正确地使用onUpgrade（和内容提供者）来处理更新而不阻塞主线程，“ Loader”是否毫无意义？

Question

This is one of the questions that involves crossing what I call the "Hello World Gulf" I'm on the "Hello world" I can use SQLite and Content Providers (and resolvers) but I now need to cross to the other side, I cannot make the assumption that onUpgrade will be quick.

Now my go-to book (Wrox, Professional Android 4 development - I didn't chose it because of professional, I chose it because Wrox are like the O'Reilly of guides - O'Reilly suck at guides, they are reference book) only touches briefly on using Loader s, so I've done some searching, some more reading and so forth.

I've basically concluded a Loader is little more than a wrapper, it just does things on a different thread, and gives you a callback (on that worker thread) to process things in, it gives you 3 steps, initiating the query, using the results of the query, and resetting the query.

This seems like quite a thin wrapper, so question 1:

Why would I want to use Loader s?

I sense I may be missing something you see, most "utilities" like this with Android are really useful if you go with the grain so to speak, and as I said Loaders seem like a pretty thin wrapper, and they force me to have callback names which could become tedious of there are multiple queries going on

http://developer.android.com/reference/android/content/Loader.html

Reading that points out that "they ought to monitor the data and act upon changes" - this sounds great but it isn't obvious how that is actually done (I am thinking about database tables though)

Presentation

How should this alter the look of my application? Should I put a loading spinning thing (I'm not sure on the name, never needed them before) after a certain amount of time post activity creation? So the fragment is blank, but if X time elapses without the loader reporting back, I show a spiny thing?

Other operations

Loaders are clearly useless for updates and such, their name alone tells one this much, so any nasty updates and such would have to be wrapped by my own system for shunting work to a worker thread. This further leads me to wonder why would I want loaders?

What I think my answer is Some sort of wrapper (at some level, content provider or otherwise) to do stuff on a worker thread will mean that the upgrade takes place on that thread, this solves the problem because ... well that's not on the main thread.

If I do write my own I can then (if I want to) ensure queries happen in a certain order, use my own data-structures (rather than Bundle s) it seems that I have better control.

What I am really looking for

Discussion, I find when one knows why things are the way they are that one makes less mistakes and just generally has more confidence, I am sure there's a reason Loader s exist, and there will be some pattern that all of Android lends itself towards, I want to know why this is.

Example:

Adapters (for ListViews) it's not immediately obvious how one keeps track of rows (insert) why one must specify a default style (and why ArrayAdapter uses toString) when most of the time (in my experience, dare I say) it is subclasses, reading the source code gives one an understanding of what the Adapter must actually do, then I challenge myself "Can I think of a (better) system that meets these requirements", usually (and hopefully) my answer to that converges on how it's actually done.

Thus the "Hello World Gulf" is crossed.

I look forward to reading answers and any linked text-walls on the matter.

Answer 1

您不应该直接使用Loader，而应该使用LoaderManager