qml 图片 image 保持宽高比

//main.qml

import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Image {
        id: m_iPdf
        sourceSize.height: 300
        fillMode: Image.PreserveAspectFit   //保持宽高比
        source: "pdf.svg"
    }

}