Android action listener to call a method in another class

Question

I have a listview with a button in each row. I have made a custom Adapter class and a ItemModel class to hold the data for each row. Inside the ItemModel class I have defined an ActionListener for the button. How can I call a method in another class from inside my button's action listener?

Right now if i say Classname clsName = new Classname(); and inside the actionlistener do clsName.methodName(variableToPass); <--- this all compiles but crashes when I click the button..Anyone know how to get this to work?

MyListModel Class

public class MyListItemModel{ //that's our book
private String title; // the book's title
private String description; //the book's description
int id; //book owner id
String key; //book key
private Context context;
Shelf shelf = new Shelf();  //shelf class


public MyListItemModel(Context c){
    this.context=c;

 }


public String getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}
public String getDescription() {
    return description;
}
public void setDescription(String description) {
    this.description = description;
}

public String getKey() {
    return key;
}

public void setKey(String key){
    this.key = key;
}


OnClickListener listener = new OnClickListener(){ // the book's action
    @Override
    public void onClick(View v) {
        //code for the button action
        //THIS DOESN'T WORK PROPERLY AND CRASHES ON CLICK. However if i use a Toast to print the key on each click - it will print the right key to screen.

        shelf.downloadBook(new String(key));

    }
};
int getBookId(){

    return title.hashCode();
}
}

MyListAdapter class - method for getView

public class MyListAdapter extends BaseAdapter {

View renderer;
List<MyListItemModel> items;
ArrayList<HashMap<String, String>> mylist;
private LayoutInflater mInflater;
private Context context;


public MyListAdapter(Context c){
    this.context=c;
    mInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

}

....

 @Override
public View getView(int position, View convertView, ViewGroup parent) {

    if(convertView==null){
        //convertView = renderer;
        convertView = mInflater.inflate(R.layout.shelfrow, null);

    }
    MyListItemModel item = items.get(position);
    TextView label = (TextView)convertView.findViewById(R.id.item_title);
    label.setText(item.getTitle());
    TextView label2 = (TextView)convertView.findViewById(R.id.item_subtitle);
    label2.setText(item.getDescription());
    Button button = (Button)convertView.findViewById(R.id.btn_download);
    button.setOnClickListener(item.listener);


    return convertView;
}

My Shelf class has a method called downloadBook(String bookKey) <-- this is what I want to call with each button click and pass this method the appropriate book key. I also have 2 xml files (shelfrow.xml and shelflist.xml). One contains the textfields and button and the other contains the listview.

Some of the code from Shelf.java class

List<MyListItemModel> myListModel = new ArrayList<MyListItemModel>();

            try{

                JSONArray entries = json.getJSONArray("entries");

                for(int i=0;i<entries.length();i++){                        

                    MyListItemModel item = new MyListItemModel(this);
                    JSONObject e = entries.getJSONObject(i);
                    item.id = i;        //user ID
                    bookKey = (e.getString("key"));
                    item.setTitle(e.getString("title"));
                    item.setDescription(e.getString("description"));

                                    myListModel.add(item);  
                        }

                    }catch(JSONException e) {
                        Log.e("log_tag", "Error parsing data "+e.toString());
                    }


                    MyListAdapter adapter = new MyListAdapter(this);
                    adapter.setModel(myListModel);
                    setListAdapter(adapter);
                    lv = getListView();
                    lv.setTextFilterEnabled(true); 

….

 public void downloadBook(String theKey) {
      //take theKey and append it to a url address to d/l
  }

Stacktrace from logcat

05-23 02:34:59.439: INFO/wpa_supplicant(14819): Reset vh_switch_counter due to receive LINKSPEED cmd 05-23 02:34:59.439: DEBUG/ConnectivityService(1346): getMobileDataEnabled returning true 05-23 02:36:39.269: DEBUG/StatusBarPolicy(6068): onSignalStrengthsChange

also this came up zygoteinit methodandargscaller.run

Answer 1

I am going to go out on a limb here, but I think I know what the issue is.

In the last snippet of code, you are not setting the key field on the MyListItemModel . You are instead setting some variable called 'bookKey' (I do not see where it is defined).

I bet if you change this line:

bookKey = (e.getString("key"));

to be this:

item.setKey(e.getString("key"));
//or item.key = e.getString("key"));

everything will work just fine for you. If you pass in a null String to the String(String) constructor, you will get a NullPointerException, as that constructor expects a non-null String.

I will mention that it is not necessary for you use the String(String) constructor, you should be fine just doing this in the fist snippet:

shelf.downloadBook(key);