java - 返回空指针的处理程序

Question

我正在尝试运行以下代码:

public class MyListActivity extends ListActivity {

private static class MyListLoadingCallback implements Handler.Callback {
    private ListActivity activity;
    private MyListManager myListManager;

    public MyListLoadingCallback(ListActivity activity,
            MyListManager articleListManager) {
        this.activity = activity;
        this.myListManager = myListManager;
    }

    @Override
    public boolean handleMessage(Message message) {
        throw new NotYetImplementedException();
    }
}

private MyListManager myListManager;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    myListManager.fetchArticles(new Handler(
            new MyListLoadingCallback(this, MyListManager)));

}

我在articleListManager.fetchArticles(new Handler(new MyListLoadingCallback(this, MyListManager)));处得到一个空指针

我的其他类(class)如下所示:

public class MyListManager  {

    public void fetchArticles(final Handler handler) {
    }
}

有人可以带我/帮助我处理这段代码以便更好地理解吗？我似乎还没有完全理解它。

Answer 1

错误似乎很清楚:)。

在抛出异常的行中只有一个“引用”被访问 (myListManager.fetchArticles(new Handler(new MyListLoadingCallback(this, MyListManager)));)，它是 >myListManager，所以它必须是NULL。查看代码，您永远不会将其初始化为任何内容，因此它确实是 NULL :)