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
Related
I am trying to know how to make the AsyncTask survives the screenOrientation change. So, I created an example for a MainActivity with AsyncTask. As shown in the code below, in
the doInBackground() method I print the incremented value of the variable "i" each second upto 7 seconds, and I publish the value of the variable "i" using publishProgress()
and display it in the TextView. while the value of varibale "i" is being published I changed the orientation of the device and I expected the App will crash, but what happened is,
that the the screenOrientation has changed and the value of the variable "i" was being published and normally displayed in the TextView without crash.
Is the AsyncTask I created not a suitable example to learn how to survive the screenOrientation?
MainActivity
public class MainActivity extends AppCompatActivity {
private final static String TAG = MainActivity.class.getSimpleName();
private TextView mtv11Up = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.mtv11Up = (TextView) findViewById(R.id.tv11_up);
new ATRetain().execute();
}
private class ATRetain extends AsyncTask<Void, Integer, Void> {
private long mStartTime;
private int i = 0;
#Override
protected void onPreExecute() {
super.onPreExecute();
this.mStartTime = TimeUtils.getTSSec();
}
#Override
protected Void doInBackground(Void... params) {
Log.i(TAG, "started");
while((TimeUtils.getTSSec() - this.mStartTime) <= 7) {
Log.i(TAG, "i: " + (++i));
publishProgress(i);
SystemClock.sleep(1000);
}
Log.i(TAG, "finished");
return null;
}
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
mtv11Up.setText(String.valueOf(values[0]));
}
}
}
AsyncTask create separate thread from UI Thread when orientation changes it recreated it self but AsyncTask is still running because it separate Background thread.
While doing some important work you can lock the screen orientation for some time until AsyncTask will complete then unlock.
Lock:
protected void onPreExecute() {
// ....
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_NOSENSOR);
}
Unlock:
protected void onPostExecute(String result) {
// ...
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED);
}
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);
Generally I update UI in postExecute method.
e.g.
public class SampleActivity extends Activity{
TextView textSample;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.aadd_addtocheck);
textSample = (TextView) findViewById(R.id.lin);
STask sampleTask = new Stask();
sampleTask.execute();
}
class GetAdd extends AsyncTask<Void, Void, JSONObject> {
#Override
protected JSONObject doInBackground(Integer... params) {
// TODO Auto-generated method stub
UserFunctions u = new UserFunctions();
return u.getNewAdd();
}
#Override
protected void onPostExecute(JSONObject result) {
super.onPostExecute(result);
textSample.setText(result.getString("Something");
}
However, my asyncTask become large and I want to move them to different class (before they were a subclass). Therefor, I wonder how to to update UI ( like setting texviews) when asynctask will be a separete class.
You pass either the Context, Activity, or the individual Views to the AsyncTask's constructor and store them as member variables, then update them on onPostExecute().
Be sure to store Context or Activity as a WeakReference to prevent memory leaks.
If you are going to put the AsyncTask in a separate file, you might be likely to reuse that AsyncTask from other Activities, so I think that the best practise would be to make a callback to the activity so it does all the UI handling.
For doing that what you should do is create an Interface like the following:
public interface OnGetAddCompletedListener {
public void onGetAddCompleted(String text);
}
Receive the callback in the constructor of your AsyncTask and call the method in it in onPostExecute
public class GetAdd extends AsyncTask<Void, Void, JSONObject> {
private OnGetAddCompletedListener callback;
public GetAdd(OnGetAddCompletedListener callback) {
this.callback = callback;
}
#Override
protected JSONObject doInBackground(Integer... params) {
// TODO Auto-generated method stub
UserFunctions u = new UserFunctions();
return u.getNewAdd();
}
#Override
protected void onPostExecute(JSONObject result) {
super.onPostExecute(result);
callback.onGetAddCompleted(result.getString("Something");
}
}
And then, implement the interface in the Activity you are executing it so it handles the UI modifications when you get the data in the AsycTask:
public class SampleActivity extends Activity implements OnGetAddCompletedListener {
TextView textSample;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.aadd_addtocheck);
textSample = (TextView) findViewById(R.id.lin);
STask sampleTask = new Stask();
sampleTask.execute();
}
public void onGetAddCompleted(String text) {
textSample.setText(text);
}
}
With this approach, if you decide to reuse that AsyncTask from other activity you will be able to do different things when the AsyncTask has ended in case you want to do so.
You can pass arguments into the constructor of your AsyncTask when you call it. Let's say that in your main activity you have the following:
TextView tv = (TextView) findViewById(R.id.my_text_view);
Stask sampleTask = new Stask(tv);
sampleTask.execute();
When you are creating your AsyncTask, you have:
class Stask extends AsyncTask ...(){
final TextView textView;
public Stask(Textview inputFromOtherClass){
this.textView = inputFromOtherClass;
}
}
This way, the TextView created in your main activity can exist as an instance in your AsyncTask.
EDIT:As someone else posted, you can do something similar for the Context, which is useful in creating various instances.
I made an application for Android that originally targeted a lower version (2.3). After I got my proof-of-concept working, I tried to get it to work on Android 4. That's when I got the NetworkOnMainThread exception.
After doing some research, I quickly found the AsyncTask, which sounded awesome. The problem is, I'm having a hard time wrapping my mind around it. For instance, here's my original code:
public void Refresh(Context c)
{
SummaryModel model = MobileController.FetchSummary(c);
TextView txtCurrentWeight = (TextView)findViewById(R.id.txtCurrentWeight);
TextView txtWeightChange = (TextView)findViewById(R.id.txtWeightChange);
TextView txtAvgPerWeek = (TextView)findViewById(R.id.txtAvgPerWeek);
if(model.ErrorMessage == "")
{
txtCurrentWeight.setText(model.CurrentWeight);
txtWeightChange.setText(model.WeightChange);
txtAvgPerWeek.setText(model.Average);
}
else
{
Toast.makeText(c, model.ErrorMessage, Toast.LENGTH_LONG).show();
txtCurrentWeight.setText("");
txtWeightChange.setText("");
txtAvgPerWeek.setText("");
}
}
I created an AsychTask like this:
public class WebMethodTask extends AsyncTask<Object, Integer, Object> {
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
#Override
protected void onPostExecute(Object result) {
super.onPostExecute(result);
SummaryModel model = (SummaryModel)result;
// Can't seem to access UI items here??
}
#Override
protected Object doInBackground(Object... params) {
Context c = (Context)params[0];
return MobileController.FetchSummary(c);
}
}
How do I access the UI items from the onPostExecute method? Or, do I have the wrong idea on how to use AsyncTask?
Thanks!
You should be able to accessUI where you put your comments (in the postExecute method)
Additionally, I would suggest to use more specialized class with for AsyncTask, so that your code looks better :
public class WebMethodTask extends AsyncTask<Object, Integer, SummaryModel> {
private Activity source;
public WebMethodTask(Activity activity) {
this.source=activity;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
#Override
protected void onPostExecute(SummaryModel model) {
super.onPostExecute(model );
TextView txtCurrentWeight = (TextView)source.findViewById(R.id.txtCurrentWeight);
TextView txtWeightChange = (TextView)source.findViewById(R.id.txtWeightChange);
TextView txtAvgPerWeek = (TextView)source.findViewById(R.id.txtAvgPerWeek);
if(model.ErrorMessage.length()==0)
{
txtCurrentWeight.setText(model.CurrentWeight);
txtWeightChange.setText(model.WeightChange);
txtAvgPerWeek.setText(model.Average);
}
else
{
Toast.makeText(c, model.ErrorMessage, Toast.LENGTH_LONG).show();
txtCurrentWeight.setText("");
txtWeightChange.setText("");
txtAvgPerWeek.setText("");
}
}
#Override
protected SummaryModel doInBackground(Context ... params) {
Context c = params[0];
return MobileController.FetchSummary(c);
}
}
Edit : Added a reference to your activity, to take your last comment into account.
However, if you acynctask can be long, it's maybe not a very good idea to keep a reference on an activity.
It would be a better design to create a listenerclass that will accept some displayModel(CummaryModel) method, and whose responsability is to cal the setText methods if the activity has not been paused / stopped in the meanwhile...
Fill the ui items with the loaded model data in the WebMethodTask#onPostExecute method.
You need a reference to your UI controls. When passing references to your UI controls to the ASyncTask you will create problems.
Assume the following scenario:
show activity (activity instance 1)
call async task with te activity as reference.
rotate your device (by default a device rotation will create a new activity) -> (activity instance 2)
when the sync task is finished, activity instance 1 is used to display the results. However the activity no longer exists causing exceptions.
The conclusion is that the ASyncTask should not be used for network activity related background tasks.
Fortunately there is a solution: RoboSpice.
RoboSpice uses another approach. Look at https://github.com/octo-online/robospice/wiki/Understand-the-basics-of-RoboSpice-in-30-seconds for a good explanation.
More information: https://github.com/octo-online/robospice
create an inner class in refresh method as
enter code herepublic void Refresh(Context c)
{
SummaryModel model = MobileController.FetchSummary(c);
TextView txtCurrentWeight = (TextView)findViewById(R.id.txtCurrentWeight);
TextView txtWeightChange = (TextView)findViewById(R.id.txtWeightChange);
TextView txtAvgPerWeek = (TextView)findViewById(R.id.txtAvgPerWeek);
if(model.ErrorMessage == "")
{
txtCurrentWeight.setText(model.CurrentWeight);
txtWeightChange.setText(model.WeightChange);
txtAvgPerWeek.setText(model.Average);
}
else
{
Toast.makeText(c, model.ErrorMessage, Toast.LENGTH_LONG).show();
txtCurrentWeight.setText("");
txtWeightChange.setText("");
txtAvgPerWeek.setText("");
}
class WebMethodTask extends AsyncTask<Object, Integer, Object> {
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
#Override
protected void onPostExecute(Object result) {
super.onPostExecute(result);
SummaryModel model = (SummaryModel)result;
// Can't seem to access UI items here??
}
#Override
protected Object doInBackground(Object... params) {
Context c = (Context)params[0];
return MobileController.FetchSummary(c);
}
}
}
In one of my app, I have a scenario where I need to do some background task. For doing that I am using Async Task. Also I am using custom progress dialog. Below is the layout of the custom progress dialog
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/layout_root"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_gravity="center_vertical|center_horizontal"
android:orientation="vertical" >
<ProgressBar
android:layout_width="60dp"
android:layout_height="60dp"
android:indeterminateDrawable="#drawable/progressloader"
android:layout_gravity="center"/>
<TextView
android:id="#+id/progressMessage"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="#color/black"
android:textSize="18sp"
android:text="Please wait...." />
</LinearLayout>
Everything works fine but when I try to set text to TextView then I am getting java NullPointerException.
AsyncTask code
private class InitialSetup extends AsyncTask<String, Integer, Long> {
ProgressDialog dialog = new ProgressDialog(getParent(),R.style.progressdialog);
#Override
protected void onPreExecute() {
dialog.show();
dialog.setContentView(R.layout.progressbar);
}
#Override
protected Long doInBackground(String... urls) {
// txtView.setText("Testing"); here I am getting the error
fetchDetails();
return 0;
}
#Override
protected void onPostExecute(Long result) {
if (this.dialog.isShowing()) {
this.dialog.dismiss();
}
populateUI(getApplicationContext());
}
}
MainActivity
public class SummaryActivity extends Activity {
final TextView txtView = (TextView)findbyid(R.id.progressMessage);
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.accountsummary);
new InitialSetup().execute("");
}
}
If I understand correctly, your TextView of which you want to set the text can be found in the xml file progressbar.xml (i.e. R.layout.progressbar). This TextView can be obtained once the content view has been set (using setContentView()). In your code you set it before this call is been and the code of mussharapp, he is calling it to early. Namely, he calls it after the setContentView(R.layout.accountsummary) call which does not contain the TextView. Consequently, the variable txtView will be NULL and you will get a NullPointerException.
What you should do is the following:
Set the variable txtView in onPreExecute, after setContentView is called.
Based on Paresh Mayani's explanation: Use the runOnUiThread method.
For the code look down below:
private class InitialSetup extends AsyncTask<String, Integer, Long> {
ProgressDialog dialog = new ProgressDialog(getParent(),R.style.progressdialog);
// The variable is moved here, we only need it here while displaying the
// progress dialog.
TextView txtView;
#Override
protected void onPreExecute() {
dialog.show();
dialog.setContentView(R.layout.progressbar);
// Set the variable txtView here, after setContentView on the dialog
// has been called! use dialog.findViewById().
txtView = dialog.findViewById(R.id.progressMessage);
}
#Override
protected Long doInBackground(String... urls) {
// Already suggested by Paresh Mayani:
// Use the runOnUiThread method.
// See his explanation.
runOnUiThread(new Runnable() {
#Override
public void run() {
txtView.setText("Testing");
}
});
fetchDetails();
return 0;
}
#Override
protected void onPostExecute(Long result) {
if (this.dialog.isShowing()) {
this.dialog.dismiss();
}
populateUI(getApplicationContext());
}
}
Yes, because you are trying to set the TextView inside the doInBackground() method, and this is not allowed,
Why not allowed? Because There is a only one Thread running which is UI Main Thread, and it doesn't allowed to update UI from thread process. read more info here: Painless Threading
So there is a solution if you want to set the TextView inside the doInBackground() method, do the UI updating operations inside the runOnUiThread method.
Otherwise, suggestion is to do all the UI display/update related operations inside the onPostExecute() method instead of doInBackground() method of your AsyncTask class.
(TextView)findViewByid(R.id.progressMessage);
should only be executed after the command setContentView().
TextView txtView;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.accountsummary);
**txtView = (TextView)findbyid(R.id.progressMessage);**
new InitialSetup().execute("");
}
Also you can only change UI elements in the main UI thread. doInBackground() is not in the main UI thread. Make UI changes in onPostExecute
public class InitialSetup extends AsyncTask<String, Integer, Long> {
private Activity activity;
ProgressDialog progressDialog;
public InitialSetup(Activity activity) {
this.activity = activity;
}
#Override
protected void onPreExecute() {
progressDialog = new ProgressDialog(activity);
progressDialog.setMessage("Starting task....");
progressDialog.show();
}
#Override
protected Long doInBackground(String... urls) {
// do something
//
return 0;
}
#Override
protected void onPostExecute(Long result) {
progressDialog.dismiss();
//Perform all UI changes here
**textView.setText("Text#2");**
}
}
The explanations are correct: You are not to make UI changes in any thread except the thread which create the UI. But AsyncTask has a method called
onProgressUpdate()
which always will run in the UI Thread. So based on the modifications by dennisg your code should look like this:
private class InitialSetup extends AsyncTask<String, String, Long> {
ProgressDialog dialog = new ProgressDialog(getParent(),R.style.progressdialog);
// The variable is moved here, we only need it here while displaying the
// progress dialog.
TextView txtView;
#Override
protected void onPreExecute() {
dialog.show();
dialog.setContentView(R.layout.progressbar);
// Set the variable txtView here, after setContentView on the dialog
// has been called! use dialog.findViewById().
txtView = dialog.findViewById(R.id.progressMessage);
}
#Override
protected Long doInBackground(String... urls) {
publishProgress("Testing");
fetchDetails();
return 0;
}
#Override
protected void onPostExecute(Long result) {
if (this.dialog.isShowing()) {
this.dialog.dismiss();
}
populateUI(getApplicationContext());
}
#Override
protected void onProgressUpdate(String... update) {
if (update.length > 0)
txtView.setText(update[0]);
}
}
Note that the type of the parameter of onProgressUpdate is the second type given in AsyncTask!
Extra: To make your code more robust you should check if the progress dialog still exists before setting the text.