在Android中制作AsyncTask的实例

Question

我有AsyncTask类，下载名称如下面的下载图像文件，当我想在另一个类中创建它的实例时，出现“方法执行（字符串）未定义类型下载程序”描述。 我应该如何制作Downloader的实例？

public class Downloader extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }


    /**
     * 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(G.FILE_OUT_PATH);

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

        return null;
    }


    /**
     * Updating progress bar
     * */
    @Override
    protected void onProgressUpdate(String... progress) {
        // setting progress percentage
    }


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

    }

}





public class Downloader extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }


    /**
     * 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(G.FILE_OUT_PATH);

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

        return null;
    }


    /**
     * Updating progress bar
     * */
    @Override
    protected void onProgressUpdate(String... progress) {
        // setting progress percentage
    }


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

    }

}

Answer 1

new Downloader().execute("your URL string here");