I am currently wondering how to use AsyncTask in multiple Activitys without copying it.
I used this Guide to do it in one Activity and that worked just fine. But to load and use this information in more than one Activity seems to me like to much work. I tried to put my LoadUrl function into another Class and just pass my Textfield I want to be edited. But my App crashes when i start it. (I am not sure if this is the right approach )
public class LoadFromUrl {
public void loadAccountInfo(String key) {
if( key != null ) {
new DownloadWebpageTask().execute();
}
}
private class DownloadWebpageTask extends AsyncTask<String, Void, String> {
#Override
protected String doInBackground(String... urls) {
// params comes from the execute() call: params[0] is the url.
try {
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve web page. URL may be invalid.";
}
}
// onPostExecute displays the results of the AsyncTask.
#Override
protected void onPostExecute(String result) {
//textView.setText(result);
}
// Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string.
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
// Only display the first 500 characters of the retrieved
// web page content.
int len = 500;
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
//Log.d(DEBUG_TAG, "The response is: " + response);
is = conn.getInputStream();
// Convert the InputStream into a string
String contentAsString = readIt(is, len);
return contentAsString;
// Makes sure that the InputStream is closed after the app is
// finished using it.
} finally {
if (is != null) {
is.close();
}
}
}
// Reads an InputStream and converts it to a String.
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len];
reader.read(buffer);
return new String(buffer);
}
}
}
and calling it in:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
selectedAccount.setKey("google.com");
loadUrl.loadAccountInfo(selectedAccount.getKey());
}
All I want to do is, load the information of an URL and use this to fill my activitys (like multiple TextViews). Every activity uses different urls and structures.
Create DownloadWebPageTask in a separate file, as a public class. Then override its constructor to pass anything you need (a textfield, key, etc).
Put DownloadWebPageTask in a separate class. Then in onPostExecute, run a callback to the activity or fragment that will update its UI. This is done by having an activity implement a callback which is an inner interface inside the the DownloadWebpageTask (doesn't have to be an inner interface!). As you can see, the inner interface I put with your code is WebpageCallbacks.
This is your asynctask in another class (the spacing isn't perfect sorry...):
public class DownloadWebpageTask extends AsyncTask<String, Void, String> {
/**
* Any activity or fragment that implements WebPageCallbacks
*/
private WebPageCallbacks callbacks;
//start by referencing your activity to call onURLLoaded() for onPostExecute()
public DownloadWebpageTask(WebPageCallbacks callbacks) {
this.callbacks = callbacks; //note: I think weak references are preferred though
}
//no changes here
#Override
protected String doInBackground(String... urls) {
// params comes from the execute() call: params[0] is the url.
try {
return downloadUrl(urls[0]);
} catch (IOException e) {
return "Unable to retrieve web page. URL may be invalid.";
}
}
// onPostExecute displays the results of the AsyncTask by callback's onURLLoaded()
#Override
protected void onPostExecute(String result) {
//each activity or fragment will has a method to change their UI
callbacks.onURLLoaded(result);
}
// Given a URL, establishes an HttpUrlConnection and retrieves
// the web page content as a InputStream, which it returns as
// a string. No changes here
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
// Only display the first 500 characters of the retrieved
// web page content.
int len = 500;
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
//Log.d(DEBUG_TAG, "The response is: " + response);
is = conn.getInputStream();
// Convert the InputStream into a string
String contentAsString = readIt(is, len);
return contentAsString;
// Makes sure that the InputStream is closed after the app is
// finished using it.
} finally {
if (is != null) {
is.close();
}
}
/**
* Any Activity or fragment that implements this will have
* onURLLoaded() method to update its own UI.
*/
public interface WebpageCallbacks {
void onURLLoaded(String result);
}
}
I would then add implements DownloadWebpageTask.WebpageCallBacks to all your fragments and activities that will use this asynctask.
Here is your activity:
public class ExampleActivity extends AppCompatActivity implements DownloadWebpageTask.WebpageCallBacks {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home);
selectedAccount.setKey("google.com");
//changed your oncreate at line below to run your accountInfo
runAccountInfo(selectedAccount.getKey());
}
.......................
//runs the asynctask to load url info from account info like your old loadURLInfo()
public void runAccountInfo(String key) {
if( key != null ) {
//get url with getURL(key)
new DownloadWebpageTask(this).execute(getURL(key));
}
}
//this will be run from onPostExecute from the asynctask
#Override
public void onURLLoaded(String result) {
textView.setText(result);
}
}
If you have the time though, I suggest to not use AsyncTask at all and look into other libraries like rxJava/rxAndroid. I hope this code is ok........
Related
I am making a guessing app in Android Studio 2.2.3 for which I need to load some data from a website. I am using an AsyncTask class, which accepts the URL of the website as a String, and returns the data as String.
The problem is that the loading is extremely slow and so the app shows a blank white screen on the phone for about 15-20 seconds until (I presume) the whole thing is downloaded.
What I want to do is show an indeterminate progress bar (I think that's what the rotating circle is called) until the app loads the data.
For this, I tried to pass in the AsyncTask, and then made the progressbar view visible in the onPreExecute() and invisible again in the onPostExecute().
But this didn't work out and it still showed the same white screen.
Here's my AsyncTask:
public class DownloadTask extends AsyncTask<String, Void, String> {
#Override
protected void onPreExecute() {
super.onPreExecute();
pb.setVisibility(ProgressBar.VISIBLE);
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
pb.setVisibility(ProgressBar.INVISIBLE);
}
#Override
protected String doInBackground(String... urls) {
String result = "";
URL url;
HttpURLConnection urlConnection;
try {
url = new URL(urls[0]);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = urlConnection.getInputStream();
InputStreamReader isr = new InputStreamReader(in);
int data = isr.read();
while (data != -1) {
char current = (char) data;
result += current;
data = isr.read();
}
return result;
} catch (Exception e) {
e.printStackTrace();
}
//if try fails
return null;
}
}
And this is when I call it in the onCreate()
DownloadTask downloadTask = new DownloadTask();
String result;
try {
String websiteUrl = "http://www.india-forums.com/celebrity/bollywood/";
result = downloadTask.execute(websiteUrl).get();
I read somewhere that the get() blocks the main UI thread, but if I remove it, I get an Incompatible types error, so couldn't still resolve it...
What am I missing/doing wrong?
Any help would be appreciated!
i appear to have a memory leak with the following asyncTask, what possible cause are there?
/**
* Async task class to get json by making HTTP call
* */
public class PostLocation extends AsyncTask<String, Void, String>
{
#Override
protected void onPreExecute()
{
}
#Override
protected String doInBackground(String... params)
{
try
{
String response = "";
URL url = new URL(BASE_URL + "receiveLocation.php");
myConnection = (HttpURLConnection) url.openConnection();
myConnection.setRequestMethod("POST");
myConnection.setDoOutput(true);
DataOutputStream wr = new DataOutputStream(myConnection.getOutputStream());
wr.writeBytes(params[0]);
int responseCode = myConnection.getResponseCode();
if (responseCode == HttpsURLConnection.HTTP_OK)
{
String line;
BufferedReader br = new BufferedReader(new InputStreamReader(myConnection.getInputStream()));
while ((line = br.readLine()) != null)
{
response += line;
}
}
else
{
return response = "";
}
return response;
}
catch (Exception e)
{
// TODO Auto-generated catch block
e.printStackTrace();
return "false";
}
}
#Override
protected void onPostExecute(String result)
{
if(result.equals("success"))
{
myConnection.disconnect();
}
}
}
this is simply posting some data to my server. What could be causing memory leaks, note this task is called in the background from a broadcast receiver using goAsync
The problem here is in your class structure.
A nested class should be declared static whenever possible, otherwise it will keep the enclosing class in memory, leading to memory leaks.
Change:
public class PostLocation extends AsyncTask<String, Void, String>
to:
public static class PostLocation extends AsyncTask<String, Void, String>
Here is an exercise:
Put a field called boolean test in your BroadcastReceiver class
Now in your nested class, try to access this field, e.g. test == true
If the nested class is not static, you will be able to access the field. This is because the instance of the class keeps the reference to the enclosing class. But if you make PostLocation class static, the field will not be available.
Yes you need to close the inputstream first and close httpconnection next. As per javadoc.
Each HttpURLConnection instance is used to make a single request but
the underlying network connection to the HTTP server may be
transparently shared by other instances. Calling the close() methods
on the InputStream or OutputStream of an HttpURLConnection after a
request may free network resources associated with this instance but
has no effect on any shared persistent connection. Calling the
disconnect() method may close the underlying socket if a persistent
connection is otherwise idle at that time.
Source
I am beginner in Android and I need some help. So, I have a procedure with sub-procedures inside. How can I finish one before starting a new one. Here is a code to better understand:
public void onCellLocationChanged(CellLocation lokacija) {
super.onCellLocationChanged(lokacija);
location = (GsmCellLocation) Phone.getCellLocation();
textCellId.setText(String.valueOf(location.getCid() % 65536));
textCellLac.setText(String.valueOf(location.getLac()));
String JSON_URL_string=JSON_URL + "?cellid=" + String.valueOf(location.getCid()%65636);
getJSON(JSON_URL_string);
myJSONString = textCellNameSakriven.getText().toString();
ParseJSON(myJSONString);
}
Problem is that myJSONString is empty, cause textCEllNameSkriven is also empty. That textView textCellNameSkriven is made when getJSON(JSON_URL_string) is finished. If I run debugger and go step by step, app goes directly from getJSON(JSON_URL_string) row to the next one and the next etc
Edit: Maybe the problem is that onPostExecute is not finished before starting ParseJSON. Here is also a code for getJSON:
private void getJSON(String url) {
class GetJSON extends AsyncTask<String, Void, String> {
ProgressDialog loading;
#Override
protected void onPreExecute() {
super.onPreExecute();
loading = ProgressDialog.show(MainActivity.this, "Please Wait...", null, true, true);
}
#Override
protected String doInBackground(String... params) {
String uri = params[0];
BufferedReader bufferedReader = null;
try {
URL url = new URL(uri);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
StringBuilder sb = new StringBuilder();
bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String json;
while ((json = bufferedReader.readLine()) != null) {
sb.append(json + "\n");
}
return sb.toString().trim();
} catch (Exception e) {
return null;
}
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
loading.dismiss();
textCellNameSakriven.setText(s);
}
}
GetJSON gj = new GetJSON();
gj.execute(url);
}
Since you are running a async task it practically runs on a different thread, so your getJson method need not wait for post execute and can return after starting the async task, so you can never be sure in this way that parseJson gets executed after textView is populated. You are running into classic race condition issue.
Your issue could be easily solved, if you have a callback which is called after postExecute is done, and you can handle parseJson there
So, something simple like , create interface MyCallback
public interface MyCallback {
public OnReadJsonDone();
}
Let your activity implement this MyCallback
public MainActivity implements MyCallback
{
...........
#Override
public OnReadJsonDone(){
parseJson();
}
Now change signature of getJson to
getJSON(string json, final MyCallback callback) {
Now in onpostexecute
//call OnReadJsonDone
callback.OnReadJsonDone()
So, all you now need is while calling getJSon pass this as second param
getJSON(JSON_URL_string,this);
Haven't tested this but you get the idea
I'm a new Android developer and I have a question. After users login, I need to get some data from an external URL and display them on one of my activities. But I've been reading and found this:
When your activity comes back to the foreground from the stopped state, it receives a call to onRestart(). The system also calls the
onStart() method, which happens every time your activity becomes
visible (whether being restarted or created for the first time).
And this
Caution: Your activity will be destroyed and recreated each time the
user rotates the screen. When the screen changes orientation, the
system destroys and recreates the foreground activity because the
screen configuration has changed and your activity might need to load
alternative resources (such as the layout).
Here and here.
So, it looks like I should not get the data I need on the onCreate method. Then where? In a previous activity and saving the data in the phone memory? That doesn't sound good to me.
Thanks in advance.
edit
I'm using AsyncTask as suggested, but everytime I switch the phone orientation, onCreate method is called.
My MainActivity:
public class MainActivity extends Activity implements AsyncResponse {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ReadJSONTask jsonTask = new ReadJSONTask();
jsonTask.delegate = this;
jsonTask.execute("http://www.myweb.com/myscript.php");
}
#Override
public void processFinish(String output) {
Toast.makeText(getApplicationContext(), output, Toast.LENGTH_LONG).show();
}
}
ReadJSONTask class:
public class ReadJSONTask extends AsyncTask<String, Void, String> {
public AsyncResponse delegate = null;
public String res;
public Boolean finish = false;
#Override
protected String doInBackground(String... url) {
String response = null;
String adres = url[0];
URL url_HTTPRequest = null;
try {
url_HTTPRequest = new URL(adres);
response = transfer(url_HTTPRequest);
} catch (MalformedURLException e) {
Log.e("URL ERROR", "MalformedURLException");
} catch (Exception e) {
Log.e("URL ERROR", "exc");
}
return response;
}
#Override
protected void onPostExecute(String result) {
Log.d("mylog", "result= " + result);
delegate.processFinish(result);
}
public String transfer(URL url) throws IOException {
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
// inputStream = url.openStream();
InputStream inputStream = urlConnection.getInputStream();
BufferedReader bin = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));
String line = bin.readLine();
StringBuffer sb = new StringBuffer();
while (line != null) {
sb.append(line);
sb.append("\r\n");
line = bin.readLine();
}
inputStream.close();
return sb.toString();
}
}
And the interface is just:
public interface AsyncResponse {
void processFinish(String output);
}
As I said, everytime I switch the phone orientation all the async process is performed (and the Toast shows up). That's exactly what I wanted to avoid in the first place.
you dont need Stop/Resume activities you can use AsyncTask class and doInBackGround method when get data from external url and show to user process Dialog for waiting
Never ever try to get the data from URL on Main thread. Always use AsyncTask for getting the data from URL
You can write in the same activity, but not in the main thread. Maybe AsyncTask will help.
I'm using AsyncTask and all the examples I found about an AsyncTask is inside an activity.
I'm trying to make an application with a lot of activity and some must download a HTML page. I don't really want to copy-paste the same code all the time in every activity. I find this to be dirty.
So I need to do it as a special class Async HttpGet and pass the function with an argument. I will execute after the doinbackground (different for every activity).
Is this possible or do I need to copy-paste my code in every activity and change the do in background to do what I need after downloading the HTML page?
Here's an AsyncTask that will download data from a url and update the calling activity.
Make sure your calling activity implements the interface DownloadDataTask.DownloadCompleteHandler and that it passes itself as parameter to the DownloadDataTask constructor.
public class DownloadDataTask extends AsyncTask<String, Integer, String> {
public interface DownloadCompleteHandler
{
public void handleDownloadComplete(String result);
}
private DownloadCompleteHandler handler;
private String url;
public DownloadDataTask(DownloadCompleteHandler handler, String url) {
this.handler = handler;
this.url = url;
}
/* AsyncTask methods */
#Override
protected String[] doInBackground(String... empty) {
return downloadData(url);
}
#Override
protected void onPostExecute(String result) {
handler.handleDownloadComplete(result);
}
/* Downloading Data */
private String downloadData(String urlStr) {
InputStream is = null;
String result = new String();
try {
is = getInputStream(urlStr);
BufferedReader in = new BufferedReader(new InputStreamReader(is));
String inputLine;
while ((inputLine = in.readLine()) != null) {
result += inputLine;
} catch (MalformedURLException ex) {
return "Malformed URL: " + ex.getMessage();
} catch (SocketTimeoutException ex) {
return "Connection timed out";
} catch (IOException ex) {
return "IOException: " + ex.getMessage();
}
finally {
if (is != null)
is.close();
}
return result;
}
private InputStream getInputStream(String urlStr) throws IOException
{
URL url = new URL(urlStr);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(7000);
conn.setConnectTimeout(7000);
conn.setRequestMethod("GET");
conn.setDoInput(true);
conn.connect();
return conn.getInputStream();
}
}
Just create a class that extends AsyncTask that you can reuse.
public abstract class MyAsyncTask extends AsyncTask<Void, Void, String> {
private final String url;
public MyAsyncTask(String url){
this.url = url;
}
#Override
protected String doInBackground(Void... params){
// get data from url.
return null;
}
}
And then to call it, just create an instance of that class.
new MyAsyncTask("http://www.google.com"){
public void onPostExecute(String result){
// update your views.
}
}.execute();
Well what you can do is create an listener for AsyncTask completion, which listens when your AsyncTask is completed and return you the data. I had created an example to execute database queries in background thread and then returning the data to the Activity. Just check it and you can create similar AsyncTask for your problem.
UPDATE:-
Also you can use BroadCastReceiver as a Listener when your AsyncTask is completed and return the value.
Interface is another option for creating a Listener for AsyncTask.
Here is a demo from my github