这是我的实现。您只需将按下的点保持在属性中，并相应地计算x，y，width，height，以使宽度和高度为正。

Rectangle {
            id: selectorRectangle
            x: 0
            y: 0
            width: 0
            height: 0
            color: "#8000abcd"
            border.color: "#00fbfb"
        }

        MouseArea {
            anchors.fill: parent
            propagateComposedEvents: true
            property var lastPressPoint: Qt.point(0,0)

            onPressed: {
                lastPressPoint.x = mouse.x;
                lastPressPoint.y = mouse.y;
            }

            onPositionChanged: {
                selectorRectangle.x = Math.min(lastPressPoint.x,mouse.x)
                selectorRectangle.y = Math.min(lastPressPoint.y,mouse.y)
                selectorRectangle.width = Math.abs(lastPressPoint.x - mouse.x);
                selectorRectangle.height =  Math.abs(lastPressPoint.y - mouse.y);
            }
            onReleased: {
                 selectorRectangle.x = 0;
                selectorRectangle.y = 0;
                selectorRectangle.width = 0;
                selectorRectangle.height = 0;
            }
        }