The document discusses adapter and cache techniques in Android. It explains that an adapter acts as a bridge between a view and underlying data. It transforms data into views. The adapter is responsible for creating a view for each item. It also discusses using view holders and lists to improve performance. It provides examples of caching views for scrolling and caching data to avoid duplicate network requests and optimize loading images.

1. Adapter and
cache technique
Trí Phạm – MultiUni - 2012

2. Adapter and cache technique
• Adapter in Android
• Cache technique in Android

3. ADAPTER IN ANDROID

4. Adapter in Android
• Adapter design pattern

5. Adapter in Android
• Adapter design pattern (con’t)

6. Adapter in Android
• Adapter design pattern (con’t)

7. Adapter in Android
• Adapter design pattern (con’t)

8. Adapter in Android
• An Adapter object acts as a bridge between an View and the
underlying data for that view.
• One side of the adapter is a data structure like a Java object
storing data. the other side of the adapter, there is view that
the data structure was transformed into.
• The Adapter is also responsible for making a View for each
item in the data set.

9. Adapter in Android

10. Adapter in Android
• Android ListView

11. Adapter in Android
• Android ListView (con’t)
– Naive and dumb way
– The correct way: List13.java
– The fast way: List14.java

12. Adapter in Android
• Considering Adapter for the List View
– Each List item in the List View would be calling its
“getView()” method.
– This method would return a view for the List.
– But creating a new View for each list item would be
complicated, and the UI would be slow down.
– Instead of creating new View for each item, Recycler
save these view and passes it to the Adapter.
– Adapter uses these view sent by the recycler, when it
has to produce any new views.

13. Adapter in Android
• View Holders
– View Holders hold some data that related to an item to
the view.
– View Holders minimizes the amount of work, while
writing the same piece of code again and again.
– These are used while creating the views, where we have
to use more than one time.
(TextView)findViewById(R.Id.text);
(ImageView)findViewById(R.Id.Icon);

14. Adapter in Android
• View Holders (con’t)
– By using the View Holders, the views are saved into a
class variable and can be called when needed.
holder.text = (TextView)findViewById(R.id.text);
holder.icon = (ImageView)findViewById(R.id.icon);
convertView.setTag(holder);
– A tag can hold any kind of object, that can be set on the
view.

15. Adapter in Android
• Android ListView

16. CACHE TECHNIQUE IN
ANDROID

17. Cache technique in Android
• Basic cache view technique (for
views that have scrolling
behavior)
• Cache data technique

18. Adapter in Android
• Basic cache view technique (for
views that have scrolling behavior)
– Demo EfficientListView

19. Adapter in Android
• Cache data technique
– Why using cache:
• Some operations are high CPU load and
time consuming. E.g.: load images from
network…
-> Never do something time consuming twice
• Mobile applications, especially Android
applications needs optimization for smooth
UI.

20. Adapter in Android
• Cache data technique
– Demo ImageDownloader with soft
(memory) cache

21. Q&A