Simple ListView Android Developer Tutorial Part 16

From exploring the various concepts related to fundamentals and to locations and maps, I would like to look at a few UI elements.


One of the simple views is a List View. In this post, I will explore a very simple list view using all the defaults provided by Android SDK and introduce you to a customized list view in the next blog article.

A List View, by name means being able to display a list of items in an order one below the other. For creating such a view, the first thing we have to do is extend the ‘ListActivity’ (android.app.ListActivity) instead of the normal Activity class.

So, here is how the class declaration should look:

public class MyListView extends ListActivity {

The ListActivity class provides a way of binding a source of data (an array or a cursor) to a ListView object through a ListAdapter.

In android, we all know that views are defined declaratively in XML files. It is the same here too. So, if we were to create our own custom ListView, we would have a declaration of this type:

<ListView android_id="@id/android:list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#000fff"
android:layout_weight="2"
android:drawSelectorOnTop="false">
</ListView>

However, if no ListView is declared, the ListActivity picks up a default ListView which fills the screen. So, in our example we will not declare any list view.

There is one more thing we need to define and that is how each row in the list should show up. This again, there are some defaults available which have names such as simple_list_item_1, simple_list_item_2, and two_line_list_item. So, in our example, I do not declare the layout for the rows but I will be using one of the defaults provided. So, in effect, I have not declared any layout – I am using the default screen layout and row layout.

Now, that we have the layouts out of our way, what else do we need for a List View. Of course, the list of data that needs to be displayed. Just to keep it simple, I will use an array of data for the same. So, here it is:

static final String[] PENS = new String[]{
"MONT Blanc",
"Gucci",
"Parker",
"Sailor",
"Porsche Design",
"Rotring",
"Sheaffer",
"Waterman"
};

Now, how do I bind this data to the default views described earlier? This is aided by a ListAdapter interface hosted by the ListActivity class that we have extended.

We need to use the setListAdapter(..) method of the ListActivity class to bid the two (data and view). Android provides many implementations of the ListAdapter. We will use the simple ArrayAdapter.

What does the ArrayAdapter expect?

It expects the context object, the row layout and the data in an array.

So here it is:

setListAdapter(new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, PENS));

With this we are done in creating the ListView.

I have added a small piece of code to show we can handle events on selecting an item in the list, by overriding the protected method shown below:

protected void onListItemClick(ListView l, View v, int position, long id) {
super.onListItemClick(l, v, position, id);
Object o = this.getListAdapter().getItem(position);
String pen = o.toString();
Toast.makeText(this, "You have chosen the pen: " + " " + pen, Toast.LENGTH_LONG).show();
}

This toasts a message with the item selected.

The complete code is downloadable here.

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Android Developers Blog Can I use this Intent

We all know that the loose coupling provided by Android through intents is one of its most powerful features. It makes it possible for us to mix and match the use of activities between various applications as though they all belong to one.

However, when I want to invoke another application that has published an intent filter, I cannot always assume that the other application is available on the phone. So, I need to check its availability and then only enable the feature to call it.

This is very well explained in the link: Android Developers Blog: Can I use this Intent?

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Install Android Studio on Ubuntu 15 10 using ubuntu developer tools center

---

remark:
ubuntu-developer-tools-center is now named Ubuntu Make officially.
Please check the updated "Install Android Studio on 64-bit Ubuntu-GNOME 15.10 with Ubuntu Make".

---

To install Android Studio on Ubuntu 15.10 using ubuntu-developer-tools-center
- install java (refer "Install Oracle java8 on Ubuntu 15.10 via PPA")
- Enter the command in Terminal:
$ sudo apt-get install ubuntu-developer-tools-center
$ udtc android

This video show installing Android Studio on 64-bit Ubuntu 15.10 (run in VirtualBox) using ubuntu-developer-tools-center.

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:p>

tablayout,or,tabbed,view,android,developer,tutorial

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TabLayout or Tabbed View Android Developer Tutorial

This tutorial is about developing a TabLayout  / tabs which is one of the very important ways of providing the UI in Android.  The default Contacts application uses this layout.

For creating a tab Layout, we need to look at 3 new aspects: TabActivity, TabHostand TabWidget.

Let us begin by looking at how we should declare the layout xml.  The root node has to be a TabHost. What is a TabHostand why is it required? It is nothing but a container for the tabbed view we want to create. It provides methods to add the tabs, remove them and to bring focus to a specific tab etc.

Within this, we need to have a two objects: TabWidgetand a FrameLayout.

The TabWidgetitself does not do much except contain a list of tab labels that exist within the parent TabHost.  Basically it is nothing but a set of labels that the user clicks in order to select a specific tab. The actual content of each tab is to be held by the 2^nd object in the TabHosti.e. a FrameLayout. Hence both the TabWidgetand FrameLayoutneed to be present on each tab. And in order to align htme one after another, we embed them into a LinearLayout.

Hence the layout XML would be like this:

<TabHost

      >="http://schemas.android.com/apk/res/android"

      android:id="@android:id/tabhost"

      android:layout_width="fill_parent"

      android:layout_height="fill_parent"

      >

<LinearLayout

      android:id="@+id/LinearLayout01"

      android:layout_width="fill_parent"

      android:layout_height="fill_parent"

      android:orientation="vertical">

<TabWidget

      android:id="@android:id/tabs"

      android:layout_width="fill_parent"

      android:layout_height="wrap_content"></TabWidget>

<FrameLayout

      android:id="@android:id/tabcontent"

      android:layout_width="fill_parent"

      android:layout_height="fill_parent"></FrameLayout>

</LinearLayout>

</TabHost>

Now, we will move on to the coding of activities for a Tabbed Layout.

In the application, I want to have 3 tabs. So how do I do it?

Each of the tabs can have either a View, launch an activity by passing an intent or create a view dynamically by using TabHost.TabContentFactory. I have chosen to show only activities in all my tabs.

So, how many activities do you think we need? 3? Sorry 4! There needs to be a main or the parent activity that would display the whole tabbed view and one activity in each of the tabs.

Now let us look at developing the main activity. This has to extend the TabActivity.  This is no different from an Activity except for the additional ability to handle multiple embedded activities or views.

So here is the main class declaration:

public class TabLayoutSample extends TabActivity {

Let us see now, how to create the first tab.

First, we need to get a handle to the TabHostthat we have declared in the XML layout file, so that we can add tab activities into it. Here is the code for the same:

      TabHost tabHost = getTabHost();  // The activity TabHost

Into this TabHost, we need to add the tab. How can we? TabHostprovides an inner class called TabSpecthat allows you to create a tab, populate its contents and add it as a tab to the TabHost.  See how it is done:

TabHost.TabSpec spec; 

// Create an Intent to launch an Activity for the tab (to be reused)

      intent = new Intent().setClass(this, WelcomeActivity.class);

      // Initialize a TabSpec for each tab and add it to the TabHost

      spec = tabHost.newTabSpec("welcome").setIndicator("Welcome",

                          res.getDrawable(R.drawable.tab_welcome))

                      .setContent(intent);

      tabHost.addTab(spec);

In the first line above, we are creating a spec variable of type TabSpec. Then we are creating an intent that would be forming the content of the first tab. Then, we associate it with the TabSpec.

Since, each tab should have a tab indicator, content and a tag to keep track of it, it is achieved through setIndicator(..) method. Even the image that should be shown in the tab at the top is set through the same method’s 2^nd parameter res.getDrawable(R.Drawable.tab_welcome). What is this and how did I set the image?

This part is a long set of steps but very easy to do. Create two images one in light color and one in dark color. Call them as welcome.png and welcome_sepia.png. Copy them into the /res/drawable-mdpi folder.  The, you need to create a state-list drawable that specifies which image to use for each tab state:

[A StateListDrawable is a drawable object defined in XML that uses a several different images to represent the same graphic, depending on the state of the object. For example, a Button widget can exist in one of several different states (pressed, focused, or neither) and, using a state list drawable, you can provide a different background image for each state.]

So, here is the tab_welcome.xml:

<?xml version="1.0"encoding="UTF-8"?>

<selector >="http://schemas.android.com/apk/res/android">

    <!-- When selected, use grey -->

    <item android:drawable="@drawable/welcome"

          android:state_selected="true"/>

    <!-- When not selected, use white-->

    <item android:drawable="@drawable/welcome_sepia"/>

</selector> Read More..

Tuesday, April 19, 2016

Android Developer Days is reloading for 2013

Android Developer Days(ADD) is now reloading for 2013. ADD 2013 will take place on June 14/15, 2013 in METU Cultural and Convention Center, Ankara, Turkey. 
ADD 2013 is targeted to be the one of the biggest international tech related community organization in EMEA. The first ADD was on May 21/22, 2012. There were 700 participants and more than 30 speakers.  ADD 2013,  June 14/15, 2013,  will have more participants, more fun, more networking and more inspiration. 
Take a look at the About, Call for submissions and Participation Form.

ADD is a community conference organized by:  

• GDG Ankara,
• GDG ?stanbul,
• ODTÜ IEEE, 
• GDG Baku,
• GTUG Brussels, 
• GDG Cluj-Napoca, 
• GDG Dnipropetrovsk, 
• GDG Eski?ehir, 
• GDG Konya, 
• GDG Kyiv, 
• GDG Lviv, 
• GDG Samsun, 
• GDG Tbilisi, 
• GDG Timi?oara

Call For Submissions

You can join the conference with the followings:

• Presentations that is 15-20 minutes or 40-45 minutes long.
• Quickie: 10 minute presentation in small rooms.
• Poster: You can show your applications in a place dedicated for posters.
• Workshop: Presentations with hands on coding, 40 minutes long.

Indicate your contribution in OpenConf and please indicate how much your presentation is going to take when submitting it to OpenConf Deadline of Call for Submissions is 1st May 2013.

Subjects:

• Future Technologies
• Mobile World
• Future of Mobile World
• New Generation Mobile Devices (Project Glass)
• Android OS
• Future Versions
• Android in Different Architectures
• Android in Different Areas(Industry, Defense, Home Electronics etc.)
• Android App Development
• New Features and Capabilities
• App Development Best Practises
• Android SDK Tools
• UI(User Interface) / UX (User Experience) Design
• App Monetization
• Ad Integration
• In-app Billing
• User Statistics
• Android NDK
• Cross Platform App Development Frameworks
• HTML5
• Javascript
• Game Development
• Google TV
• Google Playstore
• Communication Solutions (NFC, Bluetooth, Wi-fi)
• 3G, 4G Wide Band Communication
• Cloud
• Google Cloud Messaging for Android
• Google App Engine
• Augmented Reality
• Social Media
• Location Based Services and Maps
• Mobile Education (Fatih Project)
• Mobile Payment
• Security
• Arduino
• Software Development Methodologies

• Success Stories
• GWT
  
  

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Creating Android UI Programmatically

So far, in all my examples, I have been using the declarative way of creating an Android UI using XML. However, there could arise certain situations when you may have to create UI programmatically. Sincere advice would be to avoid such a design since android has a wonderful architecture where the UI and the program are well separated. However, for those few exceptional cases where we may need too… here is how we do it.

Every single view or viewgroupelement has an equivalent java class in the SDK. The structure and naming of the classes and methods is very similar to the XML vocabulary that we are used to so far.

Let us start with a LinearLayout. How would we declare it in an XML?

<?xml version="1.0"encoding="utf-8"?>

<LinearLayout >="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    >

<TextView 

    android:layout_width="fill_parent"

    android:layout_height="wrap_content"

    android:text="@string/hello"

    />

</LinearLayout>

This just contains a TextViewembedded in a LinearLayout. A very trivial example. But serves the purpose intended. Let me show how almost every single element here corresponds to a class or a method call in the class.  So the equivalent code in the onCreate(…)  method of an activity would be like this:

         super.onCreate(savedInstanceState);

      

        lLayout = newLinearLayout(this);

        lLayout.setOrientation(LinearLayout.VERTICAL);

        //-1(LayoutParams.MATCH_PARENT) is fill_parent or match_parent since API level 8

        //-2(LayoutParams.WRAP_CONTENT) is wrap_content

        lLayout.setLayoutParams(new LayoutParams(

LayoutParams.MATCH_PARENT,

LayoutParams.MATCH_PARENT));

        tView = newTextView(this);

        tView.setText("Hello, This is a view created programmatically! " +

                  "You CANNOT change me that easily :-)");

        tView.setLayoutParams(new LayoutParams(

LayoutParams.MATCH_PARENT,

LayoutParams.WRAP_CONTENT));

        lLayout.addView(tView);

        setContentView(lLayout);

Like this any layout view can be created. But from this small example you can notice two outstanding things – very tedious to code for every attribute of the view. And any simple change in the view, you need to change the code, compile, deploy and only then you see the effect of the change – unlike in a layout editor. 

You can download the sample code here.

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Sunday, April 17, 2016

SQLite DB Example Android Developer Tutorial Part 12

There are 4 ways of storing data on the android platform:

• 1.    Preferences
• 2.    SQLite Database
• 3.    Files
• 4.    Network

A word about each of them here and then I will move on to an example that shows how to work with SQLite DB that comes along with the android platform.

Preferences–

Basically used for storing user preferences for a single application or across applications for a mobile. This is typically name-value pairs accessible to the context.

Databases –

Android supports creating of databases based on SQLite db. Each database is private to the applications that creates it

Files –

Files can be directly stored on the mobile or on to an extended storage medium. By default other applications cannot access it.

Network –

Data can be stored and retrieved from the network too depending on the availability.

If an application wants to store and retrieve data for its own use, without having to share the data across applications, it can access the SQLite DB directly. There is no need of a content provider. We have seen in an earlier post how to use content providers.

In this example, we will do the following:

1.    Create a database (typically a one time activity)

2.    Create a table (typically a one time activity)

3.    Insert values into the table

4.    Retrieve the values from the table

5.    Display the retrieved values as a List view

6.    Delete all the records from the table before closing the connection to the database

Step 1: Create a database:

   sampleDB =  this.openOrCreateDatabase(SAMPLE_DB_NAME, MODE_PRIVATE, null);

This opens a database defined in the constant SAMPLE_DB_NAME, if it already exists. Else it creates a database and opens it. The second parameter is operating mode : MODE_PRIVATE meaning it is accessible to only this context. The other modes are and MODE_WORLD_WRITABLE. MODE_WORLD_READABLE

Step 2: Create a Table:

sampleDB.execSQL("CREATE TABLE IF NOT EXISTS " +

                        SAMPLE_TABLE_NAME +

                        " (LastName VARCHAR, FirstName VARCHAR," +

                        " Country VARCHAR, Age INT(3));");

Step 3: Insert values into the table:

sampleDB.execSQL("INSERT INTO " +

                        SAMPLE_TABLE_NAME +

                        " Values (Makam,Sai Geetha,India,25);");

Step 4: Retrieve values

Cursor c = sampleDB.rawQuery("SELECT FirstName, Age FROM " +

                        SAMPLE_TABLE_NAME +

                        " where Age > 10 LIMIT 5", null);

           

      if (c != null ) {

            if  (c.moveToFirst()) {

                  do {

String firstName = c.getString(c.getColumnIndex("FirstName"));

                  int age = c.getInt(c.getColumnIndex("Age"));

                  results.add("" + firstName + ",Age: " + age);

                  }while (c.moveToNext());

            }

       }

Step 5: Display the values as a list

           

       this.setListAdapter(newArrayAdapter<String>(this, android.R.layout.simple_list_item_1,results));

The statement displays it as a list as the class extends a ListActivity.

Step 6: Delete the values from the table in the finally part of the try block

finally {

            if (sampleDB != null)

                  sampleDB.execSQL("DELETE FROM " + SAMPLE_TABLE_NAME);

                  sampleDB.close();

        }

It is as simple as this to work with the SQLite DB even in android. No different from a desktop application. However, there are various overloaded methods of query() provided by the SQLIteDatabase class which can be more optimally used instead of execSQL.

The complete code for this example is downloadable here.

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