Align center of an image to the bottom of another image in flutter

Question

Currently I'm facing a problem for creating responsive design in flutter so it could work fine with the same look and feel to all screen sizes

Currently I need to create like the image below, I need the center of an image (the red one in the image below) to be aligned to the bottom of another one (the blue big image) , sometimes the red one is centered but in different screen sizes its either raised a little bit to the top or to the bottom.

This is my attempt:

class ImageAssetUtils 
{
    static Image drawImage(String imagePath, double requiredWidth, double requiredHeight) 
    {
        double screenFactor = 1.0;
        screenFactor = ScreenSize.isSmallScreenSize(myApp.navigatorState.currentContext) ? 0.8 : screenFactor;
        screenFactor = ScreenSize.isLargeScreenSize(myApp.navigatorState.currentContext) ? 1.21 : screenFactor;
        requiredWidth = requiredWidth * screenFactor;
        requiredHeight = requiredHeight * screenFactor;
        return new Image.asset(imagePath, width: requiredWidth, height: requiredHeight);
    }
}

class StyleUtils 
{
    static EdgeInsets givePadding(EdgeInsets absoluteEdges)
    {
        double screenFactor = 1.0;
        screenFactor = ScreenSize.isSmallScreenSize(myApp.navigatorState.currentContext) ? 0.75 : screenFactor;
        screenFactor = ScreenSize.isLargeScreenSize(myApp.navigatorState.currentContext) ? 1.14 : screenFactor;

        double left = absoluteEdges.left * screenFactor;
        double right = absoluteEdges.right * screenFactor;
        double top = absoluteEdges.top * screenFactor;
        double bottom = absoluteEdges.bottom * screenFactor;

        return EdgeInsets.only(left: left, right: right, top: top, bottom: bottom);
    }
}  

class Test extends StatefulWidget 
{
    @override
    _TestState createState() => _TestState();
}

class _TestState extends State<Test> 
{
    @override
    Widget build(BuildContext context)
    {
        return new Scaffold(
            backgroundColor: Color.fromRGBO(235, 235, 235, 1.0),
            body: new Stack(children: <Widget>[
                new Image.asset('some Image.png',
                    fit: BoxFit.fill,
                    width: MediaQuery.of(context).size.width,
                    height: MediaQuery.of(context).size.height * 0.33
                ),
                ListView(children: <Widget>[
                    new Padding(
                        padding: StyleUtils.givePadding(EdgeInsets.only(top: 16.0)),
                        child: new Center(
                            child: new Container(
                                child: ImageAssetUtils.drawImage("my image.png", 100.0, 100.0),
                            ),
                        )
                     )
                ]),
            ])
        );
    }
}

If any help is it will be much appreciated, thanks in advance.

Solution

The FractionalTranslation widget is used to manipulate the position of a child widget. You'll also have to pass an Offset to it, which will define the position manipulation. The child widget would be the red rectangle and the Offset would have the values x: 0.0 and y: 0.5. This would place the red rectangle lower, by the half of its height.

Now you can lay the red rectangle above the blue one. To do this, you can use the Stack widget. You'll have to set alignment: Alignment.bottomCenter, such that the red rectangle is placed at the lower edge in the center.

You can find a code example below. The blue rectangle has a third of the size of the screen. The red rectangle is half as large as the blue one.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(theme: ThemeData(), home: Home());
  }
}

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: BlueRedRects(
          big: MediaQuery.of(context).size.width / 3.0,
          small: MediaQuery.of(context).size.width / 6.0,
        ),
      ),
    );
  }
}

class BlueRedRects extends StatelessWidget {
  final double big;
  final double small;

  BlueRedRects({this.big, this.small});

  @override
  Widget build(BuildContext context) {
    return Stack(
      alignment: Alignment.bottomCenter,
      children: <Widget>[
        Container(color: Colors.blue, width: big, height: big),
        FractionalTranslation(
          translation: Offset(0.0, 0.5),
          child: Container(
            color: Colors.red,
            width: small,
            height: small,
          ),
        )
      ],
    );
  }
}