I am actually trying to archive global variables in Xamarin where any page can consume it. After a lot of research, looks like the best way to archive such thing is using the Singleton design pattern. I am facing difficulty to implement this. take a look...
global.cs
using System;
namespace xamarin_forms
{
sealed class Global
{
public string test { get; set; }
private static Global _instance = null;
private Global()
{
}
static internal Global Instance()
{
if (_instance == null)
{
_instance = new Global();
}
return _instance;
}
}
}
App.xaml.cs
using Xamarin.Forms;
namespace xamarin_forms
{
public partial class App : Application
{
Global global = Global.Instance();
public App()
{
InitializeComponent();
MainPage = new PageWelcome();
global.test = "123";
}
protected override void OnStart()
{
}
protected override void OnSleep()
{
// Handle when your app sleeps
}
protected override void OnResume()
{
// Handle when your app resumes
}
}
}
Ok, so far, I just created my singleton class with a simple test property. I set this to 123 when I initialize my application.
Now, on another page, welcome page...I'd like to read the value that I set previously on the initialization...
PageWelcome.xaml.cs
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Xamarin.Forms;
namespace xamarin_forms
{
public partial class PageWelcome : ContentPage
{
public PageWelcome()
{
InitializeComponent();
Global global = Global.Instance();
DisplayAlert("Alert", global.test, "OK");
}
}
}
Actually this is not working. It's returns me a null. So, how to use this correctly ? Thanks !
In your App's constructor, you first create an instance of PageWelcome. This instance reads the test property of your Global singleton and displays its contents in an alert. At this point, no value has been assigned to that property as far as I can see.
It is only after the PageWelcome constructor finishes that you actually assign a value to the test property of your singleton. Change your App constructor to
public App()
{
InitializeComponent();
global.test = "123";
MainPage = new PageWelcome();
}
and it should work as expected.
You don't need a Singleton.
Just create a static class with your variables static and you would be able to use them on any Page, like you want global variables.
// 1. Create static class Global with string _Test
public static class Global
{
public static void Init()
{
// your init class
}
private static string _Test { get; set; }
public static string Test
{
get => return _Test;
set => _Test = value;
}
}
// 2. Init Global in your App.cs
public App()
{
Global.Init();
}
// 3. Then use them on any page
public PageWelcome()
{
Global.Test = "123";
}
Related
I have void Start() with string snapshotJson declared inside of it, and I have private void LoadGameData() that needs to call the value of snapshotJson. Declaring snapshotJson public doesn't work, I assume because of void. From what I read I should be using getters and setters, but I have no idea how they work and every guide I've read explaining it makes it seem very simple, but they explain it so simply I don't understand how exactly I'm supposed to use it, or how I can call the value after using the get/set functions.
Could anyone explain how I can get the variable from one class to another? In my code, LoadGameData isn't able to call the value of snapshotJson, I'm not sure what I'm missing.
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
using System.IO;
using Firebase;
using Firebase.Unity.Editor;
using Firebase.Database;
using System;
public class DataController : MonoBehaviour
{
private RoundData[] allRoundData;
private PlayerProgress playerProgress;
[Serializable]
public class FirebaseStart : MonoBehaviour
{
public string snapshotJson { get; set; }
void Start()
{
// Set up the Editor before calling into the realtime database.
FirebaseApp.DefaultInstance.SetEditorDatabaseUrl("https://FIREBASEDATABASE");
// Get the root reference location of the database.
DatabaseReference reference =
FirebaseDatabase.DefaultInstance.RootReference;
FirebaseDatabase.DefaultInstance
.GetReference("allRoundData")
.GetValueAsync().ContinueWith(task => {
if (task.IsFaulted)
{
// Handle the error...
}
else if (task.IsCompleted)
{
// DataSnapshot snapshot = task.Result;
snapshotJson = JsonUtility.ToJson(task.Result);
}
});
}
}
// Use this for initialization
void Start ()
{
DontDestroyOnLoad(gameObject);
LoadGameData();
LoadPlayerProgress();
SceneManager.LoadScene("MenuScreen");
}
public RoundData GetCurrentRoundData()
{
return allRoundData [0];
}
public void SubmitNewPlayerScore(int newScore)
{
if (newScore > playerProgress.highestScore)
{
playerProgress.highestScore = newScore;
SavePlayerProgress();
}
}
public int GetHighestPlayerScore()
{
return playerProgress.highestScore;
}
// Update is called once per frame
void Update () {
}
private void LoadPlayerProgress()
{
playerProgress = new PlayerProgress();
if (PlayerPrefs.HasKey("highestScore"))
{
playerProgress.highestScore = PlayerPrefs.GetInt("highestScore");
}
}
private void SavePlayerProgress()
{
PlayerPrefs.SetInt("highestScore", playerProgress.highestScore);
}
public void LoadGameData()
{
GameData loadedData = JsonUtility.FromJson<GameData>(snapshotJson);
Console.WriteLine(snapshotJson);
allRoundData = loadedData.allRoundData;
}
The LoadGameData() method cannot access it from the Main() method because it is local to that function scope. However, you can pass the value from the Main() method to the LoadGameData() using the code below:
using System;
using System.Collections.Generic;
using System.Linq;
public class Program
{
private static void LoadGameData(String input) {
// Do something inside your input here.
}
public static void Main() {
Start();
}
public static void Start()
{
string snapshotJson = "Sample data";
// Same Class Call
LoadGameData(snapshotJson);
// Other Class Call
var otherClassInstance = new TestClass();
otherClassInstance.LoadGameData(snapshotJson);
}
}
public class TestClass {
public void LoadGameData(String input) {
// Do something inside your input here.
}
}
Assuming you refer to methods instead of classes (or rather: sharing data between objects), this is what you could do. Here's an example of a dedicated class for your Game objects, with SnaphopJson being a public property that can be accessed and changed from any other object. Changing the setter to private would ensure only it can only be read from anything but objects of this class.
public class Game
{
public string SnapshotJson { get; set; }
private void LoadGameData()
{
// load the json, e.g. by deserialization
SnapshotJson = "{}";
}
public void Start()
{
// access the content of your snapshot
var s = SnapshotJson;
}
}
If the variable snapshotJson is declared inside the body of the Start method, it will only be accessible within that method. If you want the variable to be accessible in other methods of your class, you may want to declare it as a member variable. This is how it looks like. You would need to declare it as a public property only if you need to access the value of snapshotJson outside of your class instance.
public class MyClass
{
string snapshotJson;
private void Start()
{
// Assign value to snapshotJson here
snapshotJson = "foo";
}
private void LoadGameData
{
// Use value of snapshotJson here
string s = snapshotJson;
}
}
I made a class which requires the public default constructor but
that is never called; instead another constructor is used at DataGrid.AddingNewItem.
I'd like to tell developers that the default constructor is not for their use.
Is there an attribute which suits the purpose?
I had checked DebuggerNonUserCode and MethodImplAttribute with MethodImplAttributes.InternalCall but not sure that's the proper approach.
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.dataGrid1.CanUserAddRows = true;
var list = new List<RowX>();
this.dataGrid1.ItemsSource = CollectionViewSource.GetDefaultView(list);
this.dataGrid1.AddingNewItem += (s, e) => e.NewItem = new RowX("ABC");
}
}
public class RowX
{
public RowX()
{
//this is not used. but CollectionView require this to be public or
//CanUserAddRows doesn't work.
}
public RowX(object o)
{
//this is the actual ctor.
}
public string Text { get; set; }
}
Mark it private
class Foo
{
private Foo() {}
}
You can give your constructor an access modifier.
private This means it can only be called from another constructor in that class.
public class PrivateClass
{
//Only from inside this class:
private PrivateClass()
{
}
public static PrivateClass GetPrivateClass()
{
//This calls the private constructor so you can control exactly what happens
return new PrivateClass();
}
}
internal This means only code in the same assembly (i.e. from inside your library) can access it.
public class InternalClass
{
//Only from within the same assembly
internal InternalClass(string foo)
{
}
}
Is it possible to create an instance of a private class in another private class? (Not counting within the main() program.)
And also, is it possible for a method in a private class to return a private type object?
This question came because I was following Scott Allen from PluralSight on C# Fundamentals With C#5. And on lesson 2 about classes and objects, he has a code example like this:
public GradeStatistics ComputeStatistics()
{
GradeStatistics stats = new GradeStatistics();
...
...
}
with GradeStatistics defined in a separate class file like:
class GradeStatisticss
{
}
Inlined comment: I am not talking about nested classes. What I meant is, you have two classes (separate files) and I am wondering if one class can create an instance of another class (knowing they are both private).
Edited with examples:
private class Example1
{
}
private class Example2
{
public Example1 DoSomeComputation()
{
return new Example1();
}
}
private class Example3
{
Example1 ex1 = new Example1();
}
Is Example3 able to create ex1? Can Example2 return a new instance of Example1?
Is it possible to create an instance of a private class in another private class?
Only if the private class for which you want to create an instance is declared inside the private class that wants to create the instance. If they are not nested, it's not possible.
Is it possible for a method in a private class to return a private type object?
Yes, it can.
Here's some code showing everything together:
public class Tester {
private class ThePrivateCreator {
private class TheOtherPrivateClass {
}
public Object createObject() {
return new TheOtherPrivateClass();
}
}
public void canWeDoThis() {
ThePrivateCreator c = new ThePrivateCreator();
Console.WriteLine(c.createObject());
}
}
class Program
{
public static void Main(string[] args) {
Tester t = new Tester();
t.canWeDoThis();
}
}
No. A private class cannot be accessed by another class in a different file. The reason why is that the modifier private is meant to encapsulate the data or method inside of that class. You should use the public or internal modifier if you want to access a class from a different class that is not nested. If it is nested, you can also use the protected modifier.
Not sure exactly what you had in mind, but here's one possible example:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication26
{
class Program
{
static void Main(string[] args)
{
private1 p1 = new private1();
private2 p2 = p1.foo();
Console.WriteLine(p2.Value);
Console.ReadLine();
}
private class private1
{
public private2 foo()
{
private2 p2 = new private2("I was created inside a different private class!");
return p2;
}
}
private class private2
{
private string _value;
public string Value
{
get { return _value; }
}
public private2(string value)
{
this._value = value;
}
}
}
}
I have a Program class which has:
private static ClientBase objClientBase = new ClientBase(new List<RecordType> { RecordType.none }, ModuleType.Monitor);
static void Main(string[] args)
{
objClientBase.Connect(); //IRRELEVANT
objQueueMon = new Main(); //<-INSIDE THIS IS WHERE I WANT TO ACCESS objClientBase
objClientBase.MainModuleThreadManualResetEvent.WaitOne(); //IRRELEVANT
}
This Progam creates a Main class instance as you see:
objQueueMon = new Main();
Notice that they are separated in different files, but the Main class instance is created inside the Program class.
Inside my Program class I want to access that objClientBase.
Do I have to create a constructor method and pass it or make a public access to it?
So what I want to achieve is, inside the Main class, do a objClientBase.FUNCTION
You can do exactly what you just said:
public class Main {
private ClientBase _caller;
public Main (ClientBase caller) {
_caller = caller;
}
}
Or, you can set it later
public class Main {
private ClientBase _caller;
public Main () {
}
// only your assembly sets it
internal SetClientBase(ClientBase cb) {
_caller = cb;
}
// but anyone gets it
// Now you can let some client execute "Function"
public ClientBase Caller {
{return _caller;}
}
}
Just an example
Change the constructor of your Main class to accept a ClientBase object, like this:
public class Main
{
private ClientBase _clientBase;
public Main(ClientBase clientBase)
{
_clientBase = clientBase;
}
public void SomeMethod()
{
// Use ClientBase.FUNCTION here
_clientBase.FUNCTION();
}
}
I've searched Google all day and can't find the correct answer to my issue, hoping someone here can help me.
So, in the "Main" form I have the method to show a form that needs to be centered directly above the parent form (frmMain). Normally I would call ShowDialog(this) to see the parent, but for some reason I have to set the loadNewsFeedItem to static in order to see the method from the flpNewsFeedHeader : Label derrived class (below). The OnClick event triggers the method loadNewsFeedItem().
When I call this to set the parent, I'm getting the message "Keyword 'this' is not valid in a static property, static method, or static field initializer"
namespace NewsFeeds
{
public partial class FrmMain : Form
{
public static void loadNewsFeedItem()
{
frmNewsFeedView frmFeedView = new frmNewsFeedView(FrmFuncs.selFeedID);
frmFeedView.ShowDialog(this); // Error occurs on this line, when calling this via a static method
}
}
}
public class flpNewsFeedHeader : Label
{
private int FeedID = 0;
public int theFeedID
{
get { return FeedID; }
set { FeedID = value; }
}
protected override void OnClick(EventArgs e)
{
FrmFuncs.selFeedID = FeedID;
Thread thrShowFeed = new Thread(new ThreadStart(FrmMain.loadNewsFeedItem));
thrShowFeed.Start();
}
}
Can someone please give me a corrected code example or a hint as to how to get the loadNewsFeedItem() to be visible without setting the accessor to static, or how to work around this in a static accessor?
Thanks in advance!
Chris
Edit: used ActiveForm for owner.
public partial class FrmMain : Form
{
public static void loadNewsFeedItem(Form owner)
{
frmNewsFeedView frmFeedView = new frmNewsFeedView(FrmFuncs.selFeedID);
frmFeedView.ShowDialog(owner);
}
}
}
public class flpNewsFeedHeader : Label
{
private int FeedID = 0;
public int theFeedID
{
get { return FeedID; }
set { FeedID = value; }
}
protected override void OnClick(EventArgs e)
{
FrmFuncs.selFeedID = FeedID;
// Shouldn't need a new thread. Already on the GUI thread.
FrmMain.loadNewsFeedItem (System.Windows.Forms.Form.ActiveForm);
}
}
may be you mean this:
frmFeedView.Owner = System.Windows.Forms.Form.ActiveForm;
frmFeedView.ShowDialog();
In a static method, this is meaningless. One option is to skip the parameter
frmFeedView.ShowDialog();
The other option is to setup a static variable as shown below (but beware, it can have side effects if you try to open multiple instances of FrmMain)
public partial class FrmMain : Form
{
private static FrmMain staticInstance;
public FrmMain()
{
staticInstance = this;
InitializeComponent();
...
}
public static void loadNewsFeedItem()
{
frmNewsFeedView frmFeedView = new frmNewsFeedView(FrmFuncs.selFeedID);
frmFeedView.ShowDialog(staticInstance );
}