在 Xamarin Forms 中触发属性更改方法

Question

I'm trying to call a method on a property change, This property currently changes when my Fire-base Push notification is received, Now when that happens I want to fire a method to then display a DisplayAlert.

Why? Because I essentially have flash sale's that are separated into a category from my API that I can fetch via a name so when I create a notification I pass the title as the name the display alert pops they click okay and it takes it to them to that page and set the name I need to fetch the correct "Flash sale"

Atleast this is my solution to this

My attempt so far

App.cs

  Myapp.Views.Home mPage;


 CrossFirebasePushNotification.Current.Subscribe("general");
            CrossFirebasePushNotification.Current.OnTokenRefresh += (s, p) =>
            {
                System.Diagnostics.Debug.WriteLine($"TOKEN REC: {p.Token}");
            };
            System.Diagnostics.Debug.WriteLine($"TOKEN: {CrossFirebasePushNotification.Current.Token}");

            CrossFirebasePushNotification.Current.OnNotificationReceived += (s, p) =>
            {
                try
                {
                    System.Diagnostics.Debug.WriteLine("Received");
                    if (p.Data.ContainsKey("body"))
                    {
                        Device.BeginInvokeOnMainThread(() =>
                        {
                            mPage.Message = $"{p.Data["body"]}";
                        });

                    }
                }
                catch (Exception ex)
                {

                }
            };
            CrossFirebasePushNotification.Current.OnNotificationOpened += (s, p) =>
            {
                //System.Diagnostics.Debug.WriteLine(p.Identifier);

                System.Diagnostics.Debug.WriteLine("Opened");
                foreach (var data in p.Data)
                {
                    System.Diagnostics.Debug.WriteLine($"{data.Key} : {data.Value}");
                }

                if (!string.IsNullOrEmpty(p.Identifier))
                {
                    Device.BeginInvokeOnMainThread(() =>
                    {


                    });
                }
                else if (p.Data.ContainsKey("color"))
                {
                    Device.BeginInvokeOnMainThread(() =>
                    {
                        mPage.Navigation.PushAsync(new ContentPage()
                        {
                            BackgroundColor = Color.FromHex($"{p.Data["color"]}")

                        });
                    });

                }
                else if (p.Data.ContainsKey("aps.alert.title"))
                {
                    Device.BeginInvokeOnMainThread(() =>
                    {
                        mPage.TitleMessage = $"{p.Data["aps.alert.title"]}";
                    });

                }
            };

Home

 public string Message
        {
            get
            {

                return Message;
            }
            set
            {
                Message = value;
                RaisePropertyChanged("Message");
            }
        }

        public string TitleMessage
        {
            get
            {

                return TitleMessage;

            }
            set
            {
                TitleMessage = value;
                RaisePropertyChanged("TitleMessage");
            }
        }

        protected void RaisePropertyChanged(string propertyName = "")
        {
            if (PropertyChanged != null)
            {

                App.Current.MainPage.DisplayAlert(TitleMessage, Message, "ok");
            }
        }

Answer 1

"The app just crashes after a while" is probably because you're trying to display the dialog outside of the UI thread.

if (PropertyChanged != null)
{
    App.Current.MainPage.DisplayAlert(TitleMessage, Message, "ok");
}

After you have checked for subscribers to the PropertyChanged event, you need to actually invoke the event rather than try to display the alert. The event handler of the subscriber can then deal with displaying the alert.

eg

if (PropertyChanged != null)
{
    PropertyChanged.Invoke(this, <your event args>);
}

Which can be shortened using the null conditional operator to:

PropertyChanged?.Invoke(this, <your event args>);

Your class handling the displaying of the dialog can then subscribe like:

yourInstanceName.PropertyChanged += HandleMyDialog;

Answer 2

If I understand you correctly, you can do the following. This will run MyMethod if TitleMessage changes:

public string TitleMessage
        {
            get
            {

                return TitleMessage;

            }
            set
            {
                if(TitleMessage != value){
                    TitleMessage = value;
                    RaisePropertyChanged("TitleMessage");
                    MyMethod();
                }

            }
        }