Android thread Mechanism Analysis (ppt) and androidppt

Android thread Mechanism Analysis (ppt) and androidppt

How to Use the Android Handler mechanism?

The Handler object is in the same thread as its caller. If a delayed operation is set in Handler, the calling thread will also be blocked. Each Handler object is bound to a logoff object, and each logoff object corresponds to a Message Queue (MessageQueue ). If the logoff object bound to the Handler is not specified when the Handler is created, The logoff object of the current thread is bound to the Handler by default.
In the main thread, you can directly use new Handler () to create a Handler object, which will be automatically bound to the logoff object of the main thread. If Handler is directly created in a non-main thread, an error will be reported, the Android system does not enable logoff in the main thread by default, and the Handler object must be bound to the logoff object. In this case, you must manually enable logoff in this thread. prepare () --> logoff. loop (), and then bind it to the Handler object; or use logoff. getMainLooper () to obtain the Looper of the main thread and bind it to this Handler object.
All the messages sent by Handler are added to the logoff MessageQueue. Handler contains two queues: thread queue and message queue. post () can add the thread object to the thread queue; Use Handler. sendMessage () can be used to add a message object to a message queue. The source code analysis shows that Handler has only one message queue, namely, MessageQueue. The thread object passed through post () will be encapsulated into a message object and passed into MessageQueue.
After a thread object is put into a Message Queue using post (), when logoff polls the thread for execution, it does not actually start a new thread separately, but it is still executed in the thread bound to the current logoff. Handler only calls the run () of the thread object. For example, the UI update command is defined in the Child thread. If the thread is directly enabled for execution, an error is reported () add it to the Logoff of the main thread and execute it to update the UI.
After you use sendMessage () to add a message object to a message queue, when logoff polls the message, handleMessage () of Handler is called to process it. Taking UI update as an example, if this method is used, the Logoff of the main thread is first bound to the Handler object, and handleMessage () is overloaded to process UI updates, then you can send a message to it.

Principle of android handler Mechanism

Andriod provides Handler and logoff to satisfy inter-thread communication.
Handler first-in-first-out principle.
The logoff class is used to manage Message Exchange between objects in a specific thread ).

1) loue: A thread can generate a loue object to manage the Message Queue (Message Queue) in this thread ).

2) Handler: You can construct a Handler object to communicate with logoff so as to push new messages to the Message Queue or receive messages sent by logoff from the Message Queue.

3) Message Queue: used to store messages placed by threads.

4) thread: the UI thread is usually the main thread, and Android will create a Message Queue for it when starting the program.