Get value from Instance in Flutter

Question

I am making a search request on the List with the Provider pattern.

List<Device> _devices = [
    Device(one: 'Apple', two: 'iphone'),
    Device(one: 'Samsung', two: 'Galaxy')
];

And Query is like this

List<Device> queryQuery(String value) {
return _devices
    .where((device) => device.one.toLowerCase().contains(value.toLowerCase()))
    .toList();

the result I expect to get is iphone when I passed the value Apple.

But the result on the screen that I got is [instance of ‘Device’] when I code like this

child: Text('${deviceData.getDevice('Apple')}'

I do know I should be using some kind of key using two... but I have no idea :-(

override toString() method for Device object

Alexey Filippov
– Alexey Filippov

2020-02-17 15:28:47 +00:00
Commented Feb 17, 2020 at 15:28 — Alexey Filippov
– Alexey Filippov, Commented Feb 17, 2020 at 15:28

Rémi Rousselet · Accepted Answer · 2020-02-17 15:39:45Z

3

You serialized the wrong object.

What you did end-up being similar to:

Text(Device(one: 'Apple', two: 'iphone').toString());

But you don't want to do Device.toString(). What you want instead is to pass Device.two to your Text.

As such your end result is:

Text('${chordData.chordExpand('Apple').two}')

answered Feb 17, 2020 at 15:39

Rémi Rousselet

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3 Comments

Brooklyn Lee Over a year ago

Like you said, I want to pass Device.two value to Text on the screen. But the query above returns List<Device> value and returns The getter two isn't defined for the class 'List<Device>'. error. The same errror comes when I changed the query type to Text ... The getter two isn't defined for the class 'String

Rémi Rousselet Over a year ago

Then do a .map((device) => device.two)

Brooklyn Lee Over a year ago

Hello, would you help me solve this issue? stackoverflow.com/questions/60386200/…

Dharman · Accepted Answer · 2020-02-17 21:21:50Z

1

By the look of [Instance of 'Device'], it seems the function is returning a list so it is a good idea to check if the list is empty or not. if it is not empty, one of the elements is still needed to be selected. I guess it should be Text('${chordData.chordExpand('Apple')[0].two}') in case the list is not empty.

To summarize, use something like this to handle the case when list is empty

// Inside your build method before returning the widget
var l = chordData.chordExpand('Apple'); // Returns a list of devices
String textToWrite; // Here we will store the text that needs to be written
if(l.isEmpty) textToWrite = 'No results'; // If the filter resulted in an empty list
else textToWrite = l[0].two; // l[0] is an instance of a device which has a property called two. You can select any instance from the list provided it exists

return <Your Widget>(
.....
Text(textToWrite),
.....
);

edited Feb 17, 2020 at 21:21

Dharman♦

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answered Feb 17, 2020 at 15:55

Afridi Kayal

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1 Comment

Brooklyn Lee Over a year ago

Thanks. it worked when I do .map((device) => device.two). I will add a empty check function in case the list is empty.

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