So this is another Android Walkthrough that will show you how to use the Android AsyncTask class to query for data in the background of your android activities as well as query the Sugabus API and render that data into our activity.
You already know that most of the action is in mainActivity.java and mainActivity.xml, so let's take a quick look at those.
Not much is happening in our xml, we define a button and a text box that currently only contains a placeholder. Let's talk on a high level about what the app will do at first.
Looking inside of the java, that's where most of the action is. You know at a high level that we are going to talk to webservice somehow (in this case Sugabus). This is typically done using an asynchronous task. Let's look at some code.
private class getSugasBusData extends AsyncTask<Void,Void,Object>{
//base url for all our endpoints
String baseUrl = "http://runextbus.heroku.com/";
/**
This method is executes the following code in the background thread
so that there is no crashing because of interaction with UI Thread
*/
@Override
protected Object doInBackground(Void... params) {
//initialize http client
HttpClient client = new DefaultHttpClient();
//can change this to make any url you want
String endpoint = getActiveUrl();
//initialize a GET request with whatever url you want, im using active as an example
HttpGet get = new HttpGet(endpoint);
try{
//execute the get request and store response
HttpResponse response = client.execute(get);
//get status code of http request
StatusLine statusLine = response.getStatusLine();
//initialize byte outputstream to store data
ByteArrayOutputStream bos = new ByteArrayOutputStream();
//store data from http response
response.getEntity().writeTo(bos);
//close the stream
bos.close();
//if the status code is OK
if(statusLine.getStatusCode() == HttpStatus.SC_OK){
//return data in a string
return bos.toString();
}else{
//something got messed up
return null;
}
}catch (IOException e){
//lets see what the error was
Log.e("ERROR",e.getMessage());
return null;
}
}
}So why use AsyncTask in the first place? Here's the idea, our curent activity has control of the user. If we want to make queries for information, instead of forcing the user to wait, we could preemptively look up information without holding up the current user activity*. So what we say is let's run our query in a separate thread, and do other things with the processor and the user while our app has priority. This is important because you will need your apps to be snappy!
So we have our class, what it does is pretty straightforward, we hit a button, on that button press we have a handler that creates an AsyncTask that creates a request to our webservice, if we succesfully get a response back, then we edit our textview to reflect this new information. And that's really all this app does, pretty straightforward!
*For a better understanding of why this should be done this way, check out the docs on the Android Activity Lifecycle.