I have SettingsViewModel with:
public class SettingsViewModel : BaseViewModel, ISettingsViewModel
{
public SettingsViewModel()
{
}
private string _gaugeColor;
public string GaugeColor
{
get => Preferences.Get("GaugeColor", "#17805d");
set
{
Preferences.Set("GaugeColor", value);
this.OnSettingsChanged();
this.OnPropertyChanged();
}
}
public event EventHandler<SettingsChangedEventArgs> SettingsChanged;
private void OnSettingsChanged() => this.SettingsChanged?.Invoke(this, new SettingsChangedEventArgs(this.Settings));
public Settings Settings { get; private set; }
}
}
I set color by HEX string.
Then in PanelViewModel I have:
private Color _gaugeColor;
public Color GaugeColor
{
get => Color.FromHex(Preferences.Get("GaugeColor", "#17805d"));
set
{
_gaugeColor = value;
OnPropertyChanged();
}
}
Now if I change HEX string from Settings view in UI, color does not change in PanelViewModel until I restart an application. Question is: How to make color change in PanelViewModel right after it has been changed in SettingsViewModel?
I have tried to add this into PanelViewModel, but apparently this creates a new instance of SettingsViewModel and Color does not follow into PanelViewMode. Maybe there is some direct solution and I am using Xamarin.Essentials wrong?
public PanelViewModel()
{
this.SettingsViewModel = new SettingsViewModel();
this.SettingsViewModel.SettingsChanged = OnSettingsChanged;
}
private Color _gaugeColor;
public Color GaugeColor
{
get => Color.FromHex(Preferences.Get("GaugeColor", "#17805d"));
set
{
_gaugeColor = value;
OnPropertyChanged();
}
}
private void OnSettingsChanged(object sender, SettingsChangedEventArgs e)
{
this.GaugeColor = Color.FromHex(e.Settings.GaugeColor);
}
private SettingsViewModel SettingsViewModel { get; }
https://docs.microsoft.com/en-us/dotnet/api/xamarin.essentials.preferences?view=xamarin-essentials
CodePudding user response:
Question is: How to make color change in PanelViewModel right after it has been changed in SettingsViewModel?
Yes, a simple method is to use MessagingCenter.
The MessagingCenter
class implements the publish-subscrib
e pattern, allowing message-based communication between components that are inconvenient to link by object and type references. This mechanism allows publishers and subscribers to communicate without having a reference to each other, helping to reduce dependencies between them.
You can refer to the following code:
In SettingsViewModel.cs
, we can publish a message in the constuctor of it,just as follows:
public class SettingsViewModel
{
public string Title { get; set; }
public SettingsViewModel() {
Title = "SettingsView";
MessagingCenter.Send<Object, Color>(this, "Hi", Color.Yellow);
}
}
And in PanelViewModel.cs
,we can subscribe to this message:
public class PanelViewModel
{
public string Title { get; set; }
public PanelViewModel() {
Title = "PanelView";
MessagingCenter.Subscribe<Object, Color>(this, "Hi", async (sender, arg) =>
{
System.Diagnostics.Debug.WriteLine("-----> receive color= " arg);
// here ,we can use the received color to update the UI
});
}
}
Note:
Once we receive the color, we can use the received color to update the UI, and the color field in the PanelViewModel.cs
should implement interface INotifyPropertyChanged.