Night Dreaming (by Sudar)

This week, I was not able to attend the full class due to time constraint, since I returned from a vacation on Tuesday. So my notes will not be as detailed as it used to be. I will try to provide detailed notes next week.

Getting authenticated with oAuth

So basically this week, Tony explained how to setup oAuth authentication, so that we can use the Twitter API without explicitly asking for password from the users.

In order to set it up, we have to first register for an app from Twitter. You can follow the screencast at the end of last week’s notes to do that.

Twitter4J

The next step is to include the Twitter4J jar. You can download it from the project homepage and then you have to copy it to the /lib directory of your android project. If you are using windows, then you can follow the steps given in this forum post to add Twitter4J to your android project.

Source code

You can access the source code for this week’s class from the official github repository.

See you all next week with detailed notes

As I mentioned before, Creative tech is conducting part 2 of the Developing Android App class. Like Part 1, I am planning to post my notes here so that it would be helpful for others too.

Introduction

This week, we had the Overview session by Tony (the presenter). The training started off with a brief explanation of the concepts that were covered in Part 1. Tony then explained briefly about Twitter and the explained what are the things that will be covered in the next 5 classes.

The following is the schedule for the next 5 weeks.

Week one

• Getting Authenticated with Twitter
• oAuth
• Twitter4J
• Webview and webview Client

Week two

• Advanced ListView
• List headers and footers
• Concurrent Programming with Threads
• Handlers

Week Three

• Tweeting from App
• Creating menus
• Using AsynTask to run many Concurrent tasks
• Posting tweets

Week Four

• Adding style to the App
• Themes
• Styles
• Selectors and XML Graphics
• Designing for multiple screen dimensions

Week Five

• Posting photos from the app
• Getting photos from the library
• Getting photos from the Camera
• Posting photos with twitpic4J

Homework

The homework for this week is to register an application and get authentication keys to use oAuth with Twitter. This has to be done before the next week class so that you can use to try next week’s code.

Tony has created the following screencast which explains the process of registering your application with Twitter.

There are lot of really interesting things lined up and I am very excited about this course. See you next week

You can also subscribe to my blog’s RSS feed or follow me in Twitter to receive updates about my notes for the next sessions.

This week’s homework in the android class was to create a simple ListView using ArrayAdapter instead of generic ListAdapter.

ArrayAdapter

ArrayAdapter is a special kind of ListAdapter which supplies data to ListView. You can refer to my notes for last week to know about ListView and ListAdapter. You can also read about ArrayAdapter in android documentation.

Adding views

First create an empty android project. Then edit the main.xml layout file to add a ListView. Then create another layout xml file which will contain the TextView (or any component) that will be displayed within the ListView.

Editing Activity

The next step is to change the generated activity class to extend from ListActivity. This is very important because only a ListActivity will be able to display the ListView.

Binding the adapter

The next step is to bind the ArrayAdapter to the ListActivity. We can do this by calling the setListAdapter() method.

To this method we have to pass an object of type ArrayAdapter. You can pass an object reference to this method or we can even create a new anonymous method like below.

setListAdapter(new ArrayAdapter<string>(this, R.layout.list_item, strings) {
	@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		View row;
 
		if (null == convertView) {
			row = mInflater.inflate(R.layout.list_item, null);
		} else {
			row = convertView;
		}
 
		TextView tv = (TextView) row.findViewById(android.R.id.text1);
		tv.setText(getItem(position));
 
		return row;
	}
});

We have to override the getView() method of the ArrayAdapter class to create the TextView (or any other component) which will be created for each list.

Finishing up

So that’s it, you are done. All you have to do now is to save the project and run it in the emulator. If everything is done properly, then you can see the list of items displayed in the ListView like below.

Source code

I have uploaded the entire project source code into github and you download it from there and verify it with your code.

Try to complete the homework, before the next session and do come back to view the notes and the homework for the next session too.

You can also subscribe to my blog’s RSS feed or follow me in Twitter to receive updates about my notes for the next sessions.

Like last week, I attended the session on Developing Android applications in Java by Creative Techs and O’Reilly and here are my notes which I took during the session.

Replace TextView with ListView

In this week’s session, the demo app that was created last week was modified to use the ListView element instead of TextView.

The ListView provides a nice UI for displaying the list of tasks together with a checkbox to indicate whether they were complete or not.

Screenshot

You can see the new UI of the application in the following screenshots.

ListView and ListAdapter

ListView is a control which can be used for creating list of scrollable items. The data to the ListView will be provided by ListAdapter.

You can think of ListView as the “view” component in a MVC framework and ListAdapter as the “model”

The class which is going to act as the ListAdapater should implement following methods

• getCount()
• getItem()
• getItemId()
• getView()

You can read more about ListView and ListAdapter from android documentation.

Adding ListView

To add ListView to any activity, we have to include the <ListView /> tag to the activity’s layout xml. In our sample app, the ListView tag is added to the main.xml file.

The Activity class that uses ListView should implement the ListActivity instead of plain Activity class. In our sample app, the ViewTasksActivity class is derived from the ListActivity class.

Magic ids

Android SDK provides some predefined ids which can be used some specific purposes. One such “magic id” is android:empty.

We can assign this to any element that we want to be displayed when the ListView is empty.

Homework

This week’s homework is to Build a simpler (but less flexible) way to load data into a list using an ArrayAdapter (instead of a BaseAdapter). I would be completing the homework and would be posting the explanation and the source code later this week. So stay tuned

Source code

I have uploaded source code for yesterday’s session in github and you can download it from there. I am also working in this week’s homework and will be posting the explanation and source code once I am done.

You can also subscribe to my blog’s RSS feed or follow me in Twitter to receive updates about my notes for the next sessions.

This week’s homework in the android class was to persist the task information in the sample TaskManager application across program runs, which was created during the class.

Preference API

Android provides a preference API, using which we can store task information. The preference API is very simple to use and all we have to do is to get the instance to the preference object from the Application object and then call the getString() and putString() method.

Serializing ArrayList to string

The only tricky part of the home work is that, since the preference API supports only storing and retrieving of strings, we have to serialize and de-serialize the ArrayList object which has the list of tasks into string.

Instead of writing my own code to do this conversion, I used the code from the Apache Pig project. You can check out the class from the pig’s github page.

Storing the task

In the addTask() method of the TaskManagerApplication class, we have to get the instance of the shared preference and then store the serialized ArrayList using the putString() method.

	public void addTask(Task t) {
		assert(null != t);
		if (null == currentTasks) {
			currentTasks = new ArrayList<task>();
		}
		currentTasks.add(t);
 
		//save the task list to preference
		SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
		Editor editor = prefs.edit();
		try {
			editor.putString(TASKS, ObjectSerializer.serialize(currentTasks));
		} catch (IOException e) {
			e.printStackTrace();
		}
		editor.commit();
	}

Retrieving the task

Similarly we have to retrieve the list of tasks from the preference in the onCreate() method

	public void onCreate() {
		super.onCreate();
		if (null == currentTasks) {
			currentTasks = new ArrayList<task>();
		}
 
		//		load tasks from preference
		SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
 
		try {
			currentTasks = (ArrayList<task>) ObjectSerializer.deserialize(prefs.getString(TASKS, ObjectSerializer.serialize(new ArrayList<task>())));
		} catch (IOException e) {
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}

Finishing up

So that’s it, you are done. All you have to do now is to save the project and run it in the emulator. If everything is done properly, the tasks that you enter will be saved even after you restart the app.

Source code

I have uploaded the entire project source code into github and you download it from there and verify it with your code.

Try to complete the homework, before the next session and do come back to view the notes and the homework for the next session too.

You can also subscribe to my blog’s RSS feed or follow me in Twitter to receive updates about my notes for the next sessions.