How to search for 2 different parameters in a dart list?
Is there a simple method?
Can I solve the problem using contains?
void _runFilter(String searchKeyword) {
List<Product> results = [];
if (searchKeyword.isEmpty) {
results = allProducts;
} else {
results = allProducts.where(
(element) =>
element.name.toLowerCase().contains(searchKeyword.toLowerCase()) || element.image.toLowerCase().contains(searchKeyword.toLowerCase()),
),
)
.toList();
results = results +
allProducts
.where(
(element) => element.image.toLowerCase().contains(
searchKeyword.toLowerCase(),
),
)
.toList();
}
// refresh the UI
setState(() {
filteredProducts = results;
});
}
You can write all sorts of if-else-combinations in a closure. If you use the {} notation instead of => it will become clearer. Something like this will accomplish what you are looking for:
results = allProducts.where( (element) {
if ( element.name.toLowerCase().contains(searchKeyword.toLowerCase()) {
return true;
} else if ( element.image.toLowerCase().contains(searchKeyword.toLowerCase()) {
return true;
} else {
return false;
}
}).toList();
If this step is clear, you can then try to combine individual statements into a boolean combination via || or && if this looks more convenient in your code.
Related
I've a fixed list reservedGuest. After checking the condition in for loop I want to update the seats if the membership date has expired. The list is not updating. The code is as follows. PS. The List is filled through API on init().
class MyClubController extends GetxController {
List goldLane = List.filled(3, null, growable: false);
void _alterLanesOnContractEnds() {
for (var i in goldLane) {
print("\n\n I: $i");
if (i == null ||
DateTime.parse(i['contractEnds']).isBefore(
DateTime.now(),
)) {
i = null;
print('Can be removed');
} else {
print('Cannot be removed');
}
}
update();
}
}
A for-in loop will not allow you to reassign elements of the List. When you do:
for (var i in goldLane) {
// ...
i = null;
}
you are reassigning what the local i variable refers to, not mutating the goldLane List.
You instead can iterate with an index:
void _alterLanesOnContractEnds() {
for (var i = 0; i < goldLane.length; i += 1) {
var element = goldLane[i];
print("\n\n I: $element");
if (element == null ||
DateTime.parse(element['contractEnds']).isBefore(
DateTime.now(),
)) {
goldLane[i] = null;
print('Can be removed');
} else {
print('Cannot be removed');
}
}
update();
}
You can just create a new List where unqualified guests are nullified. For example,
void _alterLanesOnContractEnds() {
goldLane = goldLane.map(
(guest) => guest == null || DateTime.parse(guest['contractEnds']).isBefore(DateTime.now()) ? null: guest
).toList(growable: false);
update();
}
You should not and cannot modify a list while iterating with its iterator.
Elaborated by Jamesdlin,
Modifying the elements of a List while iterating is fine. Modifying
the length of the List while iterating is not, but that won't be a
problem for a non-growable List.
The bottom line is you should not mutate the size of the list while iterating.
I solved it by using
goldLane.forEach(
(element) {
print('\n\n ELEMENT: $element');
if (element == null ||
DateTime.parse(element['contractEnds']).isBefore(
DateTime.now(),
)) {
int ix = goldLane.indexWhere(
(element) => element != null
? DateTime.parse(element['contractEnds']).isBefore(
DateTime.now(),
)
: true,
);
goldLane[ix] = null;
} else {
print('Cannot be removed');
}
},
);
Yet I'll test the other answers. Thank You.
can anyone help me to remove typename and unwanted fields from graph QL from flutter.how to get response as in postman. Iam using the package https://pub.dev/packages/graphql
I had the same issue, I could not find a simple way to disable __typename,
so I wrote a small program,
T removeTypename<T>(T data) =>
_removeUnwantedKeys(data, ['__typename']);
T _removeUnwantedKeys<T>(T data, List keysToRemove) {
if (data is Map && data.containsAnyOf(keysToRemove)) {
Map d = {};
data.forEach((key, value) {
if (!keysToRemove.contains(key)) d[key] = _removeUnwantedKeys(value,keysToRemove);
});
return d as T;
} else if (data is List)
return data.map((c) => _removeUnwantedKeys(c,keysToRemove)).toList() as T;
else
return data;
}
extension MapsMadeEasy<U, V> on Map<U, V>? {
bool containsAnyOf(List keys) {
if (this == null) return false;
return this!.entries.any((element) => keys.contains(element.key));
}
}
I am new in flutter. I want to do for each to check my array JSON. I know typescript is doing like this:
Object.keys(res).forEach(key => {
if (res[key].name === 'Max') {
match = true;
}
});
if (match) {
console.log ('Username has been taken');
} else {
console.log('Username is available');
}
My question is for dart language in Flutter, how to do that?
Please find the below sample code for forEach in dart, which can used in flutter also.
main() {
List<String> list = new List<String>();
list.add('apple');
list.add('ball');
list.add('cat');
list.forEach((element) => print(element));
Set<String> set = Set.from(list);
set.forEach((element) => print(element));
}
try this
var decodedData= json.decode(response.body);
for (var item in decodedDat){
if(item['name'] == 'Max'){
// if true
}
}
The Darty way to test whether an Iterable (and by extension List) contains an element that matches a predicate is with any.
bool match = list.any((s) => s == 'Max');
I want to
1.map item from observable to another one if it has already saved in database.
2.otherwise, use it as it is.
and keep their order in result.
Saved item has some property like tag, and item from observable is 'raw', it doesn't have any property.
I wrote code like this and run testMethod.
class Item {
final String key;
String tag;
Item(this.key);
#override
String toString() {
return ('key:$key,tag:$tag');
}
}
class Sample {
///this will generate observable with 'raw' items.
static Observable<Item> getItems() {
return Observable.range(1, 5).map((index) => Item(index.toString()));
}
///this will find saved item from repository if it exists.
static Future<Item> findItemByKey(String key) async {
//simulate database search
await Future.delayed(Duration(seconds: 1));
if (key == '1' || key == '4') {
final item = Item(key)..tag = 'saved';
return item;
} else
return null;
}
static void testMethod() {
getItems().map((item) async {
final savedItem = await findItemByKey(item.key);
if (savedItem == null) {
print('not saved:$item');
return item;
} else {
print('saved:$savedItem');
return savedItem;
}
}).listen((item) {});
}
The result is not expected one.
expected:
saved:key:1,tag:saved
not saved:key:2,tag:null
not saved:key:3,tag:null
saved:key:4,tag:saved
not saved:key:5,tag:null
actual:
not saved:key:2,tag:null
not saved:key:3,tag:null
not saved:key:5,tag:null
saved:key:1,tag:saved
saved:key:4,tag:saved
How to keep their order in result?
I answer myself to close this question.
According to pskink's comment, use asyncMap or concatMap solve my problem. Thanks!!
below is new implementation of testMethod.
asyncMap version:
getItems().asyncMap((item) {
final savedItem = findItemByKey(item.key);
if (savedItem != null)
return savedItem;
else
return Future.value(item);
}).listen(print);
concatMap version:
getItems().concatMap((item) {
final savedItem = findItemByKey(item.key);
if (savedItem != null)
return Observable.fromFuture(savedItem);
else
return Observable.just(item);
}).listen(print);
I'm developing Angular2 with Meteor.
When I make a little component with a recursive function, it has some weird error.
Here is my part of codes.
Not recursive - return a result
ngOnInit() {
//this.current_canvas return the right results
this.current_canvas = this.get_canvase(1);
}
get_canvase(which_canvas): Canvas[] {
if (!isNaN(which_canvas)) {
this.current_canvas_id = which_canvas;
return CanvasContents.find().map((messages: Canvas[]) => { return messages; })[0].content;
return '';
} else if(which_canvas == 'most-recent') {
this.get_canvase(1);
}
}
Recursive - Don't return a result
ngOnInit() {
//this.current_canvas Goes to NUll
this.current_canvas = this.get_canvase('most-recent');
}
get_canvase(which_canvas): Canvas[] {
if (!isNaN(which_canvas)) {
this.current_canvas_id = which_canvas;
console.log('this.current_canvas_id : ' + this.current_canvas_id);
return CanvasContents.find().map((messages: Canvas[]) => { return messages; })[0].content;
return '';
} else if(which_canvas == 'most-recent') {
this.get_canvase(1);
}
}
Have I used a wrong syntax? or is it on wrong Angular2 state to get right result?