I'm using sqflite in flutter for mobile devices's local database.
I made a test table and I success print a table's value using 'debugprint'.
But I can not print the value in device's screen. Maybe because asynchronous? (I don't know exactly)
I want to print the value in screen.
This is my source code.
This is a scaffold's body
body: Center(
child: Column(
children: <Widget>[
new Text( getFirst().toString() ),
],
),
),
And this is a function. debugPrint's value is what I wanted.
Future<String> getFirst() async {
final List<Map<String, dynamic>> maps = await _databaseHelper.db.rawQuery(
" SELECT attr1 FROM Test_t");
debugPrint(maps.toString());
return maps.toString();
}
You can't print the value as it's asynchronous. getFirst() - returns a future, to retrieve value you need to await for it.
There are few ways to do that:
FutureBuilder https://flutterigniter.com/build-widget-with-async-method-call/
https://flutter.dev/docs/development/ui/widgets/async
Could also use states to do that...
Related
Goodmorning,
I'm developing an app with flutter but I'm facing some problems with Provider (I think something miss in my knowledge).
My app fetch data from my API and displays them in listview.
In whole app I have different screen which displays different data type in listview and now I want to create filtering logic.
To avoid rewrite same code multiple times I thought to create one screen to reuse for filtering purposes but I'm facing problems with state management.
What I did:
create base model for filter information
`
enum FilterWidget { TEXT_FIELD, DROPDOWN } //to resolve necessary Widget with getWidget() (to implement)
class FilterBaseModel with ChangeNotifier {
String? value= 'Hello';
FilterWidget? widgetType;
FilterBaseModel(this.value, this.widgetType);
onChange() {
value= value== 'Hello' ? 'HelloChange' : 'Hello';
notifyListeners();
}
}
`
One screen for display filters depending on request
List<FilterBaseModel> filters = [];
FilterScreen() {
//Provided from caller. Now here for test purposes
filters.add(FilterBaseModel('Filter1', FilterWidget.TEXT_FIELD));
filters.add(FilterBaseModel('Filter2', FilterWidget.TEXT_FIELD));
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: SafeArea(
minimum: EdgeInsets.symmetric(vertical: 15, horizontal: 15),
child: SingleChildScrollView(
child: Container(
height: 400,
child: Column(
children: filters
.map(
(e) => Consumer<FilterBaseModel>(
builder: (_, filter, child) =>
ChangeNotifierProvider.value(
value: filter,
child: CustomTextField(
`your text` initialText: e.value,
onTap: () {
e.onChange();
filter.onChange();
},
),
),
),
)
.toList(),
))),
),
);
}
`
The problem is in Consumer and ChangeNotifier.value.
Screen works quite well: widget are displayed and callback are called, what is wrong? I need to use onChange method of both instance to update UI otherwhise method was called but widget is not rebuilt.
I know that probably putting consumer there is not right way but I tried also to put outside but doesn't work.
I expect to have one filter screen which receives in input filters list information, display them, handle their state managment and return their value.
P.S: this code now works, but I know is not the right way
Thank you for help!
EDIT
Have same behaviour without ChangeNotifierProvider.value. Therefore I'm more confused than before because still persist the double call to onChange for correct rebuilding.
More bit confused about ChangeNotifierProvider.value using...
I have a hive box opened in the main.dart and set it to a global variable so am able to access it from all other classes.
Now in one of my classes (settingsView.dart) which is a StatefulWidget am able to put data in the box in the form Map<String,Map<String,dynamic>>. To be specific the Map<String,dynamic> can be a Map<String,String> or Map<String,List>. e.g.
{"1A":{"num_on_roll": "34", "subjects": ["Mathematics","English","Science",...]}}
Now am also retrieving or reading this data and to display it in the UI the "num_on_roll" value in a Text widget and "subjects" value in a Wrap.
NOW THE PROBLEM.
The first ("num_on_roll") is always updated in the UI successfully but the "subjects" values in the Wrap are never updated unless I do hot restart or quit application and start it afresh, by so doing all data will be displayed successfully.
I have tried using ValueListenableBuilder to listen for changes in the box.
"class_constants" is the specific for the stored data which is Map<String,Map<String,dynamic>>.
ValueListenableBuilder(
valueListenable: Hive.box("mainDB").listenable(keys: ["class_constants"]),
builder: (context,Box box,child) {
var clsConst = box.get("class_constants", defaultValue: {});
return Wrap(
children: List.generate(
isPresent
? clsConst[classes[tab]]["subjects"].length
: selectedSubjects.length,
(index) => Text(
"${isPresent ? clsConst[classes[tab]]["subjects"][index] : selectedSubjects[index]}, ",
style: const TextStyle(
fontWeight: FontWeight.bold,
fontStyle: FontStyle.italic),
)),
);
}
),
Why is it that the data is store successfully but not displaying some part?
Please help me out.
I found the proper solution myself.
Hive has problem retrieving growable list immediately it has been put in the box. Even you must await it else it can't store!
So trick is to change growable list to non-growable list.
List list = [];
list.add(1);
list.add(2);
list.add(3);
// non-growable
List tempList = List.generate( list.length, (_)=> list[_], growable: false);
mainDB!.put('key',tempList)
;
I want to make an editable TextWidget in flutter but I don't really know how to go around it, I did some research, but still can't find a good solution.
Here's my sample code below.
I have a variable called
int qty = 1;
and so I called the variable in TextWidget
Column(
children: [
Text(
"${qty}",
style: TextStyle(),
)
],
),
I want to have these features that make user tab on the value to change it if they want, upon tap, a pop-up dialog will show to give the user the ability to change the existing value to whatever the user wants.
Please if anyone knows how, please help.
You will need a statfull widget to call setState and make the UI update with the new value stored in your qty variable. (I'am assuming that you are not using any state managment).
I wrote a possible solution for what you need.
Let look into some considerations:
Text will show whatever is in the qty as long we call setState after (or do it inside) we change the value of qty.
You need some widget to detect your tap. If you want to the text be 'clicable' then it should be wraped inside that widget.
The onTap/onPress call back of that widget should show a new widget. For this you can use the already made showDialog() and pass it a Dialog Widget. in here you will put your ui for that.
In some point of that UI you need to introduce the new value. So you can use a simple TextField that will save the introduced value, where you can assign it to qty, without forgetting to call setState! Note that it deal with strings, so you neet to do an int.parse() ou double.parse accordingly to you qty var type.
And I think that's it.
The could be other ways of doing it. This is a good and simple approach for your need.
I wrote a piece of code to help or somelse how is trying to do it:
InkWell(
// can be gesture detector, button, etc
onTap: () => showDialog(
context: context,
builder: (context) => Dialog(
child: Container(
color:
Colors.white60, // change it accordingly to you
height: 80, // change it accordingly to you
width: 200, // change it accordingly to you
child: Column(
children: [
const Text('Change your value here'),
TextField(
decoration:
InputDecoration(hintText: qty.toString()),
onChanged: (insertValue) => setState(() {
qty = int.parse(insertValue);
}),
// you can use other callBack function (like onComplete,
// onSaved), wich is more eficient than calling setState eveytime,
// but you have to do the needed adtaptions. Like onSave
// needs a key to call the save function. is easy just google it.
),
],
)),
)),
child: Text(
"${qty}",
),
),
What you are probably looking is a DropdownButton.
You would have something like this:
int qty = 1;
List<int> listOfValues = [1,2,3,4];
and then in your column you would have
DropdownButton<int>(
// This are the list of items that will appear in your dropdown menu.
// items is all the options you want your users to be able to select from,
// and it take a list of `DropdownMenuItem`. So instead of creating a `DropdownMenuItem`
// for each of the items in `listOfValues`, we iterate through it and return
// a `DropdownMenuItem`
items: listOfValues
.map((item) => DropdownMenuItem<int>(
value: item,
child: Text('$item'),
))
.toList(),
value: qty,
onChanged: (value) {
if (value != null) {
setState(() {
qty = value;
});
}
},
),
For more information on DropDownButton, check the following links:
https://api.flutter.dev/flutter/material/DropdownButton-class.html
https://www.youtube.com/watch?v=K8Y7sWZ7Q3s
Note: In a scenario where you want to increase the quantity of an item, like in a shopping cart, maybe having a button increment qty by 1 would be better.
I wanted to keep the time data stored in the mobile localcaly so when ever the app is closed and open backed i want it to be shown. that part works but when ever the button is pressed to set new time it wont update to the newly set sharedprefence to show instead of the load or the new time.
This is the function that runs every time the button is being pressed
void timeInPush()async{
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
String now =await new DateFormat.yMd().add_Hm().format(new DateTime.now());
String day =await new DateFormat.d().add_Hm().format(new DateTime.now());
sharedPreferences.setString("timeIn", now);
sharedPreferences.setString("timeOut",null);
sharedPreferences.reload();
}
This is the function for the Future builder
Future <String> timeShowtimein()async{
SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
return Future.delayed(Duration(seconds: 1),()async{
return await sharedPreferences.getString("timeIn");
});
}
And here is the UI builder
Container timeText(){
return Container(
child:Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
FutureBuilder(
future:timeShowtimein() ,
builder: (context, snapshot){
if(snapshot.hasData){
return Text("${snapshot.data}");
}else{
return Text("Loading");
}
}),
SizedBox(
width:20,
),
Text("$Timeout",style:TextStyle(
color: Colors.redAccent,
fontSize: 15.0))
],
)
);
}
Calling timeInPush() sets the values in the Shared Preferences. The problem is that it does not let the FutureBuilder know that changes have occurred.
sharedPreferences.reload() re-syncs the preferences with the native application to make sure that there are no pending changes in the dart side of things (It is stated in the documentation)
Try converting your widget to stateful and call setState(() { }) in the timeInPush() method after setting the values. This might force a rebuild and fire up the future builder again.
The problem is that it might show loading for a frame or two every time the widget rebuilds. You can fix this using initialData property = an additional variable that you might need to update manually every time you set the values in shared prefs but that will just make the code more complex. Moreover, every time you update the sharedPrefs, you will need to call setState to force the rebuild.
I will recommend rx_shared_preferences package. It's built on top of shared_preferences package and has the ability to work with streams. With StreamBuilder, you only need to update the SharedPreferences and the rebuilds inside the stream builder will be made automatically.
i want to change displayed data in Flutter? I wrote a function changeDataForTest (only a function for testing the event), which should change the data displayed in Text.
But if I click on this, it isn't changed. The value of the displayed string only changes, if i add (context as Element).reassemble(); after calling the method. Is this the normal way to go, or is there a smoother way to solve my problem?
dynamic changeDataForTest(neuerWert) {
this.data = neuerWert;
}
Column(
children: [
Center(
child: Text(
this.data + this.wiegehts,
),
),
FlatButton(
textColor: Color(0xFF6200EE),
onPressed: () {
changeDataForTest('neuerWert');
(context as Element).reassemble();
},
)
],
)
Thanks
Lukas
If you're using only a small widget, you could use a StatefulWidget using the method:
setState(() {
// change your variable
})
If your widget is complex and has lots of different possible variables, I'll not recommend using setState as this method calls the build method every time is being used.
One simple and fast option, is to use ValueNotifier:
final myVariable = ValueNotifier(false); // where you can replace 'false' with any Object
and then, using it this way:
ValueListenableBuilder(
valueListenable: myVariable,
builder: (context, value, child) {
return Text(value); // or any other use of Widgets
},
);
myVariable.value = true; // if you're looking for to change the current value
finally, if you logic is truly complex and you need to scale, I'll recommend to use a StateManagement library like:
Provider
Riverpod
BloC
Others
You can find those libraries and examples over: https://pub.dev