Flutter random Image.asset changes on hovering Button? - image

Question

I want to show a random picture everytime the user enters the page. I also have a Button (the red container with hovering) on this page, and when the user is hovering it, a new random picture shows, but it shouldn't change since the page was loaded. I think it has something to do with the setState(), but I don't know what to do. Code:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'dart:core';
import 'dart:math';
class Home2 extends StatefulWidget {
const Home2({Key? key}) : super(key: key);
#override
_Home2State createState() => _Home2State();
}
class _Home2State extends State<Home2> {
dynamic listCinematicImages = [
"assets/cinematic/1.jpg",
"assets/cinematic/2.jpg",
"assets/cinematic/3.jpg",
"assets/cinematic/4.jpg",
"assets/cinematic/5.jpg",
"assets/cinematic/6.jpg",
"assets/cinematic/7.jpg",
];
late Random rnd;
#override
bool isHoveringButton = false;
#override
Widget build(BuildContext context) {
Size size = MediaQuery.of(context).size;
return Scaffold(
backgroundColor: Colors.black,
body: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Container(
height: double.infinity,
width: size.width * 0.5,
alignment: Alignment.center,
child: InkWell(
onTap: () {
},
onHover: (hovering) {
setState(() => isHoveringButton = hovering);
},
child: Container(
height: 50,
width: 50,
color: Colors.red,
),
),
),
Container(
height: double.infinity,
width: size.width * 0.5,
child: img(),
),
],
),
);
}
Image img() {
int min = 0;
int max = listCinematicImages.length-1;
rnd = new Random();
int r = min + rnd.nextInt(max - min);
String image_name = listCinematicImages[r].toString();
return Image.asset(image_name, fit: BoxFit.cover,);
}
}
I dont know if this helps but this is some error given out:
Error: Expected a value of type 'Map<String, dynamic>', but got one of type 'Null'
at Object.throw_ [as throw] (http://localhost:60569/dart_sdk.js:5054:11)
at Object.castError (http://localhost:60569/dart_sdk.js:5013:15)
at Object.cast [as as] (http://localhost:60569/dart_sdk.js:5336:17)
at Function.as_C [as as] (http://localhost:60569/dart_sdk.js:4959:19)

Answer 1

alright there's a lot a things going on here. Let's think about this step by step. You're trying to show a new image on certain events. So we need to create a variable to keep track of the current image:
class Home2 extends StatefulWidget {
const Home2({Key? key}) : super(key: key);
#override
_Home2State createState() => _Home2State();
}
class _Home2State extends State<Home2> {
static const listCinematicImages = [
"assets/cinematic/1.jpg",
"assets/cinematic/2.jpg",
"assets/cinematic/3.jpg",
"assets/cinematic/4.jpg",
"assets/cinematic/5.jpg",
"assets/cinematic/6.jpg",
"assets/cinematic/7.jpg",
];
late String currentImage;
}
before we start worrying about the events, let's figure out how to select a random image from your list. the function you provided has the right elements but there's some funky stuff going on. a simple example I'd give is:
String _getRandomImage() {
final randomIndex = Random().nextInt(listCinematicImages.length-1);
return listCinematicImages[randomIndex];
}
now we have all the elements, we just have to update the widget at the correct time. firstly you want to set a new image every time this widget is loaded. we can do this using the initState method:
#override
void initState() {
super.initState();
final newImage = _getRandomImage();
setState(() => currentImage = newImage);
}
and you want to change the image again when a user hovers over the image. You can indeed do this with an InkWell but keep in mind according to the documentation the onHover will provide a callback every time a mouse enters AND leaves the region, so we have to make sure to only update the image when we enter the region:
InkWell(
onHover: (bool hasEntered) {
if(!hasEntered) return;
final newImage = _getRandomImage();
setState(() => currentImage = newImage);
}
);
And that's it! to put it all together with your example:
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'dart:core';
import 'dart:math';
class Home2 extends StatefulWidget {
const Home2({Key? key}) : super(key: key);
#override
_Home2State createState() => _Home2State();
}
class _Home2State extends State<Home2> {
static const listCinematicImages = [
"assets/cinematic/1.jpg",
"assets/cinematic/2.jpg",
"assets/cinematic/3.jpg",
"assets/cinematic/4.jpg",
"assets/cinematic/5.jpg",
"assets/cinematic/6.jpg",
"assets/cinematic/7.jpg",
];
late String currentImage;
#override
void initState() {
super.initState();
final newImage = _getRandomImage();
setState(() => currentImage = newImage);
}
#override
Widget build(BuildContext context) {
Size size = MediaQuery.of(context).size;
return Scaffold(
backgroundColor: Colors.black,
body: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Container(
height: double.infinity,
width: size.width * 0.5,
alignment: Alignment.center,
child: InkWell(
onHover: (bool hasEntered) {
if(!hasEntered) return;
final newImage = _getRandomImage();
setState(() => currentImage = newImage);
},
child: Container(
height: 50,
width: 50,
color: Colors.red,
),
),
),
Container(
height: double.infinity,
width: size.width * 0.5,
child: Image.asset(currentImage, fit: BoxFit.cover,);,
),
],
),
);
}
String _getRandomImage() {
final randomIndex = Random().nextInt(listCinematicImages.length-1);
return listCinematicImages[randomIndex];
}
}