Question

我有一个BlocBuilder函数，该函数会生成一列要添加到屏幕上的动画的小部件列表：

Center(
child: BlocBuilder<DetectionBloc, DetectionState>(builder: (context, state) {
    if (state is ImageDetectedState) {
    state.detections.forEach((detection) {
        stackItems.add(Positioned(
        left: detection['rect']['x'] * (_keyImageStack.currentContext.findRenderObject() as RenderBox).size.width,
        top: detection['rect']['y'] * (_keyImageStack.currentContext.findRenderObject() as RenderBox).size.height,
        child: AnimatedOpacity(
            opacity: _visible ? 1.0 : 0.0,
            duration: Duration(milliseconds: 2000),
            child: Container(
            color: Colors.pink,
            height: detection['rect']['h'] * (_keyImageStack.currentContext.findRenderObject() as RenderBox).size.height,
            width: detection['rect']['w'] * (_keyImageStack.currentContext.findRenderObject() as RenderBox).size.width,
            ),
        ),
        ));
    });
    }

    return Stack(
    key: _keyImageStack,
    alignment: Alignment.topLeft,
    children: stackItems,
    );
}),

）

问题是，当我触发setState来更改_visible变量时，出现错误： The method 'findRenderObject' was called on null.

floatingActionButton: FloatingActionButton(
onPressed: () {
    setState(() {
    _visible = !_visible;
    });
},
tooltip: 'Toggle Opacity',
child: Icon(Icons.flip),

），

我认为这与使用BlocBuilder创建AnimatedOpacity小部件有关。

还有其他方法可以实现此目的吗，或者有任何变通办法可以使这些动画正常工作？

如何触发setState更改由BlocBuilder创建的小部件中AnimationOpacity的不透明度？

0 个答案: