Android的動態圖像加載

Question

我工作的這是使用JSON採取從互聯網上內容的Android應用程序，我使用的服務加載JSON在本地數據庫中，我有兩個主要的疑慮：

1 - 如何分辨數據庫加載新數據以重新加載顯示的應用程序。

2-我有存儲在數據庫中的圖像URL，需要按需顯示，以顯示我已經用progressBar和Image視圖擴展了默認的FrameLayout，如果圖像是新的Frame Layout將顯示progressBar尚未加載，如果圖像被加載，它將被顯示，此外，新的FreamLayout有一個擴展AsyncTask的類，它通過URL檢查圖像是否存在於文件系統上，如果它不存在，則發生圖像下載。下面是我所做的課程的樣本。這是做這件事的正確方法嗎？在這種情況下，我有一些圖像在下載時被破壞，如何解決這個問題？

感謝您的協助。

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上發現了這個偉大的庫（nostra13/Android-Universal-Image-Loader（Java）），它非常完美，可以在磁盤和內存以及存儲大小上進行緩存。

黃金OLE是：不要重新:)圖像的

Answer 2

爲1日問題

• 您可以從您使用加載數據庫...現在在你的應用程序註冊爲接收服務廣播的意圖..和的onReceive接收器的方法，你可以把代碼toreload和顯示..

，爲第二個問題

• 您使用的邏輯似乎是正確的..但我無法得到你的意思是「一些圖像在下載時被破壞」..當它們被破壞時發生了什麼..？