag{ target: parent; axis: Drag.XAxis }
                    onMouseXChanged: {
                        if(drag.active){
                            selComp.width = selComp.width + mouseX
                            if(selComp.width < 50)
                                selComp.width = 50
                        }
                    }
                }
            }

            Rectangle {
                width: rulersSize
                height: rulersSize
                radius: rulersSize
                x: parent.x / 2
                y: 0
                color: "steelblue"
                anchors.horizontalCenter: parent.horizontalCenter
                anchors.verticalCenter: parent.top

                MouseArea {
                    anchors.fill: parent
                    drag{ target: parent; axis: Drag.YAxis }
                    onMouseYChanged: {
                        if(drag.active){
                            selComp.height = selComp.height - mouseY
                            selComp.y = selComp.y + mouseY
                            if(selComp.height < 50)
                                selComp.height = 50
                        }
                    }
                }
            }


            Rectangle {
                width: rulersSize
                height: rulersSize
                radius: rulersSize
                x: parent.x / 2
                y: parent.y
                color: "steelblue"
                anchors.horizontalCenter: parent.horizontalCenter
                anchors.verticalCenter: parent.bottom

                MouseArea {
                    anchors.fill: parent
                    drag{ target: parent; axis: Drag.YAxis }
                    onMouseYChanged: {
                        if(drag.active){
                            selComp.height = selComp.height + mouseY
                            if(selComp.height < 50)
                                selComp.height = 50
                        }
                    }
                }
            }
        }
    }
}

A screenshot of the example: