Here's the situation that I have. On DeckPage, I subscribe to a message like this:
public void OnAppearing()
{
RefreshLables();
MessagingCenter.Subscribe<CardFormatPageViewModel>(
this,
"RefreshDeckConfigsLabels",
sender => { RefreshLables(); });
}
private void RefreshLables()
{
-- refresh code
}
public void OnDisappearing()
{
MessagingCenter.Unsubscribe<CardFormatPageViewModel>(this,"RefreshDeckConfigsLabels");
}
This works good and I am sending a message from the CardFormatPageViewModel like this:
MessagingCenter.Send(this, "RefreshDeckConfigsLabels");
I also want to be able to send messages to DeckPage from OptionPageViewModel:
MessagingCenter.Send(this, "RefreshDeckConfigsLabels");
Plus from more models.
Is there a way I can code the subscribe so I can subscribe to one common message that will be accepted if it comes from CardFormatPageViewModel, OptionPageViewModel or the other View Models that need to make it refresh or do I have to do a subscription for every one of them?
sure
MessagingCenter.Send<object>(this, "RefreshDeckConfigsLabels");
and
MessagingCenter.Subscribe<object>(
this,
"RefreshDeckConfigsLabels",
sender => { RefreshLables(); });
Related
Could I response to someone who send his first DM to me in JDA?
This question will depend on what you need, you can use the
public void onPrivateMessageReceived(#Nonnull PrivateMessageReceivedEvent event) {
//code
}
method to get the private channel for DM's.
After that, you could check the history with the user. This would be example code, so you need to edit it to your needs:
#Override
public void onPrivateMessageReceived(#Nonnull PrivateMessageReceivedEvent event) {
if (event.getUser().isBot()) return; // Don't do anything if the user is bot (aka, self)
if (event.getChannel().getHistory().size() < 2) { //Made it <2 in case array starts with 0
event.getChannel().sendMessage("HI THIS IS THE MESSAGE I WANT TO SEND").queue();
}
}
I need to subscribe an event to handle incoming phone call. Since iOS version 11.0 CTCallCenter is deprecated we have to use CXCallObserver. I successfully implemented solution for CTCallCenter, but I am not able to subscribe event for CXCallObserver. Does anyone have working solution for CXCallObserver?
Here is my code to subscribe event for CTCallCenter..
_callCenter = new CTCallCenter();
_callCenter.CallEventHandler += CallEvent;
private void CallEvent(CTCall call)
{
CoreFoundation.DispatchQueue.MainQueue.DispatchSync(() =>
{
if(call.CallState.Equals(call.StateIncoming))
//Do something
});
}
Implement the delegate for CXCallObserver:
public class MyCXCallObserverDelegate : CXCallObserverDelegate
{
public override void CallChanged(CXCallObserver callObserver, CXCall call)
{
Console.WriteLine(call);
}
}
Then in your code, create a instance of CXCallObserver (maintain a strong reference to this) and then assign the delegate:
cXCallObserver = new CXCallObserver();
cXCallObserver.SetDelegate(new MyCXCallObserverDelegate(), null);
Functionality written inside the MessagingCenter.Subscribe() is called multiple times when i navigate to and fro multiple times in the application. But each time before subscribing, i do unsubscribe to the same in constructor as follows, still it didn't worked.
MessagingCenter.Unsubscribe<SubmitPage>(this,"Save");
MessagingCenter.Subscribe<SubmitPage>(this, "Save", (sender) =>
{
DisplayToastOnSuccessfulSubmission();
});
In my application i have 6 pages(git) and i save the data in 6th page with MessagingCenter.Send and same will be subscribed in 2nd page and saved message will be displayed in 2nd page(after navigating to that page).
Now i navigate like 2->1->2->3->4->5->6 in this particular case DisplayToastOnSuccessfulSubmission() would be called two times(because Page2 constructor is called twice).
I even tried placing the same code in OnAppearing.
I can't unsubscribe in OnDisappear as I need the event wiring up to when I reach Page6 for save.
Reproduced the same behaviour in sample project and added here https://github.com/suchithm/MessageCenterSampleApp Drop box link
What is the proper way to do this?
But each time before subscribing, I do unsubscribe to the same in constructor as follows, still it didn't worked.
MessagingCenter.Subscribe() is called multiple times, because there are two instances of Page2 in your code, both of them use MessagingCenter.Subscribe() method, that's why the Unsubscribe didn't work.
You can modify page2() to a singleton to make sure there is only one instance of Page2 in your project, after that when you send a message,
the MessagingCenter.Subscribe() is called only once.
Page2.cs:
public static Page2 instance = new Page2();
public static Page2 GetPage2Instance()
{
if(instance == null)
{
return new Page2();
}
return instance;
}
private Page2()
{
InitializeComponent();
MessagingCenter.Unsubscribe<Page2>(this, "SaveToastPage2");
MessagingCenter.Subscribe<Page2>(this, "SaveToastPage2", (sender) =>
{
DisplayToastOnSuccessfulSubmission();
}
}
When you send a message :
MessagingCenter.Send(Page2.GetPage2Instance(), "SaveToastPage2");
EDIT :
Remember that declaring constructors of Page2 class to be private to make sure there is only one instance of Page2 in your project sure.
private Page2()
{
...
}
Modify your Page1.cs code :
async void Handle_Next(object sender, System.EventArgs e)
{
await App.NavigationRef.PushAsync(Page2.GetPage2Instance(), true);
}
I faced same issue. I solved issue by passing the same parameters inn subscribe and unsubscribing as well.
MessagingCenter.Subscribe<Page1, T>(this, "Listen", async (Page1 arg1, T
listenedString) =>
{
});
Unsubscribe like below
MessagingCenter.Unsubscribe<Page1, T>(this, "Listen");
I'm using this temporary solution.
I declared a static dictionary to storage my object (to this example I used an object type).
private static Dictionary<string, object> subscribedReferencePages = new Dictionary<string, object>();
And I always storage the last subscribed page reference.
Then I compare the page reference before triggering the message method to fire only the last one.
subscribedReferencePages[pageName] = this;
MessagingCenter.Subscribe<ViewModelBase>(this, pageName, async (sender) =>
{
if (!ReferenceEquals(sender, this))
{
return;
}
this.OnInitialized();
});
To call the message method I need to pass the dictionary as parameter (instead of the "this" reference).
MessagingCenter.Send(subscribedPages[pageName], keyPageName);
Instead of unsubscribing when you navigate TO a page,
unsubscribe when you navigate AWAY from the page. At that point your instance of 'this' is still the same 'this' you think it is.
I am trying to use messaging center instead of Messenger in xamarin forms I have no idea about messaging center I tried Bellow code to subscribe and Send Message in xamarin forms
MessagingCenter.Send(this, "TodoTable", "Todo");
But I have not Idea from where I can subscribe to this message I tried bellow code :
MessagingCenter.Subscribe<TodoClass>(this, Todo, async (sender, arg) =>
{
await RefreshCommand.ExecuteAsync();
});
This is giving me error Any Help will appreciated :)
It is a quirk of XF messaging centre that (it seems) you need to know who will be sending the message, and potentially who will be receiving it.
However it can be object. The signature of subscribe is:
void MessagingCenter.Subscribe<TSender>(object subscriber, string message, Action<TSender> callback, TSender sender = null)
The trick is to subscribe thus:
MessagingCenter.Subscribe<object>(this, "messageName", Action<object> callback)
This says object or anything derived from object can be a sender, ie, everything.
However if you want to only subscribe to messages sent by a particular instance of a type:
MessagingCenter.Subscribe<MyClass>(this, "messageName", Action<MyClass> callback)
The use of the full signature is a bit suspect. Basically it is saying only if sent from the source object are subscribers who used that source object when subscribing.
MessagingCenter.Subscribe<object, string>(this, "Hi",
(sender, arg) =>
{
DisplayAlert("Message Received", "arg=" + arg, "OK");
},
BindingContext);
if you use the following to send the message it wont be received by the subscriber just above:
MessagingCenter.Send<object, string>(this, "Hi", "John");
But the following will be received
MessagingCenter.Send<object, string>(BindingContext, "Hi", "John");
Though why would you want to send a message to yourself. (Assuming the subscribe and send were in the same page in this case).
However if there were multiple pages with the exact same binding context the message will be sent to all such subscribers. Eg, pages bound to the same view model.
To improve the answer by #user2825546, if you wish to subscribe to only messages from your view-models, you need to specify the base class type when sending the message:
MessagingCenter.Subscribe<BaseViewModel, string>(this, "ShowError", (view, message) => { });
public class StartupViewModel : BaseViewModel
{
//Like this...
MessagingCenter.Send<BaseViewModel, string>(this, "ShowError", "Message");
//Or...
MessagingCenter.Send((BaseViewModel)this, "ShowError", "Message");
}
When testing, I tried to send the message as StartupViewModel, but the listener was not receiving the messages. I guessed that it would, since the class derives from the BaseViewModel.
Send Method
MessagingCenter.Send<Application>(Application.Current,"RefreshDocs");
Subscribe Method
MessagingCenter.Subscribe<Application>(Application.Current , "RefreshDocs" , (sender) =>
{
});
The goal of MVVM is to abstract away your Views from your Business Logic. This ensures great code reuse, testability, and is pretty awesome. Many MVVM Frameworks offer tools to enhance this such as data binding and dependency services to make our lives easier. These are built into Xamarin.Forms, which is awesome, but one feature less talked about is the Messaging Center. It’s entire goal is to enable ViewModels or other components to communicate with each other without having to know anything about each other besides a simple Message contract.
So for instance, let’s say you are in a master/detail setup where your MasterViewModel has a list of items and your DetailViewModel allows you to create a new item, update an item, or delete an item. When your user is on the detail page and triggers an event you need to somehow message back to your MasterViewModel that has a list of Items so the UI can react on the Master page when we navigate back.
So let’s say our MasterViewModel subscribes to “Update” and “AddNew” message events. It will then update it’s observable collection based on when it receives messages. Our DetailViewModel would then send a message in our SaveCommand to notify anyone that is subscribed to these specific messages:
public ObservableCollection<TripExpense> Expenses { get; set; }
public ExpensesViewModel()
{
Expenses = new ObservableCollection<TripExpense>();
//Subscibe to insert expenses
MessagingCenter.Subscribe<TripExpense>(this, "AddNew", (expense) =>
{
Expenses.Add(expense);
});
//subscribe to update expenxes
MessagingCenter.Subscribe<TripExpense>(this, "Update", (expense) =>
{
ExecuteUpdateExpense(expense);
});
}
private async Task ExecuteSaveCommand()
{
if (IsBusy)
return;
IsBusy = true;
//Send a message to insert/update the expense to all subscribers
if(isNew)
{
MessagingCenter.Send(expense, "AddNew");
}
else
{
MessagingCenter.Send(expense, "Update");
}
IsBusy = false;
navigation.PopAsync();
}
There you have it, messaging made easy! Don’t forget to unsubscribe if you no longer wish to receive notifications.
I am looking for a way to subscribe to events like Storing a specific object type to ServiceStack.Redis.
For example I may
using (var redisClient = new RedisClient())
using (var redisMyObjects = redisClient.As<MyObject>())
{
redisMyObjects.Store(myObject);//<-- I want this to trigger an event somehow
}
Is there anything like a OnStore event which I can hook too, anything out of the box? if not, is there any recommendation about how this should be done?
I don't think there is anything you can hook into (could be wrong).
Two options that came to mind:
1 - Make an extension method
2 - Publish a message to store your object and have a handler that listens for a response and does something. This is probably overkill since it's heading into the publish/subscribe realm. But, I think, worth looking into. (Basic example here and see Pub/Sub here).
Extension Method
public static class RedisClientExtensions
{
public static void StoreWithTrigger<T>(this IRedisTypedClient<T> redisClient, T value, Action<T> trigger)
{
redisClient.Store(value);
trigger(value);
}
}
Using ExtensionMethod
public void MyMethod()
{
using (var redisClient = new RedisClient())
using (var redisMyObjects = redisClient.As<MyObject>())
{
redisMyObjects.StoreWithTrigger<MyObject>(new MyObject(), TriggerEvent);//<-- I want this to trigger an event somehow
}
}
private void TriggerEvent<T>(T value)
{
//dosomething
}
Hope this gives you some ideas.