单击下载按钮时无响应

Question

我的应用程序中有一个下载按钮，按下时应从parse.com下载我存储文件的文件。但是当点击按钮时，没有任何反应，进度dailog会在几秒钟内消失，并且不会执行下载。

代码

public class SingleItemView extends Activity
{

ProgressDialog mProgressDialog;
String heading;
String subHeading;
String levelImg;
String apiImg;
String apiText;
String descImgOne;
String descImgTwo;
String codeText;
ImageLoader imgloader = new ImageLoader(this);

private static String file_url;



private ProgressDialog pDialog;
ImageView my_image;
// Progress dialog type (0 - for Horizontal progress bar)
public static final int progress_bar_type = 0;


@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.singleitemview);

    Intent i = getIntent();

    heading= i.getStringExtra("heading");
        subHeading = i.getStringExtra("subheading");
    levelImg = i.getStringExtra("levelimg");
        apiImg = i.getStringExtra("apiimg");
        apiText = i.getStringExtra("apitext");
        descImgOne = i.getStringExtra("descimgone");
    descImgTwo = i.getStringExtra("descimgtwo");
        codeText = i.getStringExtra("codetext");
    file_url = i.getStringExtra("download");






    TextView headingtxt = (TextView)findViewById(R.id.singleitemheading);
    TextView subheadingtxt = (TextView)findViewById(R.id.singleitemsubheading);
    TextView apitxt = (TextView)findViewById(R.id.singleitemviewapitext);
    TextView codetxt = (TextView) findViewById(R.id.singleitemviewcodetext);

    ImageView level =(ImageView) findViewById(R.id.levelimg);
    ImageView api =(ImageView) findViewById(R.id.singleitemviewapiimg);
    ImageView descone =(ImageView) findViewById(R.id.descriptionimgone);
    ImageView desctwo =(ImageView) findViewById(R.id.descriptionimgtwo);



    Button downloadbtn = (Button) findViewById(R.id.singleitemviewButton);

    headingtxt.setText(heading);
    subheadingtxt.setText(subHeading);
    apitxt.setText(apiText);
    codetxt.setText(codeText);

    imgloader.DisplayImage(levelImg, level);
    imgloader.DisplayImage(apiImg, api);
    imgloader.DisplayImage(descImgOne, descone);
    imgloader.DisplayImage(descImgTwo, desctwo);



    downloadbtn.setOnClickListener(new OnClickListener(){
        @Override
        public void onClick(View v){
            String downurl = file_url;

            new DownloadFileFromURL().execute(downurl);
        }
    });

}  

@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
        case progress_bar_type: // we set this to 0
            pDialog = new ProgressDialog(this);
            pDialog.setMessage("Downloading file. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setMax(100);
            pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            pDialog.setCancelable(true);
            pDialog.show();
            return pDialog;
        default:
            return null;
    }
}

class DownloadFileFromURL extends AsyncTask<String, String, String>
{



    /**
     * Before starting background thread
     * Show Progress Bar Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        showDialog(progress_bar_type);
    }

    /**
     * Downloading file in background thread
     * */
    @Override
    protected String doInBackground(String... f_url) {
        int count;

        try{


         URL url = new URL(f_url[0]);

        URLConnection conection = url.openConnection();
        conection.connect();
        // this will be useful so that you can show a tipical 0-100% progress bar
        int lenghtOfFile = conection.getContentLength();

        // download the file
        InputStream input = new BufferedInputStream(url.openStream(), 8192);

        // Output stream
        OutputStream output = new FileOutputStream("/sdcard/download/downloadedfile.png");

        byte data[] = new byte[1024];

        long total = 0;

        while ((count = input.read(data)) != -1) {
            total += count;
            // publishing the progress....
            // After this onProgressUpdate will be called
            publishProgress(""+(int)((total*100)/lenghtOfFile));

            // writing data to file
            output.write(data, 0, count);
        }

        // flushing output
        output.flush();

        // closing streams
        output.close();
        input.close();

    } catch (Exception e) {
        //e.printStackTrace();

        Log.e("Error: ", e.getMessage());

    }

    return null;
}

/**
 * Updating progress bar
 * */
protected void onProgressUpdate(String... progress) {
    // setting progress percentage
    pDialog.setProgress(Integer.parseInt(progress[0]));
}

/**
 * After completing background task
 * Dismiss the progress dialog
 * **/
@Override
protected void onPostExecute(String downurl) {
    // dismiss the dialog after the file was downloaded
    dismissDialog(progress_bar_type);


}

}
 }