Solved why the property that i defined in type image don't work in animation type?

[stackprogramer]

why the varrible property when i set to fg don't work?but when i set to value 100 it work!!!!!!

        
     Image {

         property int fg: 50;


          source: "Image-Core-Render/image.jpg"
         y: (menuspiral.height)/2
          width: 100; height: 100

          NumberAnimation on x {
              duration:2000
              loops: Animation.Infinite
              running:true
              from: 0; to: fg
          }
      }

[stackprogramer]

finally i define too property int fg in this type NumberAnimation
now it works...

          NumberAnimation on x {
              property int fg
              duration:2000
              loops: Animation.Infinite
              running:true
              from: 0; to: fg
          }