Mark Murphy - Beginning Android

}

}

}

Just as we check convertViewto see if it is null in order to create the row Viewsas needed, we also pull out (or create) the corresponding row’s ViewWrapper. Then accessing the child widgets is merely a matter of calling their associated methods on the wrapper.

Lists with pretty icons next to them are all fine and well. But can we create ListViewwidgets whose rows contain interactive child widgets instead of just passive widgets like TextViewand ImageView? For example, could we combine the RatingBarwith text in order to allow people to scroll a list of, say, songs and rate them right inside the list?

There is good news and bad news.

The good news is that interactive widgets in rows work just fine. The bad news is that it is a little tricky, specifically when it comes to taking action when the interactive widget’s state changes (e.g., a value is typed into a field). We need to store that state somewhere, since our RatingBarwidget will be recycled when the ListViewis scrolled. We need to be able to set the RatingBarstate based upon the actual word we are viewing as the RatingBaris recycled, and we need to save the state when it changes so it can be restored when this particular row is scrolled back into view.

What makes this interesting is that, by default, the RatingBarhas absolutely no idea what model in the ArrayAdapterit is looking at. After all, the RatingBaris just a widget, used in a row of a ListView. We need to teach the rows which model they are currently displaying, so when their checkbox is checked they know which model’s state to modify.

So, let’s see how this is done, using the activity in the FancyLists/RateListsample project at http://apress.com/. We’ll use the same basic classes as our previous demo—we’re showing a list of nonsense words, which you can then rate. In addition, words given a top rating will appear in all caps.

public classRateListDemo extendsListActivity {

TextView selection;

String[] items={"lorem", "ipsum", "dolor", "sit", "amet",

"consectetuer", "adipiscing", "elit", "morbi", "vel",

"ligula", "vitae", "arcu", "aliquet", "mollis",

"etiam", "vel", "erat", "placerat", "ante",

"porttitor", "sodales", "pellentesque", "augue",

"purus"};

@Override

publicvoid onCreate(Bundle icicle) {

super. onCreate(icicle);

setContentView(R.layout.main);

ArrayList list = newArrayList();

for(String s : items) {

list. add( new RowModel(s));

}

setListAdapter( new CheckAdapter( this, list));

selection = (TextView) findViewById(R.id.selection);

}

privateRowModel getModel(int position) {

return(((CheckAdapter) getListAdapter()). getItem(position));

}

publicvoid onListItemClick(ListView parent, View v,

int position, long id) {

selection. setText( getModel(position). toString());

}

classCheckAdapter extendsArrayAdapter {

Activity context;

CheckAdapter(Activity context, ArrayList list) {

super(context, R.layout.row, list);

this.context = context;

}

publicView getView(int position, View convertView,

ViewGroup parent) {

View row = convertView;

ViewWrapper wrapper;

RatingBar rate;

if(row== null) {

LayoutInflater inflater = context. getLayoutInflater();

row = inflater. inflate(R.layout.row, null);

wrapper = new ViewWrapper(row);

row. setTag(wrapper);

rate = wrapper. getRatingBar();

RatingBar.OnRatingBarChangeListener l =

newRatingBar. OnRatingBarChangeListener() {

publicvoid onRatingChanged(RatingBar ratingBar,

float rating, boolean fromTouch) {

Integer myPosition = (Integer)ratingBar. getTag();

RowModel model = getModel(myPosition);

model.rating = rating;

LinearLayout parent = (LinearLayout)ratingBar. getParent();

TextView label = (TextView)parent. findViewById(R.id.label);

label. setText(model. toString());

}

};

rate. setOnRatingBarChangeListener(l);

} else{

wrapper = (ViewWrapper)row. getTag();

rate = wrapper. getRatingBar();

}

RowModel model = getModel(position);

wrapper. getLabel(). setText(model. toString());

rate. setTag( new Integer(position));

rate. setRating(model.rating);

return(row);

}

}

classRowModel {

String label;

float rating = 2.0f;

RowModel(String label) {

this.label = label;

}

publicString toString() {

if(rating>=3.0) {

return(label. toUpperCase());

}

return(label);

}

}

}

Here is what is different between our earlier code and this activity and getView()implementation:

• While we are still using String[]items as the list of nonsense words, but rather than pouring that Stringarray straight into an ArrayAdapter, we turn it into a list of RowModelobjects. RowModelis this demo’s poor excuse for a mutable model; it holds the nonsense word plus the current checked state. In a real system, these might be objects populated from a Cursor, and the properties would have more business meaning.

• Utility methods like onListItemClick()had to be updated to reflect the change from a pure String modelto use a RowModel.