如何使用AsyncTask和回调接口在ListView中实现无限滚动？

问题描述

我不知道如何在ListView中实现无限滚动。 我只想在每次到达底部时将下25个问题添加到mListAllIssues视图中。

AllIssuesFragment.java：

public class AllIssuesFragment extends Fragment {

@Bind(R.id.list_all_issues) ListView mListAllIssues;
public static boolean loading;
IssuesGetter mi;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    SharedPreferences user_data = this.getActivity().getSharedPreferences("user_data", Context.MODE_PRIVATE);
    UserManager.getInstance().setUsername(user_data.getString("username", null));
    UserManager.getInstance().setPassword(user_data.getString("password", null));

    if(UserManager.getInstance().getUsername() == null || UserManager.getInstance().getPassword() == null) {
        Intent intent = new Intent(MainActivity.activity, ChangeUserActivity.class);
        startActivity(intent);
    }
    else {
        mi = new IssuesGetter(new AsyncCallback<IssuesResponse>() {
            @Override
            public void onSuccess(IssuesResponse response) {
                ArrayAdapter<IssuesResponse.Issue> adapter = new ArrayAdapter<IssuesResponse.Issue>(MainActivity.activity, android.R.layout.simple_list_item_1, response.getIssues());
                mListAllIssues.setAdapter(adapter);
            }

            @Override
            public void onError() {
                Intent intent = new Intent(MainActivity.activity, ChangeUserActivity.class);
                startActivity(intent);
            }
        });
        mi.execute(Constants.URI + Constants.ISSUES + Constants.OFFSET + 0);
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_all_issues, container, false);
    ButterKnife.bind(this, view);
    return view;
}
}

AsyncCallback.java：

public interface AsyncCallback<T> {
    void onSuccess(T response);
    void onError();
}

IssuesGetter.java：

公共类IssuesGetter扩展了AsyncTask {

private final AsyncCallback<IssuesResponse> callback;

public IssuesGetter(AsyncCallback<IssuesResponse> callback) {
    this.callback = callback;
}

@Override
protected String doInBackground(String... strings) {
    HttpURLConnection c = null;
    try {
        c = (HttpURLConnection) new URL(strings[0]).openConnection();
    } catch (IOException e) {
        e.printStackTrace();
    }
    c.setUseCaches(false);
    try {
        c.setRequestMethod("GET");
    } catch (ProtocolException e) {
        e.printStackTrace();
    }
    c.setRequestProperty("Accept", "application/json");
    c.setRequestProperty("Authorization", UserManager.getInstance().getUserPass());
    int responseCode = 0;
    try {
        responseCode = c.getResponseCode();
    } catch (IOException e) {
        e.printStackTrace();
    }
    if(responseCode == 200) {
        try {
            c.connect();
        } catch (IOException e) {
            e.printStackTrace();
        }
        BufferedReader br = null;
        try {
            br = new BufferedReader(new InputStreamReader((c.getInputStream())));
        } catch (IOException e) {
            e.printStackTrace();
        }
        StringBuilder sb = new StringBuilder();
        String output;
        try {
            while ((output = br.readLine()) != null) {
                sb.append(output);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return sb.toString();
    }
    else {
        return null;
    }
}

@Override
protected void onPostExecute(String result) {
    super.onPostExecute(result);
    if(result == null) {
        callback.onError();
    }
    else {
        IssuesResponse issues = new Gson().fromJson(result, IssuesResponse.class);
        callback.onSuccess(issues);
    }
}
}

您应该使用提供ListView项目的适配器来实现此目的。

1. 而不是返回X作为计数，而是返回X + 1
2. 从适配器检索X + 1项时，您将返回一个具有加载动画的视图，并执行AsyncTask操作以从列表视图中检索下一组项。 您的回调应该在适配器本身内。
3. 完成AsyncTask操作后，将新数据插入适配器内的内部数据结构中。
4. 根据需要调用notifyItemRangeChanged或notifyDataSetChanged。