Learning Android development - part 6&7&8
-Background threads: non-UI related, network access must be done on a background thread
techniques for background threads
MyAsyncTask extends AsyncTask<GenericParam1, GenericParam2, GenericParam3>
where:
• GenericParam1: The type of information that is needed to process the task (e.g., URLs to download)
• GenericParam2: The type of information that is passed within the task to indicate progress
• GenericParam3: The type of information
There are four methods you can override in AsyncTask. You do not need to override all of them; but you will need to override doInBackGround.
• The doInBackground() is called by AsyncTask on a background thread. It can run as long as it needs to in order to accomplish whatever work needs to be done for this specific task. Note, though, that tasks are meant to be finite – using AsyncTask for an infinite loop is not recommended.
• The doInBackground() method receives as parameters a varargs array of the first of the data types listed above – the data needed to process the task (in background)
• To doInBackground routine must return a value of the third data type listed above (which is the result of the background work).
• doInBackground can use the tasks publishProgress to pass objects of the 2nd type to onProgressUpdate.
onPostExecute() is called from the UI thread after doInBackground() completes. It receives as a parameter the value returned by doInBackground()
onPreExecute is called from the UI threadbefore the background thread executes doInBackGround. This is usually initialize a status bar or do something to indicate to the user that background work is starting.
onProgressUpdate is called from the UI thread It receives as a parameter the items (of the 2nd parameter type) published by thedoInBackground method. This is usually used to indicate some kind of status progress to the user.
- Create a subclass of AsyncTask, commonly as a private inner class of something that uses the task (e.g., an activity)
- Override one or more AsyncTask methods to accomplish the background work, plus whatever work associated with the task that needs to be done on the UI thread (e.g., update progress)
- Create an instance of the AsyncTask subclass and call execute() to have it begin doing its work
Accessing information on the internet
-URL class: The URL is used to make the necessary requests to connect to the HTTP server of the data object, query for information about the object, and download the object.
The android URL class can both parse URL strings into parts and compose URL strings from parts.
The URL getContent() method downloads and returns the content of the resource that is referred to by this URL. By default this returns an InputStream, or null, if the content type of the response is unknown.
InputStream is = (InputStream) new URL(url).getContent();
Going to the Internet requires the android.permission.INTERNET permission.
Add the following code in manifest.xml
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
Example of ActivityFragment file, downloading image in the background
/**
* A placeholder fragment containing a simple view.
*/
public class RunnablesActivityFragment extends Fragment {
private static final String TAG = "RunnablesActivity";
String myUrl =
"http://www.androidcentral.com/sites/androidcentral.com/files/styles/w680h550/public/postimages/9274/android_kitkat.jpg";
public RunnablesActivityFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_runnables, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
Button getImageButton = (Button) getActivity().findViewById(R.id.at_button);
getImageButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
Log.d(TAG, "onClick: " + myUrl);
downloadImage(myUrl);
}
});
}
private Drawable loadImageFromWeb(String url)
{
Drawable downloadedImage = null;
try
{
InputStream is = (InputStream) new URL(url).getContent();
if (is != null) {
downloadedImage = Drawable.createFromStream(is, "src name");
}
}catch (Exception e) {
System.out.println("Exc="+e);
}
return downloadedImage;
}
public void downloadImage(final String myUrl) {
new Thread(new Runnable() {
Drawable result = null;
@Override
public void run() {
try {
Log.d(TAG, "downloadImage" + " thread: "
+ Thread.currentThread().getId());
result = loadImageFromWeb(myUrl);
} catch (Exception e ) {
e.printStackTrace();
}
getActivity().runOnUiThread(new Runnable() {
@Override
public void run() {
Log.d(TAG, "downloadImage" + " runOnUiThread thread: "
+ Thread.currentThread().getId());
if (result != null) {
ImageView imageView =
(ImageView)getActivity().findViewById(R.id.at_image);
imageView.setImageDrawable(result);
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
}
else {
Log.d(TAG, "downloadImage Problem getting image");
}
}
});
}
}).start();
}
}
Another example of making the same function is using AsyncTask
public class AsyncTaskActivityFragment extends Fragment {
private static final String TAG = " AsyncTaskActivity ";
String myUrl =
"http://www.androidcentral.com/sites/androidcentral.com/files/styles/w680h550/public/postimages/9274/android_kitkat.jpg";
public AsyncTaskActivityFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_async_task, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
Button getImageButton = (Button) getActivity().findViewById(R.id.at_button);
getImageButton.setOnClickListener(new View.OnClickListener () {
public void onClick(View arg0) {
Log.d(TAG, "onClick: " + myUrl);
new DownloadImageTask().execute(myUrl);
}
});
}
private Drawable loadImageFromWeb(String url)
{
Drawable downloadedImage = null;
try
{
InputStream is = (InputStream) new URL(url).getContent();
if (is != null) {
downloadedImage = Drawable.createFromStream(is, "src name");
}
}catch (Exception e) {
System.out.println("Exc="+e);
}
return downloadedImage;
}
private class DownloadImageTask extends AsyncTask<String, Integer, Drawable> {
@Override
protected void onPreExecute() {
// do nothing for this example; but if you had a progressdialog; set it up here
}
// doInBackground is called on the background thread
// Receives the first parameter; in this case an array of strings with 1 item in it
// Needs to return something of the 3 parameter type.
// No call to publishProgress; but if publishProgress was called,
// would pass something of the 2nd parameter
@Override
protected Drawable doInBackground(String... params) {
Log.d(TAG, "PlaceholderFragment : doInBackground entry "
+ (String) params[0]);
Drawable myDrawable = loadImageFromWeb((String) params[0]);
return myDrawable;
}
// onProgressUpdate called on the UI thread
// Receives parameters of the 2nd type
@Override
protected void onProgressUpdate(Integer... progress) {
// do nothing for this example
}
// Called on UI thread after doInBackground completes;
// Receives a parameter of the 3rd type
@Override
protected void onPostExecute(Drawable result) {
Log.d(TAG, "PlaceholderFragment : onPostExecute entry");
ImageView imageView =
(ImageView)getActivity().findViewById(R.id.at_image);
if (result != null) {
imageView.setImageDrawable(result);
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
}
else
Log.d(TAG, "PlaceholderFragment : result is null"); }
}
}
-HttpURLConnection client
Decoding information retrieved from internet
Example of HttpURLConnection and Json
The get ip buttons get ip address, and location info button gets location information.
public class GetIpLocationActivityFragment extends Fragment {
private static final String TAG = "GetIpLocation";
private static final int QUERY_GET_IP = 1;
private static final int QUERY_GET_IP_LOC_INFO = 2;
private int caller = 0;
private GetNetworkInfoTask niTask = null;
Button getIpLocationInfoButton;
public GetIpLocationActivityFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_get_ip_location, container, false);
}
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
//getIpButton
Button getIpButton = (Button) getActivity().findViewById(R.id.get_ip_btn);
getIpButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
caller = QUERY_GET_IP;
String queryBase = "http://www.telize.com/jsonip";
String queryString = Uri.parse(queryBase).buildUpon().toString();
startNetworkInfoTask(queryString);
}
});
//getIpLocationInfoButton
getIpLocationInfoButton = (Button) getActivity().findViewById(R.id.get_loc_info_btn);
getIpLocationInfoButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View arg0) {
caller = QUERY_GET_IP_LOC_INFO;
TextView ipInfoTV = (TextView) getActivity().findViewById(R.id.ip_addr);
String ipInfo = ipInfoTV.getText().toString();
if (TextUtils.isEmpty(ipInfo)){
ipInfo = "8.8.8.8";
}
String queryBase = "http://www.telize.com/geoip/";
String queryString =
Uri.parse(queryBase).buildUpon().appendPath(ipInfo).toString();
startNetworkInfoTask(queryString);
}
});
}
public class GetNetworkInfoTask extends AsyncTask<String, Integer, String> {
private static final String TAG = "GetNetworkInfo";
//in intro class, pass in and use context;
private Context context = null;
GetNetworkInfoTask(Context context) {
this.context = context;
}
@Override
protected void onPreExecute() {
// do nothing for this example; but if you had a progressdialog; set it up here
}
@Override
protected String doInBackground(String... params) {
String networkInfo = getDataFromWeb((String) params[0]);
return networkInfo;
}
@Override
protected void onProgressUpdate(Integer... progress) {
// do nothing for this example
// setProgressPercent(progress[0]);
}
// Called on UI thread after doInBackground completes; receives a parameter of the 3rd type
@Override
protected void onPostExecute(String result) {
Log.d(TAG, "PlaceholderFragment : onPostExecute entry");
handleResults(result);
}
private String getDataFromWeb(String queryString) {
Log.d(TAG, "getDataFromWeb " + queryString);
String sb = null;
try {
// Open the connection and get the response from the url. Response should be in json
URL url = new URL(queryString);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
int response = urlConnection.getResponseCode();
if (response != HttpURLConnection.HTTP_OK) {
Log.e(TAG, "getDataFromWeb HttpURLConnection not ok: " + response);
} else {
Log.d(TAG, "getDataFromWeb HttpURLConnection is ok: " + response);
sb = getInputString(urlConnection);
Log.d(TAG, sb);
urlConnection.disconnect();
}
} catch (Exception e) {
Log.e(TAG, this.getClass().getSimpleName() + e + " for url: " + queryString);
e.printStackTrace();
}
return sb;
}
private String getInputString(HttpURLConnection urlConnection) {
// read the input into a string
StringBuffer sb = null;
BufferedReader in;
try {
// urlConnection.getInputStream reads the response body.
// InputStreamReader is a java class that turns a byte stream into a character stream
// BufferedReader is a java class that wraps an existing reader and buffers the input, to minimize
// interaction with the underlying reader as most requests are satisfied from accessing the buffer
in = new BufferedReader(
new InputStreamReader(urlConnection.getInputStream()));
sb = new StringBuffer("");
String line = "";
String NL = System.getProperty("line.separator");
while ((line = in.readLine()) != null) {
sb.append(line + NL);
}
in.close();
} catch (IOException e) {
Log.d(TAG, "");
e.printStackTrace();
}
return sb.toString();
}
}
public void handleResults(String results) {
Log.d(TAG, "handleResults " + results);
IpLocationInfo ipLocationInfo = null;
if (results != null) {
ParseJsonInfo parseJsonInfo = new ParseJsonInfo();
ipLocationInfo = parseJsonInfo.decodeMessage(results);
if (caller == QUERY_GET_IP) {
displayResultsIP(ipLocationInfo);
} else if (caller == QUERY_GET_IP_LOC_INFO) {
displayResultsIPLocInfo(ipLocationInfo);
}
}
}
// The following assumes your TextView id is ip_addr; modify the following to match whatever id you gave the TextView that holds the ip address.
private void displayResultsIP(IpLocationInfo ipLocationInfo){
TextView textView = (TextView)getActivity().findViewById(R.id.ip_addr);
textView.setText(ipLocationInfo.getIp());
}
private void displayResultsIPLocInfo(IpLocationInfo ipLocationInfo){
TextView textViewCountry = (TextView)getActivity().findViewById(R.id.ip_country);
textViewCountry.setText(ipLocationInfo.getCountry());
TextView textViewTZ = (TextView)getActivity().findViewById(R.id.ip_timezone);
textViewTZ.setText(ipLocationInfo.getTimezone());
TextView textViewCity = (TextView)getActivity().findViewById(R.id.ip_city);
textViewCity.setText(ipLocationInfo.getCity());
TextView textViewRegion = (TextView)getActivity().findViewById(R.id.ip_region);
textViewRegion.setText(ipLocationInfo.getRegion());
TextView textViewLatitude = (TextView)getActivity().findViewById(R.id.ip_latitude);
textViewLatitude.setText(ipLocationInfo.getLatitude());
TextView textViewLongtitude = (TextView)getActivity().findViewById(R.id.ip_longitude);
textViewLongtitude.setText(ipLocationInfo.getLongitude());
}
public void startNetworkInfoTask(String queryString) {
// Add code to kill any existing asyncTask if the button is pressed multiple times
if(niTask != null) {
AsyncTask.Status aiStatus = niTask.getStatus();
Log.d(TAG, " startHttpURLTask :doClick: aiTask status is " + aiStatus);
if(aiStatus != AsyncTask.Status.FINISHED) {
Log.v(TAG, "startHttpURLTask doClick cancel existing task if not done.");
niTask.cancel(true);
}
}
// Start the asyncTask
niTask = new GetNetworkInfoTask(getActivity());
niTask.execute(queryString);
}
}
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