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Flutter showModalBottomSheet & Textfield 制作底部评论框并解决bug

本文按照由里到外,从简单开始一步步向外的顺序。完整代码在最后一段,处理Textfield与showModalBottomSheet冲突导致键盘遮挡的bug 的代码在倒数第二段

准备

要实现的动画效果


需要用到如下的 widget / attribute / method

bottomNavigationBar
showModalBottomSheet
AnimatedPadding
TextField
复制代码


制作文本框Textfield

Row textField() {  
    return Row(    
        mainAxisAlignment: MainAxisAlignment.spaceBetween,    
        crossAxisAlignment: CrossAxisAlignment.end,    
        children: <Widget>[      
            Expanded(        
                child: new TextField(          
                    decoration: InputDecoration(            
                        hintText: 'Say something here...', //提示文字
                        border: null,            
                        focusedBorder: UnderlineInputBorder( //输入框被选中时的边框样式
                            borderSide: BorderSide(color: Colors.blue[300]),            
                        ),          
                    ),          
                    keyboardType: TextInputType.text, //键盘的类型
                    maxLength: 250, //最多字数
                    maxLines: 10, //最高行数
                ),      
            ),      
            IconButton(        
                icon: Icon(Icons.send),        
                onPressed: () {          
                    Navigator.of(context).pop();        
                },      
            )    
        ],  
    );
}复制代码

首先要使输入框和发布按钮在一行,用Row组件将Textfield & IconButton包裹起来

IconButton 的onPressed方法中 Navigator.of(context).pop(); 使得在点击发送按钮后,可以自动关闭页面

适当调整样式


制作showModalBottomSheet

showModalBottomSheet是从屏幕下方弹出的一个不占用屏幕全部空间的小页面,在显示时屏幕背景会变暗

showModalBottomSheet(    
    context: context,    
    builder: (BuildContext context){      
        return Container(        
            child: textField(),        
            padding: EdgeInsets.all(7), //在textField()的所有方向加7单位的边距(空白)
        );    
    }
);复制代码

此时用了一个Container包裹Textfield目的是为了加边距(当然也有其他的选择)


制作bottomButton

底部评论按钮,要置底,不能随着页面的滑动串位。这时可能考虑到用绝对定位,不过有更好的选择:bottomNavigationBar

在Scaffold中提供了bottomNavigationBar属性,该属性提供了:

BottomNavigationBar用于底部导航栏,BottomAppBar用于底部应用栏

BottomAppBar可以自定义,所以使用它放置底部评论按钮

bottomNavigationBar: BottomAppBar(  
    child: bottomNewCommentButton(),
),复制代码

代码很简单,一目了然


下面构造评论按钮

Container bottomNewCommentButton(){    
    return Container(      
        child: RaisedButton(        
            child: Text("Publish", style: TextStyle(fontSize: 20.0, color: Colors.white)),        
                color: Colors.blue[300],        
                onPressed: () {          
                    showModalBottomSheet(              
                        context: context,              
                        builder: (BuildContext context){                
                            return Container(                  
                                child: textField(),                  
                                padding: EdgeInsets.all(7),                
                            );              
                        }          
                    );        
                },      
            ),      
        height: 50,    
    );  
}复制代码

在onPressed中放入刚才写好的showModalBottomSheet这样点击的时候bottomsheet就会显示出来


解决bug

写到这里应该就会发现Textfield在bottomsheet中的问题:键盘会遮挡bottomsheet



经过测试后发现,添加Textfield焦点是法解决问题的

解决方法:

showModalBottomSheet(    
    context: context,    
    builder: (BuildContext context){      
        return new AnimatedPadding(        
            padding: MediaQuery.of(context).viewInsets,  //边距(必要)
            duration: const Duration(milliseconds: 100), //时常 (必要)
            child: Container(          
                child: textField(),          
                padding: EdgeInsets.all(7),        
            ),      
        );    
    }
);复制代码

showModalBottomSheet中,原有的Textfield组件外嵌套AnimatedPadding,AnimatedPadding其实是缩进变化时的动画,padding和duration是它的必要属性,缺失会报错 

AnimatedPadding api: api.flutter.dev/flutter/wid…


完整代码

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'showModalBottomSheet',
      home: BasicPage(),
    );
  }
}

class BasicPage extends StatefulWidget {
  @override
  _BasicPageState createState() => _BasicPageState();
}

class _BasicPageState extends State<BasicPage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("showModalBottomSheet"),
        ),
        body: Center(

        ),
        bottomNavigationBar: BottomAppBar(
          child: bottomNewCommentButton(),
        ),
    );
  }

  Container bottomNewCommentButton(){
    return Container(
      child: RaisedButton(
        child: Text("Publish", style: TextStyle(fontSize: 20.0, color: Colors.white)),
        color: Colors.blue[300],
        onPressed: () {
          showModalBottomSheet(
              context: context,
              builder: (BuildContext context){
                return new AnimatedPadding(
                  padding: MediaQuery.of(context).viewInsets,
                  duration: const Duration(milliseconds: 100),
                  child: Container(
                    child: textField(),
                    padding: EdgeInsets.all(7),
                  ),
                );
              }
          );
        },
      ),
      height: 50,
    );
  }

  Row textField() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      crossAxisAlignment: CrossAxisAlignment.end,
      children: <Widget>[
        Expanded(
          child: new TextField(
            decoration: InputDecoration(
              hintText: 'Say something here...',
              border: null,
              focusedBorder: UnderlineInputBorder(
                borderSide: BorderSide(color: Colors.blue[300]),
              ),
            ),
            keyboardType: TextInputType.text,
            maxLength: 250,
            maxLines: 10,
          ),
        ),
        IconButton(
          icon: Icon(Icons.send),
          onPressed: () {
            Navigator.of(context).pop();
          },
        )
      ],
    );
  }

}复制代码