Adapter and cache technique

Adapter and cache technique

Trí Phạm – MultiUni - 2012

Adapter and cache technique

• Adapter in Android

• Cache technique in Android

ADAPTER IN ANDROID

Adapter in Android

• Adapter design pattern

Adapter in Android

• Adapter design pattern (con’t)

Adapter in Android

• Adapter design pattern (con’t)

Adapter in Android

• Adapter design pattern (con’t)

• 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.

Adapter in Android

Adapter in Android

Adapter in Android

• Android ListView

Adapter in Android

• Android ListView (con’t)

– Naive and dumb way

– The correct way: List13.java

– The fast way: List14.java

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.

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);

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.

Adapter in Android

• Android ListView

CACHE TECHNIQUE IN ANDROID

• Basic cache view technique (for views that have scrolling behavior)

• Cache data technique

Cache technique in Android

Adapter in Android

• Basic cache view technique (for views that have scrolling behavior)– Demo EfficientListView

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.

Adapter in Android

• Cache data technique

– Demo ImageDownloader with soft (memory) cache

Q & A