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：

1. < ?xml version="1.0" encoding="utf-8"?>
2. < LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
3. android:orientation="vertical"
4. android:layout_width="fill_parent"
5. android:layout_height="fill_parent"
6. >
7. < TextView
8. android:layout_width="fill_parent"
9. android:layout_height="wrap_content"
10. android:text="@string/hello"
11. />
12. < Button
13. android:text="Start long running task.."
14. android:id="@+id/startBtn"
15. android:layout_width="fill_parent"
16. android:layout_height="wrap_content">
17. < /Button>
18. < /LinearLayout>

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2 主程序

Java代码：

1. package eoe.liao;
2. import java.io.BufferedInputStream;
3. import java.io.FileOutputStream;
4. import java.io.InputStream;
5. import java.io.OutputStream;
6. import java.net.URL;
7. import java.net.URLConnection;
8. import android.app.Activity;
9. import android.app.Dialog;
10. import android.app.ProgressDialog;
11. import android.os.AsyncTask;
12. import android.os.Bundle;
13. import android.util.Log;
14. import android.view.View;
15. import android.view.View.OnClickListener;
16. import android.widget.Button;
17. public class AndroAsync extends Activity {
18. public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
19. private Button startBtn;
20. private ProgressDialog mProgressDialog;
21. @Override
22. public void onCreate(Bundle savedInstanceState) {
23. super.onCreate(savedInstanceState);
24. setContentView(R.layout.main);
25. startBtn = (Button)findViewById(R.id.startBtn);
26. startBtn.setOnClickListener(new OnClickListener(){
27. public void onClick(View v) {
28. startDownload();
29. }
30. });
31. }
32. private void startDownload() {
33. String url = "http://image-7.verycd.com/0d7596f5db7df1742236466dc91311b1435702(120x120)/thumb.jpg";
34. new DownloadFileAsync().execute(url);
35. }
36. @Override
37. protected Dialog onCreateDialog(int id) {
38. switch (id) {
39. case DIALOG_DOWNLOAD_PROGRESS:
40. mProgressDialog = new ProgressDialog(this);
41. mProgressDialog.setMessage("Downloading file..");
42. mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
43. mProgressDialog.setCancelable(false);
44. mProgressDialog.show();
45. return mProgressDialog;
46. default:
47. return null;
48. }
49. }
50. class DownloadFileAsync extends AsyncTask< String, String, String> {
51. @Override
52. protected void onPreExecute() {
53. super.onPreExecute();
54. showDialog(DIALOG_DOWNLOAD_PROGRESS);
55. }
56. @Override
57. protected String doInBackground(String... aurl) {
58. int count;
59. try {
60. URL url = new URL(aurl[0]);
61. URLConnection conexion = url.openConnection();
62. conexion.connect();
63. int lenghtOfFile = conexion.getContentLength();
64. Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);
65. InputStream input = new BufferedInputStream(url.openStream());
66. OutputStream output = new FileOutputStream("/sdcard/picture.jpg");
67. byte data[] = new byte[1024];
68. long total = 0;
69. while ((count = input.read(data)) != -1) {
70. total += count;
71. publishProgress(""+(int)((total*100)/lenghtOfFile));
72. output.write(data, 0, count);
73. }
74. output.flush();
75. output.close();
76. input.close();
77. } catch (Exception e) {
78. Log.e("error",e.getMessage().toString());
79. System.out.println(e.getMessage().toString());
80. }
81. return null;
82. }
83. protected void onProgressUpdate(String... progress) {
84. Log.d("ANDRO_ASYNC",progress[0]);
85. mProgressDialog.setProgress(Integer.parseInt(progress[0]));
86. }
87. @Override
88. protected void onPostExecute(String unused) {
89. dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
90. }
91. }
92. }

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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.