Develop Reference

Asynctask inner class not updating UI textview

I have the following code which should update UI textview on Asynctask:
public class HelloWorldActivity extends Activity
{
private static TextView txtview;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
txtview = (TextView) findViewById(R.id.mainview);
}
private static class SimpleTask extends AsyncTask<Void, Void, Void> {
#Override
protected Void doInBackground(Void... res) {
try {
Thread.sleep(1500);
} catch(InterruptedException exception) {
Thread.currentThread().interrupt();
}
return null;
}
#Override
protected void onPostExecute(Void params) {
txtview.setText("Hola Mundo");
}
}
}
Particularly I'm triying to change Hello World to Hola Mundo after 1,5 seconds passed. The problem is that while running the app the text still is Hello World and doesn't change. I get no error of any sort. I have even set txtview value outside onCreate method to avoid any access problems (or so I think).
If after txtview = (TextView) findViewById(R.id.mainview); I do txtview.setText("Hola Mundo"); then it works flawlessly.
What could be the problem?

Forget to execute AsyncTask by calling AsyncTask.execute() method. do it as by adding following lines in onCreate method after initializing txtview TextView object:
SimpleTask objSimpleTask=new SimpleTask();
objSimpleTask.execute();

You have not called ASyncTask, execute it like this after initializing TextView:
txtview = (TextView) findViewById(R.id.mainview);
SimpleTask objSimpleTask=new SimpleTask();
objSimpleTask.execute();
Hope is what you want.

Currently you are forget to call AsyncTask.
But i think it is a bad practice to use AsyncTask & Thread.sleep() to update UI .
ou can simply do it with Handler.
Runnable updateUI;
Handler h = new Handler();
updateUI=new Runnable() {
#Override
public void run() {
txtview.setText("Hola Mundo");
}
};
h.postDelayed(updateUI,1500);

Assigning Values to a TextView from a different class

TestaActivity.java
public class TestaActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tvText=(TextView)findViewById(R.id.textView1);
tvText.setText("Sample");
}
}
Print.java
public class Print {
public Print(Context tempContext) {
//I want to assign the value to the tvText from here
}
}
In the above example, as you can see I have set the text in tvText to "Sample". In the same way, I need to assign the textView1 ID with some value inside Print class, once it is created.
Please help me to figure out the way to do it.

If your class Print is instantiated when TestaActivity is on the screen, then you can get tvText reference, passing to Print in some way a TestaActivity reference.
Maybe you could pass it via constructor:
From TestaActivity you do:
Print print = new Print(this);
where this represents the instance of TestaActivity.
And then in your Print code you can do:
TextView tvText = (TextView)((TestaActivity)context.findViewById(R.id.textView1));
tvText.setText("Sample");
Another solution is provide an interface from TestaActivity, transparent for the outside, which manage your changes on the textview (or whatever).
Something like that:
private TextView tvText;
public void setTvText(String str){
tvText.setText( str );
}
And then in your Print class:
((TestaActivity)context).setTvText( "Sample" );

try as:
public class Print {
protected TestaActivity context;
public Print(Context tempContext) {
context = tempContext;
}
public void changetextViewtext(final String msg){
context.runOnUiThread(new Runnable() {
#Override
public void run() {
//assign the value to the tvText from here
context.tvText.setText("Hello Test");
}
});
}
}
and call changetextViewtext from Activity for Changeing TextView Text from Print Class
public class TestaActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tvText=(TextView)findViewById(R.id.textView1);
tvText.setText("Sample");
Print myPrint = new Print(this);
myPrint.changetextViewtext("Hello World !!!");
}
}
as your need!!!!:)

#imran - the solution is correct except that you would want to pass the TextView as an argument in the constructor or the method.
Harcoding TextView in a method is bad because you cannot be reuse it.

AsyncTask : passing value to an Activity (onCreate method )

Update1
activity:
public Integer _number = 0;
#Override
public void onCreate(Bundle savedInstanceState) {
if (_number >0)
{
Log.d("onSuccessfulExecute", ""+_number);
}
else
{
Log.d("onSuccessfulExecute", "nope empty songs lists");
}
}
public int onSuccessfulExecute(int numberOfSongList) {
_number = numberOfSongList;
if (numberOfSongList >0)
{
Log.d("onSuccessfulExecute", ""+numberOfSongList);
}
else
{
Log.d("onSuccessfulExecute", "nope empty songs lists");
}
return numberOfSongList;
}
end Update1
UPDATE: AsynchTask has its own external class.
How to pass an value from AsyncTask onPostExecute()... to activity
my code does returning value from onPostExecute() and updating on UI but i am looking for a way to set the activity variable (NumberOfSongList) coming from AsynchTask.
AsyncTask class:
#Override
public void onPostExecute(asynctask.Payload payload)
{
AsyncTemplateActivity app = (AsyncTemplateActivity) payload.data[0];
//the below code DOES UPDATE the UI textView control
int answer = ((Integer) payload.result).intValue();
app.taskStatus.setText("Success: answer = "+answer);
//PROBLEM:
//i am trying to populate the value to an variable but does not seems like the way i am doing:
app.NumberOfSongList = payload.answer;
..............
..............
}
Activity:
public Integer NumberOfSongList;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//Several UI Code
new ConnectingTask().execute();
Log.d("onCreate", ""+NumberOfSongList);
}

What about using a setter method? e.g.
private int _number;
public int setNumber(int number) {
_number = number;
}
UPDATE:
Please look at this code. This will do what you're trying to accomplish.
Activity class
public class TestActivity extends Activity {
public int Number;
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.test);
Button btnDisplay = (Button) findViewById(R.id.btnDisplay);
btnDisplay.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
Toast toast = Toast.makeText(v.getContext(), "Generated number: " + String.valueOf(Number), Toast.LENGTH_LONG);
toast.show();
}
});
new TestTask(this).execute();
}
}
AsyncTask class
public class TestTask extends AsyncTask<Void, Void, Integer> {
private final Context _context;
private final String TAG = "TestTask";
private final Random _rnd;
public TestTask(Context context){
_context = context;
_rnd = new Random();
}
#Override
protected void onPreExecute() {
//TODO: Do task init.
super.onPreExecute();
}
#Override
protected Integer doInBackground(Void... params) {
//Simulate a long-running procedure.
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
Log.e(TAG, e.getMessage());
}
return _rnd.nextInt();
}
#Override
protected void onPostExecute(Integer result) {
TestActivity test = (TestActivity) _context;
test.Number = result;
super.onPostExecute(result);
}
}

Just a word of caution: Be very careful when attempting to hold a reference to an Activity instance in an AsyncTask - I found this out the hard way :). If the user happens to rotate the device while your background task is still running, your activity will be destroyed and recreated thus invalidating the reference being to the Activity.

Create a listener.
Make a new class file. Called it something like MyAsyncListener and make it look like this:
public interface MyAsyncListener() {
onSuccessfulExecute(int numberOfSongList);
}
Make your activity implement MyAsyncListener, ie,
public class myActivity extends Activity implements MyAsyncListener {
Add the listener to the constructor for your AsyncTask and set it to a global var in the Async class. Then call the listener's method in onPostExecute and pass the data.
public class MyCustomAsync extends AsyncTask<Void,Void,Void> {
MyAsyncListener mal;
public MyCustomAsync(MyAsyncListener listener) {
this.mal = listener;
}
#Override
public void onPostExecute(asynctask.Payload payload) {
\\update UI
mal.onSuccessfulExecute(int numberOfSongList);
}
}
Now, whenever your AsyncTask is done, it will call the method onSuccessfulExecute in your Activity class which should look like:
#Override
public void onSuccessfulExecute(int numberOfSongList) {
\\do whatever
}
Good luck.

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

onPostExecute() can't use MainActivity elements

I have doInBackground(). after function I want to change some TextView on MainActivity.
but When I trigger the function on main activity I got NullPointerException on TextView line.
protected String doInBackground(Object... arguments) {
some code..
return result;
}
#Override
protected void onPostExecute(String result) {
if(result!=null)
new MainActivity().setScoreListUpdate(result);
}
MainActivity:
public void setScoreListUpdate(String settings)
{
String[] yeniscore = settings.split("\\|");
if(yeniscore.length > 1)
{
birinci.setText(yeniscore[1]); << NULLPOINTEREXC.
}
}

The reason this gives a NullPointerException is that you create a new instance of MainActivity instead of working on your existing one.
What you need to do is pass a reference to your Activity to the AsyncTask and then call your method on that reference.
So in your AsyncTask-class you will have a variable:
private MainActivity myMainActivity;
Add a constructor to your AsyncTask-class:
public MyAsyncTaskClassName( MainActivity activity ) {
myMainActivity = activity;
}
Then in onPostExecute you do:
myMainActivity.setScoreListUpdate(result);

Use
MainActivity.this.setScoreListUpdate(result);
instead of
new MainActivity().setScoreListUpdate(result);
in yout postExecute method.
Also, TextView called birinci should be a field in your MainActivity class, not just a variable in the onCreate method for example.
EDIT: It works like this in my program. Check out the differences.
public class DeviceSettingsStatsActivity extends ListActivity {
AsyncTask<Void, Integer, ListAdapter> task = null;
ListAdapter listAdapter = null;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
task = new ComputeTask().execute();
}
protected void viewComputeResult(ListAdapter result) {
setListAdapter(result);
}
private class ComputeTask extends AsyncTask<Void, Integer, ListAdapter> {
#Override
protected ListAdapter doInBackground(Void... params) {
// some stuff
}
#Override
protected void onPostExecute(ListAdapter result) {
DeviceSettingsStatsActivity.this.viewComputeResult(result);
}
}
}