在其他类中使用摘要中的变量

Question

I am new to java and android development.I have created a abstract class for to display a listview in my app.I idea is that i will use common listview only changing its adapter.But i am not getting the listview defined in abstract class to use in the class which extends it.Please do help me out

Abstract Class Code

 public abstract class GeneralListView extends MasterFragment {

    protected ListView listView;



    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.common_list, container, false);
        listView = (ListView) view.findViewById(R.id.lv_common_list);
        return view;
    }

    public abstract void initializeList();

    public ListView getListView() {
        return listView;
    }


}

Class which extends the above class

 public class Test extends GeneralListView {

    private ListView listView;

    @Override
    public void initializeList() {
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(contextFragment, android.R.layout.activity_list_item, new String[]{"a", "b", "c", "d", "e", "f", "g", "h", "i", "a", "b", "c", "d", "e", "f", "g", "h", "i"});
        listView.setAdapter(adapter);

    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        getListView();
        initializeList();
    }

    @Override
    public ListView getListView() {
        return listView;
    }
}

Exception

listView.setAdapter(adapter); //null pointer exception

Answer 1

No need to override getListVIew() in child class "Test" class and you dont need the private ListView listView; attribute in your "Test" class,

To call a method or a variable in the super class you can call it directly if your not using any variable with the same name in your case you can call listView by using the super keyword

super.listView 

and call the method getListView() with super keyword

super.getListView();

Answer 2

You have to either remove the

private ListView listView;

statement, or else in constructor do add the following,

public Test(){
listView = super.getListView;//I assume this would return initialized listview
}

Answer 3

Remove

private ListView listView; 

and

@Override
public ListView getListView() {
    return listView;
}

from

public class Test extends GeneralListView {

You override the listView object in your Test subclass and that one is used instead of the instance from GeneralListView.

Answer 4

您是否可以检查是否调用了onCreateView方法的调用，因为我只能看到此方法初始化了listView引用。