These handle the case where you want different
types of view for different rows. For instance, in a contacts application you may want even rows to have pictures on the left side and odd rows to have pictures on the right. In that case, you would use:
@Override
public int getViewTypeCount() {
return 2;
}
@Override
public int getItemViewType(int position) {
return position % 2;
}
The framework uses your view type to decide
which views to hand you via convertView in your getView method. In other words, in the above example, your even rows will only get recycled views with pictures on the left side to reuse, and odd rows will only get ones with pictures on the right.
If every row in your list has the same layout, you don't need to worry about view types. In fact,
BaseAdapter.java provides a default behavior for all adapters:
public int getItemViewType(int position) {
return 0;
}
public int getViewTypeCount() {
return 1;
}
This indeed provides you with the same view type for every row.
Edit - to outline the general flow:
- You bind data to your
AdapterView using an adapter.
- The
AdapterView tries to display items that are visible to the user.
- The framework calls
getItemViewType for row n, the row it is about to display.
- The framework checks its recycled views pool for views of row
n's type. It doesn't find any because no views have been recycled yet.
getView is called for row n.- You call
getItemViewType for row n to determine what type of view you should use.
- You use an if/switch statement to inflate a different xml file depending on which view type is required.
- You fill the view with information.
- You return the view, exiting
getView, and your row's view is displayed to the user.
Now, when a view is recycled by scrolling off the screen it goes into a recycled views pool that is managed by the framework. These are essentially organized by view type so that a view of the correct type is given to you in
convertView parameter in your
getView method:
- The framework again calls
getItemViewType for the row it wants to display.
- This time, there is a view in the recycled pool of the appropriate type.
- The recycled view is passed to you as the
convertView parameter to your getView method.
- You fill the recycled view with new information and return it.
android
