I am trying to save some settings but the tutorial I am following(android tutorial) is not helping as I am stuck on the first line of code since it seems monodroid does it differently?
select your mode to be either private or public.
int mode= Activity.MODE.PRIVATE;
// get the sharedPreference of your context.
SharedPreference s mySharedPreferences ; mySharedPreferences=getSharedPreferences(“Name_of_your_preference”,mode);
// retrieve an editor to modify the shared preferences
SharedPreferences.Editor editor= mySharedPreferences.edit();
/* now store your primitive type values. In this case it is true, 1f and Hello! World */
editor.putBolean(“myBoolean”,true);
editor.putFloat(“myFloat”,1f);
editor.putString(“myString”,” Hello! World”);
//save the changes that you made
editor.commit();
I don't see Activity.MODE.PRIVATE; in monodroid.
Here is my func to do this:
protected void SaveSetting(string name, string value)
{
var prefences = GetSharedPreferences(Consts.Application.SETTINGS_FILE, FileCreationMode.Private);
var editor = prefences.Edit();
editor.Remove(name);
editor.PutString(name, value);
editor.Commit();
}
Assuming you mean MODE_PRIVATE, it should be Android.Content.FileCreationMode.Private.
Fortunately you don't really have to know that, as we mapped the int in GetSharedPreferences to take the Android.Content.FileCreationMode enum, so intellisense should help you out.
Related
I am pretty amateur in LLVM. I am trying to write a loop pass in which I need to know which function I'm in. Is there any way to find that?
I want to do this in the following runOnLoop function:
virtual bool runOnLoop(Loop *L, LPPassManager &LPM) override {
}
You need
StringRef Name = L->getHeader()->getParent()->getName();
I have stored variables in a class with their code names.
Suppose I want to get XVG from that class, I want to do
String getIconsURL(String symbol) {
var list = new URLsList();
//symbol = 'XVG'
return list.(symbol);
}
class URLsList{
var XVG = 'some url';
var BTC = 'some url';
}
Can someone help me achieve this or provide me with a better solution?
Dart when used in flutter doesn't support reflection.
If it's text that you want to have directly in your code for some reason, I'd advise using a text replace (using your favourite tool or using intellij's find + replace with regex) to change it into a map, i.e.
final Map<String, String> whee = {
'XVG': 'url 1',
'BTC': 'url 2',
};
Another alternative is saving it as a JSON file in your assets, and then loading it and reading it when the app opens, or even downloading it from a server on first run / when needed (in case the URLs need updating more often than you plan on updating the app). Hardcoding a bunch of data like that isn't necessarily always a good idea.
EDIT: how to use.
final Map<String, String> whee = .....
String getIconsURL(String symbol) {
//symbol = 'XVG'
return whee[symbol];
}
If you define it in a class make sure you set it to static as well so it doesn't make another each time the class is instantiated.
Also, if you want to iterate through them you have the option of using entries, keys, or values - see the Map Class documentation
I'd just implement a getProperty(String name) method or the [] operator like:
class URLsList{
var XVG = 'some url';
var BTC = 'some url';
String get operator [](String key) {
switch(key) {
case 'XVG': return XVG;
case 'BTC': return BTC;
}
}
}
String getIconsURL(String symbol) {
var list = new URLsList();
return list[symbol];
}
You can also use reflectable package that enables you to use reflection-like code by code generation.
Assuming that the class is being created from a JSON Object, you can always use objectName.toJSON() and then use the variable names are array indices to do your computations.
Is there a way that we could save a map object into shared preferences so that we can fetch the data from shared preferences rather than listening to the database all the time.
actually i want to reduce the amount of data downloaded from firebase. so i am thinking of a solution to have a listener for shared prefs and read the data from shared prefs.
But i dont see a way of achieving this in flutter or dart.
Please can someone help me to achieve this if there is a workaround.
Many Thanks,
Mahi
If you convert it to a string, you can store it
import 'dart:convert';
...
var s = json.encode(myMap);
// or var s = jsonEncode(myMap);
json.decode(...)/jsonDecode(...) makes a map from a string when you load it.
Might be easier with this package:
https://pub.dartlang.org/packages/pref_dessert
Look at the example:
import 'package:pref_dessert/pref_dessert.dart';
/// Person class that you want to serialize:
class Person {
String name;
int age;
Person(this.name, this.age);
}
/// PersonDesSer which extends DesSer<T> and implements two methods which serialize this objects using CSV format:
class PersonDesSer extends DesSer<Person>{
#override
Person deserialize(String s) {
var split = s.split(",");
return new Person(split[0], int.parse(split[1]));
}
#override
String serialize(Person t) {
return "${t.name},${t.age}";
}
}
void main() {
var repo = new FuturePreferencesRepository<Person>(new PersonDesSer());
repo.save(new Person("Foo", 42));
repo.save(new Person("Bar", 1));
var list = repo.findAll();
}
Package is still under development so it might change, but any improvements and ideas are welcomed! :)
In dart's Shared Preferences there is no way to store Map directly but you can easily trick this by, converting Map to String then save it as usual, and when you need it to retrieve the String and then convert it back to Map. So simple!
Convert your map into String using json.encode() and then save it,
When you need your map use json.decode() to get back your map from the string.
import 'dart:convert';
import 'package:shared_preferences/shared_preferences.dart';
final yourStr = sharedPreferences.getString("yourkey");
var map = json.decode(yourStr);
sharedPreferences.setString("yourkey", json.encode("value"));
For those who don't like to convert String to JSON or vice versa, personally recommend localstorage, this is the easiest way I had ever found to store any data<T> in Flutter.
import 'package:localstorage/localstorage.dart';
final LocalStorage store = new LocalStorage('myapp');
...
setLocalStorage() async {
await store.ready; // Make sure store is ready
store.setItem('myMap', myMapData);
}
...
Hope this helps!
I would like to pass a primitive (int, bool, ...) by reference. I found a discussion about it (paragraph "Passing value types by reference") here: value types in Dart, but I still wonder if there is a way to do it in Dart (except using an object wrapper) ? Any development ?
The Dart language does not support this and I doubt it ever will, but the future will tell.
Primitives will be passed by value, and as already mentioned here, the only way to 'pass primitives by reference' is by wrapping them like:
class PrimitiveWrapper {
var value;
PrimitiveWrapper(this.value);
}
void alter(PrimitiveWrapper data) {
data.value++;
}
main() {
var data = new PrimitiveWrapper(5);
print(data.value); // 5
alter(data);
print(data.value); // 6
}
If you don't want to do that, then you need to find another way around your problem.
One case where I see people needing to pass by reference is that they have some sort of value they want to pass to functions in a class:
class Foo {
void doFoo() {
var i = 0;
...
doBar(i); // We want to alter i in doBar().
...
i++;
}
void doBar(i) {
i++;
}
}
In this case you could just make i a class member instead.
No, wrappers are the only way.
They are passed by reference. It just doesn't matter because the "primitive" types don't have methods to change their internal value.
Correct me if I'm wrong, but maybe you are misunderstanding what "passing by reference" means? I'm assuming you want to do something like param1 = 10 and want this value to still be 10 when you return from your method. But references aren't pointers. When you assign the parameter a new value (with = operator), this change won't be reflected in the calling method. This is still true with non-primitive types (classes).
Example:
class Test {
int val;
Test(this.val);
}
void main() {
Test t = new Test(1);
fn1(t);
print(t.val); // 2
fn2(t);
print(t.val); // still 2, because "t" has been assigned a new instance in fn2()
}
void fn1(Test t) {
print(t.val); // 1
t.val = 2;
}
void fn2(Test t) {
t = new Test(10);
print(t.val); // 10
}
EDIT
I tried to make my answer more clear, based on the comments, but somehow I can't seem to phrase it right without causing more confusion. Basically, when someone coming from Java says "parameters are passed by reference", they mean what a C/C++ developer would mean by saying "parameters are passed as pointers".
As dart is compiled into JavaScript, I tried something that works for JS, and guess what!? It worked for dart!
Basically, what you can do is put your value inside an object, and then any changes made on that field value inside that function will change the value outside that function as well.
Code (You can run this on dartpad.dev)
main() {
var a = {"b": false};
print("Before passing: " + a["b"].toString());
trial(a);
print("After passing: " + a["b"].toString());
}
trial(param) {
param["b"] = true;
}
Output
Before passing: false
After passing: true
One of the way to pass the variables by reference by using the values in List. As arrays or lists are Pass by reference by default.
void main() {
List<String> name=['ali' ,'fana'];
updatename(name);
print(name);
}
updatename(List<String> name){
name[0]='gufran';
}
Try this one, This one of the simplest way to pass by reference.
You can use ValueNotifier
And, you can pass it as ValueListenable to classes or methods that needs to know up-to-date value, but should not edit it:
class Owner {
final theValue = ValueNotifier(true);
final user = User(theValue);
...
}
class User {
final ValueListeneble<bool> theValue;
User(this.theValue);
...
}
It provides more functionality than actually needed, but solves the problem.
If ValueNotifier + ValueListenable do not work for you (you want to make sure the client does not listen to every change of the value, or your package is pure Dart package and thus cannot reference Flutter libraries), use a function:
class Owner {
int _value = 0;
int getValue() => _value;
void increase() => _value++;
}
void main() {
final owner = Owner();
int Function() obtainer = owner.getValue;
print(obtainer());
owner.increase();
print(obtainer());
}
Output will be:
0
1
This approach has memory usage related downside: the obtainer will hold the reference to the owner, and this, even if owner is already not referenced, but obtainer is still reachable, owner will be also reachable
and thus will not be garbage collected.
If you do not want the downside, pass the smaller container than the entire owner:
import 'package:flutter/foundation.dart';
class ListenableAsObtainer<T> implements ValueObtainer<T> {
ListenableAsObtainer(this._listenable);
final ValueListenable<T> _listenable;
#override
T get value => _listenable.value;
}
class FunctionAsObtainer<T> implements ValueObtainer<T> {
FunctionAsObtainer(this._function);
final T Function() _function;
#override
T get value => _function();
}
class ValueAsObtainer<T> implements ValueObtainer<T> {
ValueAsObtainer(this.value);
#override
T value;
}
/// Use this interface when the client needs
/// access to the current value, but does not need the value to be listenable,
/// i.e. [ValueListenable] would be too strong requirement.
abstract class ValueObtainer<T> {
T get value;
}
The usage of FunctionAsObtainer will still result in holding the owner from garbage collection, but two other options will not.
Just to make it clear:
void main() {
var list1 = [0,1,2];
var modifiedList1 = addMutable(list1, 3);
var list2 = [0,1,2];
var modifiedList2 = addImmutable(list2, 3);
print(list1);
print(modifiedList1);
print(list2);
print(modifiedList2);
}
List<int> addMutable(List<int> list, int element){
return list..add(element);
}
List<int> addImmutable(List<int> list, int element){
return [...list, element];
}
Output:
[0, 1, 2, 3]
[0, 1, 2, 3]
[0, 1, 2]
[0, 1, 2, 3]
All variables are passed by value. If a variable contains a primitive (int, bool, etc.), that's it. You got its value. You can do with it whatever you want, it won't affect the source value. If a variable contains an object, what it really contains is a reference to that object.
The reference itself is also passed by value, but the object it references is not passed at all. It just stayed where it was. This means that you can actually make changes to this very object.
Therefore, if you pass a List and if you .add() something to it, you have internally changed it, like it is passed by reference. But if you use the spread operator [...list], you are creating a fresh new copy of it. In most cases that is what you really want to do.
Sounds complicated. Isn't really. Dart is cool.
Have been seeing the term "Expando" used recently with Dart. Sounds interesting. The API did not provide much of a clue to me.
An example or two could be most helpful!
(Not sure if this is related, but I am most anxious for a way to add methods (getters) and/or variables to a class. Hoping this might be a key to solving this problem. (hint: I am using the Nosuchmethod method now and want to be able to return the value of the unfound method.))
Thanks in advance,
_swarmii
Just to clarify the difference between expando and maps: as reported in the groups, expando has weak references.
This means that a key can be garbage collected even if it's still present in the expando (as long as there are no other references to it).
For all other intents and purposes it's a map.
Expandos allow you to associate objects to other objects. One very useful example of this is an HTML DOM element, which cannot itself be sub-classed. Let's make a top-level expando to add some functionality to an element - in this case a Function signature given in the typedef statement:
typedef CustomFunction(int foo, String bar);
Expando<CustomFunction> domFunctionExpando = new Expando<CustomFunction>();
Now to use it:
main(){
// Assumes dart:html is imported
final myElement = new DivElement();
// Use the expando on our DOM element.
domFunctionExpando[myElement] = someFunc;
// Now that we've "attached" the function to our object,
// we can call it like so:
domFunctionExpando[myElement](42, 'expandos are cool');
}
void someFunc(int foo, String bar){
print('Hello. $foo $bar');
}
I played with it a little bit. Here's what I've got.
import 'dart:html';
const String cHidden = 'hidden';
class ExpandoElement {
static final Expando<ExpandoElement> expando =
new Expando<ExpandoElement>("ExpandoElement.expando");
final Element element;
const ExpandoElement._expand(this.element);
static Element expand(Element element) {
if (expando[element] == null)
expando[element] = new ExpandoElement._expand(element);
return element;
}
// bool get hidden => element.hidden; // commented out to test noSuchMethod()
void set hidden(bool hidden) {
if (element.hidden = hidden)
element.classes.add(cHidden);
else
element.classes.remove(cHidden);
}
noSuchMethod(InvocationMirror invocation) => invocation.invokeOn(element);
}
final Expando<ExpandoElement> x = ExpandoElement.expando;
Element xquery(String selector) => ExpandoElement.expand(query(selector));
final Element input = xquery('#input');
void main() {
input.classes.remove(cHidden);
assert(!input.classes.contains(cHidden));
input.hidden = true;
assert(x[input].hidden); // Dart Editor warning here, but it's still true
assert(!input.classes.contains(cHidden)); // no effect
input.hidden = false;
assert(!x[input].hidden); // same warning, but we'll get input.hidden via noSuchMethod()
assert(!input.classes.contains(cHidden));
x[input].hidden = true;
assert(input.hidden); // set by the setter of ExpandoElement.hidden
assert(input.classes.contains(cHidden)); // added by the setter
assert(x[input].hidden);
assert(x[input].classes.contains(cHidden)); // this is input.classes
x[input].hidden = false;
assert(!input.hidden); // set by the setter
assert(!input.classes.contains(cHidden)); // removed by the setter
assert(!x[input].hidden);
assert(!x[input].classes.contains(cHidden));
// confused?
assert(input is Element);
assert(x[input] is! Element); // is not
assert(x[input] is ExpandoElement);
assert(x is Expando<ExpandoElement>);
}