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问题:

When using a AsyncTaskLoader how would you update a progressbar showing the status as it is being updated? Normally you wait for the callback to remove when done, but how to do running updates? Would you let the main thread (ui) poll the data as it is being set or something?

Edit: I'm talking about AsyncTaskLoader, look at the loader part. Here is link to class: http://developer.android.com/reference/android/content/AsyncTaskLoader.html

I want to use it because its the future :), I know how to do this with AsyncTask.

回答1:

You can do that with loaders, but you need to keep and update a WeakReference on your Activity :

public class LoaderTestActivity extends FragmentActivity implements LoaderCallbacks<Void> {
    private static final int MAX_COUNT = 100;

    private ProgressBar progressBar;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_async_task_test);

        progressBar = (ProgressBar) findViewById(R.id.progressBar1);
        progressBar.setMax(MAX_COUNT);
        AsyncTaskCounter.mActivity = new WeakReference<LoaderTestActivity>(this);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_async_task_test, menu);
        return true;
    }

    public void onStartButtonClick(View v) {
        startWork();
    }

    void startWork() {
        getSupportLoaderManager().initLoader(0, (Bundle) null, this);
    }

    static class AsyncTaskCounter extends AsyncTaskLoader<Void> {
        static WeakReference<LoaderTestActivity> mActivity;

        AsyncTaskCounter(LoaderTestActivity activity) {
            super(activity);
            mActivity = new WeakReference<LoaderTestActivity>(activity);
        }

        private static final int SLEEP_TIME = 200;

        @Override
        public Void loadInBackground() {
            for (int i = 0; i < MAX_COUNT; i++) {
                try {
                    Thread.sleep(SLEEP_TIME);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                Log.d(getClass().getSimpleName(), "Progress value is " + i);
                Log.d(getClass().getSimpleName(), "getActivity is " + getContext());
                Log.d(getClass().getSimpleName(), "this is " + this);

                final int progress = i;
                if (mActivity.get() != null) {
                    mActivity.get().runOnUiThread(new Runnable() {

                        @Override
                        public void run() {
                            mActivity.get().progressBar.setProgress(progress);
                        }
                    });
                }
            }
            return null;
        }

    }

    @Override
    public Loader<Void> onCreateLoader(int id, Bundle args) {
        AsyncTaskLoader<Void> asyncTaskLoader = new AsyncTaskCounter(this);
        asyncTaskLoader.forceLoad();
        return asyncTaskLoader;
    }

    @Override
    public void onLoadFinished(Loader<Void> arg0, Void arg1) {

    }

    @Override
    public void onLoaderReset(Loader<Void> arg0) {

    }

}

回答2:

You can use handler, i think it will be lighter for system than intent

public class MyFragmentActivity extends FragmentActivity{
private final static int MSGCODE_PROGRESS = 1;
private final static int MSGCODE_SIZE = 2;

    private final Handler mHandler = new Handler() {
    public void handleMessage(Message msg) {
        Bundle bundle = msg.getData();
        if(null != bundle){
            int data = msg.getData().getInt(BUNDLE_PROGRESS);
            if(msg.what == MSGCODE_SIZE){
                mProgressBar.setMax(data);
            } else if(msg.what == MSGCODE_PROGRESS){
                mProgressBar.setProgress(data);
            }
        }
    }
};
}

Set mHandler to constructor of AsyncTaskLoader and from loadInBackground you can update progress

Bundle bundle = new Bundle();
bundle.putInt(BUNDLE_PROGRESS, lenghtOfFile);
Message msg = new Message();
msg.setData(bundle);
msg.what = MSGCODE_SIZE;
mHandler.sendMessage(msg);

回答3:

I broadcast an Intent to the Activity (and it's received by a BroadcastReceiver). I'm not very happy with this solution but it works. The AsynTask publishProgress is really easier to use. Did you find some other solution ?

回答4:

I'm using this with my AsyncTaskLoader, inside of loadInBackground

runOnUiThread(new Runnable() {
    public void run() {
        //UI code
    }
});

However, this doesn't work with an configuration change (like orientation change). I'm not convinced AsyncTaskLoader is the best to use if you need to update the UI, but it works best when handling configuration changes. I don't know why they created both an AsyncTaskLoader and an AsyncTask each with their own tradeoffs. Just frustrates and confuses developers. On top of that AsyncTaskLoader has very little documentation.

回答5:

I just had this problem. I used a static AtomicInteger in my activity to store the progress. The loader updates it via a callback and the activity polls it and displays the progress.

In the loader callback onLoadFinished I hide my progress panel, which causes the polling loop to exit.

Usually I'd avoid static state, but I think overall this is simpler than the alternatives. In my case, I have a different layout in landscape, so I'm happier leaving the orientation changes behaving as normal.

private Handler progressHandler; // init with new Handler(getMainLooper())
private static AtomicInteger progress = new AtomicInteger(0);

...

private void beginProgressUiUpdates() {
    progress.set(0);
    displayProgress();
    progressHandler.postDelayed(pollProgress, PROGRESS_POLL_PERIOD_MILLIS);
}

private Runnable pollProgress = new Runnable() {
    public void run() {
        if (findViewById(R.id.progressPanel).getVisibility() == View.VISIBLE) {
            displayProgress();
            progressHandler.postDelayed(pollProgress, PROGRESS_POLL_PERIOD_MILLIS);
        }
    }
};

private void displayProgress() {
    ((ProgressBar)findViewById(R.id.progressBar)).setProgress(progress.get());
}