Android中使用AsyncTask做下載進度條

AsyncTask是個不錯的東西，可以使用它來做下載進度條。代碼講解如下：

1. package com.example.downloadfile;
3. import java.io.File;
4. import java.io.FileOutputStream;
5. import java.io.InputStream;
6. import java.net.HttpURLConnection;
7. import java.net.URL;
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.os.Environment;
15. import android.util.Log;
16. import android.widget.TextView;
18. public class DownloadFile extends Activity {
20. public static final String LOG_TAG = "test";
22. private ProgressDialog mProgressDialog;
23. public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
26. File rootDir = Environment.getExternalStorageDirectory();
28. //定義要下載的文件名
29. public String fileName = "test.jpg";
30. public String fileURL = "https://lh4.googleusercontent.com/-HiJOyupc-tQ/TgnDx1_HDzI/AAAAAAAAAWo/DEeOtnRimak/s800/DSC04158.JPG";
32. @Override
33. public void onCreate(Bundle savedInstanceState)
34. {
35. super.onCreate(savedInstanceState);
37. setContentView(R.layout.main);
38. TextView tv = new TextView(this);
39. tv.setText("Android Download File With Progress Bar");
41. //檢查下載目錄是否存在
42. checkAndCreateDirectory("/mydownloads");
44. //執行asynctask
45. new DownloadFileAsync().execute(fileURL);
46. }
49. class DownloadFileAsync extends AsyncTask<String, String, String> {
51. @Override
52. protected void onPreExecute() {
53. super.onPreExecute();
54. showDialog(DIALOG_DOWNLOAD_PROGRESS);
55. }
58. @Override
59. protected String doInBackground(String... aurl) {
61. try {
62. //連接地址
63. URL u = new URL(fileURL);
64. HttpURLConnection c = (HttpURLConnection) u.openConnection();
65. c.setRequestMethod("GET");
66. c.setDoOutput(true);
67. c.connect();
69. //計算文件長度
70. int lenghtOfFile = c.getContentLength();
73. FileOutputStream f = new FileOutputStream(new File(rootDir + "/my_downloads/", fileName));
75. InputStream in = c.getInputStream();
77. //下載的代碼
78. byte[] buffer = new byte[1024];
79. int len1 = 0;
80. long total = 0;
82. while ((len1 = in.read(buffer)) > 0) {
83. total += len1; //total = total + len1
84. publishProgress("" + (int)((total*100)/lenghtOfFile));
85. f.write(buffer, 0, len1);
86. }
87. f.close();
89. } catch (Exception e) {
90. Log.d(LOG_TAG, e.getMessage());
91. }
93. return null;
94. }
96. protected void onProgressUpdate(String... progress) {
97. Log.d(LOG_TAG,progress[0]);
98. mProgressDialog.setProgress(Integer.parseInt(progress[0]));
99. }
101. @Override
102. protected void onPostExecute(String unused) {
103. //dismiss the dialog after the file was downloaded
104. dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
105. }
106. }
109. public void checkAndCreateDirectory(String dirName){
110. File new_dir = new File( rootDir + dirName );
111. if( !new_dir.exists() ){
112. new_dir.mkdirs();
113. }
114. }
116. @Override
117. protected Dialog onCreateDialog(int id) {
118. switch (id) {
119. case DIALOG_DOWNLOAD_PROGRESS: //we set this to 0
120. mProgressDialog = new ProgressDialog(this);
121. mProgressDialog.setMessage("Downloading file...");
122. mProgressDialog.setIndeterminate(false);
123. mProgressDialog.setMax(100);
124. mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
125. mProgressDialog.setCancelable(true);
126. mProgressDialog.show();
127. return mProgressDialog;
128. default:
129. return null;
130. }
131. }
132. }