CODEWITHSUNDEEP
javaandroidmultithreadingperformance
Evin1_
Evin1_

Reputation: 12906

Android - What is a Handler Message?

I'm talking about this class.

The main documentation states:

Defines a message containing a description and arbitrary data object that can be sent to a Handler. This object contains two extra int fields and an extra object field that allow you to not do allocations in many cases.

I would love to see a little and compact example on when and how to use them.

Upvotes: 3

Views: 799

Answers (2)

CommonsWare
CommonsWare

Reputation: 1007658

So I would assume that it is some kind of communication between different threads

You can attach a Handler to the main application thread (a.k.a., UI thread), and you can create separate HandlerThread instances for other threads with associated Handler instances.

One thread can send a Message, via a Handler, where the Handler will process the Message on its own thread, in the handleMessage() method. For example, a regular background Thread could package the results of its work (e.g., downloaded data) into a Message, and give that to a Handler attached to the main application thread. That Handler will get the Message in handleMessage(), called on the main application thread, and can then update the UI safely using the data from the background thread.

This is a very low-level means of inter-thread communication in Android. More often, you are better served using something a bit higher-order, like an event bus.

Why to use them instead of using SharedPreferences

SharedPreferences are for data storage, not inter-thread communication.

or maybe a Singleton class?

While a singleton can provide a central point of data, on its own, it does not provide any sort of inter-thread communication.

I would love to see a little and compact example on when and how to use them.

For 99% of Android developers, the answer is: don't use them. Use something that is built on top of Handler and Message, such as:

  • AsyncTask
  • LocalBroadcastManager
  • Square's Otto
  • greenrobot's EventBus
  • etc.

Upvotes: 6

Khan Laoji
Khan Laoji

Reputation: 19

A Thread can have one handler and one messageQueue only, a message is some arbitrary data that is handled by the handler whom put on it's messageQueue, the messageQueue loop every message and process them until it has no more message, all data are versatile and executed asap, no need to save it on HDD, it's low level code you dont deal with it often

Upvotes: 1

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