从文件服务器下载随机图片

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。我试图将它们下载到我的应用程序中。我无法将这些图像生成到我的应用程序中。我跟着导游从这个博客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

有几个问题，你的代码：

• 您尝试进行网络操作（从远程服务器下载文件）从UI线程。 网络操作必须从另一个线程执行。否则 - 异常被抛出。

的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(); 

更好的办法是使用的AsyncTask或IntentService（其也执行上单独的线程的代码）

• 第二件事 - 你不能只用输入流的大小来创建int数组：如果图像太大，可能会失败。尝试打破下载与固定大小的段（比如2058个字节每个段）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(); 
      } 
  } 
  
  }