MessagingConnection

in namespace DotVVM.BusinessPack.Messaging

Usage & Scenarios

Establishes a connection to a SignalR hub and allows specifying handlers for client-side hub methods.

Sample 1: Basic connection

To establish a connection to a SignalR hub, place the MessagingConnection control in the page and specify the URL of the hub.

You can use the IsConnected property to detect whether the connection is active or not.

You can define one or more MessageHandler controls to run commands when methods are called on the hub.

The MessageHandler controls can be defined:

Inside this MessagingConnection control. See MessageHandler - Sample 1] for more info.
Outside this control. In this case, you need to set the ConnectionId property on both MessagingConnection and MessageHandler controls to the same value. See MessageHandler - Sample 2] for more info.

page.dothtml
ViewModel.cs

<bp:MessagingConnection ServiceUrl="/hubs/Chat" 
                        IsConnected="{value: IsConnected}">
    ...
</bp:MessagingConnection>

public class SampleViewModel : DotvvmViewModelBase
{
    public bool IsConnected { get; set; }
}

Sample 2: Connection events

To handle various connection lifecycle events, you can bind to the Connected and Disconnected events, and also to Reconnecting and Reconnected events.

The Error event will be triggered whenever there is an error (connecting to the hub, sending a message). Since any error means that the connection is broken, this event is typically accompanied by one of the other events.

It is recommended to use static commands since the events may be fired in a quick sequence.

page.dothtml
ViewModel.cs

<bp:MessagingConnection ServiceUrl="/hubs/Chat" 
                        Connected="{staticCommand: Events.Add("Connected")}" 
                        Disconnected="{staticCommand: Events.Add("Disconnected")}" 
                        Reconnecting="{staticCommand: Events.Add("Reconnecting")}" 
                        Reconnected="{staticCommand: Events.Add("Reconnected")}" 
                        Error="{staticCommand: Events.Add("Error")}"> 
    ...
</bp:MessagingConnection>

public class SampleViewModel : DotvvmViewModelBase
{
    public List<string> Events { get; set; } = new();
}

Sample 3: Reconnect settings

The MessagingConnection control has the TryReconnect property which specifies whether the control should try to reconnect automatically when the connection is lost.

The ReconnectTimeout property specifies the number of seconds after which the reconnect will be performed (default is 30 seconds).

The ReconnectAttempts property can be used to restrict the number of attempts for reconnection (default is 30 attempts, 0 means that the reconnects will be attempted infinitely).

page.dothtml

<bp:MessagingConnection ServiceUrl="/hubs/Chat" 
                        TryReconnect="true" 
                        ReconnectAttempts="0" 
                        ReconnectTimeout="5"> 
    ...
</bp:MessagingConnection>

Sample 4: Send messages to the hub

You can call hub methods on the server by using the _messaging variable in the static commands bindings.

In order to reference the connection which you want to send the message, you need to set the ConnectionId of the MessagingConnection control to some value. Then, you can use this id in the binding.

<bp:MessagingConnection ServiceUrl="/hubs/Chat" 
                        ConnectionId="Chat">
    <bp:MessageHandler MethodName="IncomingMessage" 
                       Command="{staticCommand: (ChatMessageDTO o) => Messages.Add(o)}" />
</bp:MessagingConnection>

<dot:Repeater DataSource="{value: Messages}" WrapperTagName="ul"> 
    <li>{{value: Author}}: {{value: Text}}</li>
</dot:Repeater>

<form>
    <dot:TextBox Text="{value: AutorName}" />: 
    <dot:TextBox Text="{value: NewMessage}" /> 
    <dot:Button Text="Send" 
                IsSubmitButton="true" 
                Click="{staticCommand: _messaging.GetConnection("Chat").InvokeAsync("SendMessage", AuthorName, NewMessage)}" />
</form>

public class SampleViewModel : DotvvmViewModelBase
{
    public List<ChatMessageDTO> Messages { get; set; } = new();

    public string AutorName { get; set; } = "user";

    public string NewMessage { get; set; }
}

public class ChatMessageDTO 
{
    public string Text { get; set; }
    public string Author { get; set; }
}

public class ChatHub : Hub 
{

    public async Task SendMessage(string autor, string text) 
    {
        await this.Clients.AllExcept(Context.ConnectionId)
            .SendAsync("IncomingMessage", new ChatMessageDTO() { Author = author, Text = text });
    }

}

Show all inherited properties

Properties

Name	Type	Description	Notes	Default Value
ClientIDMode	ClientIDMode	Gets or sets the client ID generation algorithm.	attribute inner element static value bindable default	Static
ConnectionId	String		attribute inner element static value bindable default	null
DataContext	Object	Gets or sets a data context for the control and its children. All value and command bindings are evaluated in context of this value. The DataContext is null in client-side templates.	attribute inner element static value bindable default	null
ID	String	Gets or sets the control client ID within its naming container.	attribute inner element static value bindable default	null
IncludeInPage	Boolean	Gets or sets whether the control is included in the DOM of the page.	attribute inner element static value bindable default	True
IsConnected	Boolean		attribute inner element static value bindable default	False
MessageHandlers	List<MessageHandler>		attribute inner element static value bindable default	null
ReconnectAttempt	Int32		attribute inner element static value bindable default	30
ReconnectTimeout	Int32		attribute inner element static value bindable default	30
ServiceUrl	String		attribute inner element static value bindable default	/__dotvvm_businesspack_messaging/default
TryReconnect	Boolean		attribute inner element static value bindable default	True

Events

	Name	Type	Description
	Connected	ICommandBinding
	Disconnected	ICommandBinding
	Error	ICommandBinding
	Reconnecting	ICommandBinding

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