Creating First Android App with Eclipse

This is the start of the many of the Simplified android tutorials and it starts with a very simple android application.To make things easier this whole tutorial follows a set of steps.

1. First, Create a Project Named ‘Application01’ by going to File->New->Android Application. Provide the Minimum and Maximum Android Version Requirements as you wish. Keep other project settings as usual and Click ‘Finish’.









2. Go inside the Application01->res->layout->activity_main.xml and start adding form items. You can either copy the XML code I’ve provided below or add button yourself.




<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.buttonclick.MainActivity"
    tools:ignore="MergeRootFrame" >

    <TextView
        android:id="@+id/textView_01"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="The Total Value Is : " 
        android:layout_marginTop="10dp"
        android:textColor="#ff0000"
        android:textStyle="bold"
        />

    <Button
        android:id="@+id/btn_incrementer"
        android:layout_width="fill_parent"
        android:layout_height="82dp"
        android:text="Increment" 
        android:layout_marginTop="40sp"/>

    <TextView
        android:id="@+id/textView_02"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/textView_01"
        android:layout_alignBottom="@+id/textView_01"
        android:layout_centerHorizontal="true"
        android:text=""
        android:textAppearance="?android:attr/textAppearanceSmall" />

    <Button
        android:id="@+id/btn_decrementer"
        android:layout_width="fill_parent"
        android:layout_height="82dp"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/btn_incrementer"
        android:text="Decrement" />

</RelativeLayout>




3. Finally your app front end should look like below.

   
   
   
   
   
4. Then, start Changing Main_Activity.java which is inside Application01->src->com.example.application01->Main_Activity.java. You can either copy or paste the code that I’ve provided below or write the code yourself.
   
   
   

   package com.example.application01;
   
   import android.app.Activity;
   import android.app.ActionBar;
   import android.app.Fragment;
   import android.os.Bundle;
   import android.view.LayoutInflater;
   import android.view.Menu;
   import android.view.MenuItem;
   import android.view.View;
   import android.view.ViewGroup;
   import android.widget.Button;
   import android.widget.TextView;
   import android.os.Build;
   
   public class MainActivity extends Activity {
   
    Button dec,inc;
    TextView dis;
    int count=0;
    
       @Override
       protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);
           setContentView(R.layout.activity_main);
   
           if (savedInstanceState == null) {
               getFragmentManager().beginTransaction()
                       .add(R.id.container, new PlaceholderFragment())
                       .commit();
           }
           
           /* MyCode Starts Here */
           
           dec = (Button) findViewById(R.id.btn_dec);
           inc = (Button) findViewById(R.id.btn_inc);
           dis = (TextView)findViewById(R.id.display_value);
           
           dec.setOnClickListener(new View.OnClickListener() {
      
      @Override
      public void onClick(View arg0) {
       // TODO Auto-generated method stub
       
       count++;
       dis.setText(String.valueOf(count));
       
       
      }
     });
           
           inc.setOnClickListener(new View.OnClickListener() {
      
      @Override
      public void onClick(View v) {
       // TODO Auto-generated method stub
       
       count--;
       dis.setText(String.valueOf(count));
      }
     });
             
           /* My Code Ends Here */
       }
   
   
       @Override
       public boolean onCreateOptionsMenu(Menu menu) {
           
           // Inflate the menu; this adds items to the action bar if it is present.
           getMenuInflater().inflate(R.menu.main, menu);
           return true;
       }
   
       @Override
       public boolean onOptionsItemSelected(MenuItem item) {
           // Handle action bar item clicks here. The action bar will
           // automatically handle clicks on the Home/Up button, so long
           // as you specify a parent activity in AndroidManifest.xml.
           int id = item.getItemId();
           if (id == R.id.action_settings) {
               return true;
           }
           return super.onOptionsItemSelected(item);
       }
   
       /**
        * A placeholder fragment containing a simple view.
        */
       public static class PlaceholderFragment extends Fragment {
   
           public PlaceholderFragment() {
           }
   
           @Override
           public View onCreateView(LayoutInflater inflater, ViewGroup container,
                   Bundle savedInstanceState) {
               View rootView = inflater.inflate(R.layout.fragment_main, container, false);
               return rootView;
           }
       }
   
   }

   
   
5. If you intend to write code, make sure to add your Code inside protected void onCreate(Bundle savedInstanceState) method. Declare all the Variables inside public class MainActivity { } class.



6. You should cast the Android Widget Button dec to XML Button like, dec = (Button) findViewById(R.id.btn_dec);



7. Write the Button Click Event like follows.

dec.setOnClickListener(new View.OnClickListener() {

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub

count++;
dis.setText(String.valueOf(count));


}
});