android中使用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>

更多相关文章

随机推荐