當圖像顯示時ListView滾動滯後？

Question

我的列表視圖在滾動時滯後。這看起來像是延遲加載，但每次顯示圖像時都會發生延遲。

我使用的是在這裏找到http://www.androidhive.info/2012/02/android-custom-listview-with-image-and-text/的ImageLoader的，這是我的適配器：

public class EventAdapter extends ArrayAdapter<Event>{ 
    public ListImageLoader imageLoader; 
    public DisplayImageOptions imgDispOpts; 
    private ArrayList<Event> objects; 

    public EventAdapter(Context context, int textViewResourceId, ArrayList<Event> objects,ListImageLoader imageLoader) { 
     super(context, textViewResourceId, objects); 
     this.objects = objects; 
     this.imageLoader = imageLoader; 
    } 
    /* 
    * we are overriding the getView method here - this is what defines how each 
    * list item will look. 
    */ 
     @SuppressLint("DefaultLocale") 
     @Override 
     public View getView(int position, View convertView, ViewGroup parent){ 
      Event event = objects.get(position); 
      // assign the view we are converting to a local variable 
      View v = convertView; 
      ViewHolder holder; 

      // first check to see if the view is null. if so, we have to inflate it. 
      // to inflate it basically means to render, or show, the view. 
      if (v == null) { 
       LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
       v = inflater.inflate(R.layout.list_row, null); 
       System.out.println("new Viewholder"); 
       holder = new ViewHolder(); 
       holder.listTimeString = (TextView) v.findViewById(R.id.listTimeString); 
       holder.date =(TextView) v.findViewById(R.id.Date); 
       holder.title = (TextView) v.findViewById(R.id.title); 
       holder.shortInfo = (TextView) v.findViewById(R.id.shortinfo); 
       holder.ageIcon = (ImageView) v.findViewById(R.id.listAgeIcon); 
       holder.thumb = (ImageView) v.findViewById(R.id.wideListImage); 
       holder.header = (RelativeLayout) v.findViewById(R.id.headerLayout); 
       holder.rowLayout = (RelativeLayout) v.findViewById(R.id.rowlayout); 
       holder.listVenueIcon = (ImageView) v.findViewById(R.id.listVenueIcon); 
       holder.eventRowLayout = (RelativeLayout) v.findViewById(R.id.eventrowlayout); 
       v.setTag(holder); 
      } 
      else{ 
       holder = (ViewHolder) v.getTag(); 
      } 
      /* 
      * Recall that the variable position is sent in as an argument to this method. 
      * The variable simply refers to the position of the current object in the list. (The ArrayAdapter 
      * iterates through the list we sent it) 
      * 
      * Therefore, i refers to the current Item object. 
      */ 

      if (event != null) { 

       // This is how you obtain a reference to the TextViews. 
       // These TextViews are created in the XML files we defined. 

       //SET FONTS 
       Typeface tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/myriad.otf"); 
       holder.title.setTypeface(tf); 
       holder.shortInfo.setTypeface(tf); 
       Typeface tf2 = Typeface.createFromAsset(getContext().getAssets(),"fonts/agencyr.ttf"); 
       holder.date.setTypeface(tf2); 
       // check to see if each individual textview is null 
       // if not, assign some text! 
       if(event.isBig()){ 
        //holder.rowLayout.getLayoutParams().height=230; 
        holder.shortInfo.setHeight(80); 
        holder.shortInfo.setMaxLines(5); 
        holder.shortInfo.setText(event.getInfo()); 
       } 
       else{ 
        //holder.rowLayout.getLayoutParams().height=125; 
        //holder.listVenueIcon.setImageResource(R.drawable.ikon_bar); 
        holder.shortInfo.setHeight(16); 
        holder.shortInfo.setMaxLines(1); 
        holder.shortInfo.setText(event.getInfo()); 
       } 
       if(event.isClub()){ 
        holder.listVenueIcon.setImageResource(R.drawable.ikon_klubb); 
       } 
       else{ 
        holder.listVenueIcon.setImageResource(R.drawable.ikon_bar); 

       } 
       if (event.isNewDay()){ 
        holder.date.setText(event.getDay().toUpperCase()); 
        holder.header.setVisibility(View.VISIBLE); 
       } else{ 
        holder.header.setVisibility(View.GONE); 
       } 
       if (holder.title != null){ 
        holder.title.setText(event.getHost().toUpperCase()); 
       } 
       if(holder.ageIcon!= null){ 
        switch(Integer.parseInt(event.getAge())){ 
        case(19): 
         holder.ageIcon.setImageResource(R.drawable.event_info_19); 
         break; 

        ... 
        more cases 
        ... 

        case(30): 
         holder.ageIcon.setImageResource(R.drawable.event_info_30); 
         break; 
        default: 
         holder.ageIcon.setImageResource(R.drawable.event_info_18); 
         break; 
        } 
       } 
       if(holder.thumb != null){ 
        imageLoader.DisplayImage(event.getThumbURL(), holder.thumb); 
       } 
       if(holder.listTimeString != null){ 
        String tempTimeString = event.getStartTime() + " - " + event.getEndTime(); 
        holder.listTimeString.setText(tempTimeString); 
       } 
      } 

      // the view must be returned to our activity 
      return v; 

     } 
     static class ViewHolder{ 
      RelativeLayout eventRowLayout; 
      TextView listTimeString; 
      TextView date; 
      TextView title; 
      TextView shortInfo; 
      ImageView ageIcon; 
      ImageView thumb; 
      RelativeLayout header; 
      RelativeLayout rowLayout; 
      ImageView listVenueIcon; 
     } 
} 

任何想法？

編輯：我在onCreate異步加載imageURL，這將是一個完美的地方來緩存圖像，你可以看到如何在鏈接中使用ImageLoader做到這一點？

Answer 1

我解決它通過創建和ImageLoader.java

public void cacheImage(String url){ 
    Bitmap bmp = getBitmap(url); 
    memoryCache.put(url, bmp); 
} 

使用下面的函數 緩存在背景圖像I創建ImageLoader的的一個實例中，由靜態引用它，然後調用

AsyncClass.imageLoader.cacheImage（url）;

其中AsyncClass是我對ImageLoader進行靜態引用並將其稱爲「imageLoader」的類。

Answer 2

是的，通過使用內存緩存來解決滯後現象。您可以從here中閱讀原始文章。

我已經實現了我的EntryArrayAdapter，它使用內存緩存來防止滾動列表視圖時的緩慢和滯後。

public class EntryArrayAdapter extends ArrayAdapter<JSONObject> { 
private final Context context; 
private final ArrayList<JSONObject> values; 
private final LruCache<String, Bitmap> cache; 

static class ViewHolder { 
     public TextView title; 
     public TextView city; 
     public TextView outlet; 
     public TextView service; 
     public ImageView photo; 
} 

public EntryArrayAdapter(Context context, ArrayList<JSONObject> values) { 
    super(context, R.layout.layout_list_item); 
    this.context = context; 
    this.values = values; 

    final int maxMemory = (int) (Runtime.getRuntime().maxMemory()/1024); 

     // Use 1/8th of the available memory for this memory cache. 
     final int cacheSize = maxMemory/8; 

     cache = new LruCache<String, Bitmap>(cacheSize) { 
      @Override 
      protected int sizeOf(String key, Bitmap bitmap) { 
       // The cache size will be measured in kilobytes rather than 
       // number of items. 
       return bitmap.getRowBytes()/1024; 
      } 
     }; 
} 

/* (non-Javadoc) 
* @see android.widget.ArrayAdapter#getCount() 
*/ 
@Override 
public int getCount() {  
    return values != null ? values.size() : 0; 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    View rowView = convertView; 
    ViewHolder holder; 

    if (rowView == null) { 
     LayoutInflater inflater = (LayoutInflater) context 
      .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 

     rowView = inflater.inflate(R.layout.layout_list_item, parent, false); 
     // set references 
     holder = new ViewHolder(); 

     holder.title = (TextView) rowView.findViewById(R.id.titleText); 
     holder.city = (TextView) rowView.findViewById(R.id.cityText); 
     holder.outlet = (TextView) rowView.findViewById(R.id.outletText); 
     holder.service = (TextView) rowView.findViewById(R.id.visaMasterText);  
     holder.photo = (ImageView) rowView.findViewById(R.id.itemImage); 
     rowView.setTag(holder); 
    } 
    else { 
     holder = (ViewHolder) rowView.getTag(); 
    } 

    try { 
     JSONObject obj = values.get(position); 

     Bitmap bmp = getBitmapFromMemCache(obj.getString("id")); 
     if (bmp == null) { 
      bmp = BitmapHelper.decodeSampledBitmapFromResource(obj.getString("photo"), 96, 96);   
      addBitmapToMemoryCache(obj.getString("id"), bmp); 
     } 

     holder.title.setText(obj.getString("title")); 
     holder.city.setText(obj.getString("city")); 
     holder.outlet.setText(obj.getString("outlet")); 
     holder.service.setText(obj.getString("service"));   
     holder.photo.setImageBitmap(bmp); 


    } catch (JSONException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 

    return rowView; 
} 

public void addBitmapToMemoryCache(String key, Bitmap bitmap) { 
    if (getBitmapFromMemCache(key) == null) { 
     cache.put(key, bitmap); 
    } 
} 

public Bitmap getBitmapFromMemCache(String key) { 
    return cache.get(key); 
} 

Answer 3

我建議您使用Android-Universal-Image-Loader進行異步映像加載，緩存和顯示。