Android calling AsyncTask right after an another finished

Question

I have some problem with Android AsyncTask. There is an Activity which contains some TextView a button and a picture. When an user entered this activity I start an asynctask

Answer 1

1:

You could write the code for authTask and then for imageTask, one after the other, within a single doInBackground(). This single AsyncTask instance would be fire by a single execute() statement. This may or may not be practical depending on needed UI interactions.

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2:

Edit: as noted by kabuku this information is mostly for HoneyComb+. Pre HoneyComb I would definitely go with option 1 above. executeOnExecutor() is api level 11+

In receent versions, execute() will send your AsyncTasks in series by default (ICS+). If you want to make sure this happens, specify the serial executor.

In your case this would be:

authTask.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);
// Image task will only be done AFTER textViewTask is done
imageTask.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR);

And for newer versions a simple

...
// ICS+ and pre honeycomb (I think)
authTask.execute();
// Image task will only be done AFTER textViewTask is done
imageTask.execute();
...

From the AsycnTask.execute() documentation:

Note: this function schedules the task on a queue for a single background thread or pool of threads depending on the platform version. When first introduced, AsyncTasks were executed serially on a single background thread. Starting with DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. After HONEYCOMB, it is planned to change this back to a single thread to avoid common application errors caused by parallel execution.

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PS: To run tasks independent of each other you must use the AsyncTask.THREAD_POOL_EXECUTOR. That requires a different executor:

// Go parallel! (NOT what you want)
task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);