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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


  • 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
<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>

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