Imagine an Activity popping out of nowhere suddenly in front of the user. And even more irritating, the user doesn’t even know whether a button was clicked. Though these are very small animation implementations but these animations enhance the user experience to a new level. This blog deals with the animations in Loklak Wok Android, a peer message harvester of Loklak Server.

Activity transition animation

Activity transition is applied when we move from a current activity to a new activity or just go back to an old activity by pressing back button.

In Loklak Wok Android, when user navigates for search suggestions from TweetHarvestingActivity to SuggestActivity, the new activity i.e. SuggestActivity comes from right side of the screen and the old one i.e. TweetHarvestingActivity leaves the screen through the left side. This is an example of left-right activity transition. For implementing this, two xml files which define the animations are created, enter.xml and exit.xml are created.

<set
   xmlns:android="http://schemas.android.com/apk/res/android"
   android:shareInterpolator="false">

   <translate
       android:duration="500"
       android:fromXDelta="100%"
       android:toXDelta="0%"/>
</set>

NOTE: The entering activity comes from right side, that’s why android:fromXDelta parameter is set to 100% and as the activity finally stays at extreme left, android:toXDelta parameter is set to 0%.

As the current activity, in this case TweetHarvestingActivity, leaves the screen from left to the negative of left. So, in exit.xml the android:fromXDelta parameter is set to 0% and android:toXDelta parameter is set to -100%.

Now, that we are done with defining the animations in xml, it’s time we apply the animations, which is really easy. The animations are applied by invoking Activity.overridePendingTransition(enterAnim, exitAnim) just after the startActivity method. For example, in openSuggestActivity

private void openSuggestActivity() {
   Intent intent = new Intent(getActivity(), SuggestActivity.class);
   startActivity(intent);
   getActivity().overridePendingTransition(R.anim.enter, R.anim.exit);
}

Touch Selectors

Using touch selectors background color of a button or any clickable can be changed, this way a user can see that the clickable responded to the click. The background is usually light accent color or a lighter shade of the icon present in button.

There are three states involved while a clickable is touched, pressed, activated and selected. And a default state, i.e. the clickable is not clicked. The background color of each state is defined in a xml file like media_button_selector, which is present in drawable directory.

<selector xmlns:android="http://schemas.android.com/apk/res/android">

   <item android:drawable="@color/media_button_touch_selector_backgroud" android:state_pressed="true"/>
   <item android:drawable="@color/media_button_touch_selector_backgroud" android:state_activated="true"/>
   <item android:drawable="@color/media_button_touch_selector_backgroud" android:state_selected="true"/>

   <item android:drawable="@android:color/transparent"/>
</selector>

The selector is applied by setting it as the background of a clickable, for example, touch selector applied on Location image button present in fragment_tweet_posting.xml .

<ImageButton
   android:layout_width="40dp"
   android:layout_height="40dp"
   …
   android:background="@drawable/media_button_selector" />

Notice the change in the background color of the buttons when clicked.

Resources:

Some youtube videos for getting started:

• Newboston: https://www.youtube.com/watch?v=n4IyvL-ACbk
• Smartherd (from #5.1 to #5.8): https://www.youtube.com/playlist?list=PLlxmoA0rQ-Lzd9-NUrP5Wi18OMi4R-zs_