Android的动态图像加载

Question

我工作的这是使用JSON采取从互联网上内容的Android应用程序，我使用的服务加载JSON在本地数据库中，我有两个主要的疑虑：

1 - 如何分辨数据库加载新数据以重新加载显示的应用程序。

2-我有存储在数据库中的图像URL，需要按需显示，以显示我已经用progressBar和Image视图扩展了默认的FrameLayout，如果图像是新的Frame Layout将显示progressBar尚未加载，如果图像被加载，它将被显示，此外，新的FreamLayout有一个扩展AsyncTask的类，它通过URL检查图像是否存在于文件系统上，如果它不存在，则发生图像下载。下面是我所做的课程的样本。这是做这件事的正确方法吗？在这种情况下，我有一些图像在下载时被破坏，如何解决这个问题？

感谢您的协助。

public class ImageLoader extends FrameLayout 
    { 
private String imageURL; 
private ImageView img; 
private ProgressBar pb; 
private boolean isLoaded; 
File rootDir = new File("/data/data/com.ait.kw.pharmacy/files"); 
private static final String TAG = "FrameLayoutExpander"; 

    //defining file name and url 
    public String fileName = ""; 
    public String fileURL = ""; 

public ImageLoader(Context context , AttributeSet attr) { 
    super(context,attr); 
    isLoaded = false; 
    img = new ImageView(context , null); 
    pb = new ProgressBar(context,null , android.R.attr.progressBarStyle); 
    img.setVisibility(View.INVISIBLE); 
    pb.setVisibility(View.VISIBLE); 
    FrameLayout.LayoutParams params = new FrameLayout.LayoutParams(
      LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT); 
    super.addView(img,params); 
    super.addView(pb,params); 
    checkAndCreateDirectory("/images"); 

} 

public ImageLoader(Context context, AttributeSet attr, int defaultStyle) 
{ 
    super(context, attr, defaultStyle); 
    isLoaded = false; 
    img = new ImageView(context , null); 
    pb = new ProgressBar(context,null , android.R.attr.progressBarStyle); 
    img.setVisibility(View.INVISIBLE); 
    pb.setVisibility(View.VISIBLE); 
    super.addView(img); 
    super.addView(pb); 
    checkAndCreateDirectory("/images"); 
    isLoaded = checkImaeExists(rootDir.getAbsolutePath()+"/images/"+fileName); 
    } 
public void setImageResource(int resId) { 
    pb.setVisibility(View.GONE); 
    img.setVisibility(View.VISIBLE); 
    img.setImageResource(resId); 
    } 

public void setImageDrawable(Drawable drawable) { 
    pb.setVisibility(View.GONE); 
    img.setVisibility(View.VISIBLE); 
    img.setImageDrawable(drawable); 
    } 

public void startLoad(String url) 
{ 
    setImageURL(url); 
    loadImage(); 
} 

public void setImageURL(String url) 
{ 
    imageURL = url; 
    fileName = imageURL.substring(imageURL.lastIndexOf("/")+1); 
    isLoaded = checkImaeExists(rootDir.getAbsolutePath()+"/images/"+fileName); 
} 
public void loadImage() 
{ 
    if(! isLoaded) 
    { 
     DownloadFileAsync d = new DownloadFileAsync(); 
     d.execute(imageURL); 
    } 
    else 
    { 
     Drawable d = Drawable.createFromPath(rootDir + "/images/" + fileName); 
     setImageDrawable(d); 
    } 
} 
//this is our download file asynctask 
class DownloadFileAsync extends AsyncTask<String, String, String> { 


    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 
    } 


    @Override 
    protected String doInBackground(String... aurl) { 

     try { 
      //connecting to url 
      URL u = new URL(imageURL); 
      HttpURLConnection c = (HttpURLConnection) u.openConnection(); 
      c.setRequestMethod("GET"); 
      c.setDoOutput(true); 
      c.connect(); 

      //lenghtOfFile is used for calculating download progress 
      int lenghtOfFile = c.getContentLength(); 

      //this is where the file will be seen after the download 
      FileOutputStream f = new FileOutputStream(new File(rootDir + "/images/", fileName)); 
      //file input is from the url 
      InputStream in = c.getInputStream(); 

      //here's the download code 
      byte[] buffer = new byte[1024]; 
      int len1 = 0; 
      long total = 0; 

      while ((len1 = in.read(buffer)) > 0) { 
       total += len1; //total = total + len1 
       publishProgress("" + (int)((total*100)/lenghtOfFile)); 
       f.write(buffer, 0, len1); 
      } 
      f.close(); 

     } catch (Exception e) { 
      Log.d(TAG, e.getMessage()); 
     } 

     return null; 
    } 

    @Override 
    protected void onPostExecute(String unused) 
    { 
     //dismiss the dialog after the file was downloaded 
     isLoaded = true; 
     Drawable d = Drawable.createFromPath(rootDir + "/images/" + fileName); 
     setImageDrawable(d); 
    } 
} 

//function to verify if directory exists 
public void checkAndCreateDirectory(String dirName){ 
    File new_dir = new File(rootDir + dirName); 
    if(!new_dir.exists()){ 
     new_dir.mkdirs(); 
    } 
} 

public boolean checkImaeExists(String filename) 
{ 
    File file = new File(filename); 

    return file.exists(); 

} 
} 

Answer 1

我在github.com上发现了这个伟大的库（nostra13/Android-Universal-Image-Loader（Java）），它非常完美，可以在磁盘和内存以及存储大小上进行缓存。

黄金OLE是：不要重新:)图像的

Answer 2

为1日问题

• 您可以从您使用加载数据库...现在在你的应用程序注册为接收服务广播的意图..和的onReceive接收器的方法，你可以把代码toreload和显示..

，为第二个问题

• 您使用的逻辑似乎是正确的..但我无法得到你的意思是“一些图像在下载时被破坏”..当它们被破坏时发生了什么..？