android 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"); //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; } } }

配置文件

注意打开文件保存权限

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.downloadfile" android:versionCode="1" android:versionName="1.0"> <uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> <uses-sdk android:minSdkVersion="4" /> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".DownloadFile" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>

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