start learning android here

Best site to learn android http://www.javatpoint.com/android-simple-caller-talker-example

download pdf http://www.tutorialspoint.com/android/android_tutorial.pdf


Best example http://www.theappguruz.com/category/android/

Swift Application Development for ios

http://code.tutsplus.com/categories/mobile-development
http://programmerguru.com/android-tutorial/

Implicit Intents

These intents do not name a target and the field for the component name is left blank. Implicit intents are often used to activate components in other applications. For example:

// Implicit Intent by specifying a URI
Intent i = new Intent(Intent.ACTION_VIEW, 
Uri.parse("http://www.example.com"));

// Starts Implicit Activity
startActivity(i); 

explicite 

1. button1.setOnClickListener(new OnClickListener(){  
2.          public void onClick(View view) {  
3.           Intent i = new Intent(getApplicationContext(), ActivityTwo.class);  
4.           i.putExtra("Value1", "Android By Javatpoint");  
5.           i.putExtra("Value2", "Simple Tutorial");  
6.           // Set the request code to any code you like, you can identify the  
7.           // callback via this code  
8.           startActivity(i); 

Android Fragment is the part of activity, it is also known as sub-activity. There can be more than one fragment in an activity. Fragments represent multiple screen inside one activity.

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http://manojprasaddevelopers.blogspot.in/2014/07/generate-sha1-key-using-terminal.html