Android之ProgressBar即时显示下载进度详解

这里利用 progressbar 即时显示下载进度。 

途中碰到的问题： 

1、主线程中不能打开 url，和只能在主线程中使用 toast 等 

2、子线程不能修改 ui 

3、允许网络协议 

4、暂停下载和继续下载
 　 ........ 

fragment_main 布局文件 

<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"
  tools:context="com.dragon.android.textbar.mainactivity$placeholderfragment" >

  <!-- prigressbar 进度条 -->
  <!-- progress 当前进度 -->
  <!-- indeterminate 不明确的  默认false -->
  <progressbar
    android:id="@+id/progressbar1"
    style="?android:attr/progressbarstylehorizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_centerinparent="true"
    android:max="100"
    android:progress="0"
    android:indeterminate="true"/>

  <button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignparenttop="true"
    android:layout_centerhorizontal="true"
    android:onclick="startload"
    android:layout_margintop="86dp"
    android:background="#009fee"
    android:text="@string/start"
    android:textcolor="#ffffff" />

  <textview
    android:id="@+id/textview1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@+id/progressbar1"
    android:background="@null"
    android:layout_alignparentleft="true" />
  
</relativelayout>

strings.xml 

<?xml version="1.0" encoding="utf-8"?>
<resources>

  <string name="app_name">hwdownload</string>
  <string name="hello_world">hello world!</string>
  <string name="action_settings">settings</string>
  <string name="start">开始</string>
  <string name="stop">暂停</string>
  <string name="contin">继续</string>

</resources>

（问题3）在 androidmanifest 文件中配置
 <!-- 请求网络权限 -->
    <uses-permission  android:name="android.permission.internet"/>

mainactivity（问题1、2） 

package com.dragon.android.textbar;

import java.io.ioexception;
import java.io.inputstream;
import java.net.httpurlconnection;
import java.net.url;

import android.app.activity;
import android.os.bundle;
import android.view.view;
import android.widget.button;
import android.widget.progressbar;
import android.widget.textview;
import android.widget.toast;

/**
 * 只有创建一个 view 的线程才可以改变这个 view 的ui!!! 主线程也叫 ui 线程
 */
public class mainactivity extends activity {
  private progressbar progressbar1;
  private button button1;
  private textview textview1;

  @override
  protected void oncreate(bundle savedinstancestate) {
    super.oncreate(savedinstancestate);
    setcontentview(r.layout.fragment_main);

    progressbar1 = (progressbar) findviewbyid(r.id.progressbar1);
    button1 = (button) findviewbyid(r.id.button1);
    textview1 = (textview) findviewbyid(r.id.textview1);

  }

  public void startload(view view) {
     string text = (string) button1.gettext();
    // 设置按钮内容 ----并没有用...
    button1.settext(text.equals(getresources().getstring(r.string.start)) ? r.string.stop
        : (text.equals(getresources().getstring(r.string.stop)) ? r.string.contin
            : r.string.stop));
    progressbar1.setindeterminate(false);

    new thread(new runnable() {
      private int percent;

      @override
      public void run() {
        try {
          // 打开 url 必须在子线程
          url url = new url(
              "http://b.zol-img.com.cn/sjbizhi/images/9/540x960/1472549276394.jpg");
          httpurlconnection conn = (httpurlconnection) url.openconnection();
          // conn.setrequestmethod("get");
          // conn.setreadtimeout(5000);
          // conn.setconnecttimeout(5000);

          int contentlength = conn.getcontentlength();

          if (conn.getresponsecode() == httpurlconnection.http_ok) {
            inputstream is = conn.getinputstream();

            byte[] buffer = new byte[1024];
            int len = -1;
            int sum = 0;
            while ((len = is.read(buffer)) != -1) {
              sum += len;
              // 注意强转方式，防止一直为0
              percent = (int) (100.0 * sum / contentlength);
              // 在主线程上运行的子线程
              runonuithread(new runnable() {

                @override
                public void run() {
                  progressbar1.setprogress(percent);
                  textview1.settext(percent + "%");
                  if (percent == progressbar1.getmax()) {
                    toast.maketext(mainactivity.this,
                        "下载完成!", toast.length_short)
                        .show();
                  }
                }
              });
            }
            is.close();
            conn.disconnect();
          }
        } catch (ioexception e) {
          e.printstacktrace();
        }
      }
    }).start();
  }
}

**************然而并没有解决问题4,要用断点续传,但是还不会存放assets资源.....***************

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