Android中使用AsyncTask做下载进度条实例代码

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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