Flutter开发报错和解决

一. flutter: Another exception was thrown: A GlobalKey was used multiple times inside one widget's child list.

1. 错误信息：

flutter: Another exception was thrown: A GlobalKey was used multiple times inside one widget's child list'

添加NavigatorObserver报错.png

2. 原因导致：

我在添加NavigatorOberver时，调用了previousRoute.settings.name。

  MaterialApp (
      ...
      navigatorObservers: [
        GLObserver(),
      ],
)

class GLObserver extends NavigatorObserver {
  @override
  void didPush(Route route, Route previousRoute) {
    // 当调用Navigator.push时回调
    super.didPush(route, previousRoute);
    //可通过route.settings获取路由相关内容
    //route.currentResult获取返回内容
    //....等等
    print('didPush' + route.settings.name +  previousRoute.settings.name);
  }

  @override
  void didPop(Route route, Route previousRoute) {
    super.didPop(route, previousRoute);
    print('didPop' + route.settings.name);
  }
}

3. 深入分析：

然后我发现，具体得原因是因为第一次打开应用的时候，previousRoute是null，然后调用了一个为null变量的属性，就会报上述错误。我改为如下代码验证一下：

class GLObserver extends NavigatorObserver {

  @override
  void didPush(Route route, Route previousRoute) {
    super.didPush(route, previousRoute);
   if (previousRoute == null) {
      print('null');
    }else {
      print(previousRoute);
      print('notNull');
    }
    //  验证代码
    var ddd = null;
    print(ddd.sdd);
  }

然后运行，最后报的错误信息一样

flutter: Another exception was thrown: A GlobalKey was used multiple times inside one widgets child list.
flutter: Another exception was thrown: A GlobalKey was used multiple times inside one widgets child list.

但是这次又新的发现，就是拉到报错信息的开始，发现flutter是给出了具体报错的详细信息的。😳，原先我一直没往上拉。

2019-04-12 09:47:21.158308+0800 FlutterMix[34482:2965311] flutter: ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
2019-04-12 09:47:21.163617+0800 FlutterMix[34482:2965311] flutter: The following NoSuchMethodError was thrown building CupertinoTheme:
2019-04-12 09:47:21.163807+0800 FlutterMix[34482:2965311] flutter: The getter 'sdd' was called on null.
2019-04-12 09:47:21.163951+0800 FlutterMix[34482:2965311] flutter: Receiver: null
2019-04-12 09:47:21.164111+0800 FlutterMix[34482:2965311] flutter: Tried calling: sdd
2019-04-12 09:47:21.166094+0800 FlutterMix[34482:2965311] flutter:
2019-04-12 09:47:21.166236+0800 FlutterMix[34482:2965311] flutter: When the exception was thrown, this was the stack:

4. 解决办法：

相信看到这里，都知道怎么解决了，调用属性之前判断是否为null即可。

二、Unhandled Exception: type '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, dynamic>'

报错：Map的类型不对

// 错误
Unhandled Exception: type '_InternalLinkedHashMap<dynamic, dynamic>' is not a subtype of type 'Map<String, dynamic>'

解决办法：转换一下 😁

new Map<String, dynamic>.from(snapshot.value);

三、 Text控件设置连续的多个空格

可用在显示时，首行文本头部缩进或者其它用处。

 (listBean.defaultFlag == 1 ? '''          ''' : "") + listBean.addressStr,

解决办法：使用三个点语法