android - 从文件服务器下载随机图像

Question

这是我的尝试。我的文件托管在我自己的服务器上，主要是 JPG 文件。我正在尝试将它们下载到我的应用程序中。我未能将这些图像生成到我的应用程序中。我遵循此博客中的指南 http://getablogger.blogspot.gr/2008/01/android-download-image-from-server-and.html

我的xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView 
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Hello World, HTTPImage load test"
/>
<Button android:id="@+id/get_imagebt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Get an image"
android:layout_gravity="center"
/> 
<ImageView android:id="@+id/imview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
/>
</LinearLayout>

编码

package com.example.downloadimages;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;




public class MainActivity extends Activity {

    ImageView imView;
    String imageUrl="http://myfilehosting.com/";
    Random r;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        r= new Random();

        Button bt3= (Button)findViewById(R.id.get_imagebt);
        bt3.setOnClickListener(getImgListener);
        imView = (ImageView)findViewById(R.id.imview);
    }

    View.OnClickListener getImgListener = new View.OnClickListener()
    {

        public void onClick(View view) {
        // TODO Auto-generated method stub

        //i tried to randomize the file download, in my server i put 4 files with name like
        //jpg0.jpg, jpg1.jpg, jpg2.jpg so different file is downloaded in button press
        int i =r.nextInt()%4;
        downloadFile(imageUrl+i+".jpg");

        }

        Bitmap bmImg;
        void downloadFile(String fileUrl){
        URL myFileUrl =null; 
        try {
        myFileUrl= new URL(fileUrl);
        } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }
        try {
        HttpURLConnection conn= (HttpURLConnection)myFileUrl.openConnection();
        conn.setDoInput(true);
        conn.connect();
        int length = conn.getContentLength();
        int[] bitmapData =new int[length];
        byte[] bitmapData2 =new byte[length];
        InputStream is = conn.getInputStream();

        bmImg = BitmapFactory.decodeStream(is);
        imView.setImageBitmap(bmImg);
        } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }





};
};
}

Answer 1

你的代码有几个问题:

• 您正在尝试从 UI 线程执行网络操作(从远程服务器下载文件)。 网络操作必须从另一个线程执行。否则 - 抛出异常。

从另一个线程启动代码的方法之一是:

new Thread(new Runnable() {

        @Override
        public void run() {
            downloadFile(imageUrl+i+".jpg");
        }
    }).start();

更好的方法是使用 AsyncTask 或 IntentService(它们也在单独的线程上执行代码)

• 第二件事 - 您不能只创建具有输入流大小的 int 数组:如果图像太大，它可能会失败。尝试将下载分解为固定大小的段(比如每个段 2058 字节)，例如:

  private HttpURLConnection conn;
  private InputStream stream;
  private FileOutputStream out;
  
  private double fileSize;
  private double downloaded;
  
  
  public void downloadFile(String fileURL, String fileName) {
  try {
  
      conn = (HttpURLConnection) new URL(fileURL).openConnection();
      fileSize = conn.getContentLength();
      File file = new File(fileName);
  
      out = new FileOutputStream(file);
      conn.connect();
  
      stream = conn.getInputStream();
  
      while (status == DOWNLOADING) {
          byte buffer[];
  
          if (fileSize - downloaded > MAX_BUFFER_SIZE) {
              buffer = new byte[MAX_BUFFER_SIZE];
          } else {
              buffer = new byte[(int) (fileSize - downloaded)];
          }
          int read = stream.read(buffer);
  
          if (read == -1) {
  
              out.close();
              if (conn != null) {
                  conn.disconnect();
              }
  
              break;
          }
  
          out.write(buffer, 0, read);
          downloaded += read;
      }
  
  } catch (Exception e) {
      Log.e("downloadFile():", e.getMessage());
      if (conn != null) {
          conn.disconnect();
      }
  }
  
  }