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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