CommunityToolkit.Mvvm8.1 message notification (4)

Description

In order to separate different modules of the application and reduce references between modules, CommunityToolkit.Mvvm provides a message notification function, which can facilitate data transfer between modules.

Send a message

Method: WeakReferenceMessenger.Default.Send

The official recommendation is to use ValueChangedMessage to encapsulate data transmission

//Send send message
 WeakReferenceMessenger. Default. Send( "qq1" );

 //Special attention: directly passing the value can only be a reference type, and the value type cannot be compiled successfully (for example: the following 2 sentences will not work)
 //WeakReferenceMessenger.Default.Send(11, "token_1");
 //WeakReferenceMessenger.Default.Send(true, "token_1");

 //The above is also possible, but the official recommendation is to use ValueChangedMessage to encapsulate data transfer
 WeakReferenceMessenger.Default.Send<ValueChangedMessage , string>( new ValueChangedMessage( "qq1 from UserControlLeftViewModel") , "token_1" );

It is recommended to bring the token name when sending messages, so that it is convenient for subscription receivers to filter data

WeakReferenceMessenger.Default.Send<ValueChangedMessage , string>( new ValueChangedMessage( "qq1 from UserControlLeftViewModel") , "token_1" );  

Send message passing object

 public class MyUserMessage
     {
         public string UserName
         {
             get; set;
         }

      

         public int Age
         {
             get; set;
         }
     }

//Send sends a complex data
 var _data1 = new MyUserMessage() { Age = 18 , UserName = "qq" };
           
 WeakReferenceMessenger.Default.Send<ValueChangedMessage , string>( new ValueChangedMessage( _data1 ), "token_class" );

Send a message and return a response value

 /// 

     /// Must inherit RequestMessage RequestMessage means the type of returned data is string
     /// 
     public class MyMessage : RequestMessage
     {
         public string Datas;

         public int Ids;
     }

 //result receives the returned value
             //MyMessage must inherit from RequestMessage
             var _data2 = new MyMessage() { Datas = "qqq" , Ids = 100 };
             var result1 = WeakReferenceMessenger.Default.Send( _data2, "token_Response");
             if ( result1 != null )
             {
                 //Get the returned value
                 var val = result1. Response;

                 Name = val;

             }

Receive subscription news

Two ways to receive:

Method 1. Inherit ObservableRecipient

Method 2. Implement interface IRecipient

Method 1 is more flexible than Method 2, and Method 1 is recommended

Receiver remember to set IsActive=true to receive the message

We receive message data in OnActivated of vm

 [ObservableProperty]
         private string name = "hello";

         public UserControlTopViewModel ()
         {
             //Note that you have to write in this way before you can answer
             IsActive = true;
         }

 protected override void OnActivated ()
         {
             //RegisterThe first type is generally its own type, and the second is the type of received data
             //The first parameter of the Register method is generally this, and the second parameter is a method that can get the received value
             Messenger.Register( this , ( r , message ) =>
             {
                 Name = Name + "Received msg:" + message;
             } );

             //RegisterThe first type is generally its own type, the second is the type of received data, and the third is the type of token data
             //The first parameter of the Register method is generally this, the second parameter is token, and the third parameter is a method that can get the received value
             //Messenger.Register( this , "token_1" , ( r , message ) =>
             //{

             // Name = Name + "Received msg:" + message;
             //} );
             //ValueChangedMessage
             Messenger.Register<UserControlTopViewModel , ValueChangedMessage , string>( this , "token_1" , ( r , message ) =>
             {

                 Name = Name + "Received msg:" + message.Value;
             } );



             //Messenger.Register( this , "token_class" , ( r , user ) =>
             //{
             // Name = Name + "Received msg:" + user.UserName + user.Age;
             //} );
             Messenger.Register<UserControlTopViewModel , ValueChangedMessage , string>( this , "token_class" , ( r , user ) =>
             {
                 Name = Name + "Received msg:" + user.Value.UserName + user.Value.Age;
             } );


             Messenger.Register( this , "token_Response" , ( r , message ) =>
             {
                 Name = Name + "Received msg:" + message.Datas;

                 //Reply is a reply, so you can return a value
                 message.Reply( "UserControlTopViewModel gives you the return value" );

             } );
         }

Self Demo address:

https://github.com/aierong/WpfDemo/tree/main/WpfDemoNet6/MessengerDemo

My Series
A.Sql Server2005 Transact-SQL new weapon learning
B.MCAD learning
C.Code Reading Summary
D.ASP.NET State Management
E.DB (database)
F.WAP
G.WinForm

H.Flex

I hope the knowledge mentioned above can give you some hints, and welcome to exchange and correct.
Author: aierong
Source: http://www.cnblogs.com/aierong
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