Question

我尝试使用asynkTask在后台创建进度条。我正在从服务器下载文件并使用进度条显示文件下载的进度这很正常。

要创建此进度条，请参阅此link。

我的代码：

 package com.example.androidhive;

   import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileOutputStream;
 import java.io.InputStream;
import java.io.OutputStream;
 import java.net.URL;
 import java.net.URLConnection;

 import android.app.Activity;
  import android.app.Dialog;
 import android.app.ProgressDialog;
import android.graphics.drawable.Drawable;
 import android.os.AsyncTask;
import android.os.Bundle;
  import android.os.Environment;
 import android.util.Log;
 import android.view.View;
 import android.widget.Button;
 import android.widget.ImageView;
 import android.widget.ProgressBar;

 public class AndroidDownloadFileByProgressBarActivity extends Activity {

// button to show progress dialog
Button btnShowProgress;

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

String file = Environment.getExternalStorageDirectory()+"/MyAudio";
ProgressBar progressBar;
// File url to download
private static String file_url = "my url";

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

    // show progress bar button
    btnShowProgress = (Button) findViewById(R.id.btnProgressBar);
    // Image view to show image after downloading
    my_image = (ImageView) findViewById(R.id.my_image);


    File f = new File(file);
    if (!f.exists()) {
        f.mkdirs();
    } else {
        // f.delete();
    }
    progressBar = (ProgressBar) findViewById(R.id.progressBar1);
    /**
     * Show Progress bar click event
     * */
    btnShowProgress.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // starting new Async Task
            if (progressBar.getVisibility() != View.VISIBLE) {
                progressBar.setVisibility(View.VISIBLE);
            }
            new DownloadFileFromURL().execute(file_url);
        }
    });
}

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();
}

/**
 * Showing Dialog
 * */
@Override
protected Dialog onCreateDialog(int id) {
    switch (id) {
    case progress_bar_type:
        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;
    }
}

/**
 * Background Async Task to download file
 * */
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();
            // getting file length
            int lenghtOfFile = conection.getContentLength();

            // input stream to read file - with 8k buffer
            InputStream input = new BufferedInputStream(url.openStream(),
                    8192);

            // Output stream to write file
            // OutputStream output = new
            // FileOutputStream("/sdcard/Audio/downloadedfile.jpg");
            OutputStream output = new FileOutputStream(file+
                    "audio.zip");

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

    /**
     * After completing background task Dismiss the progress dialog
     * **/
    @Override
    protected void onPostExecute(String file_url) {
        // dismiss the dialog after the file was downloaded
        // dismissDialog(progress_bar_type);
        if (progressBar.getVisibility() != View.VISIBLE) {
            progressBar.setVisibility(View.VISIBLE);
        }
        // Displaying downloaded image into image view
        // Reading image path from sdcard
        String imagePath = Environment.getExternalStorageDirectory()
                .toString() + "/downloadedfile.jpg";
        // setting downloaded into image view
        // my_image.setImageDrawable(Drawable.createFromPath(imagePath));
    }

}
    }

但我的问题是当我关闭我的应用程序并重新打开我的进度条没有显示。但我的文件下载在后台。我想显示下载文件的进度，如果应用程序将关闭并重新打开它我想显示下载进度。

如何创建这个任何一个请帮助我...

Answer 1

据我所知，当您离开应用时，您所显示的进度条等所有ui更新都会“死亡”。您可以查看活动生命周期here以获取更多信息。

您可以尝试使用同步适配器方法（虽然实现起来有点困难）。

阅读here。在开发人员文档的示例中，您可以根据自己的需要进行调整，即创建通知以显示下载进度，而不是依赖用户是否离开您的应用。

如何在后台运行进度条？

1 个答案: