更改GridView.count的填充时出现Flutter抛出异常

Question

我正在尝试在我的应用程序中使用gridview。但是每当我将gridview的padding更改为20.0时，都会引发异常：

Another exception was thrown: SliverGeometry is not valid: The "maxPaintExtent" is less than the "paintExtent".

这是异常的详细版本：

I/flutter (18662): The following assertion was thrown during performLayout():
I/flutter (18662): SliverGeometry is not valid: The "maxPaintExtent" is less than the "paintExtent".
I/flutter (18662): The maxPaintExtent is 239.28571428571428, but the paintExtent is 239.2857142857143. Maybe you have
I/flutter (18662): fallen prey to floating point rounding errors, and should explicitly apply the min() or max()
I/flutter (18662): functions, or the clamp() method, to the paintExtent? By definition, a sliver can't paint more than
I/flutter (18662): the maximum that it can paint!
I/flutter (18662): The RenderSliver that returned the offending geometry was:
I/flutter (18662):   RenderSliverGrid#80894 relayoutBoundary=up2 NEEDS-LAYOUT NEEDS-PAINT
I/flutter (18662):   creator: SliverGrid ← SliverPadding ← Viewport ← _ScrollableScope ←
I/flutter (18662):   IgnorePointer-[GlobalKey#12cb3] ← Semantics ← Listener ← _GestureSemantics ←
I/flutter (18662):   RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#74675] ←
I/flutter (18662):   _ScrollSemantics-[GlobalKey#bd1a3] ← RepaintBoundary ← CustomPaint ← ⋯
I/flutter (18662):   parentData: paintOffset=Offset(80.0, 80.0) (can use size)
I/flutter (18662):   constraints: SliverConstraints(AxisDirection.down, GrowthDirection.forward, ScrollDirection.idle,
I/flutter (18662):   scrollOffset: 0.0, remainingPaintExtent: 310.0, crossAxisExtent: 280.0, crossAxisDirection:
I/flutter (18662):   AxisDirection.right, viewportMainAxisExtent: 330.0, remainingCacheExtent: 560.0 cacheOrigin: 0.0 )
I/flutter (18662):   geometry: SliverGeometry(scrollExtent: 239.3, paintExtent: 239.3, maxPaintExtent: 239.3,
I/flutter (18662):   hasVisualOverflow: true, cacheExtent: 239.3)
I/flutter (18662):   currently live children: 0 to 39

这是我的应用的外观，其网格视图填充为20.0：

这是我的代码：

return new Container(
  child: new SafeArea(
    child: new Column(

      crossAxisAlignment: CrossAxisAlignment.center,
      children: <Widget>[
        new Container(
          color: Colors.red[900],
          child: new SizedBox(
            width: MediaQuery.of(context).size.width,
            height: 158.0,
            child: new Center(
              child: new Text('Hello World', style: new TextStyle(fontFamily: 'RobotoCondensed', fontSize: 25.0, color: Colors.white))
              )
            )
          ),

        new Expanded(

          child: new GridView.count(
            padding: new EdgeInsets.all(20.0),
            mainAxisSpacing: 5.0,
            crossAxisSpacing: 5.0,
            crossAxisCount: 7,

            children: List.generate(40, (index){
              return new Container(
                color: Colors.pink[300],
                );
              }
              )
            ) //GridView

          ),



      ]
      ), 
    )

  );

但是当我将gridview填充更改为50.0或80.0时，它不会引发异常。

这是我的应用的外观，其网格视图填充为50.0：  

我已经看到一些与this相关的错误。

该异常表明，也许我已成为浮点数舍入错误的牺牲品，应该将min（）或max（）函数或钳位（）方法显式应用于paintExtent。

但是我应该在哪里找到这个paintExtent变量？我在GridView.count中找不到它。

我将不胜感激。