颤振 - 在底部绘制一个矩形

Question

我想绘制一个矩形在底部只有Rect对象Rect.fromLTRB没有绘制。

我不知道我是以错误的方式解释Rect对象还是我错误地编写了drawRect对象。

你能帮我画一个矩形的底部吗？

import 'package:flutter/material.dart'; 

void main() { 
    runApp(new MaterialApp(home: new HomePage())); 
} 

class HomePage extends StatefulWidget { 
    @override 
    HomePageState createState() => new HomePageState(); 
} 

class HomePageState extends State<HomePage> { 
    @override 
    Widget build(BuildContext context) { 
    return new Scaffold(
     body: new Stack(
     children: <Widget>[ 
      new Positioned(
      bottom: 0.0, 
      left: 0.0, 
      right: 0.0, 
      top: 0.0, 
      child: new CustomPaint(
       painter: new Sky(), 
      ) 
     ), 
     ] 
    ) 
    ); 
    } 
} 

class Sky extends CustomPainter { 
    @override 
    void paint(Canvas canvas, Size size) { 
    canvas.drawRect(
     new Rect.fromLTRB(
     0.0, 100.0, 0.0, 0.0 
    ), 
     new Paint()..color = new Color(0xFF0099FF), 
    ); 
    } 

    @override 
    bool shouldRepaint(Sky oldDelegate) { 
    return false; 
    } 
} 

Answer 1

你的左和右是相同的（0.0），所以它绘制一个空的矩形。坐标从顶部开始，所以底部应该>顶部;尝试这种

新Rect.fromLTRB（ 0.0，0.0，20.0，100.0 ）

Answer 2

遵循其中矩形是在屏幕的底部的代码：

import 'package:flutter/material.dart'; 
import 'dart:ui' as ui; 

void main() { 
    runApp(new MaterialApp(home: new HomePage())); 
} 

class HomePage extends StatefulWidget { 
    @override 
    HomePageState createState() => new HomePageState(); 
} 

class HomePageState extends State<HomePage> { 

    @override 
    Widget build(BuildContext context) { 
    final ui.Size logicalSize = MediaQuery.of(context).size; 
    final double _width = logicalSize.width; 
    final double _height = logicalSize.height; 
    double _rectHeight = 50.0; 
    return new Scaffold(
     body: new Stack(
     children: <Widget>[ 
      new Positioned(
      bottom: 0.0, 
      left: 0.0, 
      top: _height - _rectHeight, 
      right: 0.0, 
      child: new CustomPaint(
       painter: new Sky(_width, _rectHeight), 
       child: new Text('$_width'), 
      ) 
     ), 
     ] 
    ) 
    ); 
    } 
} 

class Sky extends CustomPainter { 
    final double _width; 
    final double _rectHeight; 
    Sky(this._width, this._rectHeight); 

    @override 
    void paint(Canvas canvas, Size size) { 
    canvas.drawRect(
     new Rect.fromLTRB(
     0.0, 0.0, this._width, _rectHeight 
    ), 
     new Paint()..color = new Color(0xFF0099FF), 
    ); 
    } 

    @override 
    bool shouldRepaint(Sky oldDelegate) { 
    return false; 
    } 
}