Handler's role

In Android, only the thread that initially creates a view hierarchy can access this structure. The implication is that the thread that originally created the interface cannot access interface elements. In a thread that does not create an interface, how does one output the content to the interface element? The Android platform provides a mechanism called message queue to solve the problems encountered in the above application. First, create an interface instance in the interface thread that can be associated with the message queue of the interface thread. Other threads can send messages to the Message Queue of the interface thread through this interface, finally, an interface thread outputs the message content to the interface container. This interface instance is a handler.