Iam using flutter and I am trying to get a value from shared_preferences that I had set before, and display it in a text widget. but i get Instance of Future<String> instead of the value. here is my code:
Future<String> getPhone() async {
final SharedPreferences prefs = await SharedPreferences.getInstance();
final String patientPhone = prefs.getString('patientPhone').toString();
print(patientPhone);
return patientPhone;
}
Future<String> phoneOfPatient = getPhone();
Center(child: Text('${phoneOfPatient}'),))
There is await missing before prefs.getString( and use setState() instead of returning the value. build() can't use await.
String _patientPhone;
Future<void> getPhone() async {
final SharedPreferences prefs = await SharedPreferences.getInstance();
final String patientPhone = await /*added */ prefs.getString('patientPhone');
print(patientPhone);
setState(() => _patientPhone = patientPhone);
}
build() {
...
Center(child: _patientPhone != null ? Text('${_patientPhone}') : Container(),))
}
If you don't have the option to use await or async you can do the following.
getPhone().then((value){
print(value);
});
and then assign a variable to them. From that, you'll have the result from the value.
Related
I have next piece of flutter code, to get shared preference key-value
I do understand why _blueUriInit is always NULL
I assume that you are forgot to provide the value for that key before call to get its value, you need to first assign value to it first:
Future<bool> saveData(String key, dynamic value) async {
final prefs = await SharedPreferences.getInstance();
return prefs.setString(key, value);
}
and call it like this:
void initState() {
saveData('blueUri', 'test');
setState(() {
_blueUriInit = getValue('blueUri');
});
super.initState();
}
now next time you open your app, getValue should return you test.
you can create this function for setting value
static setUserID(String key, String value) async {
final SharedPreferences preferences = await SharedPreferences.getInstance();
preferences.setString(key, value);
}
Use case :
await SharedValue.setUserID("Email", "demo#gmail.com");
And For getting value from shared preference you can use this function
static Future<String?> getUserID(String key) async {
final SharedPreferences preferences = await SharedPreferences.getInstance();
return preferences.getString(key);
}
Use case :
userName = await SharedValue.getUserID("Email");
First you need to setString with key and value (name is key)
Future setValue() async {
final prefs = await SharedPreferences.getInstance();
prefs.setString("name", "Hitarth");
}
getString with key (here i took "name" as key)
Future getValue(String key) async {
final prefs = await SharedPreferences.getInstance();
String value = prefs.getString(key) ?? "NULL";
return value;
}
store in variable callin getValue
void initState() {
setState(() {
_blueUriInit = getValue("name");
});
super.initState();
}
I can't work out how to return a string from a function in Dart (a Flutter app).
I am using SharedPreferences to capture input from the user. I have two functions, one to save preferences:
save(key, value) async {
final prefs = await SharedPreferences.getInstance();
prefs.setString(key, value);
print('saved $value');
}
and one to read preferences:
read(key) async {
final prefs = await SharedPreferences.getInstance();
final value = prefs.getString(key) ?? 0;
print('$value');
}
This is working, but when I try to replace the print line with a return:
read(key) async {
final prefs = await SharedPreferences.getInstance();
final value = prefs.getString(key) ?? 0;
return('$value');
}
to return a string for the value, it throws an error:
type 'Future' is not a subtype of type 'String'
I have tried calling it many MANY different ways, but can't figure out what I assume is an incredibly basic problem. I noticed in some posts that this is a suggested solution, which works to print out the value, but I don't want to print it, i want it as a String variable:
read(mykey).then((value) => '$value');
I need to combine the value with other some other string values and make some minor manipulations (so printing it isn't helpful)
UPDATE
I have defined the function as #Stijn2210 suggested, but am still having problems getting the output i need.
Future<String> read(key) async {
final prefs = await SharedPreferences.getInstance();
final value = await prefs.getString(key) ?? '';
return value;
}
When I call this function from my app (this is a simplified snippet):
void onDragEnd(DraggableDetails details, User user) {
final minimumDrag = 100;
Future<String> myvalue;
if (details.offset.dx > minimumDrag) {
user.isSwipedOff = true;
save(user.imgUrl, 'Dog');
}
myvalue = read(user.imgUrl);
print(myvalue);
It's printing :
Instance of 'Future'
Whereas I want myvalue to be 'Dog'... Appreciate any insights!!
Really appreciate your answer #Stijn2202
Solution was to edit the method definition:
Future<void> onDragEnd(DraggableDetails details, User user) async
and then call the read function from the method with this:
final String myvalue = await read(user.imgUrl);
getString is a Future, which you can handle by using await or as you are doing, using then
However, in my opinion using await is your better option. This would look like this:
Future<String> getMyString() async {
final prefs = await SharedPreferences.getInstance();
final value = await prefs.getString(key) ?? '';
// Don't use 0, since it isnt an int what you want to return
return value;
}
EDIT:
based on your code snippet, this is how you should call your read method:
Future<void> onDragEnd(DraggableDetails details, User user) async {
final minimumDrag = 100;
if (details.offset.dx > minimumDrag) {
user.isSwipedOff = true;
save(user.imgUrl, 'Dog');
}
final String myvalue = await read(user.imgUrl);
print(myvalue);
}
Now I'm not sure if onDragEnd is actually allowed to be Future<void>, but let me know if it isn't
Just await for the value. It will return Dog and not instance of Future.
String someName=await myvalue;
As the value is Future, await keyword will wait until the task finishes and return the value
I've create an initState in my page and call callData to get favId (type : List) every I open this page. But, when the application start, my compiler show this error message :
_TypeError (type 'List<String>' is not a subtype of type 'String')
and this is my getData's function :
getData(favId) async {
SharedPreferences pref = await SharedPreferences.getInstance();
return pref.getStringList(favId);
}
also this is my saveData's function :
void saveData() async {
SharedPreferences pref = await SharedPreferences.getInstance();
pref.setStringList("id", favId);
}
How to fix this problem and I can call getData every I open this page in my application?
Thank you :)
if you want to save and retrieve List to and from SharedPreferences, you to use same key to save and retrieve the value.
here is a simple example,
const favKey = 'favoriteKey';
To save data,
void saveData(String favKey, List<String> favorites) async {
SharedPreferences pref = await SharedPreferences.getInstance();
pref.setStringList(favKey,favorites);
}
To retrive data,
getData(String favKey) async {
SharedPreferences pref = await SharedPreferences.getInstance();
return pref.getStringList(favKey);
}
Note: You need to use same key to set and get data using SharedPreference.
"id" is a String, you need to store a List<String> into setStringList
There are the steps if you want to add an item to the list:
List<String> ids = await getData(favId);
ids.add("id");
saveData(ids, favId);
then change the saveData() to
void saveData(ids, favId) async {
SharedPreferences pref = await SharedPreferences.getInstance();
pref.setStringList(ids, favId);
}
getData()
List<String> getData(favId) async {
SharedPreferences pref = await SharedPreferences.getInstance();
return pref.getStringList(favId);
}
I need to get an URL from Flutter's Shared Preferences widget and insert it into the Image.network widget. So here's the class I created;
class GetSharedPrefs() {
static getCurrentNameSF() async {
String currentname;
SharedPreferences prefs = await SharedPreferences.getInstance();
currentname = prefs.getString("currentname");
print(currentname);
}
}
I tried turning the method into a variable called "spavatar" and inserting it into the build;
String spavatar = GetSharedPrefs.getCurrentNameSF().toString();
inserted into;
icon: Image.network(
spavatar,
),
But it throws the following error:
I/flutter (24368): The following _TypeError was thrown attaching to the render tree:
I/flutter (24368): type 'Future<dynamic>' is not a subtype of type 'String'
So how do I get the result of the function into the Image.network widget which requires a URL? Or is there another way I should do this?
This function must resturn a value and as it async method, it has to be a Future<type>:
class GetSharedPrefs {
static Future<String> getCurrentNameSF() async {
String currentname;
SharedPreferences prefs = await SharedPreferences.getInstance();
currentname = prefs.getString("currentname");
print(currentname);
return currentname;
}
}
Now call:
String spavatar = await GetSharedPrefs.getCurrentNameSF();
getCurrentNameSF() is async, so you can't use it in a synchronous method like the build.
You might want to keep the SharedPreferences instance as a state. To do that though, you have to initialize it in the initState method :
SharedPreferences prefs;
#override
void initState() {
super.initState();
// anonymous async function
() async {
prefs = await SharedPreferences.getInstance();
}();
}
Now you can do :
Image.network(prefs?.getString("currentname") ?? "alternative")
?? is a null-aware operator. It returns the value on the right side if the left one is null.
I used both suggestions in the end. First, declare the variable as a placeholder;
String currentname = "https://example.com/defaultavatar.png";
Then;
SharedPreferences prefs;
#override
void initState() {
super.initState();
() async { prefs = await SharedPreferences.getInstance();
currentname = await prefs.getString("currentname");
}();
}
and then;
Image.network(
currentname ,
height: 30,
width: 30,
),
I have to initialise the state of widget variable with the value stored in StoredProcedure.
void initState() {
widget.query = fetchMake();
super.initState();
}
Future<String> fetchMake() async{
final prefs = await SharedPreferences.getInstance();
return prefs.getString(key);
query.toString();
}
But the issue is that it cant assign that value to query variable and showing error value to type future string cannot assign to string flutter
How can I do that?
fetchMake is async so you have to put await where you call that method but it will not work because you are calling it in initState.
So You have to assign widget.query variable value in that function only. Moreover, as you get data you have to call setState, so data you receive reflect in ui.
In addition to that you have to check query is null or not where you are using it because when first time build method call it will not have any data.
String query;
void initState() {
fetchMake();
super.initState();
}
fetchMake() async{
final prefs = await SharedPreferences.getInstance();
setState((){
query = prefs.getString(key) ?? 'default';
});
}
You can try:
String query;
void initState() {
super.initState();
fetchMake().then((value) {
setState(() {
query = value;
});
});
}
Future<String> fetchMake() async{
final prefs = await SharedPreferences.getInstance();
return prefs.getString(key);
}
1, You can not set state with widget.query.
2, Create a variable query on state of Widget.
3, fetchMake is a async function => using then to wait result.