Develop Reference

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

Show ProgressBar in another thread

For a few days a have some problem.
I need to show simple ProgressBar (not dialog) while doing some stuff in main thread...
I thought its a very simple question, but i cant do this, help me please.
First i tried simple setVisibility(View.VISIBLE) before and setVisibility(View.GONE) after.
But this is doing in the same thread, and ProgressBar freezed while my function working.
Now i have this code, but i have some error, and i dont know whats wrong..
my simple layout :
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<ProgressBar
android:id="#+id/loading"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:visibility="gone" />
</FrameLayout>
i have a base activity :
public class BaseActivity extends Activity {
public ProgressBar loading;
public class ProgressBarShow extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... unused) {
return(null);
}
protected void onProgressUpdate() {
}
protected void onPreExecute() {
loading.setVisibility(View.VISIBLE);
}
protected void onPostExecute() {
}
}
}
and finally my working activity , which extends BaseActivity
public class SearchActivity extends BaseActivity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
loading = (ProgressBar) findViewById(R.id.loading);
new ProgressBarShow().execute();
//doing long stuff
//new ProgressBarHide().execute(); there isnt, but sense the same
}
}
I have many activities, which need progress bar, thats why i have created BaseActivity,
to not to dublicate code.
I need to do long work (stuff function) in main thread, because i want to freeze main window and not to allow user do anything (click button etc..), just show working ProgressBar.
Whats wrong in my example? Or give me some advice how can i do this better

class ProgressTask extends AsyncTask<Integer, Integer, Void>{
ProgressBar progress;
Context context;
public ProgressTask(ProgressBar progress, Context context) {
this.progress = progress;
this.context = context;
}
#Override
protected void onPreExecute() {
// initialize the progress bar
// set maximum progress to 100.
progress.setMax(100);
}
#Override
protected Void doInBackground(Integer... params) {
// get the initial starting value
int start=params[0];
// increment the progress
for(int i=start;i<=100;i+=5){
try {
boolean cancelled=isCancelled();
//if async task is not cancelled, update the progress
if(!cancelled){
publishProgress(i);
SystemClock.sleep(1000);
}
} catch (Exception e) {
Log.e("Error", e.toString());
}
}
return null;
}
//Has direct connection to UI Main thread
//Called everytime publishProgress(int) is called in doInBackground
#Override
protected void onProgressUpdate(Integer... values) {
progress.setProgress(values[0]);
Toast.makeText(context, "test"+values[0], Toast.LENGTH_SHORT).show();
}
#Override
protected void onPostExecute(Void result) {
// async task finished
Log.v("Progress", "Finished");
}
#Override
protected void onCancelled() {
progress.setMax(0);
}
}

Use AsyncTask http://developer.android.com/guide/topics/fundamentals/processes-and-threads.html Put your ProgressBar in it, while all work is doing in main thread

Refresh Game Score TextView using AsyncTask

I am writing a board game in Android where the UI consists of textViews for the scores (CPUScore and PlayerScore). The problem I have is that the UI does not update the score from its initial value when onCreate is called. I have looked at similar questions and the solution most suggested is to use AsyncTask to update the UI thread in the background. However I did not find a solution that dealt explicitly with how to use textViews in AsyncTask.
Here is my attempt:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//....
setContentView(R.layout.main_layout);
//.....
//------------ textViews declared here don't refresh -------------------
TextView playerScoreForm = (TextView) findViewById(R.id.PlayerTotalScore);
playerScoreForm.setText(Integer.toString(PlayerTotal));
playerScoreForm.invalidate();
TextView CPUScoreForm = (TextView) findViewById(R.id.CPUTotalScore);
CPUScoreForm.setText(Integer.toString(CPUTotal));
CPUScoreForm.invalidate();
//--------------------------------------------------------------------------
//AsyncTask method:
new updatePlayerScore().execute(PlayerTotal);
new updateCPUScore().execute(CPUScoreForm);
}
The AsyncTask subclasses:
private class updatePlayerScore extends AsyncTask<TextView, Void, Void> {
#Override
protected TextView doInBackground(TextView... params) {
// what to put here??
}
return playerScoreForm;
}
#Override
protected void onProgressUpdate(Integer... values) {
//??
}
protected void onPostExecute(Integer result) {
playerScoreForm.setText(Integer.toString(result));
}
}
private class UpdateCPUScore extends AsyncTask<TextView, Integer, Integer> {
// same syntax as updatePlayerScore
}
Question:
how do I transfer the textViews that I declared in the onCreate method to the AsyncTask method? I am stumped. I am fairly new to Android development.

a) I'm pretty sure you shouldn't need to invalidate the TextViews after you set them; Android should do that automagically.
b) In theory you'd set your TextView references to be member variables and then reference them in onPostExecute instead of passing them into doInBackground. doInBackground in turn will take whichever bits of data enable you to calculate the new score. What you would do on doInBackground is whatever action would cause a new score to be calculated. The return value from doInBackground gets passed into onPostExecute. You would then update the TextView (now a member variable) with this data in onPostExecute. Does that make sense? You haven't actually posted any code here that would update those score values.
See here for a quick example.
private TextView myScoreView; //initialized in onCreate as you do above.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//....
setContentView(R.layout.main_layout);
//.....
myScoreView = (TextView) findViewById(R.id.PlayerTotalScore);
myScoreView.setText(Integer.toString(PlayerTotal));
new updatePlayerScore().execute(1,2); //parameters for calculation
}
private class updatePlayerScore extends AsyncTask<Integer, Integer, Integer> {
#Override
protected TextView doInBackground(Integer... params) {
int score = params[0] + 2 * params[1];
return score;
}
#Override
protected void onProgressUpdate(Integer... values) {
//if you want to provide some indication in the UI that calculation
//is happening, like moving a progress bar, that's what you'd do here.
}
#Override
protected void onPostExecute(Integer scoreCalculationResult) {
myScoreView.setText(Integer.toString(scoreCalculationResult));
}
}
Edit: If you don't want to do the calculation logic in doInBackgroundThread, you probably just want to use:
runOnUiThread(new Runnable(){
#Override
public void run(){
myScoreView.setText(PlayerScoreValue);
}
});
Or:
myScoreView.post(new Runnable(){
#Override
public void run(){
myScoreView.setText(PlayerScoreValue);
}
});

You can pass the TextView in the constructor of the AsyncTask and update it from the onPostExecute method
private class updatePlayerScore extends AsyncTask<Void, Void, Integer> {
private TextView view;
public updatePlayerScore(TextView textView){
this.view = textView;
}
#Override
protected Integer doInBackground(Void... params) {
int score = 0;
//do you calculation the
return score;
}
protected void onPostExecute(Integer result) {
view.setText(Integer.toString(result));
}
}
note: if you Activity configuration change for any reason i.e the user rotate the device and the you AsyncTask hasn't finish it task the update of you TextView will not be updated so you should retain an instance of you AsyncTask and update the the TextView

AsyncTask and the setContentView

I have this code for managing some countrys on my database;
class checkCountryAsync extends AsyncTask<String, String, String> {
#Override
protected void onPreExecute() {
super.onPreExecute();
setContentView(R.layout.main);
}
#Override
protected String doInBackground(String... aurl) {
MDPIActivity.this.runOnUiThread(new Runnable() {
public void run() {
CountryTable country = new CountryTable() ;
country.EnterCountry();
}
});
return null;
}
}
With this, I would like to set the content View and then in background, that the method onBackground works, but I have still to wait for the content view until the onBackground method is not finished.
Thank you.

i don't see any reason for putting the setContentView() in the onPreExecute method, it should be in the onCreate method to avoid any kind of NullPointerException when you will try to find your views, and for your AsyncTask , you should just use the onPostExecute() which is executed after the method doInBackground()

Please try this one, think its work.`class checkCountryAsync extends AsyncTask {
#Override
protected void onPreExecute() {
super.onPreExecute();
setContentView(R.layout.main);
}
#Override
protected String doInBackground(String... aurl) {
CountryTable country = new CountryTable() ;
country.EnterCountry();
return null;
}
}
`

You should try publishProgress() and onProgressUpdate() methods.

ViewFlipper.addView() gives Exception, while Showing Progress Dialog in AsyncTask

What I want: I want to show a progress dialog while adding views dynamically to my ViewFlipper.
What I have: I have used an AsyncTask to achieve this. The ViewFlipper is declared in my Main Activity, I am adding views to ViewFlipper in the doInBackground() of AsyncTask.
What is the problem: I am getting an exception on the viewFlipper.addView() statement and the exception is " Main has leaked window com.android.internal.policy.impl ..... that was originally added here. " , something like this.
Here is the code:
public class Main extends Activity
{
private ViewFlipper viewFlipper;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main_flipper);
viewFlipper = (ViewFlipper)findViewById(R.id.id_vf_main);
new LoadData().execute();
// Some other tasks.
}
class LoadData extends AsyncTask<Object, Void, String>
{
protected ProgressDialog progressDialog;
#Override
protected void onPreExecute()
{
super.onPreExecute();
progressDialog = ProgressDialog.show(Main.this,"Loading", "Loading Data...", true, false);
}
#Override
protected String doInBackground(Object... parametros)
{
for (int i = 0; i < Login.data_Channel_Name.size(); i++)
{
LayoutInflater inflater = getLayoutInflater();
RelativeLayout rl_main = (RelativeLayout) inflater.inflate(R.layout.main,null);
TextView tv_channelNumber = (TextView)rl_main.findViewById(R.id.id_tv_ChannelNumber);
if(tv_channelNumber != null)
{
tv_channelNumber.setText("Some Number");
}
TextView tv_channelName = (TextView)rl_main.findViewById(R.id.id_tv_ChannelName);
if(tv_channelName != null)
{
tv_channelName.setText("Some name");
}
viewFlipper.addView(rl_main);
}
return null;
}
#Override
protected void onPostExecute(String result)
{
super.onPostExecute(result);
progressDialog.dismiss();
}
}
}

You are trying to interact with the UI from the background thread which isn't allowed. You are allowed to mess with the UI in your onPostExecute() and onPreExecute() methods. There is another method; onProgressUpdate() you can use like so:
protected void onProgressUpdate(Integer... progress) {
// on UI thread!
viewFlipper.addView(rl_main);
}
Obviously you'll need to handle passing the view to this method by creating a field or something. You can call this within your doInBackground() with the following:
publishProgress(0);
The function is typically used for updating the percentage on a loading bar or similar (hence passing the integer) but should work fine your your purposes.