java - android listview loadmore按钮与xml解析

Question

嗨，我必须在 Android 应用程序中使用 xml 解析来开发带有加载更多按钮的 ListView 。

在这里我遇到了一些问题。

我的 xml feed 为空意味着如何隐藏最后一页上的加载更多按钮。

我在这里使用了下面的代码。

public class CustomizedListView extends Activity {
// All static variables
private String URL = "http://dev.mmm.com/xctesting/xcart444pro/retrieve.php?page=1";
// XML node keys
static final String KEY_SONG = "Order"; 
    static final String KEY_TITLE = "orderid";
static final String KEY_DATE = "date";
static final String KEY_ARTIST = "payment_method";
    int current_page = 1;
ListView lv;
LazyAdapter adapter;
ProgressDialog pDialog; 

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    lv = (ListView) findViewById(R.id.list);

    ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();

    XMLParser parser = new XMLParser();
    String xml = parser.getXmlFromUrl(URL); // getting XML from URL
    Document doc = parser.getDomElement(xml); // getting DOM element

    NodeList nl = doc.getElementsByTagName(KEY_SONG);
    // looping through all song nodes <song>
    for (int i = 0; i < nl.getLength(); i++) {
        // creating new HashMap
        HashMap<String, String> map = new HashMap<String, String>();
        Element e = (Element) nl.item(i);
        // adding each child node to HashMap key => value
        map.put(KEY_ID, parser.getValue(e, KEY_ID));
        map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
        map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));
              songsList.add(map);
    }

    Button btnLoadMore = new Button(this);
    btnLoadMore.setText("Load More");

    btnLoadMore.setBackgroundResource(R.drawable.lgnbttn);
    // Adding Load More button to lisview at bottom
    lv.addFooterView(btnLoadMore);

    // Getting adapter
    adapter = new LazyAdapter(this, songsList);
    lv.setAdapter(adapter);
                btnLoadMore.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // Starting a new async task
            new loadMoreListView().execute();
        }
    });
}
    private class loadMoreListView extends AsyncTask<Void, Void, Void> {

        @Override 
        protected void onPreExecute() {
            // Showing progress dialog before sending http request
            pDialog = new ProgressDialog(
                    CustomizedListView.this);
            pDialog.setMessage("Please wait..");
            //pDialog.setIndeterminateDrawable(getResources().getDrawable(R.drawable.my_progress_indeterminate));
            pDialog.setIndeterminate(true);
            pDialog.setCancelable(false);
            pDialog.show(); 

            pDialog.setContentView(R.layout.custom_dialog);


        }
        protected Void doInBackground(Void... unused) {

                    current_page += 1;

                    // Next page request
                    URL = "http://dev.mmm.com/xctesting/xcart444pro/retrieve.php?page=" + current_page;

                    ArrayList<HashMap<String, String>> songsList = new ArrayList<HashMap<String, String>>();

                    XMLParser parser = new XMLParser();
                    String xml = parser.getXmlFromUrl(URL); // getting XML from URL
                    Document doc = parser.getDomElement(xml); // getting DOM element

                    NodeList nl = doc.getElementsByTagName(KEY_SONG);


                    NodeList nl = doc.getElementsByTagName(KEY_SONG);
                    if (nl.getLength() == 0)
                      {
                          btnLoadMore.setVisibility(View.GONE);
                          pDialog.dismiss();

                      }
                      else

                    // looping through all item nodes <item>
                    for (int i = 0; i < nl.getLength(); i++) {
                        // creating new HashMap
                        HashMap<String, String> map = new HashMap<String, String>();
                        Element e = (Element) nl.item(i);

                        // adding each child node to HashMap key => value
                        map.put(KEY_ID, parser.getValue(e, KEY_ID));
                        map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
                        map.put(KEY_ARTIST, parser.getValue(e, KEY_ARTIST));
                 songsList.add(map);
                    }

                    // get listview current position - used to maintain scroll position
                    int currentPosition = lv.getFirstVisiblePosition();

                    // Appending new data to menuItems ArrayList
                    adapter = new LazyAdapter(
                            CustomizedListView.this,
                            songsList);
                    lv.setAdapter(adapter);
             lv.setSelectionFromTop(currentPosition + 1, 0);


            }
            });

            return (null);
        }


        protected void onPostExecute(Void unused) {
            // closing progress dialog
            pDialog.dismiss();

        }
    }
}

编辑:

这里我必须运行应用程序意味着 ListView 显示在每页 4 个项目上。我的最后一页有 1 个项目。请引用此屏幕截图:lastpage在最后一页中，我必须单击“加载更多”按钮意味着必须进行下一个 Activity 并成功隐藏空白页面上的按钮..请引用此屏幕截图:empty page-so hide the button

我必须检查空页的情况:

    if (nl.getLength() == 0)
                    {
                        btnLoadMore.setVisibility(View.GONE);
                        pDialog.dismiss();

                    }

我怎样才能写最后一页的条件??????请帮助我

这里我希望需要o/p隐藏最后一页上的按钮。

请帮助我。我如何检查条件。以编程方式给我一些代码。

Answer 1

首先，为什么要在 AsyncTaks 中使用 runOnUiThread？这应该是没有必要的。必须在后台运行的代码，在 doInBackground 方法中就足够了。

此外，您可以使用 AsyncTask 的第三个参数类型将 doInBackground 的结果返回到 onPostExecute。然后根据结果，您可以更改按钮的可见性。

为此，对按钮(在您的例子中为 btnLoadMore)的引用应该是一个实例变量，因此它应该在类中定义，而不是在 onCreate 方法中。否则将无法从此方法外部访问它。

我认为当提要为空时节点列表将为空？然后它看起来像这样:

public class CustomizedListView extends Activity {

    private Button btnLoadMore;

    public void onCreate(){
        btnLoadMore = new Button(this);
        <do stuff>
        btnLoadMore.setOnClickListener(new View.OnClickListener() {

           @Override
           public void onClick(View arg0) {
               // Starting a new async task
               new LoadMoreListView().execute();
           }
        });

        new LoadMoreListView().execute();// execute the AsyncTask once in the onCreate, so you don't have to duplicate the code here to load the listview.

    }

    private class LoadMoreListView extends AsyncTask<Void, Void, Boolean> {

        @Override 
        protected void onPreExecute() {
            < Show dialog>;
        }

        @Override
        protected Void doInBackground(Void... unused) {
           Boolean listIsEmpty;

           < Page request>;
           < Retrieve element list>;
           < If element list size == 0, listIsEmpty = true; return listIsEmpty>;

           < Process elements, fill list etc.>;
           < End of doInBackground, listIsEmpty = false; return listIsEmpty>;

        }

        @Override
        protected void onPostExecute(Boolean listIsEmpty) {
            < If listIsEmpty == true -> btnLoadMore.setVisibility(View.GONE);>
            < Close dialog>
        }
    }
}
}