How to solve Must Override a Superclass Method Error

Ever import some Android sample code into eclipse and get the dreaded  "Must Override a Superclass Method Error"?
In this blog post I am going to explain the source of the problem and how to fix it.

You might receive an error like this:
The method onClick(View) of type new View.OnClickListener(){} must override a superclass method Java Problem

The Source of the Problem: The project was written with a Java JDK Compiler compliance level of 1.6 but your eclipse setting is 1.5.

How to fix the problem: 


Right click on your project and select "properties"

Select "Java Compiler" 

Make sure "Enable project specific settings" is checked

Change the "Compiler compliance level:" to 1.6

Save the changes. 

Now select "Project" > "Clean..." 

Your project should now build without any errors.

Please feel free to post comments or questions. I usually post a reply within a day or two.

Android Garage Door App

Ever wanted to check your garage door from you Android phone?
Now You can Open and Close Your Garage Door with Your Phone.

This "How To" guide is a complete tutorial, taking you through the entire process step by step. I have included a working Android app you can use "as-is" or use it as a starting point and improve it. At the end of the tutorial, I will document some things I would recommend be added to the app.

Let's get started. Open eclipse and start a new project. If you need help setting up your development environment, I have created a detailed step by step guide. Here is a link.

How to Setup Android Development Environment

Create a new project
Project name: Garage Door App
Build target: I targeted Android 2.3.1 but I believe the code would run as low as 1.6. So if you phone is not lower than v2.3.1 select the appropriate API
Application name: Garage Door App
Package name: com.acm.blog.example.garagedoorapp
Check "Create activity:" and name it "MainActivity"
Min SDK version: 9 (again if you target a lower API adjust this number to the appropriate API level)

Here is what our app is going to look like when done.

It is made up of three controls.

1. An open garage door button.
2. A close garage door button.
3. And finally a status display which will let us know when the door is open or closed. I also coded it so when you touch the display graphic the app will check the door and update the status.

Let's start coding!

Step 1: Create the layout by editing the main.xml file already created for us. If you new to Android the layout might be a little confusing. Here is a complete explanation of the layout file.

Starting on line 1 and ending on line 19 is a "Linear Layout" that encompasses the entire layout. We specify that the orientation is vertical. As new controls get added they appear at the bottom. We also set the background to our brushed aluminum graphic. Lines 2-4 are a Linear layout with a TextView for "Garage Door Opener". I wrapped the TextView in a linear layout so I could center it with android:gravity="center_horizontal" I used a frame layout on lines 5-12 so that I can layer controls on top of each other. I wanted the progress bar to be dead center of our status graphic. Lines 6-8 is our status graphic that is centered with the property android:gravity="center_horizontal" Lines 9-11 is the progress bar that we display while making our web service calls in a background thread. Also centered. Lines 13-18 is a linear layout (outside of the frame so it appears below it). This linear layout is set to stack the controls horizontally with the following property  android:orientation="horizontal". We have two image buttons in this layout.

Main.xml

Step 2: Before we code our main activity let's create a helper class to make the http calls to the Netduino.

• Right click on the project name and select New > Class
• Name it "WebService.java". Now lets go through the code.
• Line 2 we will make a constant string containing the Netduino IP address

public class WebService {
 private final String WEBSERVICE_URL = "http://192.168.0.153/";
  ...
  ...

• Line 3 declare an HttpClient we will use to make the HTTP cals

public class WebService {
 private final String WEBSERVICE_URL = "http://192.168.0.153/";
 private HttpClient client;
 ...

• Create a constructor and in it instantiate our HttpClient

...
    public WebService(){
        client = new DefaultHttpClient();
    }
  ...

• Create a private method that calls the webservice and parses the retun

private String MakeHTTPCall(String method){
  HttpGet get = new HttpGet(WEBSERVICE_URL + method);
  try {
   // Create a response handler
            ResponseHandler responseHandler = new BasicResponseHandler();
            String responseBody = client.execute(get, responseHandler);
            return responseBody;
  } catch (IOException e) {       // -|
   e.printStackTrace();       // |--> Oops something went wrong!
  } catch (Exception e) {        // |
   e.printStackTrace();       // -|
  }
  return "failed";         //Return "failed" if we encounter an error
 }

• Create a new HTTP get passing in the web service URL and the method name

private String MakeHTTPCall(String method){
  HttpGet get = new HttpGet(WEBSERVICE_URL + method);
  try {
   // Create a response handler
            ResponseHandler responseHandler = new BasicResponseHandler();
            String responseBody = client.execute(get, responseHandler);
            return responseBody;
  } catch (IOException e) {       // -|
   e.printStackTrace();       // |--> Oops something went wrong!
  } catch (Exception e) {        // |
   e.printStackTrace();       // -|
  }
  return "failed";         //Return "failed" if we encounter an error
 }

• Instantiate a new BasicResponseHandler to parse our webservice return into a string
• Create a String variable to hold the return and call execute on the HttpClient
• We pass in the HttpGet variable and the response handler

private String MakeHTTPCall(String method){
  HttpGet get = new HttpGet(WEBSERVICE_URL + method);
  try {
   // Create a response handler
            ResponseHandler responseHandler = new BasicResponseHandler();
            String responseBody = client.execute(get, responseHandler);
            return responseBody;
  } catch (IOException e) {       // -|
   e.printStackTrace();       // |--> Oops something went wrong!
  } catch (Exception e) {        // |
   e.printStackTrace();       // -|
  }
  return "failed";         //Return "failed" if we encounter an error
 }

• Return the result from the HTTP GET call. We wrap the HTTP call in try catch.

private String MakeHTTPCall(String method){
  HttpGet get = new HttpGet(WEBSERVICE_URL + method);
  try {
   // Create a response handler
            ResponseHandler responseHandler = new BasicResponseHandler();
            String responseBody = client.execute(get, responseHandler);
            return responseBody;
  } catch (IOException e) {       // -|
   e.printStackTrace();       // |--> Oops something went wrong!
  } catch (Exception e) {        // |
   e.printStackTrace();       // -|
  }
  return "failed";         //Return "failed" if we encounter an error
 }

WebService.java

public class WebService {
 private final String WEBSERVICE_URL = "http://192.168.0.153/";
 private HttpClient client;
    public WebService(){
        client = new DefaultHttpClient();
    }

    public String IsGarageDoorOpen(){
     for(int i = 0; i < 5; i++){
         String s = MakeHTTPCall("checkdoor");
      if(s.equals("failed") == false)
       return s; //Got a response return result
     }
     return "failed";  //Oh well we tried 5 times without success
 }
 public String ActivateGarageDoor(){
  for(int i=0; i < 5; i++){
   String s = MakeHTTPCall("activatedoor");
      if(s.equals("failed") == false)
       return s; //Got a response return result
  }
  return "failed";
 }
 
 private String MakeHTTPCall(String method){
  HttpGet get = new HttpGet(WEBSERVICE_URL + method);
  try {
   // Create a response handler
            ResponseHandler responseHandler = new BasicResponseHandler();
            String responseBody = client.execute(get, responseHandler);
            return responseBody;
  } catch (IOException e) {       // -|
   e.printStackTrace();       // |--> Oops something went wrong!
  } catch (Exception e) {        // |
   e.printStackTrace();       // -|
  }
  return "failed";         //Return "failed" if we encounter an error
 }

}

Step 3: Let's edit our Main Activity.

• Line 2 is our progress bar we will display while we check the status of the garage door in a background thread. It is always a good idea to let the user know when the app is working in the background.
• Line 3 is an instance of our ImageView we will use to display the status of the garage door.
• Line 4 is an instance of our web service helper class. 

public class MainActivity extends Activity {
 private ProgressBar progressBar1;
 private ImageView status;
 private WebService ws;

Now let's add some code to the onCreate method

• On line 9 we turn of the window title bar.
• Line 12 instantiate the progress bar.
• Line 13 the ImageView we are using to display the status of the garage door.
• Lines 14-19 set the on click listener so we can check the status of the garage door when someone touches the status image. We someone clicks the ImageView we execute an AsyncTask to check the garage door in a background thread.
• Line 20 instantiate our Open ImageButton.
• Lines 21-26 set the on click listener for the open button. When the open button is clicked we activate the garage door with an AsyncTask on a background thread.
• Lines 27-33 is the same for the Close button.
• Lines 34-48 We create a Timer to check the status of the garage door every fifteen minutes again on a background thread.

@Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);
  setContentView(R.layout.main);
  ws = new WebService();
  progressBar1 = (ProgressBar) findViewById(R.id.progressBar1);
  status = (ImageView) findViewById(R.id.Status_ImageView);
  status.setOnClickListener(new OnClickListener() {      
     public void onClick(View v) {      // Check garage door
      new CheckGarageDoorAsync().execute();   // when status
                 // image clicked
     } 
    }); 
  ImageButton openButton = (ImageButton) findViewById(R.id.OpenButton);
  openButton.setOnClickListener(new OnClickListener() {
   @Override
   public void onClick(View arg0) {
    new ActivateGarageDoorAsync().execute();
   }
  });
  ImageButton closeButton = (ImageButton) findViewById(R.id.CloseButton);
  closeButton.setOnClickListener(new OnClickListener() {
   @Override
   public void onClick(View arg0) {
    new ActivateGarageDoorAsync().execute();
   }
  });
  final Handler handler = new Handler();
  Timer t = new Timer();
  t.scheduleAtFixedRate(new TimerTask() {
   @Override
   public void run() {
    handler.post(new Runnable() {
     public void run() {
      Log.d("z", "check garage door");
      setUI(ws.IsGarageDoorOpen());
     }
    });
   }
  }, 0, 900000);
  new CheckGarageDoorAsync().execute();
 }
}

Lines 56-92 is a method that sets our UI depending on the state of the garage door. If the garage door is open we disable the open button and set the display to "Open" and of course the opposite if its closed.

private void setUI(String mode) {
  if (mode.equals("Open")) {
   ImageButton o = (ImageButton) findViewById(R.id.OpenButton);
   o.setImageResource(R.drawable.open_button_alt); // Open button
               // depressed
   o.setEnabled(false);        // Disable open button
   ImageButton c = (ImageButton) findViewById(R.id.CloseButton);
   c.setImageResource(R.drawable.close_button);  // Closed button up
   c.setEnabled(true);        // Enable close button
   ImageView status = (ImageView) findViewById(R.id.Status_ImageView);
   status.setImageResource(R.drawable.status_open); // Set status
                // graphic
  } else if (mode.equals("Closed")) {
   ImageButton o = (ImageButton) findViewById(R.id.OpenButton);
   o.setImageResource(R.drawable.open_button);  // Open button up
   o.setEnabled(true);        // Enable open button
   ImageButton c = (ImageButton) findViewById(R.id.CloseButton);
   c.setImageResource(R.drawable.close_button_alt); // Close button
                // depressed
   c.setEnabled(false);         // Disable close button
   ImageView status = (ImageView) findViewById(R.id.Status_ImageView);
   status.setImageResource(R.drawable.status_closed);// Set status
                 // graphic
  } else {
   ImageButton o = (ImageButton) findViewById(R.id.OpenButton);
   o.setImageResource(R.drawable.open_button_alt);  // Open button
                // depressed
   o.setEnabled(false);         // Disable open button
   ImageButton c = (ImageButton) findViewById(R.id.CloseButton);
   c.setImageResource(R.drawable.close_button_alt); // Close button
                // depressed
   c.setEnabled(false);         // Disable close button
   ImageView status = (ImageView) findViewById(R.id.Status_ImageView);
   status.setImageResource(R.drawable.status_unknown);// Set status
                  // graphic
  }
 }

Lines 97-117 We create an AsyncTask to check the status of the garage door. Using an AsyncTask allows us the make an http call on a background thread so our app does not become un-responsive and geneate an "ANR" error. If you perform a long task on the UI thread and the user presses a key and there is no response within 5 seconds Android will generate an ANR error message asking the user to wait or to close. You should never perform a network call on the UI thread. We implement three methods of the AsyncTask.

1. onPreExecute(). This is performed on the UI thread. We turn on the progress bar indicating we are checking the door.
2. doInBackground(). This is performed in a background thread. In this method we check the garage door state by calling our IsGarageOpen method on our web service class. We then pass the results to onPostExecute() method.
3. onPostExecute(). This is performed on the UI thread. This method sets all the controls based on the state of the garage door.

private class CheckGarageDoorAsync extends AsyncTask {
  @Override
  protected void onPreExecute() {
   setUI("Unkown");            // While we check disable all buttons and clear status display
   progressBar1.setVisibility(View.VISIBLE); // Display progress bar
  }
 
  @Override
  protected String[] doInBackground(Void... arg0) {
   String r = ws.IsGarageDoorOpen();    // Make webservice call to check
              // garage door
   return new String[] { r };      // Return result
  }
 
  @Override
  protected void onPostExecute(String[] result) {
   progressBar1.setVisibility(View.INVISIBLE); // Hide progress bar
   setUI(result[0]);        // Pass result to setUI method to sync the UI
  }
 
 }

Lines 122-161 We create another AsyncTask to activate the garage door. Here is the complete MainActivity class.
MainActivity.java

public class MainActivity extends Activity {
 private ProgressBar progressBar1;
 private ImageView status;
 private WebService ws;

 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);
  setContentView(R.layout.main);
  ws = new WebService();
  progressBar1 = (ProgressBar) findViewById(R.id.progressBar1);
  status = (ImageView) findViewById(R.id.Status_ImageView);
  status.setOnClickListener(new OnClickListener() {      
     public void onClick(View v) {      // Check garage door
      new CheckGarageDoorAsync().execute();   // when status
                 // image clicked
     } 
    }); 
  ImageButton openButton = (ImageButton) findViewById(R.id.OpenButton);
  openButton.setOnClickListener(new OnClickListener() {
   @Override
   public void onClick(View arg0) {
    new ActivateGarageDoorAsync().execute();
   }
  });
  ImageButton closeButton = (ImageButton) findViewById(R.id.CloseButton);
  closeButton.setOnClickListener(new OnClickListener() {
   @Override
   public void onClick(View arg0) {
    new ActivateGarageDoorAsync().execute();
   }
  });
  final Handler handler = new Handler();
  Timer t = new Timer();
  t.scheduleAtFixedRate(new TimerTask() {
   @Override
   public void run() {
    handler.post(new Runnable() {
     public void run() {
      Log.d("z", "check garage door");
      setUI(ws.IsGarageDoorOpen());
     }
    });
   }
  }, 0, 900000);
  new CheckGarageDoorAsync().execute();
 }

 /*
  * Set UI components Garage Open Open button is disabled Close button is
  * enabled Status graphic - OPEN Garage Closed Open button is enabled Close
  * button is disabled Status graphic - Closed Garage Unknown Open button is
  * disabled Close button is disabled Status graphic - black
  */
 private void setUI(String mode) {
  if (mode.equals("Open")) {
   ImageButton o = (ImageButton) findViewById(R.id.OpenButton);
   o.setImageResource(R.drawable.open_button_alt); // Open button
               // depressed
   o.setEnabled(false);        // Disable open button
   ImageButton c = (ImageButton) findViewById(R.id.CloseButton);
   c.setImageResource(R.drawable.close_button);  // Closed button up
   c.setEnabled(true);        // Enable close button
   ImageView status = (ImageView) findViewById(R.id.Status_ImageView);
   status.setImageResource(R.drawable.status_open); // Set status
                // graphic
  } else if (mode.equals("Closed")) {
   ImageButton o = (ImageButton) findViewById(R.id.OpenButton);
   o.setImageResource(R.drawable.open_button);  // Open button up
   o.setEnabled(true);        // Enable open button
   ImageButton c = (ImageButton) findViewById(R.id.CloseButton);
   c.setImageResource(R.drawable.close_button_alt); // Close button
                // depressed
   c.setEnabled(false);         // Disable close button
   ImageView status = (ImageView) findViewById(R.id.Status_ImageView);
   status.setImageResource(R.drawable.status_closed);// Set status
                 // graphic
  } else {
   ImageButton o = (ImageButton) findViewById(R.id.OpenButton);
   o.setImageResource(R.drawable.open_button_alt);  // Open button
                // depressed
   o.setEnabled(false);         // Disable open button
   ImageButton c = (ImageButton) findViewById(R.id.CloseButton);
   c.setImageResource(R.drawable.close_button_alt); // Close button
                // depressed
   c.setEnabled(false);         // Disable close button
   ImageView status = (ImageView) findViewById(R.id.Status_ImageView);
   status.setImageResource(R.drawable.status_unknown);// Set status
                  // graphic
  }
 }

 /*
  * Check the garage door on background thread with an AsyncTask
  */
 private class CheckGarageDoorAsync extends AsyncTask {
  @Override
  protected void onPreExecute() {
   setUI("Unkown");            // While we check disable all buttons and clear status display
   progressBar1.setVisibility(View.VISIBLE); // Display progress bar
  }

  @Override
  protected String[] doInBackground(Void... arg0) {
   String r = ws.IsGarageDoorOpen();    // Make webservice call to check
              // garage door
   return new String[] { r };      // Return result
  }

  @Override
  protected void onPostExecute(String[] result) {
   progressBar1.setVisibility(View.INVISIBLE); // Hide progress bar
   setUI(result[0]);        // Pass result to setUI method to sync the UI
  }

 }

 /*
  * Activate the garage door on a background thread with an AsyncTask
  */
 private class ActivateGarageDoorAsync extends
   AsyncTask {
  @Override
  protected void onPreExecute() {
   setUI("Unkown");        // While we check disable all buttons and clear
              // display graphic
   progressBar1.setVisibility(View.VISIBLE); // Display progress bar
  } 

  @Override
  protected String[] doInBackground(String... arg0) {
   String start = ws.IsGarageDoorOpen();

   String r = ws.ActivateGarageDoor();   // Activate garage door
   for (int i = 0; i < 60; i++) {     // Give the door up to 1 minute to
              // close/open
    try {
     Thread.sleep(1000);     // Pause for 1 second
    } catch (InterruptedException e) {
     e.printStackTrace();
    }
    r = ws.IsGarageDoorOpen();     // Check the door status
    if (r.equals(start) == false && r.equals("failed") == false)
     break;         // The door is done opening/closing
   }
   return new String[] { r };      // Return the status of garage
  }

  @Override
  protected void onProgressUpdate(String... values) {

  }

  @Override
  protected void onPostExecute(String[] result) {
   progressBar1.setVisibility(View.INVISIBLE);
   setUI(result[0]);
  }

 }
}

You can get the entire project source code here


To learn how to build the hardware required to monitor and control your garage door read my post here. http://androidcodemonkey.blogspot.com/2011/09/mobile-app-to-monitor-open-and-close.html. If you have any questions please feel free to leave a comment. I usually answer questions within a day or two.

Android app to monitor & open and close garage door

Have you ever wanted to know if your garage door is open without having to go and check it? There have been many blog posts to light an LED when you leave your garage door open, but I want something more convenient. I decided to write an Android app that would allow me to monitor my garage door and even open or close from anywhere. I am going to provide complete instructions for building the required hardware and the android app code.

Monitor your garage door with an Android app

What is required? We need to build the following:

• Using a Netduino board (or an Arduino board with an Ethernet shield) build a sensor to detect if the garage door is open or closed. I chose an infrared phototransistor so I would not have to make physical contact with the door and because it's cheap! Like $1.13 cheap!
  Build and program a garage door sensor
• To open or close the garage door I wired an Optoisolator to a spare garage door opener.
  Build and program a garage door opener
  

  

  Open and close garage door with your Netduino

• Write a program (or you might hear it referred to as a sketch) to check the sensor and determine if the door is open or close and report it back over HTTP
• Even though it's not required, I wrote a second RESTful webservice to talk to the Netduino web server (see diagram). That way the Netduino webserver is never exposed outside my private network. I have another computer with the RESTful webservice that has a layer of authentication that is exposed to the internet.
• And finally an Android app that will display if the garage door is open or closed as well as open or close it. Here are step by step instructions (with complete source code) for writing the Android App.

I will be covering each step with a detailed post.

Store and Get an Object in Android Shared Preferences

Can I store and retrieve an object in Android Shared Preferences? Yes! This tutorial will walk you through a complete tutorial. Source code included! There are times when you need to store a lightweight object in Shared Preferences. I stress lightweight. We are going to use Google's JSON library to do the object serialization/de-serialization.

• Let's create a new project.

Download the latest gson jar from http://code.google.com/p/google-gson/downloads/list. I am using version 1.7. Place the jar somewhere convenient (If I intend to use the jar in several projects, I will place in a folder outside of my project). For this example, I will create a new folder called "lib" inside the project folder. Place the jar you downloaded in "lib" folder. Now we need to add a reference to gson jar.

• Open the project properties. Right click on project name "ObjectsInSharedPreferenceSample" or whatever you called your project and select "Properties"

• Select "Java Build Path" > "Add External JARS..."

• Let's add a custom class that we are going to store and retrieve in the Shared Preferences. Add a new class "MyObject"

• To keep the example simple, lets add just two public properties to our "MyObject" class
• public int myValue;
• public String MyLabel;
• Add two buttons and two EditText. Make sure to add the onClick directive the XML so when the button is pressed our methods are executed.

• Let's write some code. In the MainActivity add the following method. This method will be called when the store button is pressed. It will create an instance of "MyObject" and set the "MyValue" string to what ever you type in the EditText inputEditText. Then it will convert the object to a string using the gson library and store that string in the SharedPreferences.

public void storeButton_Clicked(View v){
     EditText inputEditText = (EditText) findViewById(R.id.inputEditText);
     MyObject obj = new MyObject();
     obj.myValue = 2;
     obj.MyLabel = inputEditText.getText().toString();
     SharedPreferences appSharedPrefs = PreferenceManager
  .getDefaultSharedPreferences(this.getApplicationContext());
  Editor prefsEditor = appSharedPrefs.edit();
  Gson gson = new Gson();
  String json = gson.toJson(obj);
  prefsEditor.putString("MyObject", json);
  prefsEditor.commit();
  Toast.makeText(this, "Object stored in SharedPreferences", Toast.LENGTH_LONG);
    }

• Now let's get the object from shared preferences and display it's properties in the outputEditText. 

public void getButton_Clicked(View v){
     EditText outputEditText = (EditText) findViewById(R.id.outputEditText);
  SharedPreferences appSharedPrefs = PreferenceManager
  .getDefaultSharedPreferences(this.getApplicationContext());
  Gson gson = new Gson();
  String json = appSharedPrefs.getString("MyObject", "");
  MyObject obj = gson.fromJson(json, MyObject.class);
  outputEditText.setText("obj.MyLabel: [" + obj.MyLabel + "] obj.MyValue: [" + obj.myValue + "]");
    }

Run the program. Save an object and retrieve it from SharedPreferences. To keep things as simple as possible I only included required code. There is a lot of code missing that you will want to add like error checking and running off the UI thread. But this will get you started.

Following is the complete source code for your review.

Eclipse Dark Color Theme

I discovered http://www.eclipsecolorthemes.org for conveniently creating your own personal color scheme for eclipse. I am making available the dark theme I have been using for some time. Try it out or create your own easily on http://www.eclipsecolorthemes.org.

Color scheme import instructions

1. Download the my color scheme from http://www.eclipsecolorthemes.org or create your own.

2. Choose "File" > "Import"

3. Choose "Preferences" then "Next"

4. Browse to the ".epf" file you downloaded and select it.Then press "Finish".

And now your code window should immediately display your new color scheme.

Android app & Netduino plus to monitor and open garage door

I have started a new blog on the Netduino plus board. This is my first foray into embedded programming. I just received an Arduino Uno board and a Netduino plus board. I am going to chronicle a home automation project that includes the following elements (I will be documenting everything you need if you want to join me!) 

• Netduino plus with garage door sensor
• Open and close the garage door with the Netduino plus
• Send commands to the Netduino over HTTP
• A RESTful webservice that talks to the Netduino plus over HTTP
• Write an Android app that talks to the RESTful webservice that talks to the Netduino
• An Android app to monitor my garage door and open/close it.

I will be posting every step of this project with parts lists, instructions and code examples. If you want to learn more here are some links.

• Blog about my embedded projects and code examples (http://netduinohacking.blogspot.com/)
• Arduino (an open-source electronics prototyping platform)
• Netduino plus