Android - Basic Steps (Intent)

Application Components

• Activity
• Primary class for user interaction
• Provide the GUI
• Main 3 components
• Services - Support ground back operations
• Support interaction with remote processes
• BroadcastReceiver - Responds to an event on the device
• An example is the sms
• ContentProvider - Allow to share data among applications
• Uses database-style inferface

Building an App

http://developer.android.com/tools/building/index.html

1. Define resources
2. Package
3. Manifest
• http://developer.android.com/guide/topics/manifest/manifest-intro.html
4. Install & Run
• Signing the app http://developer.android.com/tools/publishing/app-signing.html

Activity

• The activity order is established in the task backstack
• The activity lifecycle
• Resumed / Running
• Paused
• Stopped
• Methods for an activity
• onCreate
• onStart - when the app become visible
• onResume - when is able to interact with the user
• onPause
• onStop - when the app become invisible
• onDestroy - in not called when android kill the app by the lack of memory
• onRestart - when the user press back and show the previous activity

Invoke and activity

• startActivity
• startActivityForResult
• When this method is used, override the method onActivityResut()

@Override

protected void onActivityResult(int requestCode, int resultCode, Intent data) {

if (resultCode == Activity.RESULT_OK

&& requestCode == PICK_CONTACT_REQUEST) {

               }

          }

Tips

• To avoid Resume the activity when change from vertical to landscape position change the configuration in the AndroidManifest file.

In the AndroidManifest.xml inside the tags; <application> , <activity>. Add the line

android:configChanges="orientation|keyboardHidden|screenSize"

Intents

• Data Structure that represents 
• Operation to be performed (Select a contact, dial a phone number)
• Event that has ocurred

Intent Field

• Action
• Data
• Category
• Type
• Ex: IMAGE/*, IMAGE/PNG, IMAGE/JPG, TEXT/HTML
• Component
• Extra 
• Flag

Actions

• ACTION_DIAL
• Ex:  Intent intent = new Intent(Intent.ACTION_DIAL);
• ACTION_EDIT - Display data to edit
• ACTION_SYNC - Synchonize device data with server
• ACTION_MAIN - Starts an initial activity of app

Data

• To pass data to an Intent is through an URI
• Ex: Intent intent = new Intent(Intent.ACTION_DIAL, Uri.parse("tel:+55555"));

Category

• Additional information that can handle the intent
• CATEGORY_BROWSER
• CATEGORY_LAUNCHER - Initial activity of a task & is listed in the top-level app launcher

Type

• Define the type of the information
• Intent.setType(String type)
• Intent.setDataAndType(Uri data, String type)

Component

• Used when there is only one component that should receive the intent
• Intent intent = new Intent( Context packageContext, Class<?> cls)
• setComponent()
• setClassName()
• setClass()

Extra

• Add extra information in a Map form (Key-value pairs)
• Intent.EXTRA_EMAIL
• to set extra data depends of the intent

Flag

• Show how the intent has to handle
• FLAG_ACTIVITY_NO_HISTORY -this does not put the activity in the History Stack
• FLAG_DEBUG_LOG_RESOLUTION - this show more logging information when the intent is processed

Invoke another activity

• Directly
• Intent helloAndroidIntent = new Intent(Context packageContext, Class<?> cls)
• Indirectly
• In this case Android, only compare with the available applications that match in:
• Action
• Data (Type & URI)
• Category
• Can specified in the AndroidManifest.xml, including the data
• To receive implicit intents an activity should specify an IntenFilter tag
• <category android:name="android.intent.category.DEFAULT" />
• Also can specify a Priority
• Values can be > 1000 , < 1000
• Higher values. higher priorities 
• http://developer.android.com/guide/components/intents-filters.html

<activity>

  <intent-filter>

       .....

       <action android:name="android.intent.action.DIAL" />
       <category android:name="android.intent.category.DEFAULT" />

       .....

  </intent-filter>

  <data

     android:mimeType="string"

     android:scheme="string"

     android:host="string"

     android:port="string"

     android:path="string"

     android:pathPattern="string"

     android:pathPrefix="string"

  />

</activity>

Invoke activity from another application

• Invoker application
• In the Activity call the other activity using startActivity() method
• startActivity(new Intent(ACTIVITY_OTHER_APP));
• ACTIVITY_OTHER_APP - is the activity defined in the AndroidManifest in the other app
• Calling application
• In the AndroidManifest define the <intent-filter> to link the activity to be called.

<activity>

    <intent-filter>

                  <action android:name="ACTIVITY_OTHER_APP" />

                  <category android:name="android.intent.category.DEFAULT" />

    </intent-filter>

</activity>