Android 新手，请帮我理解这段代码

Question

I am following a book's examples to learn Android and came accross this code:

public class DynamicDemo extends ListActivity { 
  TextView selection; 
  private static final String[] items={"lorem", "ipsum", "dolor", 
          "sit", "amet"}
  @Override 
  public void onCreate(Bundle icicle) { 
    super.onCreate(icicle); 
    setContentView(R.layout.main); 
    setListAdapter(new IconicAdapter()); 
    selection=(TextView)findViewById(R.id.selection); 
  } 

  public void onListItemClick(ListView parent, View v, 
                             int position, long id) { 
   selection.setText(items[position]); 
  } 

  class IconicAdapter extends ArrayAdapter<String> { 
    IconicAdapter() { 
      super(DynamicDemo.this, R.layout.row, R.id.label, items); 
    } 

    public View getView(int position, View convertView, 
                       ViewGroup parent) { 
      View row=super.getView(position, convertView, parent); 
      ImageView icon=(ImageView)row.findViewById(R.id.icon); 

      if (items[position].length()>4) { 
        icon.setImageResource(R.drawable.delete); 
      } 
      else { 
        icon.setImageResource(R.drawable.ok); 
      } 

      return(row); 
    } 
  }
} 

I actually understand the code except for in the constructor why do we say:

super(DynamicDemo.this, R.layout.row, R.id.label, items);

That is the only part that is confusing me.
Thanks!
R

Answer 1

All that's doing is invoking the superclass constructor (ie ArrayAdapter ). This must be the first line in the subclass constructor.

---

I recommend you read the Using the Keyword super tutorial.

Answer 2

There are multiple things going on in there.

First off, that is a super call, so it is calling the ArrayAdapter 's constructor. It is calling this constructor: http://developer.android.com/reference/android/widget/ArrayAdapter.html#ArrayAdapter(android.content.Context, int, int, T[])

The first parameter is a use of this that actually gets the current instance of the DynamicDemo class. This is used since DynamicDemo extends ListActivitty which extends Activity which eventually extends Context, the type of object you need there.

The next two parameters are resource IDs which it asks for.

The last parameter is an array it needs to populate the adapter.

Answer 3

You are passing the custom layout to your ArrayAdapter R.layout.row, which has the image field.

While rendering this you are again asking the super view(custom view) and modifying the image as per your requirement.

I believe, you can create the view directly in your GetView without using the base constructor

If you separate the IconicAdapter in separate class, you will have to pass the items list while instantiating the class

Answer 4

super(DynamicDemo.this, R.layout.row, R.id.label, items);



@Param  DynamicDemo.this : context
@param R.layout.row : list item layout reference
@param R.id.label : id of textView for which you want to setText string at position i from String-Array (items)
@param items : arrays list containing strings you want to show in list