AI 149494: Minor improvements to wording in design tips for missing activity and notifications

  <li><a href=#tips>Design Tips

    <ol>

      <li><a href=#activity_not_reused_tip>Don't specify intent filters in an activity that won't be re-used</a></li>

      <li><a href=#others_to_reuse_tip>Don't define your own URI schemes</a></li>

      <li><a href=#reusing_tip>Handle where a re-used activity is missing</a></li>

      <!-- <li><a href=#others_to_reuse_tip>Don't define your own URI schemes</a></li> -->

      <li><a href=#reusing_tip>Handle case where no activity matches</a></li>

      <li><a href=#activity_launching_tip>Consider how to launch your activities</a></li>

      <li><a href=#activities_added_to_task_tip>Allow activities to add to current task</a></li>

      <li><a href=#notifications_return_tip>Notifications should be easy to return from</a></li>

      <li><a href=#notifications_get_back_tip>Notifications should let user easily get back</li>

      <li><a href=#use_notification_tip>Use the notification system</a></li>

      <li><a href=#taking_over_back_key>Don't take over BACK key unless you absolutely need to</a></li>

    </ol>

<ol>

  <li><a href="{@docRoot}guide/topics/fundamentals.html">Application Fundamentals</a></li>

  <li><a href="http://android-developers.blogspot.com/2009/05/activities-and-tasks.html">Activities and Tasks blog post</a></li>

</ol>

</div>

<p>

  When the user takes an action on some data, such as touching a

  mailto:info@example.com link, they are actually initiating an Intent

  object which then gets resolved to a particular component (we will

  consider only activity components here). So, the result of a user

  touching a mailto: link is an Intent object that the system tries to

  match to an activity. If that Intent object was written explicitly

  naming an activity (an <em>explicit intent</em>), then the system

  immediately launches that activity in response to the user

  object, or just an <em>intent</em>,  which then gets resolved to a

  particular component (we consider only activity components here).

  So, the result of a user touching a mailto: link is an Intent object 

  that the system tries to match to an activity. If that Intent object was

  written explicitly naming an activity (an <em>explicit intent</em>),

  then the system immediately launches that activity in response to the user

  action. However, if that Intent object was written without naming an

  activity (an <em>implicit intent</em>), the system compares the Intent

  object to the <em>intent filters</em> of available activities. If more

<p>

  Your applications can re-use activities made available from other

  applications. In doing so, you cannot presume that external activity

  will always be present — you must handle the case that the

  external activity is not installed. Do this in the way you find most

  appropriate, such as dimming the user control that accesses it (such

  as a button or menu item), or displaying a message to the user that

  sends them to the location to download it, such as the Market.

  applications. In doing so, you cannot presume your intent will always

  be resolved to a matching external activity — you must handle the case

  where no application installed on the device can handle the intent.

</p>

<p>

  You can either test that an activity matches the intent, which you can do

  before starting the activity, or catch an exception if starting the

  activity fails. Both approaches are descibed in the blog posting

  <a href="http://android-developers.blogspot.com/2009/01/can-i-use-this-intent.html">Can

  I use this Intent?</a>.

</p>

<p>

  To test whether an intent can be resolved, your code can query the package manager.

  The blog post provides an example in the isIntentAvailable() helper method.

  You can perform this test when initializing the user interface.

  For instance, you could disable the user control that initiates

  the Intent object, or display a message to the user that lets them go

  to a location, such as the Market, to download its application.

  In this way, your code can start the activity (using either startActivity() 

  or startActivityForResult()) only if the intent has tested to resolve

  to an activity that is actually present.

</p>

<h3 id=activity_launching_tip>Consider how you want your activities to be launched or used by other applications</h3>

</p>

<h3 id="notifications_return_tip">Notifications should be easy for the user to return from</h3>

<h3 id="notifications_get_back_tip">Notifications should let the user easily get back to the previous activity</h3>

<p>

  Applications that are in the background or haven't been run can

  send out notifications to the user letting them know about events

  of interest. For example, Calendar can send out notifications of

  upcoming events, and Email can send out notifications when new

  messages arrive. One of the user interface rules is that when the

  user is in activity A and gets a notification for activity B and

  Applications that are in the background or not running can have

  services that send out notifications to the user letting them know about

  events of interest. Two examples are Calendar, which can send out notifications of

  upcoming events, and Email, which can send out notifications when new

  messages arrive. One of the user interface guidelines is that when the

  user is in activity A, gets a notification for activity B and

  picks that notification, when they press the BACK key, they should

  go back to activity A. 

</p>

  <ul>

    <li>

      <b>The application has a dedicated activity for

      notification</b> - For example, when the user receives a

      Calendar notification, the act of selecting that

      <b>The chosen activity is dedicated for notification only</b> -

      For example, when the user receives a

      Calendar notification, choosing that

      notification starts a special activity that displays a list

      of upcoming calendar events — a view available only

      of upcoming calendar events — this view is available only

      from the notification, not through the Calendar's own user

      interface. After viewing this upcoming event, to ensure that

      the user pressing the BACK key will return to the activity

    </li>

    <li>

      <b>The user choosing the notification brings the activity to

      <b>The chosen activity is not dedicated, but always comes to

      the foreground in its initial state</b> - For example, in

      response to a notification, the Gmail application is brought

      to the foreground presenting the list of conversations. You

      do this by having the user's response to the notification

      trigger an intent to launch the activity with the clear top

      flag set. (That is, you put {@link

      response to a notification, when the Gmail application comes

      to the foreground, it always presents the list of conversations.

      You can ensure this happens by setting a "clear top" flag in the

      intent that the notification triggers.  This ensures that when the

      activity is launched, it displays its initial activity, preventing

      Gmail from coming to the foreground in whatever state the user last

      happened to be viewing it. (To do this, you put {@link

      android.content.Intent#FLAG_ACTIVITY_CLEAR_TOP

      FLAG_ACTIVITY_CLEAR_TOP} in the intent you pass to

      startActivity()). This prevents Gmail from coming to the

      foreground in whatever state the user last happened to be

      viewing it.

      FLAG_ACTIVITY_CLEAR_TOP} in the intent you pass to startActivity()). 

    </li>

  </ul>

<p>

  There are other ways to handle notifications, such as bringing the

  activity to the foreground set to display specific data, such as the

  ongoing text message thread of a particular person.

  activity to the foreground, set to display specific data, such as

  displaying the text message thread for the person who just sent a

  new text message.

</p>

<p>