Question

我的代码中有一个奇怪的行为：使用asyncTask在模拟器上解析本地xml文件比在主线程上解析它需要更长的时间。

这是我的AsyncTask代码：

public class MostraTutti extends SherlockActivity {
ListView lv;
final List<ListViewItem> items = new ArrayList<MostraTutti.ListViewItem>();
final ArrayList<String> nome = new ArrayList<String>();
final ArrayList<String> immagine = new ArrayList<String>();
...

final   int array_image2[] ={R.drawable.iodocloroidrossichinolina,R.drawable.acidoacetilsalicilico,
        ...};

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

    setContentView(R.layout.mostra_tutti);
    lv = (ListView) findViewById(R.id.listView);
    getSupportActionBar().setDisplayShowHomeEnabled(false);

    RssFeedTask rssTask = new RssFeedTask();
       rssTask.execute();

}

private class RssFeedTask extends AsyncTask<String, Void, String> {
    private ProgressDialog Dialog;
    String response = "";

    @Override
    protected void onPreExecute() {
        Dialog = new ProgressDialog(MostraTutti.this);
        Dialog.setMessage("Leggo le sostanze...");
        Dialog.show();
    }

        @Override
        protected String doInBackground(String... urls) {
            InputStream xmlFile = getResources().openRawResource(R.raw.sostanze);
            try {

            DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            final Document document = documentBuilder.parse(xmlFile);
            document.getDocumentElement().normalize();
            NodeList nodeList = document.getElementsByTagName("sostanza");

            for (int i = 0; i < nodeList.getLength(); i++) {
            final int   indice = i;

            nome.add(document.getElementsByTagName("nome").item(indice).getTextContent());
            iupac.add(document.getElementsByTagName("iupac").item(indice).getTextContent());
            aspetto.add(document.getElementsByTagName("aspetto").item(indice).getTextContent());
            formula.add(document.getElementsByTagName("formula").item(indice).getTextContent());
            immagine.add(document.getElementsByTagName("immagine").item(indice).getTextContent());
            appartenenza.add(document.getElementsByTagName("appartenenza").item(indice).getTextContent());
            spiegazione.add(document.getElementsByTagName("spiegazione").item(indice).getTextContent());
            tempFus.add(document.getElementsByTagName("temperaturaFusione").item(indice).getTextContent());
            tempEboll.add(document.getElementsByTagName("temperaturaEbollizione").item(indice).getTextContent());
            solubilita.add(document.getElementsByTagName("solubilita").item(indice).getTextContent());
            note.add(document.getElementsByTagName("eccezioni").item(indice).getTextContent());

            String str = document.getElementsByTagName("formula").item(indice).getTextContent();

            str = str.replaceAll("0", "\u2080");
            str = str.replaceAll("1", "\u2081");
            str = str.replaceAll("2", "\u2082");
            str = str.replaceAll("3", "\u2083");
            str = str.replaceAll("4", "\u2084");
            str = str.replaceAll("5", "\u2085");
            str = str.replaceAll("6", "\u2086");
            str = str.replaceAll("7", "\u2087");
            str = str.replaceAll("8", "\u2088");
            str = str.replaceAll("9", "\u2089");

            final String stringa = str;
            formulaConvertita.add(stringa);

                    //CustomListViewAdapter adapter = new CustomListViewAdapter(MostraTutti.this,items);
                    //lv.setAdapter(adapter);
                    items.add(new ListViewItem()
                    {{
                        ThumbnailResource = array_image2[indice];
                        Title = document.getElementsByTagName("nome").item(indice).getTextContent();
                        SubTitle = stringa;
                    }});   
            };

        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        } catch (ParserConfigurationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SAXException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }   

        return response;
}
        @Override
        protected void onPostExecute(String result) {
            Dialog.dismiss();
            CustomListViewAdapter adapter = new CustomListViewAdapter(MostraTutti.this,items);
            lv.setAdapter(adapter);

            lv.setOnItemClickListener(
                    new OnItemClickListener()
                    {
                        public void onItemClick(AdapterView<?> arg0, View v, int position, long id)
                        {                           
                            Context context = getBaseContext();
                           Intent myIntent = new Intent(context, Dettagli.class);

                           myIntent.putExtra("nome_sostanza",nome.get(position));
                         //  myIntent.putExtra("formula",formula.get(position));
                           myIntent.putExtra("iupac",iupac.get(position));                  
                           myIntent.putExtra("aspetto",aspetto.get(position));                 
                           myIntent.putExtra("appartenenza",appartenenza.get(position));
                           myIntent.putExtra("solubilita",solubilita.get(position));
                           myIntent.putExtra("tempFus",tempFus.get(position));
                           myIntent.putExtra("tempEboll",tempEboll.get(position));
                           myIntent.putExtra("spiegazione",spiegazione.get(position));
                           myIntent.putExtra("immagine", array_image2[position]);
                           myIntent.putExtra("formulaConvertita", formulaConvertita.get(position));
                           myIntent.putExtra("note", note.get(position));
                           startActivityForResult(myIntent, 0);
                        }

                        }
                 );
        }
        }

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getSupportMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

class ListViewItem {
public int ThumbnailResource;
public String Title;
public String SubTitle;
}
}

这是我没有AsyncTask的代码：

public class MostraTutti extends SherlockActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.mostra_tutti);
    getSupportActionBar().setDisplayShowHomeEnabled(false);

    final ListView lv = (ListView) findViewById(R.id.listView);
    final List<ListViewItem> items = new ArrayList<MostraTutti.ListViewItem>();
    final ArrayList<String> nome = new ArrayList<String>();
    final ArrayList<String> immagine = new ArrayList<String>();
    ...

    final   int array_image2[] ={R.drawable.iodocloroidrossichinolina,R.drawable.acidoacetilsalicilico,
            ...};

InputStream xmlFile = getResources（）。openRawResource（R.raw.sostanze）;

    try {

        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        final Document document = documentBuilder.parse(xmlFile);
        document.getDocumentElement().normalize();
        //tagHandler.handleChannelTag(document);
        NodeList nodeList = document.getElementsByTagName("sostanza");

        for (int i = 0; i < nodeList.getLength(); i++) {
        final int   indice = i;

        nome.add(document.getElementsByTagName("nome").item(indice).getTextContent());
        iupac.add(document.getElementsByTagName("iupac").item(indice).getTextContent());
        aspetto.add(document.getElementsByTagName("aspetto").item(indice).getTextContent());
        formula.add(document.getElementsByTagName("formula").item(indice).getTextContent());
        immagine.add(document.getElementsByTagName("immagine").item(indice).getTextContent());
        appartenenza.add(document.getElementsByTagName("appartenenza").item(indice).getTextContent());
        spiegazione.add(document.getElementsByTagName("spiegazione").item(indice).getTextContent());
        tempFus.add(document.getElementsByTagName("temperaturaFusione").item(indice).getTextContent());
        tempEboll.add(document.getElementsByTagName("temperaturaEbollizione").item(indice).getTextContent());
        solubilita.add(document.getElementsByTagName("solubilita").item(indice).getTextContent());
        note.add(document.getElementsByTagName("eccezioni").item(indice).getTextContent());

        String str = document.getElementsByTagName("formula").item(indice).getTextContent();

        str = str.replaceAll("0", "\u2080");
        str = str.replaceAll("1", "\u2081");
        str = str.replaceAll("2", "\u2082");
        str = str.replaceAll("3", "\u2083");
        str = str.replaceAll("4", "\u2084");
        str = str.replaceAll("5", "\u2085");
        str = str.replaceAll("6", "\u2086");
        str = str.replaceAll("7", "\u2087");
        str = str.replaceAll("8", "\u2088");
        str = str.replaceAll("9", "\u2089");

        final String stringa = str;
        formulaConvertita.add(stringa);

        items.add(new ListViewItem()
            {{
                ThumbnailResource = array_image2[indice];
                Title = document.getElementsByTagName("nome").item(indice).getTextContent();
                SubTitle = stringa;
            }});
        }
    } catch (IOException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (ParserConfigurationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (SAXException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }       
    CustomListViewAdapter adapter = new CustomListViewAdapter(this,items);
    lv.setAdapter(adapter);

    lv.setOnItemClickListener(
            new OnItemClickListener()
            {
                public void onItemClick(AdapterView<?> arg0, View v, int position, long id)
                {                           
                    Context context = getBaseContext();
                   Intent myIntent = new Intent(context, Dettagli.class);

                   myIntent.putExtra("nome_sostanza",nome.get(position));
                 //  myIntent.putExtra("formula",formula.get(position));
                   myIntent.putExtra("iupac",iupac.get(position));                  
                   myIntent.putExtra("aspetto",aspetto.get(position));                 
                   myIntent.putExtra("appartenenza",appartenenza.get(position));
                   myIntent.putExtra("solubilita",solubilita.get(position));
                   myIntent.putExtra("tempFus",tempFus.get(position));
                   myIntent.putExtra("tempEboll",tempEboll.get(position));
                   myIntent.putExtra("spiegazione",spiegazione.get(position));
                   myIntent.putExtra("immagine", array_image2[position]);
                   myIntent.putExtra("formulaConvertita", formulaConvertita.get(position));
                   myIntent.putExtra("note", note.get(position));
                   startActivityForResult(myIntent, 0);
                }

                }
         );
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getSupportMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

class ListViewItem {
public int ThumbnailResource;
public String Title;
public String SubTitle;
}
}

主线程1的模拟器差异是16秒，AsyncTask的差异是1分钟！

Answer 1

我将此问题标记为重复，但上次我这样做时，审稿人投了反对票。

无论哪种方式，原因是AsyncTask的{{1}}在背景优先级中运行，并且必须与所有其他后台任务共享最多10％的CPU时间，例如您的RSS阅读器等等 - 无论系统多么空闲。

对于detailed discussion and solution, see here。

Answer 2

UI线程上的16秒仍然太多并且它不是解决方案 - 每次都会被ANR对话框击中。所以有一些建议是：

优化doInBackground()内的代码。
考虑使用其他XML解析器，它可以提高性能。
如果适合您的应用程序逻辑，请将此代码移至后台Service，以便在用户未与您的应用程序交互时使其处理数据。将信息存储在数据库中，并在打开Activity时加载它。

使用AsyncTask进行Xml解析比在主Thread中进行解析要慢

2 个答案: