Flutter中比较常见的问题

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1.使用AppBar后如何去掉左边的返回箭头。我们查看原代码

    Widget leading = widget.leading;
    if (leading == null && widget.automaticallyImplyLeading) {
      if (hasDrawer) {
        leading = IconButton(
          icon: const Icon(Icons.menu),
          onPressed: _handleDrawerButton,
          tooltip: MaterialLocalizations.of(context).openAppDrawerTooltip,
        );
      } else {
        if (canPop)
          leading = useCloseButton ? const CloseButton() : const BackButton();
      }
    }
    if (leading != null) {
      leading = ConstrainedBox(
        constraints: const BoxConstraints.tightFor(width: _kLeadingWidth),
        child: leading,
      );
    }

修改方式为, leading为null,automaticallyImplyLeading为false:

appBar: AppBar(
    leading: null,
    automaticallyImplyLeading: false,
)

2. 使用flutter的canvas做文字绘制的时候用到的api为TextPainter

3. 使用flutter绘制控件的时候想做到控件超出屏幕范围后自动换行,那么请参考Wrap,可以轻松实现如下的布局:

4. 要实现类似安卓原生ViewPager的UI,请使用PageView,注意定义自己的PageController,然后可以利用PageController的jumpToPage(int)实现自定义的Page页的跳转

5. 要实现类似顶部和底部导航栏,请参考TabBar,适当的时候可以和AppBar结合使用

6. flutter is a SingleTickerProviderStateMixin but multiple tickers were created. 报错,原因是多个地方调用setState请求重绘,但是state使用的是SingleTickerProviderStateMixin ,将其改成TickerProviderStateMixin即可。

7. 解决类冲突的问题,比如,我自定义一个Banner.dart类,这个类跟系统的Banner冲突,那么我们可以这样解决。
 

import 'package:flutter/material.dart';
import 'package:myproject/Banner.dart' as myproject;
 
//这样使用我们自己的Banner
myproject.Banner _myBanner;
//系统的Banner
Banner _banner;

8. 解决Android手机布局浸入到状态栏的问题,用一个SafeArea进行包装即可,如下:

SafeArea(top: true,
    child: MaterialApp(
        home: ,
    ),
);

9. 在切换tabbar或者pageview的时候要保存上一个tab widget的状态,参考AutomaticKeepAliveClientMixin既可,如下:

//假如PageView有四个子页面
 
 @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: PageView(
          controller: pageController,
          children: <Widget>[
            ArticlesPage(),
            ProjectPage(),
            NavigationPage(),
            CollectionArticlesPage(),
          ],
          onPageChanged: changePage,
        ),
        bottomNavigationBar: Navigations(_page, changePage));
  }
 
 
 
//然后在子Page的State分别实现with AutomaticKeepAliveClientMixin,wantkeepAlive返回true
 
class ArticlesPageState extends State<ArticlesPage> with AutomaticKeepAliveClientMixin{
  @override
  bool get wantKeepAlive => true;
}
 
class ProjectPageState extends State<ProjectPage> with AutomaticKeepAliveClientMixin{
  @override
  bool get wantKeepAlive => true;
}
 
class NavigationPageState extends State<NavigationPage> with AutomaticKeepAliveClientMixin{
  @override
  bool get wantKeepAlive => true;
}
 
class CollectionArticlesPageState extends State<CollectionArticlesPage> with AutomaticKeepAliveClientMixin{
  @override
  bool get wantKeepAlive => true;
}

10. Android手机启动时候白屏的问题解决,android/app/src/main/res/drawable/launch_background.xml中定义了自定义splash的方法:

<?xml version="1.0" encoding="utf-8"?>
<!-- Modify this file to customize your launch splash screen -->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@android:color/white" />
 
    <!-- You can insert your own image assets here -->
    <!-- <item>
        <bitmap
            android:gravity="center"
            android:src="@mipmap/launch_image" />
    </item> -->
</layer-list>

将<item>注释去掉,替换为自己的launcher_image即可 。

11.  界面存在输入框的时候,点击后软键盘将页面顶起来导致页面重绘的问题(Android fitsystem),可以通过将Scaffold的resizeToAvoidBottomPadding属性设置为false来关闭重绘,如下:

return Scaffold(
      resizeToAvoidBottomPadding: false,
);

12. 修改TextFiled的边界宽度,可以通过decoration的contentPadding属性进行修改,如下:

return TextField(
        decoration: InputDecoration(
          contentPadding: EdgeInsets.all(8),
        ),
);

13. 如果想实现一个布局,在某些条件下显示,可以采用Offstage布局,动态控制其offstage属性值即可

14. 如果出现弹出输入法的时候导致Overflow错误,可以将布局镶嵌到SingleChildScrollView中,比如:

return Scaffold(
      body: SingleChildScrollView(
        child: Container(
          constraints: BoxConstraints(
            maxHeight: MediaQuery.of(context).size.height,
            maxWidth: MediaQuery.of(context).size.width,
          ),
        ),
    ),
);

15. GridView的item宽高默认是1:1,可以通过修改childAspectRatio的值来进行宽高的修改,该值代表宽:高

16. flutter中绘制虚线,使用path_drawing

17. flutter 中禁用GridView的滚动,可以使用physics属性,取值为NeverScrollableScrollPhysics(),如下:

GridView.count(
      physics: NeverScrollableScrollPhysics(),
);

18. flutter隐藏状态栏,使用:

SystemChrome.setEnabledSystemUIOverlays([]);

 

 

本文来自:https://blog.csdn.net/email_jade/article/details/85317859

标签:flutter

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