Mark Murphy - Beginning Android

• The ArrayAdaptersubclass ( CheckAdapter) in getView()looks to see if convertViewis null. If so, we create a new row by inflating a simple layout (see the following code) and also attach a ViewWrapper(also in the following code). For the row’s RatingBar, we add an anonymous onRatingChanged()listener that looks at the row’s tag ( getTag()) and converts that into an Integer, representing the position within the ArrayAdapterthat this row is displaying. Using that, the checkbox can get the actual RowModelfor the row and update the model based upon the new state of the rating bar. It also updates the text adjacent to the RatingBarwhen checked to match the rating-bar state.

• We always make sure that the RatingBarhas the proper contents and has a tag (via setTag()) pointing to the position in the adapter the row is displaying.

The row layout is very simple: just a RatingBarand a TextViewinside a LinearLayout:

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:orientation="horizontal"

>

android:id="@+id/rate"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:numStars="3"

android:stepSize="1"

android:rating="2" />

android:id="@+id/label"

android:paddingLeft="2px"

android:paddingRight="2px"

android:paddingTop="2px"

android:textSize="40sp"

android:layout_width="fill_parent"

android:layout_height="wrap_content"/>

The ViewWrapperis similarly simple, just extracting the RatingBarand the TextViewout of the row View:

classViewWrapper {

View base;

RatingBar rate = null;

TextView label = null;

ViewWrapper(View base) {

this.base = base;

}

RatingBar getRatingBar() {

if(rate== null) {

rate = (RatingBar)base. findViewById(R.id.rate);

}

return(rate);

}

TextView getLabel() {

if(label== null) {

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

}

return(label);

}

}

And the result (Figure 9-3) is what you would expect, visually.

Figure 9-3. The RateListDemo application, as initially launched

This includes the toggled checkboxes turning their words into all caps (Figure 9-4).

Figure 9-4. The same application, showing a top-rated word

The rating list in the previous section works, but implementing it is very tedious. Worse, much of that tedium would not be reusable except in very limited circumstances. We can do better.

What we’d really like is to be able to create a layout like this:

xmlns:android="http://schemas.android.com/apk/res/android"

android:orientation="vertical"

android:layout_width="fill_parent"

android:layout_height="fill_parent" >

android:id="@+id/selection"

android:layout_width="fill_parent"

android:layout_height="wrap_content"/>

android:id="@android:id/list"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:drawSelectorOnTop="false"

/>

where, in our code, almost all of the logic that might have referred to a ListViewbefore “just works” with the RateListViewwe put in the layout:

public classRateListViewDemo 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);

setListAdapter( newArrayAdapterString( this,

android.R.layout.simple_list_item_1, items));

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

}

publicvoid onListItemClick(ListView parent, View v,

int position, long id) {

selection. setText(items[position]);

}

}

Things get a wee bit challenging when you realize that in everything up to this point in this chapter, never were we actually changing the ListViewitself. All our work was with the adapters, overriding getView()and inflating our own rows and whatnot.

So if we want RateListViewto take in any ordinary ListAdapterand “just work,” putting checkboxes on the rows as needed, we are going to need to do some fancy footwork. Specifically, we are going to need to wrap the “raw” ListAdapterin some other ListAdapterthat knows how to put the checkboxes on the rows and track the state of those checkboxes.

First we need to establish the pattern of one ListAdapteraugmenting another. Here is the code for AdapterWrapper, which takes a ListAdapterand delegates all of the interface’s methods to the delegate (from the FancyLists/RateListViewsample project at http://apress.com/):

public classAdapterWrapper implementsListAdapter {

ListAdapter delegate = null;

public AdapterWrapper(ListAdapter delegate) {

this.delegate = delegate;

}

publicint getCount() {

return(delegate. getCount());

}

publicObject getItem(int position) {

return(delegate. getItem(position));