Develop Reference

ListFragment with AsyncTask not showing ProgressDialog

I have a ListFragment which has an AsyncTask in it to write data to a remote store. I need to have a ProgressDialog show status while the data is being sent since this may take a considerable time depending on the number of files being stored remotely. I have done this successfully from an Activity, but I am having issues showing progress within the ListFragments AsyncTask.
This is complicated by the fact that I need to show updates within the doInBackground method of the task, since that is where the major of the work is being done. That said, the ProgressDialog is not showing up at all even in the non-UI bound onPreExecute() method. Looking at other posts for ProgressDialogs I am using passing getActivity() to the ProgressDialog. Also this mechanism is working with several other Activity classes I am using else where, just not here. I am probably just missing something obvious so any help is appreciated.
Here is a code example - forgive me if it does not compile or has a mistake - I had to remove boatloads of code to boil it down to the problem at hand:
public class MyFragment extends ListFragment {
private ProgressDialog mProgress;
private void hideProgress() {
if (mProgress != null) {
mProgress.dismiss();
mProgress = null;
}
}
private void showProgress(String message) {
if (mProgress != null) {
mProgress.dismiss();
mProgress = null;
}
mProgress = ProgressDialog.show(getActivity(), null, message, true, false);
}
protected void updateProgressMessage(String message) {
if (mProgress != null && mProgress.isShowing()) {
mProgress.setMessage(message);
}
}
public syncForms() {
new syncPendingFormsResultTask().execute();
}
private class syncTask extends AsyncTask<Object, String, Boolean> {
#Override
protected void onCancelled() {
hideProgress();
}
#Override
protected void onPreExecute() {
showProgress("Submitting Form...");
}
#Override
protected Boolean doInBackground(Object... params) {
onProgressUpdate("Uploading Form");
}
#Override
protected void onProgressUpdate(String... values) {
String message = values[0];
updateProgressMessage(message);
}
#Override
protected void onPostExecute(Boolean result) {
showProgress("Upload Complete...");
hideProgress();
}
}
}
}
The syncForms() is the method called to initiate the task.

AsyncTask cannot update progress when slowly creating an object in background

I know how to use AsyncTask to download file, create a zip file or so.. as I call publishProgress() in my loop.
I got stuck when doInBackground() has a single slow line, no loops here, just creating an object where its constructor has slow loops.
I'm not sure about the reasonable way of updating progress in such case.
Here's a sample code:
public class Session {
private QQActivity activity;
public int createdParts;
public DailyClass daily;
private void checkDaily() {
if(!isDailyReady){
new SetAsyncQQDaily().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
}
class SetAsyncQQDaily extends AsyncTask<Void, Void, String> {
#Override
protected String doInBackground(Void... params) {
String sdq = null;
daily = new DailyClass(Session.this); //Very very Slow!
// Do other network http
sdq = new String(Base64.encode(bos.toByteArray(),Base64.DEFAULT));
// Do some work
return sdq;
}
#Override
protected void onPostExecute(String sdq) {
//Never mind
}
#Override
protected void onPreExecute() {
Toast.makeText(activity,"Preparing the daily. Get ready!",Toast.LENGTH_LONG).show();
}
#Override
protected void onProgressUpdate(Void... values) {
//TODO: Update Value of leftBar
activity.leftBar.setProgress((100*createdParts)/Utils.DAILY_PART_COUNT);
}
}
}
In the slow constructor class, I can set-back an integer of the current progress: createdParts, but cannot call publishProgress.
public class DailyClass implements Serializable {
public DailyClass(Session session){
for(int i=1;i<=partCount;i++ ){ //Very slow loop
session.createdParts = i; //TODO: reflect value to progress bar!?
for(int j=0;j<questionsCount;j++){
objects[i-1][j] = createDefined(i);
}
Log.d("Daily","created part"+i);
}
}
//Bla .. !
}
I also though of passing the object of the AsyncTask to the slow constructor in order to call publishProgress() from there, but cannot. As publishProgress() is accessible only from doInBackground()
What's the best practice?

How update UI within AsyncTask

I want download details from web and update the UI within the doInBackground(),
For that I think I must get reference to activity within that method .How can I do it or is there another way to do that? What must be the something parameter? Or can’t update UI real-time?
public class DownloadActivity extends ListActivity {
public class DownloadItems extends AsyncTask<Something,Integer,Long> {
#Override
protected Long doInBackground(DownloadActivity... params) {
Toast.makeText(params[0], getIntent().getExtras().get("location").toString(), Toast.LENGTH_SHORT).show();
return null;
}
}
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
new DownloadItems().execute(Something);
}
}

You can either use a Handler or update your UI in onPostExecute(), which I recommend. Let your Async take care of its background logic and update the UI when that work is finished.

The best way is to simply move anything which affects UI into onPostExecute() because it's there to allow you to update the UI, it's the point of it.
There are other ways but when using AsyncTask there's really no reason not to use this.
public class DownloadActivity extends ListActivity {
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
new DownloadItems(this).execute();
}
public class DownloadItems extends AsyncTask<Something,Integer,Long> {
private Context context;
public DownloadItems(Context c){
context = c;
}
#Override
protected Long doInBackground(DownloadActivity... params) {
// Do something
return null;
}
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
Toast.makeText(context, context.getIntent().getExtras().get("location").toString(), Toast.LENGTH_SHORT).show();
}
}
}

You can create a constructor for passing or adding Context as a parameter.
public class DownloadItems extends AsyncTask<Something,Integer,Long> {
Context context;
public DownloadItems(Context cntx){
context = cntx;
}
#Override
protected Long doInBackground(DownloadActivity... params) {
//Toast.makeText(params[0], getIntent().getExtras().get("location").toString(), Toast.LENGTH_SHORT).show();
Toast.makeText(context, "String test", Toast.LENGTH_SHORT).show();
return null;
}
}
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
new DownloadItems(this).execute(Something);
}
By passing the context of the activity you can make any operation that are context related.

You can't execute UI operations in doInBackground(), you must do them in onPostExecute(). In DownloadActivity, you will create an instance of DownloadItems, and pass it the url where you want to download your stuff :
For example :
public class DownloadActivity extends ListActivity {
private void someMethod() {
DownloadItems yourTask = new DownloadItems(getApplicationContext());
yourTask.execute(yourUrl);
}
In the AsyncTask, you will do your download operations in doInBackground() and return the result so it can be handled by onPostExecute() :
public class DownloadItems extends AsyncTask<Something,Integer,Long> {
Context mContext;
public DownloadItems(Context context){
mContext = context;
}
#Override
protected String doInBackground(String... params) {
String theResult;
// download operations using url stored in params[0], and where you set theResult variable (for example...)
return theResult;
}
In onPostExecute(), you deal with the result, for example in your code above, you can call the Toast :
#Override
protected void onPostExecute(String result) {
Toast.makeText("YOUR TAG", result, Toast.LENGTH_SHORT).show();
}

You can call this in doInBackground:
runOnUiThread(new Runnable() {
public void run() {
//Your code
}
});
But isn't right... Please read the AsyncTask for more details, or use the onPostExecute to update UI...

Wait for AsyncTask to finish

Hi I'm making Login page that access MySQL database. But my Activity always runs the code that check fail/success before it finishes the AsyncTask.
I tried using asynctask.get() method, but it just freeze my UI and doesn't work.
I tried this answer that said I should call the result-checker method inside onPostExecute().
But since I need to change the TextView to show success/failed, it results in NullPointerException because I instantiate the TextView inside onCreate().
I can't move the TextView instantiation into constructor because it will return NullPointerException unable to instantiate activity ComponentInfo.
Login.java
public class Login extends Activity{
//declare global Views here
protected void onCreate(Bundle bundle){
//Setup views
}
protected void onClick(View v){
//Setup necessary variables
AsyncClass async = new AsyncClass(this);
async.execute(username, password);
}
public void checkSuccess(boolean success){
if(success)
textView1.setText("Success");
else
textView1.setText("Failed");
}
}
AsyncClass.java
public class AsyncClass extends AsyncTask<String, String, JSONObject>{
protected JSONObject doInBackground(String... params){
//access database
}
protected void onPostExecute(JSONObject json){
//read the json result
Login login = new Login();
login.checkSuccess(true);
}
}
Any solution? Thanks

How about making AsyncTask as your inner class?
So your code should look something like below.
public class Login extends Activity {
//declare global Views here
protected void onCreate(Bundle bundle) {
//Setup views
}
protected void onClick(View v) {
new AsyncClass().execute(username, password);
}
public void checkSuccess(boolean success) {
if (success) textView1.setText("Success");
else textView1.setText("Failed");
}
class AsyncClass extends AsyncTask < String, String, JSONObject > {
protected JSONObject doInBackground(String...params) {
//access database
}
protected void onPostExecute(JSONObject json) {
checkSuccess(true / false);
}
}
}

try this
protected void onPostExecute(JSONObject json){
//read the json result
Login login = (Login)context; // object that you pass to task constructor
login.checkSuccess(true);
}
Also you can add progress dialog to your task to indicate some job execution
public class BaseTask<T> extends AsyncTask<Object, Void, T> {
public Context context;
public ProgressDialog dialog;
public BaseTask(Context context) {
this.context = context;
this.dialog = new ProgressDialog(context);
}
#Override
protected void onPreExecute() {
this.dialog.setMessage(context.getResources().getString(R.string.loading));
this.dialog.show();
}
#Override
protected T doInBackground(Object... objects) {
//....
return something;
}
#Override
protected void onPostExecute(T result) {
if (dialog != null && dialog.isShowing())
dialog.dismiss();
// do something
}
}

You cannot edit the UI from the async task thread. In order to make updates to the UI thread, use the onProgressUpdate() method. This method is part of your AsyncTask class, is actually executed in the main UI Thread (I hope you use the async task as a nested class btw, since it is declared public I guess your not. You should change that). The onProgressUpdate() Method is called by the OS itself if you call publishProgress(...) inside your Async task.
A small sample:
protected JSONObject doInBackground(String... params){
publishProgress("test");
}
/**
* This method is part of the Async Task
*/
protected void onProgressUpdate(String... progress) {
login.checkSuccess(true);
}

I would use it this way, just override your onPostExecute where you need it or create a own interface
//create a object f your asyncclass and
//override the onPostExecute where you need it
mInfo = new ASYNCCLASS({
#Override
public void onPostExecute(Object result){
//doSomething something with your views!
}
}).execute();
Waiting is not the answer, because you do not know how long your Asynctask will take to end.
Code above is not tested, just pseudoce, but it should show what i mean.
Do not have my IDE round here, so if anybody would correct the brackets if neccessary would be great!
Greetz

Android Why does my app Force to close?

I admit, I'm new at this whole Android stuff. I am trying to make an app but randomly I get Force close errors and I really don't know why. My application has many activities, none of them finish() when I start a new one. I get data from the web (via web services and direct image downloading) and I use AsyncTask a lot. Most of the time it crashes on the asynctask. Here is a sample on how I do things:
private BackTask backTask;
Activity ctx = this;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.trackslist);
backTask = new BackTask();
backTask.execute();
}
protected class BackTask extends AsyncTask<Context, String, myObject>
{
#Override
protected myObject doInBackground(Context... params)
{
try{
if (hasInternet(ctx)==true)
{
//access the web SERVICE here
//initialize myObject WITH result FROM the web
return myObject
}
else
{
return null
}
}catch(Exception ex){
return null;
}
}
#Override
protected void onPreExecute()
{
super.onPreExecute();
}
#Override
protected void onProgressUpdate(String... values)
{
super.onProgressUpdate(values);
}
#Override
protected void onCancelled()
{
super.onCancelled();
}
#Override
protected void onPostExecute( myObject result )
{
super.onPostExecute(result);
if (result==null || result.isEmpty())
{
//no valid result, show a message
}
else
{
//result valid do something with it
}
}
}
#Override
public void onPause()
{
if (backTask!=null && ! backTask.isCancelled())
{
backTask.cancel(true);
}
super.onPause();
}
public void btnStartOnClick(View target) {
Intent intent = new Intent(this, MyNewActivity.class);
startActivity(intent);
}
When the activity gets onPause() the task is being canceled. I am not sure what happens during the try/catch if a error appears, from what I've did, it should return null, but I think here I miss something. As I said before, randomly I get a force close even if I am on another Activity. This is really frustrating as I can't offer a app that has this behavior. So, what am I doing wrong ?

There is problem in your code. I have corrected as follows: You find I have added this while calling async task.
Your async task accept context as argument and you was not passing that.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.trackslist);
backTask = new BackTask();
backTask.execute(this);
}

You need to ask inside your AsyncTask class for isCancelled() and then decide what to do.
Check this question. It has a good explanation by Romain Guy:
You can stop an AsyncTask. If you call
cancel(true), an interrupt will be
sent to the background thread, which
may help interruptible tasks.
Otherwise, you should simply make sure
to check isCancelled() regularly in
your doInBackground() method. You can
see examples of this at
code.google.com/p/shelves.