I post here because I have a difficult question.
I have a class that extends TabNewsActivity of Activity
This class contains a nested class TabNewsActivity: DownloadData which extends to AsyncTask >>
This class TabNewsActivity displays the recovered data from my web service, a spot DownloadData is asynchronous which allows me to retrieve the values of my web service in a list.
To perform an update values (in my application => refresh) I have to do this:
DownloadData (). Execute ();
But I can not do it out of my context TabNewsActivity: s
I would like a way to re execute this command, but in another tab for example.
Thank you for your help
Suggest making your DownloadData subclass in a separate class file, not a nested class of TabNewsActivity. You can pass it a Handler to act as a completion callback perhaps. This way you can execute DownloadData from TabNewsActivity, and pass it a Handler to call in TabNewsActivity upon completion. The same could hold true when calling it from another class.
AsyncTask execute() method is static so you dont need an instance of anything to call it. You call it like this:
AsyncTask.execute();
That will run what you have in your doInBackground() method. As far as I know you should be able to call AsyncTask.execute() anywhere in your app as long as you import AsyncTask.
Use AsyncTask inside of a Service.
Related
I'm wondering where I should place my AsyncTask in my android project. As of right now I'm implementing an AsyncTask as a private class of my activity its running under. What I am going to do is in each activity that has a network call I will implement its own private class of AsyncTask. I have a few questions though
In The preexecute method it says I can interact with the activity and place a spinner or progress bar. I do this by using My_Activity_Class_Name.this. So my question is does that line of code reference the activity the AsyncTask is called from? If so I believe that will be a static method. How do i actually pass in the instance of the class so I can interact with non static functions?
I want to place all my Async code into one class for its respective needs. My quesiotn though is if i need to return a type back to the class that calls the Async method how can I return a value? Also is this the best practice?
You should make your inner private AsyncTask class - static. This is because otherwise it will have implicit reference to your Activity - this means that if your Activity will be recreated - ie. due to config change - then your AsyncTask will still hold your activity reference causing reference leak. This means you should pass reference to your activity to AsyncTask in ie. constructor of AsyncTask, and keep it in WeakReference (WeakReference/AsyncTask pattern in android).
So my question is does that line of code reference the activity the ASYNC Task is called from?
yes, but only if your AsyncTask class is non static
If so I beleve that will be a static method. How do i actually pass in the instance of the class so i can interact with non static functions?
its not a static method, with My_Activity_Class_Name.this you can access non static methods of your Activity class.
My quesiotn though is if i need to return a type back to the class that calls the Async method how can I return a value? Also is this the best practice?
You can call a method on your Activity class, there is nothing wrong with that. Remember that you cannot access UI widgets from non UI thread. So update your Activity widgets from onPostExecute which is called on UI thread.
I am new to Android Development and have a question (will probably show my newbie status). I am calling an asynchtask from a custom activity. Once the asynch task is completed onPostExecute I would like to call back into my activity and set a pojo (Map()). I know that onPostExecute seems to run on the UI thread but I am not sure how to get visibility into the calling Activity.
The goal is to be able to have some variables set in my activity and ideally the webservice call will already be completed.
Thanks,
Craig
If the AsyncTask is a subclass of the activity, it has access to all public, protected, and private variables of the superclass. If its not, you need to write a public function in the Activity class to set the variables, and call it from the AsyncTask. That will probably require you to pass the activity to the AsyncTask via the constructor and save it in a member variable of the task.
I was trying to use the managedquery() in android to get back a cursor when working with a content provider. I used this because it was mentioned that this will handle the closing of the cursor by itself when the activity is paused or resumed.
But however this works on the Activity class only. But I have more than one background threads using the asynctask in android. I do a same fetch of list in more than one thread. So its repetitive code. This is because i cant call a function of one thread class from other thread dobackground(). Is there a easy and safe way to avoid this repetitive code. Kindly advice. Thank you for your help and time.
Can't you have an abstract asynctask class which implements this db query code (if that's all you're doing in the background thread, then put it in doInBackground(), otherwise put it in a private method), and then have your concrete child classes which extend this abstract class call super.doInBackground or call that private method?
E.G.
private abstract AbstractQueryTask extends AsyncTask<Long, Void, Long> {
protected Cursor querycode{
//put your query code here
}
}
public ConcreteQueryTask extends AbstractQueryTask {
//put the doInBackground and onPostExecute implementations here
}
I am new to android development. I would like to accomplish a task described as follows:
A main activty which calls external class(the other class would extend AsyncTask) to parse xml and receive json by requesting to web service and starts a ProgressDialog.
The class performs xml and json parsing in its doInBackground method.
In the onPostExecute method after parsing is complete, dismiss the ProgressDialog that was set in the main activity.
I could do this by passing the ProgressDialog object to the parsing class and dismissing the same object in its onPostExecute method.
I think passing an instance of UI object as argument is not a good approach to program, I hope there must be some other ways to work around.
Please suggest.
Thank you
The easiest way to decouple these is to use an interface:
Define a call-back interface (let's call it WorkDoneListener) with a single method: workDone().
Declare your activity class to implement WorkDoneListener and implement workDone() to dismiss the dialog.
Define the AsyncTask's constructor to accept a WorkDoneListener. Stash the reference in a member field.
In onPostExecute, call the listener's workDone() method.
Ted's answer is what you should do if your AsyncTask is too big and you want to declare it in other file. However, keep in mind that usually you declare the AsyncTask inside your UI class:
public class YourActivity extends Activity{
private class YourAsyncTask extends AsynkTask<etc.>{
}
}
In fact, if you are using you AsyncTask from that activity only (I mean, if you are not using it anywhere else), declaring the AsyncTask as a inner class is a good design practice.
I want to tell you about the structure of my classes.
I have an HttpUtilities class, from which I am doing requests(send and get JSON objects) to server. It's a public class with private constructor and static methods.
I have also user class which manipulates data(set string to JSON, and JSON to ...).
Within my activity I have declared the instance of user class.
There are some methods(SignIn, SignOut, InserToListView) there which call corresponding methods of httpUtilities.
Now, I want, that for each event of user, using AsynkTask do request to server and change ui.
I want to call method(for example InserToListview) of user class within new Thread using AsynkTask.
It would be easier if you tried your hand at this first and then asked questions later, but here is some general advice to get you started:
Subclass AsyncTask.
Implement doInBackground, calling your insert method.
(Wherever you are calling your insert method now) instantiate your subclass of AsyncTask.
Call the execute method on your new custom AsyncTask object.
Store your AsyncTask in an instance variable so you can cancel it later on.