Android中使用AsyncTask做下载进度条实例代码

概述androidAsyncTask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：

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,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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