I am trying to bind my Label's Text
property to the Model's Counter
property, but it's not updating with every timer increment.
This might be a duplicated question but I really do not understand where I've made a mistake.
It looks like it can take the initial value, but it doesn't update every second like it is supposed to.
In the Form Constructor:
public partial class Form1 : Form
{
Model model;
public Form1()
{
InitializeComponent();
model = new Model();
Binding binding = new Binding("Text", model, "Counter", true, DataSourceUpdateMode.OnPropertyChanged);
label1.DataBindings.Add(binding);
}
}
My Model
class:
public class Model: INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
// This method is called by the Set accessor of each property.
// The CallerMemberName attribute that is applied to the optional propertyName
// parameter causes the property name of the caller to be substituted as an argument.
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
if (PropertyChanged != null)
{
//Console.WriteLine(propertyName);
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
private static Timer timer;
private int counter;
public int Counter
{
get { return counter; }
set
{
counter = value;
NotifyPropertyChanged();
}
}
public Model()
{
counter = 0;
SetTimer();
}
public void SetTimer()
{
timer = new Timer(1000);
timer.Elapsed += Timer_Elapsed;
timer.AutoReset = true;
timer.Enabled = true;
}
private void Timer_Elapsed(object sender, ElapsedEventArgs e)
{
Counter++;
}
}
A couple of examples, using a System.Windows.Forms.Timer that replaces the System.Timers.Timer you're using now.
The latter raises its Elapsed
event in ThreadPool Threads. DataBindings, as many other objects, don't work cross-Thread.
You can read some other details here:
Why does invoking an event in a timer callback cause following code to be ignored?
The System.Windows.Forms.Timer
is instead already synchronized, its Tick
event is raised in the UI Thread.
New Model class using this Timer:
using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows.Forms;
public class Model : INotifyPropertyChanged, IDisposable
{
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
private readonly Timer timer;
private int counter;
public Model() {
counter = 0;
timer = new Timer() { Interval = 1000 };
timer.Tick += this.Timer_Elapsed;
StartTimer();
}
public int Counter {
get => counter;
set {
if (counter != value) {
counter = value;
NotifyPropertyChanged();
}
}
}
public void StartTimer() => timer.Start();
public void StopTimer() => timer.Stop();
private void Timer_Elapsed(object sender, EventArgs e) => Counter++;
public void Dispose(){
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing) {
lock (this) {
if (timer != null) timer.Tick -= Timer_Elapsed;
timer?.Stop();
timer?.Dispose();
}
}
}
}
In case you want to use a System.Threading.Timer
, you need to synchronize its Elapsed event with the UI Thread, since, as mentioned, a PropertyChanged notification cannot be marshalled across Threads and your DataBindings won't work.
You can use (mainly) two methods:
WindowsFormsSynchronizationContext
and Post to it to update a Property value.System.Threading.Timer
's SynchronizingObject property.Elapsed
event will be raised in the same Thread as the Sync object.Note: You cannot declare a Model object as a Field and initialize at the same time: there's no SynchronizationContext until after the starting Form has been initialized. You can initialize a new Instance in the Constructor of a Form or any time after:
public partial class Form1 : Form
{
Model model = new Model(); // <= Won't work
// ------------------------------------------
Model model = null; // <= It's OK
public Form1()
{
InitializeComponent();
// Using the SynchronizationContext
model = new Model();
// Or, using A Synchronizing Object
model = new Model(this);
var binding = new Binding("Text", model, "Counter", true, DataSourceUpdateMode.OnPropertyChanged);
label1.DataBindings.Add(binding);
}
}
A modified Model class that makes use of both:
using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Timers;
public class Model : INotifyPropertyChanged, IDisposable
{
public event PropertyChangedEventHandler PropertyChanged;
internal readonly SynchronizationContext syncContext = null;
internal ISynchronizeInvoke syncObj = null;
private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
private System.Timers.Timer timer;
private int counter;
public Model() : this(null) { }
public Model(ISynchronizeInvoke synchObject)
{
syncContext = SynchronizationContext.Current;
syncObj = synchObject;
timer = new System.Timers.Timer();
timer.SynchronizingObject = syncObj;
timer.Elapsed += Timer_Elapsed;
StartTimer(1000);
}
public int Counter {
get => counter;
set {
if (counter != value) {
counter = value;
NotifyPropertyChanged();
}
}
}
public void StartTimer(int interval) {
timer.Interval = interval;
timer.AutoReset = true;
timer.Start();
}
public void StopTimer(int interval) => timer.Stop();
private void Timer_Elapsed(object sender, ElapsedEventArgs e)
{
if (syncObj is null) {
syncContext.Post((spcb) => Counter += 1, null);
}
else {
Counter += 1;
}
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing) {
lock (this) {
if (timer != null) timer.Elapsed -= Timer_Elapsed;
timer?.Stop();
timer?.Dispose();
}
}
}
}