android中使用AsyncTask做下载进度条

AsyncTask是个不错的东西，可以使用它来做下载进度条。代码讲解如下：

package com.example.downloadfile;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import android.app.Activity;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.widget.TextView;

public class DownloadFile extends Activity {

public static final String LOG_TAG = "test";

private ProgressDialog mProgressDialog;
public static final int DIALOG_DOWNLOAD_PROGRESS = 0;

File rootDir = Environment.getExternalStorageDirectory();

//定义要下载的文件名
public String fileName = "test.jpg";
public String fileURL = "https://lh4.googleusercontent.com/-HiJOyupc-tQ/TgnDx1_HDzI/AAAAAAAAAWo/DEeOtnRimak/s800/DSC04158.JPG";

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

setContentView(R.layout.main);
TextView tv = new TextView(this);
tv.setText("Android Download File With Progress Bar");

//检查下载目录是否存在
checkAndCreateDirectory("/mydownloads");秋天的故事

//执行asynctask
new DownloadFileAsync().execute(fileURL);
}

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

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

@Override
protected String doInBackground(String... aurl) {

try {
//连接地址
URL u = new URL(fileURL);
HttpURLConnection c = (HttpURLConnection) u.openConnection();
c.setRequestMethod("GET");
c.setDoOutput(true);
c.connect();

//计算文件长度
int lenghtOfFile = c.getContentLength();

FileOutputStream f = new FileOutputStream(new File(rootDir + "/my_downloads/", fileName));

InputStream in = c.getInputStream();

//下载的代码
byte[] buffer = new byte[1024];
int len1 = 0;
long total = 0;

while ((len1 = in.read(buffer)) > 0) {
total += len1; //total = total + len1
publishProgress("" + (int)((total*100)/lenghtOfFile));
f.write(buffer, 0, len1);
}
f.close();

} catch (Exception e) {
Log.d(LOG_TAG, e.getMessage());
}

return null;
}

protected void onProgressUpdate(String... progress) {
Log.d(LOG_TAG,progress[0]);
mProgressDialog.setProgress(Integer.parseInt(progress[0]));
}

@Override
protected void onPostExecute(String unused) {
//dismiss the dialog after the file was downloaded
dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
}
}

public void checkAndCreateDirectory(String dirName){
File new_dir = new File( rootDir + dirName );
if( !new_dir.exists() ){
new_dir.mkdirs();
}
}

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