写在前面

上一篇博客 Flutter实战之一起写个WanAndroid客户端 简单介绍了一下Flutter版本WanAndroid项目，这一篇主要记录项目中碰到的一些问题，避免大家在这些坑中再花太多的时间。

项目地址

github地址 目前已经有54个star，喜欢的话可以给个星鼓励一下

WanAndroid项目Release版运行效果

开发环境搭建及模拟器相关

PANIC: Missing emulator engine program for 'x86' CPU.

在启动模拟器运行Flutter时可能出现如上错误，原因是 Sdk（AndroidSDK安装位置 )/ tools下文件丢失，删除重新安装就好了。步骤如下图：

取消2中Andrid SDK Tools的勾选，然后点击Apply开始卸载，卸载完成之后，勾选Andrid SDK Tools，然后点击Apply开始安装。完成之后重启AndroidStudio(记得重启)

操作图

Error while initializing the Dart VM

Windows开发环境下，Android在打包之后成功之后，安装release版apk时闪退,并且出现错误日志

Error while initializing the Dart VM

可能的原因是flutter sdk的版本不对。我是直接删除了flutter sdk文件下所有文件，然后再次下载 官方地址下最新的sdk(记得是下载官方文档那里的)
https://flutter.io/setup-windows/ 大概20行左右，点击下载安装 然后重启AS，再打包

WanAndroid项目相关

首页直接在MaterialApp中直接使用Navigator.push

class WanAndroidApp extends StatefulWidget {
  @override
  _WanAndroidState createState() => new _WanAndroidState();
}
class _WanAndroidState extends State<WanAndroidApp>
    with TickerProviderStateMixin {

  @override
  Widget build(BuildContext context) {
    initData();
    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
          title: new Text('标题'),
          actions: <Widget>[
            new IconButton(
                icon: new Icon(Icons.search),
                onPressed: () {
Navigator.push(context,new MaterialPageRoute(
                     builder: (context) => new SearchPage()));
                })
          ],
        ),
        body: ...
    );
  }
}

直接点击是搜索按钮，会报错,具体信息如下，为什么呢？

The following assertion was thrown while handling a gesture: Navigator operation requested with a context that does not include a Navigator. The context used to push or pop routes from the Navigator must be that of a widget that is a descendant of a Navigator widget.

Another exception was thrown: Navigator operation requested with a context that does not include a Navigator.

stackoverflow上有人给出了答案，如下

Think of the widgets in Flutter as a tree, with the context pointing to whichever node is being built with the build function. In your case, you have
--------------------------------------------------------------
MainScreen    <------ context
  --> MaterialApp
   (--> Navigator built within MaterialApp)
      --> Scaffold
        --> App Bar
          --> ...
        --> Center
          --> ...
--------------------------------------------------------------
So when you're using the context to find the Navigator, you're using a context for the MainScreen which isn't under the navigator.

意思就是此时Navigator.push(context..中的contexts是MainScreen中的context

来自https://stackoverflow.com/questions/50124355/flutter-navigator-not-working

RefreshIndicator在ListView条目较少时不触发下拉刷新

RefreshIndicator是根据下拉时的偏移量触发刷新，当条目较少时(未占满一个屏幕)，ListView不能滚动，所以无法触发下拉刷新，给ListView的physice属性设置值为new AlwaysScrollableScrollPhysics()，让ListView在任何情况下都可以滑动，也就可以触发RefreshIndicator的刷新。

Widget listView = new ListView.builder(
  //注意这里physics
  physics: new AlwaysScrollableScrollPhysics(),
  itemCount: listData.length,
  itemBuilder: (context, i) => buildItem(i),
  controller: _contraller,
);

TarBarView每次切换时其条目Widget都会执行initState()

在其条目Widget的xxxState方法扩展AutomaticKeepAliveClientMixin，并返回true (看到简书这篇文章才知道)
慎用！！！如果大于等于3个tab，这个有bug，最好不用
当前tab切到任意非相邻tab(如:第一个tab切换到第三个)，会报错

class ArticleListPageState extends State<ArticleListPage>
    with AutomaticKeepAliveClientMixin {

  //  with AutomaticKeepAliveClientMixin 并且get wantKeepAlive返回true,tab切换时,不会每次执行initState
  //来自 https://www.jianshu.com/p/edb741ab5997
  @override
  bool get wantKeepAlive => true;
}

后续会再慢慢完善这篇博客

我的博客 canhuah的博客