Android 中下载文件到sdcard和进度条小结

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;
3. import java.io.BufferedInputStream;
4. import java.io.FileOutputStream;
5. import java.io.InputStream;
6. import java.io.OutputStream;
7. import java.net.URL;
8. import java.net.URLConnection;
9. import android.app.Activity;
10. import android.app.Dialog;
11. import android.app.ProgressDialog;
12. import android.os.AsyncTask;
13. import android.os.Bundle;
14. import android.util.Log;
15. import android.view.View;
16. import android.view.View.OnClickListener;
17. import android.widget.Button;
19. public class AndroAsync extends Activity {
21. public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
22. private Button startBtn;
23. private ProgressDialog mProgressDialog;
24. /** Called when the activity is first created. */
26. @Override
27. public void onCreate(Bundle savedInstanceState) {
28. super.onCreate(savedInstanceState);
29. setContentView(R.layout.main);
30. startBtn = (Button)findViewById(R.id.startBtn);
31. startBtn.setOnClickListener(new OnClickListener(){
32. public void onClick(View v) {
33. startDownload();
34. }
35. });
36. }
38. private void startDownload() {
39. String url = "http://image-7.verycd.com/0d7596f5db7df1742236466dc91311b1435702(120x120)/thumb.jpg";
40. new DownloadFileAsync().execute(url);
41. }
44. @Override
45. protected Dialog onCreateDialog(int id) {
46. switch (id) {
47. case DIALOG_DOWNLOAD_PROGRESS:
48. mProgressDialog = new ProgressDialog(this);
49. mProgressDialog.setMessage("Downloading file..");
50. mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
51. mProgressDialog.setCancelable(false);
52. mProgressDialog.show();
53. return mProgressDialog;
54. default:
55. return null;
56. }
57. }
59. class DownloadFileAsync extends AsyncTask< String, String, String> {
60. @Override
61. protected void onPreExecute() {
62. super.onPreExecute();
63. showDialog(DIALOG_DOWNLOAD_PROGRESS);
64. }
67. @Override
68. protected String doInBackground(String... aurl) {
69. int count;
70. try {
71. URL url = new URL(aurl[0]);
72. URLConnection conexion = url.openConnection();
73. conexion.connect();
74. int lenghtOfFile = conexion.getContentLength();
75. Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);
76. InputStream input = new BufferedInputStream(url.openStream());
77. OutputStream output = new FileOutputStream("/sdcard/picture.jpg");
78. byte data[] = new byte[1024];
79. long total = 0;
80. while ((count = input.read(data)) != -1) {
81. total += count;
82. publishProgress(""+(int)((total*100)/lenghtOfFile));
83. output.write(data, 0, count);
84. }
85. output.flush();
86. output.close();
87. input.close();
88. } catch (Exception e) {
89. Log.e("error",e.getMessage().toString());
90. System.out.println(e.getMessage().toString());
91. }
92. return null;
93. }
94. protected void onProgressUpdate(String... progress) {
95. Log.d("ANDRO_ASYNC",progress[0]);
96. mProgressDialog.setProgress(Integer.parseInt(progress[0]));
97. }
100. @Override
101. protected void onPostExecute(String unused) {
102. dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
103. }
104. }
107. }

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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.