Lecture Slides for List Views [Android ]
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The document discusses list views and adapters for software development on portable devices. It describes the problem of loading large lists inefficiently and solutions like populating views on demand. It explains Android list views and adapters, including how they recycle views to reduce object churn. It provides examples of using list activities with different adapter types and layouts, and discusses optimizing performance by reusing views and using a view holder pattern.
Lecture Slides for List Views [Android ]
- 1. ListView and Adapters Software Development for Portable Devices BITS Pilani Goa Campus Sem I 2011-12
- 2. CS C314 Software Development For Portable Devices Foundation of :
- 3. Problem?? Performance 10,000 entries in a list! Less than 10% shown but fetched completely
- 4. Solution?? Populate on Demand Google image search Recycle views to reduce object churn
- 5. Android – ListView Its a view capable of displaying scrollable list of items It only creates views (widget) if needed It recycles views, e.g. if a row is not displayed anymore it will be recycled and only its content will change.
- 7. Adapters extends "BaseAdapter“ "ArrayAdapter" can handle data based on Arrays "SimpleCursorAdapter" handle database related data Your own "CustomAdapter"
- 8. Android - ListActivity If Activity is primarily showing a list you should extend the activity "ListActivity“ It simplifies the handling of a "ListView“ Set Listadapter in the onCreate(), via the method setListAdapter(). Register the click by onListItemClick(ListView l, View v, int position, long id) CS C314 Software Development For Portable Devices
- 9. onListItemClick Parameters l : The ListView where the click happened v : The view that was clicked within the ListView position : The position of the view in the list id : The row id of the item that was clicked CS C314 Software Development For Portable Devices
- 10. ListActivity with ArrayAdapter and Android standard layout See the code FirstExample CS C314 Software Development For Portable Devices
- 11. ListActivity with own layout See the code SecondExample Define the layout in xml for each row Define our own arrayAdapter and using Id telling adapter which UI element is the text CS C314 Software Development For Portable Devices
- 12. ListActivity with flexible layout See the code ThirdExample Override getView(). Performance is not optimized.. Think why? CS C314 Software Development For Portable Devices
- 13. Performance Issues Creating Java objects for each row is time and memory consumption. findViewById() is a expensive operation Android recycles rows (views) which are not displayed anymore. CS C314 Software Development For Portable Devices
- 14. Optimized Way Using existing rows saves memory and CPU consumption . convertView - The old view to reuse avoid doing findViewById() if not necessary ViewHolder pattern 175% faster then the older procedure CS C314 Software Development For Portable Devices
- 15. ViewHolder The ViewHolder stores a reference to the required views in a row ViewHolder is then attached to the row via the method setTag() row is recycled we can get the ViewHolder via getTag() method much faster then the repetitive call of findViewById() CS C314 Software Development For Portable Devices
- 16. Optimized way See the code CS C314 Software Development For Portable Devices
- 17. Your task Your task is to implement the View holder pattern in the Add food class CS C314 Software Development For Portable Devices
- 18. Interacting rows Your row layout can also contain views which interact with the underlying data model. Example : Checkboxes CS C314 Software Development For Portable Devices
- 19. Try Out LongClickListeners Single Vs Multiple selection Header and Footers CS C314 Software Development For Portable Devices
- 20. References Spinner tutorial : http://developer.android.com/resources/tutorials/views/hello-spinner.html ArrayAdapter: http://developer.android.com/resources/tutorials/views/hello-spinner.html CS C314 Software Development For Portable Devices
Editor's Notes
- #10: position is the clicked element's position in your Adapter (so you can doadapter.getItem(position) ) row id is the id that corresponds to that element, what your Adapter returns in the getItemId()method.