Android Messaging mechanism

First, Handler 1. Use <1> Define a Handler in the main thread, overriding the Handlemessage method

  //in the main thread, define aHandler
  PrivateHandlerHandler=NewHandler () {
      //This method is executed in the main thread.
      @Override
      Public voidHandlemessage(Message msg) {
         Tv_result. SetText (Msg.obj. toString ());
      }
};

<2> sending messages using handler created in the main thread in child threads

    Message msg=message ();
    Msg.obj=content;
    handler. SendMessage (msg); // Send Message

2, Handler principle
A child thread is not able to manipulate the UI thread directly, it needs to be sent to the (MessageQueue) message queue by handler, and then the Looper will continue to loop
get this message, and then get the message through the Handlemessage method execution
The role of handler is to send messages and process messages.
The role of Looper is to take messages in Message Queuing (MessageQueue)
Looper is created on the mainline Cheng. 3. The use of the Message what property <1> set What's value

    Message msg=message ();
    Msg.what =requestexception;
    handler. SendMessage (msg);

<2> in the Handlemessage method, perform different actions

    @Override
    Public voidHandlemessage(Message msg) {
        Switch(Msg. What){
             Caserequestsuccess://Request succeeded
                Tv_result. SetText (Msg.obj. toString ());
Break ;
 CaseRequestnotfind://target resource does not exist
                Toast.Maketext(Mainactivity.This ,"target resource does not exist", Toast.Length_short). Show ();
Break
 Caserequestexception://exception
                Toast.Maketext(Mainactivity.This ,"server busy Please wait ... ", Toast.Length_short). Show ();
        }
}

about Message: can be created by , in such a way, to reduce the creation of objects.



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Android Messaging mechanism