Android - Lists, adapters and recycling

1. Android
Lists, adapters and recycling

2. Bibliography
1. Wallace Jackson, Android Apps for Absolute
Beginners, Apress, 2017
2. Hello Views,
http://developer.android.com/guide/tutorials/vi
ews/index.html
3. Android Application Fundamentals,
http://developer.android.com/guide/topics/fun
damentals.html
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3. Contents
• MVC
• Lists
– Model
– Adaptor
• List Elements
– Simple
– from XML
• ListActvity
• Optimization
– Recycling
– Tags
– Cache
• GridView
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4. Model View Controller
• Pattern
• Splits
– UI
– Program
– Data storage
• Advantages
– Programing with components
– Easier to maintain
• Disadvantages
– May be slow
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5. MVC Empirical
Database (Model)
Display (View) Program logic (Controller)
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6. MVC Schematics
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7. Observer
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8. Observator
• Pattern
• Splits
– Observed object
– Observer
• Advantages
– Programming with
components
– Easier to maintain
– Standard way
• Disadvantages
– May be slow
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9. Gmail - Notification
New email
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10. Specific Activities
• ListActivity
– Specially for a list
– May have other components
– List ID
• android:id=“@android:id/list”
• Special functions
– onListItemClick (…)
– setListAdapter (…)
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11. Functioning principle (MVC)
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12. Adapter
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13. ListView
• A vertical container
– Similar with ScrollView
– Optimized for movement
• Identical components
– Each row
– Almost true ;)
• Adapter’s role
– Creates these components
• Events
– setOnItemClickListener (…)
– setOnItemLongClickListener (…)
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14. Adapter
• Part of View
• Specifies the way of
display
– Adapts the data
– Modifies the View
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15. ListView Adapter
• Predefined
– ArrayAdapter
• User defined
– Implementation of ListAdapter
– Extend BaseAdapter
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16. Usage of ArrayAdapter (XML)
• Example
– Static list
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17. Usage of ArrayAdapter (Java)
• Example
– Static List
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18. Usage of ArrayAdapter (XML)
• Example
– Dynamic List
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19. Usage of ArrayAdapter (Java)
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20. A simple list
• ListView
– Contains a list
– android:id=“@android:id/list”
• Elements of the list
– android.R.layout.simple_list_item_1
• Static
– May use String[]
• Dynamic
– Use ArrayList<String>
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21. The List with complex elements
• Elements
– Components
• EditView
• ImageView
• Container
• Adapter custom-made
– Implement ListAdapter
– Extend BaseAdapter
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22. Extend BaseAdapter
• View getView (int position, View convertView,
ViewGroup list)
• int getCount ()
• Object getItem (int position)
• long getItemId (int position)
• int getViewTypeCount ()
• int getItemViewType (int position)
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23. Extend BaseAdapter (XML)
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24. Extend BaseAdapter (Java)
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25. Extend BaseAdapter (Java)
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26. Extend BaseAdapter (Java)
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27. Extend BaseAdapter (Java)
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28. Recycling
• Objects reusage
• Avoid object creation
– new is bad for memory!
• Use
– Buffers
– Lists
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29. Optimisation
Inefficient!!!
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30. Optimisation
Recycling
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31. Different types of elements?
int getViewTypeCount ()
int getItemViewType (int position)
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32. One more problem
Slow!!!
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33. Tags (for View)
• void setTag (Object tag)
• Object getTag ()
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34. Efficient using Tag
Utilizarea tag-ului
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35. GridView
• Identical with ListView
– Extend BaseAdapater
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36. The new RecyclerView
• A new way of building lists
– Uses several layouts
• Not just a LinearLayout
– The developer has to use recycling and tagging
• Extend RecyclerView.Adapter
– onCreateViewHolder()
• Inflate the view
– onBindViewHolder()
• Set the View’s data
– getItemCount()
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37. Conclusions
• Lists
– Linear containers
– Contain components
• Including containers
• ListActivity
– Activity with special functions for list
• Adapter
– Formats the data from the model for the list
– Simple
– Custom made
– Recycling of elements
• Elements
– Described in XML
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38. Keywords
• MVC
• Adaptor
• Classes
– ListActivity
– ListView
– GridView
– View
– ArrayAdapter
– BaseAdapter
– ArrayList
• Interfaces
– ListAdapter
• Recycling
• Tags
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39. Questions
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