Android：SAX 解析器进度监控

Question

我有一个解析 InputStream 的 SAX DefaultHandler。我不知道 XML 中有多少元素，所以我不能指望它们在 endElement 或类似的。我确实知道 InputStream 的字节长度（从 http 标头读取），但我找不到获取解析过程当前字节进度的方法。

有没有办法获取解析过程的当前进度（即处理的位）？

DefaultHandler 的调用方式如下：

SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
parser.parse(inputStream, myDefaultHandler);

Answer 1

对于仍在寻找答案的任何人， 尝试在派生的 FilterInputStream 的构造函数中传递 ProgressBar：

ProgressFilterInputStream.java

import java.io.FilterInputStream;
import java.io.InputStream;
import java.io.IOException;

import android.widget.ProgressBar;
import android.util.Log;


public class ProgressFilterInputStream extends FilterInputStream {

int counter = 0;
ProgressBar progressBar;

public ProgressFilterInputStream(InputStream in, ProgressBar progressBar) {
    super(in);
    this.progressBar = progressBar;
    this.progressBar.setMax(69);  // SET MAX ACCORDIN TO THE DDMS LOGGING MESSAGE
}

@Override
public int read(byte[] buffer, int offset, int count) throws IOException {
    progressBar.setProgress(counter++);
    Log.i("PFIS" , "Counter: " + counter);
    return super.read(buffer, offset, count);
}
}

我在我的 AsyncTask 中使用了它

MyActivity.java

final ProgressBar bar_progress = (ProgressBar) findViewById(R.id.bar_progress);
ProgressFilterInputStream pfis = new ProgressFilterInputStream(getAssets().open("DATA.xml") , bar_progress );           
Reader reader = new InputStreamReader(pfis, "UTF-8");
InputSource is = new InputSource(reader);

// create the factory
SAXParserFactory factory = SAXParserFactory.newInstance();

// create a parser
SAXParser parser = factory.newSAXParser();

// create the reader (scanner)
XMLReader xmlreader = parser.getXMLReader();

// instantiate our handler
SaxHandler myHandler = new SaxHandler();

// assign our handler
xmlreader.setContentHandler(myHandler);

// perform the synchronous parse
xmlreader.parse(is);

Answer 2

从 lx222 答案扩展，我实现了 AsyncTask，ProgressDialog。晚了，但我希望它对某人有用：D

public class OpenXMLFileOperator extends AsyncTask<Void, Integer, Void>{
    private ProgressDialog progressDialog;
    private String filePath;
    private Context context;
    public OpenFileOperator(Context context,String filePath){
        this.context = context;
        this.filePath = filePath;
    }

    @Override
    protected Void doInBackground(Void... arg0) {                               
        try {                               
            if (filePath != null) {

                File file = new File(filePath);
                if (file.exists()) {    
                    InputStream stream = new FileInputStream(file);
                    ProgressFilterInputStream pfis = new ProgressFilterInputStream(stream,file.length());
                    Reader reader = new InputStreamReader(pfis, "UTF-8");

                    YourXMLHandle yourHandle = new YourXMLHandle();                 
                    android.util.Xml.parse(reader,yourHandle);

                    stream.close();
                    reader.close();
                    pfis.close();          
                }                
            }
        }catch (Exception e) {
            if (BuildConfig.DEBUG) Log.e(TAG, "Exception", e);
        }
        return null;
    }

    @Override
    protected void onPreExecute() {
        try{
            progressDialog = new ProgressDialog(context);
            progressDialog.setMessage("Loading file");
            progressDialog.setCancelable(false);
            progressDialog.setIndeterminate(false);
            progressDialog.setMax(100);
            progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);           
            progressDialog.show();
        }catch(Exception e){
            if (BuildConfig.DEBUG) Log.e(TAG,"onPostExecute",e);
        }

        super.onPreExecute();
    }

    @Override
    protected void onCancelled() {
        try{
            if (progressDialog!=null && progressDialog.isShowing()){
                progressDialog.dismiss();
            }
        }catch(Exception e){
            if (BuildConfig.DEBUG) Log.e(TAG,"onPostExecute",e);
        }
        super.onCancelled();
    }

    @Override
    protected void onPostExecute(Void result) { 
        try{
            if (progressDialog!=null && progressDialog.isShowing()){
                progressDialog.dismiss();
            }
        }catch(Exception e){
            if (BuildConfig.DEBUG) Log.e(TAG,"onPostExecute",e);
        }

        //TODO: to do something after file loaded
        super.onPostExecute(result);
    }

    @Override
    protected void onProgressUpdate(Integer... values) {        
        int progress = values[0];
        if (progressDialog!=null) {            
            progressDialog.setProgress(progress);
        }
        super.onProgressUpdate(values);
    }

    private class ProgressFilterInputStream extends FilterInputStream {
        private int counter = 0;
        private long fileLength;
        private int maximum = 100;
        public ProgressFilterInputStream(InputStream in, long fileLength) {
            super(in);
            this.fileLength = fileLength;
        }

        @Override
        public int read(byte[] buffer, int offset, int count) throws IOException {
            if (counter==0){
                maximum = (int)(fileLength/buffer.length);
            }
            publishProgress((counter++)*100/maximum);
            return super.read(buffer, offset, count);
        }
    }
}

Answer 3

您可以通过编写 FilterInputStream 来包装现有的 inputStream 来做到这一点。在过滤器的 read() 方法中，增加一个计数器，并提供一个 getter，以便其他东西可以跟踪当前计数。

由于解析器可能会提前读取，这将是近似值，但这可能是您能做的最好的。