Android使用AsyncTask实现多线程下载的方法

本文实例讲述了android使用asynctask实现多线程下载的方法。分享给大家供大家参考，具体如下：

public class mainactivity extends activity implements onclicklistener {
  private button btn1, btn2, btn3;
  private progressbar progressbar1, progressbar2, progressbar3;
  private imageview img1, img2, img3;
  private static final string img_uri = "//www.jb51.net/images/logo.gif";
  @override
  protected void oncreate(bundle savedinstancestate) {
    super.oncreate(savedinstancestate);
    setcontentview(r.layout.activity_main);
    initview();
    initlistener();
  }
  /**
   * 初始化监听器
   */
  private void initlistener() {
    btn1.setonclicklistener(this);
    btn2.setonclicklistener(this);
    btn3.setonclicklistener(this);
  }
  /**
   *
   * 初始化控件
   */
  private void initview() {
    btn1 = (button) findviewbyid(r.id.btn1);
    btn2 = (button) findviewbyid(r.id.btn2);
    btn3 = (button) findviewbyid(r.id.btn3);
    progressbar1 = (progressbar) findviewbyid(r.id.progressbar1);
    progressbar2 = (progressbar) findviewbyid(r.id.progressbar2);
    progressbar3 = (progressbar) findviewbyid(r.id.progressbar3);
    img1 = (imageview) findviewbyid(r.id.img1);
    img2 = (imageview) findviewbyid(r.id.img2);
    img3 = (imageview) findviewbyid(r.id.img3);
  }
  @override
  public boolean oncreateoptionsmenu(menu menu) {
    // inflate the menu; this adds items to the action bar if it is present.
    getmenuinflater().inflate(r.menu.main, menu);
    return true;
  }
  @override
  public void onclick(view arg0) {
    // 点击按钮模拟下载
    mydownloadasy down = new mydownloadasy();
    down.execute(img_uri, arg0.getid() + "");
  }
  /**
   * 1.params，传递给后台任务的参数类型。
   *
   * 2.progress，后台计算执行过程中，进步单位（progress　units）的类型。（就是后台程序已经执行了百分之几了。）
   *
   * 3.result， 后台执行返回的结果的类型。
   */
  class mydownloadasy extends asynctask<string, integer, bitmap> {
    private static final string tag = "asy";
    private int clickbtn = 0;
    private void i(string object) {
      log.i(tag, object);
    }
    @override
    protected void onpreexecute() {
      // todo auto-generated method stub
      super.onpreexecute();
      i("準備運行線程");
      progressbar1.setprogress(0);// 进度条复位
      progressbar2.setprogress(0);// 进度条复位
      progressbar3.setprogress(0);// 进度条复位
    }
    @override
    protected bitmap doinbackground(string... arg0) {
      switch (integer.parseint(arg0[1])) {
      case r.id.btn1:
        clickbtn = 1;
        break;
      case r.id.btn2:
        clickbtn = 2;
        break;
      case r.id.btn3:
        clickbtn = 3;
        break;
      default:
        break;
      }
      i("正在后台执行");
      publishprogress(0);
      // 下载图片
      httpclient hc = new defaulthttpclient();
      // 等待2s
      sleepwait();
      publishprogress(50);
      httpget hg = new httpget(arg0[0]);// 获取jb51的logo
      final bitmap bm;
      try {
        httpresponse hr = hc.execute(hg);
        bm = bitmapfactory.decodestream(hr.getentity().getcontent());
      } catch (exception e) {
        return null;
      }
      sleepwait();
      publishprogress(100);
      // mimageview.setimagebitmap(result); 不能在后台线程操作ui
      return bm;
    }
    /**
     * 等待2s钟
     */
    private void sleepwait() {
      try {
        thread.sleep(2000);
      } catch (interruptedexception e1) {
        // todo auto-generated catch block
        e1.printstacktrace();
      }
    }
    protected void onprogressupdate(integer... values) {
      // 动态更新
      i("進度更新");
      switch (clickbtn) {
      case 1:
        progressbar1.setprogress(values[0]);// 更新进度条的进度
        break;
      case 2:
        progressbar2.setprogress(values[0]);// 更新进度条的进度
        break;
      case 3:
        progressbar3.setprogress(values[0]);// 更新进度条的进度
        break;
      default:
        break;
      }
    }
    protected void onpostexecute(bitmap result) {
      // todo auto-generated method stub
      super.onpostexecute(result);
      i("线程执行完成");
      if (result != null) {
        i("下载图片成功");
        switch (clickbtn) {
        case 1:
          img1.setimagebitmap(result);
          break;
        case 2:
          img2.setimagebitmap(result);
          break;
        case 3:
          img3.setimagebitmap(result);
          break;
        default:
          break;
        }
      } else {
        i("下载图片失败");
      }
    }
    @override
    protected void oncancelled() {
      // todo auto-generated method stub
      super.oncancelled();
      i("取消线程");
      switch (clickbtn) {
      case 1:
        progressbar1.setprogress(0);// 进度条复位
        break;
      case 2:
        progressbar2.setprogress(0);// 进度条复位
        break;
      case 3:
        progressbar3.setprogress(0);// 进度条复位
        break;
      default:
        break;
      }
    }
  }
}

xml:

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:paddingbottom="@dimen/activity_vertical_margin"
  android:paddingleft="@dimen/activity_horizontal_margin"
  android:paddingright="@dimen/activity_horizontal_margin"
  android:paddingtop="@dimen/activity_vertical_margin"
  tools:context=".mainactivity" >
  <tablelayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_centerhorizontal="true" >
    <tablerow>
      <button
        android:id="@+id/btn1"
        android:text="@string/btn1" />
      <progressbar
        android:id="@+id/progressbar1"
        style="?android:attr/progressbarstylehorizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />
      <imageview
        android:id="@+id/img1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentdescription="@id/img1"
        android:src="@drawable/ic_launcher" />
    </tablerow>
    <tablerow>
      <button
        android:id="@+id/btn2"
        android:text="@string/btn2" />
      <progressbar
        android:id="@+id/progressbar2"
        style="?android:attr/progressbarstylehorizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />
      <imageview
        android:id="@+id/img2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentdescription="@id/img2"
        android:src="@drawable/ic_launcher" />
    </tablerow>
    <tablerow>
      <button
        android:id="@+id/btn3"
        android:text="@string/btn3" />
      <progressbar
        android:id="@+id/progressbar3"
        style="?android:attr/progressbarstylehorizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" />
      <imageview
        android:id="@+id/img3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentdescription="@id/img3"
        android:src="@drawable/ic_launcher" />
    </tablerow>
  </tablelayout>
</relativelayout>

androidmanifast:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
  package="com.xunfang.asynctackdemo"
  android:versioncode="1"
  android:versionname="1.0" >
  <uses-sdk
    android:minsdkversion="10"
    android:targetsdkversion="10" />
  <!-- 访问网络的权限 -->
  <uses-permission android:name="android.permission.internet" >
  </uses-permission>
  <application
    android:allowbackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/apptheme" >
    <activity
      android:name="com.xunfang.asynctackdemo.mainactivity"
      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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希望本文所述对大家android程序设计有所帮助。