未为类型“Object”定义运算符“*”。尝试定义运算符“*”错误

问：

        body:Center(
          child: TweenAnimationBuilder(
            tween: Tween(begin: 0.0,end: 1.0),
            duration: Duration(seconds: 4),
            builder: (context,value,child){
              int percentage = (value! * 100).ceil();
              return Container(
                width: size,
                height: size,
                child: Stack(
                  children: [
                    ShaderMask(
                      shaderCallback: (rect){
                        return SweepGradient(
                            startAngle: 0.0,
                            endAngle: TWO_PI,
                            stops: const [0.0,0.5],
                            // 0.0 , 0.5 , 0.5 , 1.0
                            center: Alignment.center,
                            colors: [Colors.blue,Colors.grey.withAlpha(55)]
                        ).createShader(rect);
                      },
                      child: Container(
                        width: size,
                        height: size,
                        decoration: BoxDecoration(
                            shape: BoxShape.circle,
                            image: DecorationImage(image: Image.asset("assets/images/radial_scale.png").image)
                        ),
                      ),
                    ),
                   

int 百分比 = （value！ * 100）.ceil（）;我不能在代码行中做乘法。未为类型“Object”定义运算符 ''。尝试定义运算符 ''。我收到此错误。