Android开发中怎么实现一个图片下载功能

发布时间：2020-11-24 15:22:35 作者：Leah
来源：亿速云阅读：166

本篇文章给大家分享的是有关Android开发中怎么实现一个图片下载功能，小编觉得挺实用的，因此分享给大家学习，希望大家阅读完这篇文章后可以有所收获，话不多说，跟着小编一起来看看吧。

1.普通的下载方式

布局文件：

<&#63;xml version="1.0" encoding="utf-8"&#63;>
<LinearLayout
 xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent">
 <ImageView android:src="@drawable/icon"
   android:layout_width="wrap_content"
   android:id="@+id/imgPic"
   android:layout_gravity="center|center_vertical"
   android:layout_height="fill_parent">
 </ImageView>
</LinearLayout>

java文件

public class DownloadImage extends Activity {
  private ImageView imgPic;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.download_image);
    imgPic = (ImageView) findViewById(R.id.imgPic);
    String url = "http://ww1.sinaimg.cn/bmiddle/6834c769jw1djjf4p3p9rj.jpg";
    loadRmoteImage(url);
  }
  /**
   * @param imgUrl
   *   远程图片文件的URL
   *
   *   下载远程图片
   */
  private void loadRmoteImage(String imgUrl) {
    URL fileURL = null;
    Bitmap bitmap = null;
    try {
      fileURL = new URL(imgUrl);
    } catch (MalformedURLException err) {
      err.printStackTrace();
    }
    try {
      HttpURLConnection conn = (HttpURLConnection) fileURL
          .openConnection();
      conn.setDoInput(true);
      conn.connect();
      InputStream is = conn.getInputStream();
      int length = (int) conn.getContentLength();
      if (length != -1) {
        byte[] imgData = new byte[length];
        byte[] buffer = new byte[512];
        int readLen = 0;
        int destPos = 0;
        while ((readLen = is.read(buffer)) > 0) {
          System.arraycopy(buffer, 0, imgData, destPos, readLen);
          destPos += readLen;
        }
        bitmap = BitmapFactory.decodeByteArray(imgData, 0,
            imgData.length);
      }
    } catch (IOException e) {
      e.printStackTrace();
    }
    imgPic.setImageBitmap(bitmap);
  }

2.带进度条的下载

有时候网络差，或者是图片太大，会出现黑屏的情况，用户体验比较差，那么增加一个进度条是提高用户体验的好方法

/**
 * @author xushilin xsl xushilin@kingtoneinfo.com
 * @version： 创建时间：2011-7-27 下午02:55:56
 * 说 明: android中下载图片
 * 修改历史：
 */
public class DownloadImage extends Activity {
  private ImageView imgPic;
  private ProgressBar progressBar;
  private int totalSize=0;
  private int size=0;
  private Handler mHandler;
  String url = "http://ww1.sinaimg.cn/bmiddle/6834c769jw1djjf4p3p9rj.jpg";
  private Bitmap bitmap=null;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.download_image);
    imgPic = (ImageView) findViewById(R.id.imgPic);
    progressBar = (ProgressBar) findViewById(R.id.progressBar);
    progressBar.setProgress(getProgressInt(progressBar.getMax()));
    mHandler = new Handler() {
      public void handleMessage(Message msg) {
        progressBar.setProgress(getProgressInt(progressBar.getMax()));
        if(bitmap!=null){
          imgPic.setImageBitmap(bitmap);
        }
      }
    };
    new Thread(){
      public void run(){
        loadRmoteImage(url);
      }
    }.start();
  }
  /**
   * @param imgUrl
   *   远程图片文件的URL
   *
   *   下载远程图片
   */
  private void loadRmoteImage(String imgUrl) {
    URL fileURL = null;
    try {
      fileURL = new URL(imgUrl);
    } catch (MalformedURLException err) {
      err.printStackTrace();
    }
    try {
      HttpURLConnection conn = (HttpURLConnection) fileURL
          .openConnection();
      conn.setDoInput(true);
      conn.connect();
      InputStream is = conn.getInputStream();
      int length = (int) conn.getContentLength();
      totalSize=length;
      if (length != -1) {
        byte[] imgData = new byte[length];
        byte[] buffer = new byte[512];
        int readLen = 0;
        int destPos = 0;
        while ((readLen = is.read(buffer)) > 0) {
          System.arraycopy(buffer, 0, imgData, destPos, readLen);
          destPos += readLen;
          size=destPos;
          mHandler.sendEmptyMessage(1);
          Thread.sleep(100);
        }
        bitmap = BitmapFactory.decodeByteArray(imgData, 0,
            imgData.length);
        mHandler.sendEmptyMessage(1);
      }
    } catch (IOException e) {
      e.printStackTrace();
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
  private int getProgressInt(int max) {
    int result = (totalSize > 0) &#63; (int) (size * max * 1.0 / totalSize) : 0;
    return result;
  }
}

以上就是Android开发中怎么实现一个图片下载功能，小编相信有部分知识点可能是我们日常工作会见到或用到的。希望你能通过这篇文章学到更多知识。更多详情敬请关注亿速云行业资讯频道。

Android开发中怎么实现一个图片下载功能

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