Android加载器与处理程序

Question

The loaders help in asynchronously getting the data from a data source. We can achieve the same effect using Handlers , where we can kick off a thread or execute a Executor and can fetch the data in that thread. Once data is fetched, we can update the UI using the UI handler Message mechanism. Then why do go for coding the complex loaders when we can achieve the same by using Handlers .

Answer 1

Loaders were introduced to make it easier in implementing correct data loading on android platform. This means:

• doing all the heavy stuff on background thread
• safely introducing loaded data in UI
• caching of data, this means improving speed
• loaders can live outside the Activity lifecycle, so if you have config change then your data is not destroyed
• loaders will be reloaded once your data store changes

using Handlers,Executors, or AsyncTasks does not take into account all above points. Your will have to manage this by yourself, and this is the work android developers put into Loaders implementation.

Ie. using AsyncTask for loading some data requires you to watch out for screen rotations, ie. you must somehow retain reference to your AsyncTask that might still do something in background once you activity is recreated due to screen rotation.