View source for Start New Activity

The Android development paradigm introduces for the developer the “Activity”: <> During development you will find it easy to wrap-up parts of the functionality of your code into independent activities, with their own life cycle. More about activity life cycle on the Android developers website.

With all activities make sure to declare them in the AndroidManifest.xml
 <activity android:name=".MyPasswordsActivity" android:label="MyPasswords"></activity>

Easy (just start activity)
Assume you have the MainActivity, and a SecondaryActivity you want to start, this may be done in the easiest way:

 Intent intent = new Intent(Intent.ACTION_VIEW);
 intent.setClassName(this, SecondaryActivity.class.getName());
 startActivity(intent);

Medium (pass some params as well)
Now imagine you want to pass some data to the new intent. You will achieve this using the Bundle class, to encapsulate your data. Example:

 Intent intent = new Intent();
 Bundle bun = new Bundle();
 
 bun.putString("param_string", "the actual string"); // add two parameters: a string and a boolean
 bun.putBoolean("param_bool", true);
 
 intent.setClass(this, SecondaryActivity.class);
 intent.putExtras(bun);
 startActivity(intent);

In the SecondaryActivity, you will need to access these params. This is how:

 Bundle bun = getIntent().getExtras();
 String param1 = bun.getString("param_string");
 boolean param2 = bun.getBoolean("param_bool");

Advanced (return some data)
So we passed some parameters to the SecondaryActivity, but let’s assume we want some results as well. From MainActivity one will pack parameters and all others like in the examples above, and than one will call SecondaryActivity as follows:

 startActivityForResult(intent, R.id.secondaryactivity_finished);

where secondaryactivity_finished is just some id, that the MainActivity will be looking for in it’s onActivityResult, as follows:

 protected void onActivityResult(int requestCode, int resultCode, Intent data)
 {
      switch(requestCode)
      {
          case R.id.secondaryactivity_finished:
          if (resultCode == RESULT_OK)
          {
          Bundle res = data.getExtras();
          String result = res.getString(”param_result”);
          }
          break;
      } // end switch
 }

In onActivityResult, one simply follows the activities that returned and their error/success codes, and as in the example above may get data passed by the SecondaryActivity. In our case SecondaryActivity returned a string under the name "param_result".

On the other side, in SecondaryActivity, one will need to pack “param_result” as follows.

 private void ReturnToParent()
 {
    Bundle conData = new Bundle();
    conData.putString("param_return", "text returned to MainActivity");
    Intent intent = new Intent();
    intent.putExtras(conData);
    setResult(RESULT_OK, intent);
    finish();
 }

Some useful default activities:
Part of the beauty of Android is that you can encapsulate other functionality/activities in your own code, just by writing a few lines of code. Below is a list of useful activities one may consider to use:

1. Writing an email

 Intent intent = new Intent(Intent.ACTION_SENDTO, Uri.parse("mailto:office@example.com"));
 intent.putExtra("subject", "my subject");
 intent.putExtra("body", "my message");
 startActivity(intent);

2. Browse to a web-page

 Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(”http://www.google.com”));
 startActivity(intent);

3. Write a SMS

 Intent intent = new Intent(Intent.ACTION_SENDTO, Uri.parse("sms://"));
 intent.putExtra("address", "");
 intent.putExtra("sms_body", "my message");
 startActivity(intent);

4. Search something on Google

 Intent intent = new Intent(Intent.ACTION_WEB_SEARCH );
 intent.putExtra(SearchManager.QUERY, "search this text");
 startActivity(intent);

5. Get the Wiktionary of some word

 Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://en.wiktionary.org/wiki/" + "word"));
 startActivity(intent);

6. Get the Wikipedia page of some words

 String uri = "http://en.wikipedia.org/wiki/" + "my text";
 Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(uri));
 startActivity(intent);