Android 中下载文件到sdcard和进度条小结

 

这里小结下，如何用android的模拟器去创建一个sdcard,并且学习如何在android中去下载一个网上的文件，保存到android，并且下 载时，会显示一个进度条.上述讲的就是我们这一篇代码要实现的内容。这篇内容其实是很重要的，大家可要好好的看了哦。
　
       1 页面结构，提供一个button,点BUTTON时，去下载一个图片，main.xml设计如下：

Java代码：

< ?xml version="1.0" encoding="utf-8"?>
< LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
< TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello"
/>
< Button
android:text="Start long running task.."
android:id="@+id/startBtn"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
< /Button>
< /LinearLayout>

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       2 主程序

Java代码：

package eoe.liao;
import java.io.BufferedInputStream;
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.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

import android.view.View.OnClickListener;
import android.widget.Button;
public class AndroAsync extends Activity {
public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
private Button startBtn;
private ProgressDialog mProgressDialog;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
startBtn = (Button)findViewById(R.id.startBtn);
startBtn.setOnClickListener(new OnClickListener(){
public void onClick(View v) {
startDownload();
}
});
}
private void startDownload() {
String url = "http://image-7.verycd.com/0d7596f5db7df1742236466dc91311b1435702(120x120)/thumb.jpg";
new DownloadFileAsync().execute(url);
}
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case DIALOG_DOWNLOAD_PROGRESS:
mProgressDialog = new ProgressDialog(this);
mProgressDialog.setMessage("Downloading file..");
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setCancelable(false);
mProgressDialog.show();
return mProgressDialog;
default:
return null;
}
}
class DownloadFileAsync extends AsyncTask< String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
showDialog(DIALOG_DOWNLOAD_PROGRESS);
}
@Override
protected String doInBackground(String... aurl) {
int count;
try {
URL url = new URL(aurl[0]);
URLConnection conexion = url.openConnection();
conexion.connect();
int lenghtOfFile = conexion.getContentLength();
Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);
InputStream input = new BufferedInputStream(url.openStream());
OutputStream output = new FileOutputStream("/sdcard/picture.jpg");
byte data[] = new byte[1024];
long total = 0;
while ((count = input.read(data)) != -1) {
total += count;
publishProgress(""+(int)((total*100)/lenghtOfFile));
output.write(data, 0, count);
}
output.flush();
output.close();
input.close();
} catch (Exception e) {
Log.e("error",e.getMessage().toString());
System.out.println(e.getMessage().toString());
}
return null;
}
protected void onProgressUpdate(String... progress) {
Log.d("ANDRO_ASYNC",progress[0]);
mProgressDialog.setProgress(Integer.parseInt(progress[0]));
}
@Override
protected void onPostExecute(String unused) {
dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
}
}
}

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      注意这里，在startdownload 方法中，调用了DownloadFileAsync内部类，这个内部类充分利用了AsyncTask的异步工作特性，是很方便 的，onProgressUpdate是让进度条完成后消失。最后，要记得在androidmanifest.xml中的< /application>后加入< uses-permission android:name="android.permission.INTERNET" />让能有访问互联网的能力.