CODEWITHSUNDEEP
androidandroid-listviewandroid-viewandroid-adapternotify
onmyway133
onmyway133

Reputation: 48185

How android's BaseAdapter notifyDataSetChanged method work?

In the document for the method notifyDataSetChanged of class BaseAdapter noted that "Notifies the attached observers that the underlying data has been changed and any View reflecting the data set should refresh itself."

Supposed I changed the 3rd element in my string array (array data for the ListView), what "any View reflecting the data set should refresh itself" means ? Does the 3rd view item in my list view be notified ?

Also, how is notifyDataSetChanged() and getView() concerned ?

Upvotes: 3

Views: 6089

Answers (1)

user
user

Reputation: 87064

Supposed I changed the 3rd element in my string array (array data for the listview), what "any View reflecting the data set should refresh itself" means ?

It means that any view which shows/is based on/uses that data(the string array in your case) should be invalidated(remeasured, redrawn) in order to show the user the new set of data.

Does the 3rd view item in my list view be notified?

No, the parent ListView will be notified. When you set the adapter on a ListView, an observer(from the ListView) will be set for that adapter. Calling notifyDataSetChanged on the adapter will announce that observer from the ListView that something has happen to the data. At this moment the ListView will recreate the rows to show the new data.

Also, how is notifyDataSetChanged() and getView() concerned ?

I'm not sure I understand what you ask. The getView method of an adapter is used by the ListView to obtain a new row each time this is required. When you call notifyDataSetChanged on the adapter this will trigger the observer in the ListView. As it's time to recreate the list, the ListView will call the getView method of the adapter to show the necessary number of rows(the ones visible on the screen). So each time you call notifyDataSetChanged the getView method will be called for the visible rows.

Upvotes: 8

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