如何使用 Jsoup 解析 ListView 中的 li 类

Question

我正在解析一个网页http://abcsur.info/clasificados/inmuebles/casas，该页面每周都会刷新和更改。我想在 [li class#li.list-group-items] 上展示广告。

我的想法是将此 li 类添加到列表视图中。在几个网站搜索后，我写了这段代码，但是应用程序崩溃（NullPointerException）

public class Casas extends Activity {

public Casas(){}
// URL Address
String url = "http://abcsur.info/clasificados/inmuebles/casas";
ProgressDialog mProgressDialog;


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

            new Title().execute();


}

// Title AsyncTask
private class Title extends AsyncTask<Void, Void, Void> {


    List<String> items;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        mProgressDialog = new ProgressDialog(Casas.this);
        mProgressDialog.setTitle("ABC sur");
        mProgressDialog.setMessage("Cargando...");
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
        try {
            Document document = Jsoup.connect(url).get();
            Elements li = document.select("ul.list-group");
            List<String> items = new ArrayList<String>();
            for (Element item : li) {
                items.add(item.text());
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        ListView lv = (ListView) findViewById(R.id.listView);
        ArrayAdapter adaptador = new ArrayAdapter<String>(Casas.this,
                android.R.layout.simple_list_item_1, items);
        lv.setAdapter(adaptador);

        mProgressDialog.dismiss();
    }
}

}

有什么想法吗？

Logcat

   Process: info.androidhive.abcsur, PID: 2923
   java.lang.NullPointerException: Attempt to invoke interface method 'int   java.util.List.size()' on a null object reference
        at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
        at android.widget.ListView.setAdapter(ListView.java:487)
        at info.androidhive.abcsur.InmueblesFolder.Casas$Title.onPostExecute(Casas.java:92)
        at info.androidhive.abcsur.InmueblesFolder.Casas$Title.onPostExecute(Casas.java:49)
        at android.os.AsyncTask.finish(AsyncTask.java:636)
        at android.os.AsyncTask.access$500(AsyncTask.java:177)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:653)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

更新后（有效！）

 public class Casas extends Activity {

public Casas(){}
// URL Address
String url = "http://abcsur.info/clasificados/inmuebles/casas";
ProgressDialog mProgressDialog;


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

            new Title().execute();


}

// Title AsyncTask
private class Title extends AsyncTask<Void, Void, Void> {

    String lii;
    List<String> items;
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        mProgressDialog = new ProgressDialog(Casas.this);
        mProgressDialog.setTitle("ABC sur");
        mProgressDialog.setMessage("Cargando...");
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {

        try {
            Document document = Jsoup.connect(url).get();
            Elements li = document.select("li.list-group-items");
            items = new ArrayList<String>();
            for (Element item : li) {
                items.add(item.text());
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        ListView lv = (ListView) findViewById(R.id.listView);
        ArrayAdapter adaptador = new ArrayAdapter<String>(Casas.this,
                android.R.layout.simple_list_item_1, items);
        lv.setAdapter(adaptador);
        adaptador.notifyDataSetChanged();
        mProgressDialog.dismiss();
    }
}

}

还有 XML

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ListView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/listView" />
</RelativeLayout>

Answer 1

您已经在onPreExecute 之前声明了List<String> items;。您还在doInBackground 中声明并启动了相同的ArrayList。

List<String> items = new ArrayList<String>();

当您在onPostExecute() 上将items 添加到ArrayAdapter 时，它指的是doInBackground 中的顶部ArrayList 项不是 ArrayList items。

由于它引用了您尚未启动的顶部 ArrayList，因此会在空对象引用上为您提供 java.util.List.size() 错误。

所以，只要改变，

List<String> items = new ArrayList<String>();

到，

items = new ArrayList<String>();

在doInBackground.