can someone tell me, how do get a Stringvalue from a thread to the mainActivity?
i have a thread like this:
public class XMLHandler extends DefaultHandler {
XMLDataCollected data = new XMLDataCollected();
......
......
public String getInformation() {
String information = "";
if (data.getData().equals("residential")) {
information = "Stadt";
}
return information;
}
}
in the mainActivity i tried to set the value into a textview like this:
textView.setText(xmlHandler.getInformation());
i does not work after all. what i am doing wrong? any solutions and advices? thanks in advance
If you have a SeparateThread class then you need to create one Interface say
public interface FetchValueListener{
public void sendValue(String value_to_send);
}
And your acctivity will be implementing this interface and thus sendValue(value_to_send) method will be added to your activity.
Next step would be when you create the object of the THread class then you need to pass the object of that interface in the paramater as follows:
public class myThreadClass{
FetchValueListener mllistener;
myThreadClass(FetchValueListener listenerObj){
mllistener=listenerObj;
}
}
Now when you want to send some value to the activity from thread you can just simply call
mllistener.sendValue(value_you_wan_to_send);
And inside your actiivty you will get the value in the sendValue() method..
In that method you need to post the data to runnable using the handler so that you can make changes to the UI like setText etc.....
If you directly try to set the value of text view in that method you will get an exception.
Related
I am creating a program that fetch the value from online . I have use AsynTask class for background process. i am fetching the some values from web and set value in class variables.My problem is that values are setting in variables in very late. and my execution processed further and find variables values null. How can i check that doInBackground() method is processed completely and values are sets in variable. so that i can use these variables values.
One of the best method is to use a kind of observer design pattern.
So first create an Interface with contain a method (depend on your return value, etc) :
public interface OnTaskCompleted{
void onTaskCompleted(String xml);
}
Then you need to implement this interface to your activity wich instantiate your asynctack, see:
public class MainActivity extends SherlockFragmentActivity implements OnTaskCompleted
Then to finish, you gonna pass the instance of MainActivity (wich by polymorphisme is also OnTaskCompleted) to your asyntask. Here my asyntask class handler is named XMLParser
public class XMLParser {
private OnTaskCompleted listener;
public XMLParser(OnTaskCompleted mainActivity, String url){
getXMLFromURL(mainActivity,url);
}
[......]
//here when the work is done you call the OnTaskComplete Method
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
//CALL HERE
listener.onTaskCompleted(result);
}
}
I hope it'll help you. Works like a charm for me.
In my application I need to call a web service to get some data from the internet. To avoid blocking the UI I use an AsyncTask to do that. But I'm having problems to pass the return value correctly for further use. I guess I'm making some architectural mistakes here. So this is how my application is/should be structured:
MainActivity: An Activity containing a TextView, a Button and a SoapParser (see below). I want to call the web service by pressing the Button, parse the result and display it in the TextView.
SoapRequestTask: An AsyncTask with a callback mechanism like this. The return value of doInBackground() is a SoapObject and is passed to the listener as a parameter in the callback method listener.onTaskCompleted(SoapObject) in onPostExecute().
SoapRequestManager: A class that should have a method public SoapObject makeRequest(someParams). This method is supposed to use my AsyncTask and return my SoapObject from its doInBackground().
MySpecialRequestManager: Extends SoapRequestManager and has different methods to call the web service for different results. Each of these methods uses makeRequest(someParams) of the superclass.
SoapParser: A class that parses a SoapObject to a String so it can be displayed in my Activity's TextView. It should have a method like public String parseResult(SoapObject).
How do I use the callback and the return value correctly? Which class should implement the callback interface?
Just a quick snippet because you asked for some code. This might help get you started
In the AsyncTask's postExecute() method in SoapRequestTask
Intent intent = new Intent("send_data");
intent.setAction("SEND_DATA"); // don't NEED this, as we implicitly
// declare our intent during initialization
intent.putExtra("data_return_key", mData); // where mData is what you want to return
sendBroadcast(intent);
Then for SoapRequestManager
public class SoapRequestManager implements BroadcastReceiver{
int mData; // assuming our data is an int in this example
// Default constructor
public SoapRequestManager(){
registerReceiver(this, new IntentFilter("send_data"));
// if you use setAction use the below registration instead
// registerReceiver(this, new IntentFilter("SEND_DATA"));
}
//... All of the stuff you have in the class already
#Override
public void onReceive(Context context, Intent intent){
// For this example let's say mData is an integer value
// if you use setAction, check that the intent is the correct one via
// if (intent.getAction().equals("SEND_DATA"))
mData = intent.getIntExtra("data_return_key");
}
}
Ok so now I have Class A that contains some spinners that values will be populated by Class B that extends AsnycTask which grabs the spinner values from a web service. In class B i manage to retrieve the values, showing in a Toast. The problem now is how do I pass those spinner values back to Class A?
I've tried
Can OnPostExcecute method in AsyncTask RETURN values?
by passing Class A to Class B and store the value in a public variable of Class A like below
#Override
protected void onPostExecute(String result)
{
classA.classAvariable = result;
}
However whenever I try to read the classAvariable i always get a NullPointer Exception.
Seems like the variable was never assigned with the result.
For readability purpose I needed to seperate Class B instead of using as an inline class.
Any ideas my fellow Java programmers?
Problem here is that when you execute your AsynchTask, its doInBackground() methode run in separate thread and the thread that have started this AsynchTask move forward, Thereby changes occur on your variable by AsynchTask does not reflect on parent thread (who stated this AsynchTask) immediately.
Example --
class MyAsynchTask
{
doInbackground()
{
a = 2;
}
}
int a = 5;
new MyAsynchTask().execute();
// here a still be 5
Create a interface like OnCompletRequest() then pass this to your ClassB constructor and simply call the method inside this interface such as complete(yourList list) in the method of onPostExecute(String result)
You can retrieve the return value of protected Boolean doInBackground() by calling the get() method of AsyncTask class :
E.g. you have AsyncTask class as dbClass like
dbClass bg = new dbClass(this);
String Order_id = bg.execute(constr,data).get();
Here I am passing constr as URL and data as string of inputs to make my class dynamic.
But be careful of the responsiveness of the UI, because get() waits for the computation to complete and will block the UI thread.
I'm trying to make an application that uses Asynctask. Particularly, I want to make different http petitions with different JSON in different activities without the activity being frozen while the communication is done.
At first I thought to use asynctask as a private inner class in those activities, but I saw that they share a lot of code. So I thought to make a single class and play with broadcast receivers as I need to monitorize when I receive the result of the http petition, and isn't good to interfere with activity directly in the onPostExecute while in a different class.
What I want to know is, what is more efficient and better practice. Make a class that has the shared code and extends asynctask, then doing inner classes for each activity that extends that one or make a single asynctask that sends broadcast and receive them with each activity when needed.
Excuse my poor english, if needed I'll try to specify more clearly.
Thanks in advance
Background
What I want to know is, what is more efficient and better practice. Make a class that has the shared code and extends asynctask, then doing inner classes for each activity that extends that one or make a single asynctask that sends broadcast and receive them with each activity when needed.
I'm unclear as to why these are your only two options. Create a single AsyncTask, such as JsonPetitionTask, then push a new JsonPetitionTask.Data object. This object would contain your URL, your JSON, and any other data you need.
Setting up the AsyncTask
Something like this:
public class JsonPetitionTask extends AsyncTask<JsonPetitionTask.Data, Integer, Boolean> {
protected Boolean doInBackground(JsonPetitionTask.Data... args) {
for (int i = 0; i < args.length; i++) {
JsonPetitionTask.Data data = args[i];
// Send your JSON; check for errors, and return false if needed.
if (isCancelled()) break;
}
return true;
}
protected void onProgressUpdate(Integer... progress) {
// Show progress?
}
protected void onPostExecute(Boolean result) {
// result is your success true/false.
}
public static class Data {
public String jsonContent;
public String petitionUrl;
public Data(String content, String url) {
jsonContent = content;
petitionUrl = url;
}
}
}
Calling the JsonPetitionTask
Then you can call it like so:
JsonPetitionTask.Data data = new JsonPetitionTask.Data(myJSON, myURL);
new JsonPetitionTask().execute(data);
And voilà, you've executed your AsyncTask using only one class with no receivers.
Implementing a callback
Now, if you want to register a callback (something to execute that is specific to the calling code), that's a bit trickier. If this is part of what you're looking for, I'll be glad to edit this post and explain it.
To add a callback, we can use the Runnable class to execute some code after the job is done.
Firstly, we need to add a new field in the Data inner class:
public Runnable callback;
Next, before we call execute(), we need to add a new callback to our data object.
data.callback = new Runnable() {
public void run() {
// Whatever code you want to run on completion.
}
};
Third, in the JsonPetitionTask class, we need a list of things to run:
private ArrayList<Runnable> mRunnables = new ArrayList<Runnable>();
Make sure, in each iteration of the doInBackground() loop, that you do mRunnables.add(data.callback);.
Lastly, in onPostExecute(), we need to call this:
protected void onPostExecute(Boolean result) {
for (Runnable r : mRunnables)
if (r != null) r.run();
}
I do realize I didn't send result to the Runnable, however I didn't feel like implementing a new Runnable type just to handle that. If you need this, I guess that's a bit of homework for you!
The way I found the best is just simply create public class that extends AsyncTask and then you just override onPostExecute function in every activity you use it.
Example:
MyDataTask dataTask = new MyDataTask() //you can add your parameters in class constructor
{
#Override
protected void onPostExecute(Object result) //replace Object with your result type
{
MyActivity.this.doStuff(result); //use result in current activity
}
};
you can also create some custom functions to set private variables in datatask
dataTask.AddParam("user", username);
dataTask.AddParam("pass", pass);
and then just execute it with your args...
dataTask.execute(myArgs);
I have used Async task class as single class. And for every Webservice call i have used unique IntentFilter to Broadcast response.
Put that Broadcast receiver in every class. You have perfect solution.
Its working well.
I know that stuff of calling the new activity and pass the object value from one activity to another by using putExtra and getExtra function. but i want to pass the value without calling and start the new activity. Is it possible ?
If yes then let me know how i can do it ?
You can also use the Application class for declaring global variables
class Globalclass extends Application {
private String myState;
public String getState(){
return myState;
}
public void setState(String s){
myState = s;
}
}
class TempActivity extends Activity {
#Override
public void onCreate(Bundle b){
...
MyApp appState = ((MyApp)getApplicationContext());
String state = appState.getState();
...
}
}
UPDATED :
Checkout this nice Tutorial about how to do that.
Application Class Using as Global
for this you can use static variable or SharedPreferences or if you heavy data then you can use SQlite.
You can take the help of database like SQLite or you may go for Constant class concept where you can make a public static variable and store your data in one activity and access in other activity.Hope this will help you.
There're a lot of ways to pass a value to an activity:
You can use an Intent with FLAG_ACTIVITY_REORDER_TO_FRONT. In this case onNewIntent() method will be called for already started activity.
You can use static fields or static methods to pass new data to your activity. But it's not a good method really because sometimes application is terminated even if it's foreground and all static data is lost.
You can send new data to an activity using broadcast messages. In this case the activity must register a BroadcastReceiver.
I think it's not very difficult to make up a few more ways to pass arguments.
You may want to use handler's handleMessage() and pass the object in a message .
Handler handler = new Handler(){
#Override
public void handleMessage(Message msg) {
}
};
You can then call handler.handleMessage(msg), you can assign any object to msg.onj