Raspberry Pi Android App communication

For making an app work, you don't only need a layout. You also need the code running in the background.

The language we are going to use is Java, because all android apps are written in Java. So lets start coding.

First of all, you need to download the attached file.
This file is a library so you can easily use JSON.

Place this file in:
directiory/app_name/app/src/main/java/company/app_name/JSONParser.java

For me it's:
C:/Users/Laurens1/Desktop/instructables/Instructables/app/src/main/java/Laurens_wuyts/Instructables/JSONParser.java

After that you can open JSONParser in android studio. You now need to change the first line to:
package company.app_name;

Ok now we can start writing the main code.
Open the file MainActivity.java

First make a new Progress-dialog. This is used to display when the code is executing and you need to wait.

Place this in the main class.
private ProgressDialog pDialog;

Then we need a JSONparser object to send the data. So place this line under the previous line:
JSONParser jsonParser = new JSONParser();

Now we need two EditText items, so we can extrude the inserted text. This goes under the JSONParser.
EditText editText;
EditText editText2;

We move on to the oncreate function. Here we need to link the EditTexts from above with the real edittexts in the layout. You do it like this:
editText = (EditText) findViewById(R.id.Name);
editText2 = (EditText) findViewById(R.id.part_nr);

At the end we need to create a new class for connecting to the server and sending the previous typed info.
This is the class Create_part:

class Create_Part extends AsyncTask {

@Override protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(MainActivity.this);
pDialog.setMessage(“Sending part to the database…”); //Set the message for the loading window
pDialog.setIndeterminate(false);
pDialog.setCancelable(true);
pDialog.show(); //Place the loading message on the screen
}

@Override protected String doInBackground(String… args) {

String String_name = editText.getText().toString(); //Get the inserted text from the editText files
String Int_Part = editText2.getText().toString();

List params = new ArrayList<>();
params.add(new BasicNameValuePair(“Name”, String_name)); //Add the parameters to an array
params.add(new BasicNameValuePair(“part_nr”, Int_Part));

// Do the HTTP POST Request with the JSON parameters
// Change “RaspberryPi_IP to your home IP address or Noip service

JSONObject json = jsonParser.makeHttpRequest(“RaspberryPi_IP/db_create.php”, “POST”, params);

try {

int success = json.getInt(“success”);

if(success == 1){

Intent i = new Intent(getApplicationContext(), ConfirmActivity.class);
// Open a new activity to confirm it was sent. We're going to create it later.
startActivity(i);
finish();

}

} catch (JSONException e) {

e.printStackTrace();

}

return null;

}

protected void onPostExecute(String file_url){

pDialog.dismiss(); // Close the loading window when ready

}

}

Now you can make a new function called Send. In this function you call Create_Part. Like so:

public void Send(View view) {

new Create_Part().execute();

}

In the activity_main.xml you now change the onclick action of the button on the right to:
Send

Ok your almost done, now you only need to make a new activity like you see in the image.

Change the activity name to: ConfirmActivity

Click Finish

Now go again to strings.xml and change the “hello_world” string from Hello World! to The part was created.

Now it should be done.

Rebuild the app and test it on your phone!

Step 8: Resume