Hello all at first I want to mention that I've tried a lot of solutions here but it didn't work for me.
I bring the list from the database through the following code:
var listCat = [];
Future getdata() async {
apiURL = '***************.php';
var response = await http.post(Uri.parse(apiURL));
var responsebody = jsonDecode(response.body);
if (responsebody.length >0){
for (int i = 0; i < responsebody.length; i++) {
listCat.add(responsebody[i]['name']+ ':' + responsebody[i]['image'].toString());
}
return responsebody;
}else{
}
}
As is obvious in the code above I am trying to get the name and image and this is not a problem right now I want to store this listCat in SharedPreferences until I recall it from all pages of the app
I have the following class to save SharedPreferences:
class APIPreferences {
static SharedPreferences ? _preferences;
static const _keyMuinCat = 'MuinCat';
static Future init() async => _preferences = await SharedPreferences.getInstance();
static Future setMuinCat(String MuinCat) async => await _preferences!.setString(_keyMuinCat, MuinCat);
static String? getMuinCat() => _preferences!.getString(_keyMuinCat);
}
Then I save what I need to save by the following line:
APIPreferences.setMuinCat(listCat.toString());
Then I can bring pre-stored data from any location where I need it through the following code:
CatList = APIPreferences.getMuinCat() ?? '';
I tried to do the following thing now to save the list in the first code above:
var listCat = [];
Future getdata() async {
apiURL = '***************.php';
var response = await http.post(Uri.parse(apiURL));
var responsebody = jsonDecode(response.body);
if (responsebody.length >0){
for (int i = 0; i < responsebody.length; i++) {
listCat.add(responsebody[i]['name']+ ':' + responsebody[i]['image'].toString());
APIPreferences.setMuinCat(listCat.toString());
}
return responsebody;
}else{
}
}
But it didn't work. I don't really know how to deal with it.
How can I save it and then bring it to use with ListView.
instead of:
_preferences!.setString(_keyMuinCat, "some string");
use:
_preferences!.setStringList(_keyMuinCat, ["some", "strings", "in", "list"]);
So in your code, the setMuinCat method needs to be:
static Future setMuinCat(List<String> muinCat) async => await _preferences!.setStringList(_keyMuinCat, muinCat);
and then you call it like this:
APIPreferences.setMuinCat((listCat as List).map((v) => v.toString()).toList());
To save the list in shared preferences you need to pass as jsonEncode(yourList data) and when you will fecth the shared list you will again jsonDecode(your list)
await prefs.setString('YOUR KEY', json.encode(YOURMAP()));
Related
I have a list of userIDs and I want to get a value from the database for each user and write it to a new list. But the for loop doesn't wait for the future and throws the error "Unhandled Exception: RangeError (index): Invalid value: Valid value range is empty: 0"
List userIDs = ["gsdgsgsgda32", "gwerszhgda7h", "fsdgz675ehds"];
Future <dynamic> getList() async {
List items=[];
for (var i = 0; i < userIDs.length; i++) {
items[i] = await getUserItems(userIDs[i]);
}
return items;
}
Future <String?> getUserItems(String? _userID) async {
String? userItem=" ";
final FirebaseApp testApp = Firebase.app();
final FirebaseDatabase database = FirebaseDatabase.instanceFor(app: testApp);
database.ref().child('users').child(_userID!).once().then((pdata) {
userItem = pdata.snapshot.child('item').value as String?;
});
return userItem;
}
This is not problem with future. List items is empty so when you call items[0] = 3; there is no items[0] and you get RangeError. Proper way to add element to list is call items.add(3)
So your code should look like this:
List userIDs = ["gsdgsgsgda32", "gwerszhgda7h", "fsdgz675ehds"];
Future <dynamic> getList() async {
List items=[];
for (var i = 0; i < userIDs.length; i++) {
final item = await getUserItems(userIDs[i]);
items.add(item);
}
return items;
}
Future <String?> getUserItems(String? _userID) async {
String? userItem=" ";
final FirebaseApp testApp = Firebase.app();
final FirebaseDatabase database = FirebaseDatabase.instanceFor(app: testApp);
database.ref().child('users').child(_userID!).once().then((pdata) {
userItem = pdata.snapshot.child('item').value as String?;
});
return userItem;
}
By using .then you are telling dart to continue running and come back when the Future completes.
Instead you should use await inside getUserItems.
You have to fiddle around a bit but here's a suggestion to start with:
Future <String?> getUserItems(String? _userID) async {
String? userItem=" ";
final FirebaseApp testApp = Firebase.app();
final FirebaseDatabase database = FirebaseDatabase.instanceFor(app: testApp);
userItem = (await database.ref().child('users').child(_userID!).once()).snapshot.child('item').value as String?
return userItem;
}
Also using String? for userItem and setting it to " " is a bit of an anti pattern. Since you allow it to be nullable i'd suggest having it as null writing your logic around that.
Try to use it like this
Future <dynamic> getList() async {
List items=[];
userIDs.forEach((item) async {
items.add(await getUserItems(item));
});
return items;
}
I have a String List in my shared preferences that's meant to store account numbers which can then be used to make a call from the API:
List<String> accountList = [];
Future _getListData() async {
SharedPreferences myPrefs = await SharedPreferences.getInstance();
for(var i = 0; i < myPrefs.getStringList('accounts').length; i++){
accountList.add(myPrefs.getStringList('accounts')[i]);
}
//prints values from shared preferences
print(accountList);
}
Future<List<dynamic>> fetchData() async {
_getListData();
//prints an empty list
print(accountList);
try {
if (accountList == null) {
var result = await http.get(apiUrl);
List<dynamic> accountInfo = (json.decode(result.body));
return accountInfo;
} else {
List<dynamic> accountInfo = [];
for(var i = 0; i < accountList.length; i++){
var result =
await http.get(apiUrl + "/api/Data/GetCustomer?accntnum=" + accountList[i]);
accountInfo.add(json.decode(result.body));
}
return accountInfo;
}
} catch (e) {
print(e);
}
}
When calling the Future function "fetchData()" from my FutureBuilder in the widget it returns an empty list. However within the scope of the "_getListData()" function it prints the list witht he appropriate values. How can I make it such that "fetchData()" gets the intended list?
Just add an await before _getListData() here:
Future<List<dynamic>> fetchData() async {
await _getListData();
//prints an empty list
print(accountList);
i have a list of volumes that looks like this
['9v9JXgmM3F0C','RoAwAAAAYAAJ','RYAwAAAAYAAJ']
i have a ready funtion that sends Individual volumes and retruns a Map.
Future<BookIdVolume> getBooksByVolume(volume) async {
var searchUrl = 'https://www.googleapis.com/books/v1/volumes/$volume';
var response = await http.get(searchUrl);
var responseBody = jsonDecode(response.body);
return BookIdVolume.fromJson(responseBody);
}
Im trying to create a method to store each of volumes in a list and retrun it.
I have tryed using loops for and forEach but it keeps retruning either [] or null
im i doing somthing wong ? is thier a better better way to do it ?
I'm guessing you're getting null back because you're not building the url properly for each volume. Try this.
final volumeList = ['9v9JXgmM3F0C', 'RoAwAAAAYAAJ', 'RYAwAAAAYAAJ'];
final baseUrl = 'https://www.googleapis.com/books/v1/volumes/';
List<BookIdVolume> bookList = [];
void buildBookList() async {
for (String volume in volumeList) {
final url = '$baseUrl$volume';
final book = await getBooksByVolume(url);
bookList.add(book);
}
}
Then you remove the first line from the getBooksByVolume function because you're already sending the full url.
Future<BookIdVolume> getBooksByVolume(url) async {
var response = await http.get(url);
var responseBody = jsonDecode(response.body);
return BookIdVolume.fromJson(responseBody);
}
I have a scenario where the following function is called again and again whenever the user hits the "Load More" button.
The problem I'm facing is, that it replaces previously loaded data with a new one. Instead, it should add to the bottom of the Listview.Builder
Future fetchData() async{
var url = "url_goes_here";
final response = await http.get(url);
if (response.statusCode == 200) {
var resBody = jsonDecode(response.body);
var data = resBody['data'] as List;
if (data.isNotEmpty) {
setState(() {
listVariable = data
.map<ModelClass>((json) => ModelClass.fromJson(json))
.toList();
});
}
}
}
List<ModelClass> listVariable =List<ModelClass>(); //describe the object that way.
--------and---------
data.map<ModelClass>((json) {
listVariable.add(ModelClass.fromJson(jsonn));
} )).toList();
You should add received data to your listVariable, not assign a new value. Try this code:
final listVariable = <ModelClass>[];
...
Future fetchData() async {
var url = "url_goes_here";
final response = await http.get(url);
if (response.statusCode == 200) {
var resBody = jsonDecode(response.body);
var data = resBody['data'] as List;
if (data.isNotEmpty) {
final list = data.map<ModelClass>((json) => ModelClass.fromJson(json));
setState(() {
listVariable.addAll(list); // HERE: addAll() instead of assignment
});
}
}
}
I was able to figure out answer myself.
setState(() {
listVariable.addAll(data
.map<ModelClass>((json) => ModelClass.fromJson(json))
.toList();
}));
#Mol0ko and #hasan karaman both are right but #Mol0ko
Makes better sense when you have a set of data to addAll to existing data.
I try to use compute in Flutter. Here I try to pass multiple parameters inside a Map. But the code in my function myFunction does not work. I get no errors or something else. My code seems to be ignored. Do you find an error here?
Compute function:
Map map = Map();
map['resultList'] = resultList;
map['_getImageFileFromAssets'] = _getImageFileFromAssets;
map["picturesData"] = picturesData;
map["albumID"] = albumID;
await compute(myFunction, map);
Calls the following function:
Future<bool> myFunction(map) async {
var resultList = map["resultList"];
var _getImageFileFromAssets = map["_getImageFileFromAssets"];
var picturesData = map["picturesData"];
var albumID = map["albumID"];
print("Starten");
for (var i = 0; i < resultList.length; i++) {
print(i);
File imageFile = await _getImageFileFromAssets(resultList[i]);
final appDir = await syspath.getApplicationDocumentsDirectory();
final fileName = path.basename(imageFile.path);
final savedImage =
await File(imageFile.path).copy('${appDir.path}/$fileName');
// Creating thumbnails
final thumb = image.decodeImage(await File(savedImage.path).readAsBytes());
final thumbImage = image.copyResize(thumb, width: 500);
new File('${appDir.path}/$fileName-thumb-500.jpg')
.writeAsBytes(image.encodeJpg(thumbImage));
final finalThumbImage = File('${appDir.path}/$fileName-thumb-500.jpg');
picturesData.add(Picture(
album: albumID,
path: savedImage.path,
thumbPath: finalThumbImage.path,
timestamp: Timestamp.now()));
}
return true;
}
Ok, some code - I put this in dartpad.dev:
import 'package:flutter/foundation.dart';
void main() {
Map map = Map();
compute(myFunction, map).then((result) => print(result));
}
Future<bool> myFunction(Map map) async {
print("Starten");
// fake long process
await Future.delayed(Duration(seconds: 5));
return true;
}
and get this as a console result:
Starten
true
Also: is there a reason you need the "map" parameter in your function to be dynamic? If not, I'd declare it as type Map (like I did now).