ListView Adapter优化

//方案一 - adapter优化
public class listviewAdapterDemo1 extends BaseAdapter {

    private String[] mArrData;
    private ListView listView;
    private AsyncImageLoader asyncImageLoader;
    private final LayoutInflater inflater;

    public listviewAdapterDemo1(String[] mArrData, Context mContext, ListView listView) {
        this.mArrData = mArrData;
        this.listView = listView;
        asyncImageLoader = new AsyncImageLoader();
        inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public int getCount() {
        return this.mArrData.length;
    }

    @Override
    public Object getItem(int arg0) {
        return mArrData[arg0];
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    /***
     * 1.控件对象内存为一个
     * 2.view对象只会创建可视对象次数（有的是8次）根据屏幕可视listview的数量而定，在加载超过可视postion数据时不会重新创建
     *   但是需要每次重新加载数据
     *   
     *   从节省内存的角度出发，这种更合理，毕竟加载数据不需要占用内存
     */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ViewHolder viewholder;
        Log.d("dd", "Position:" + position+"------");
        if (convertView == null) {
            Log.d("dd", "Position:" + position);
            convertView = inflater.inflate(R.layout.list_item_icon_text, null);
            viewholder = new ViewHolder();
            viewholder.icon = (ImageView) convertView.findViewById(R.id.icon);
            viewholder.text = (TextView) convertView.findViewById(R.id.text);
    
            convertView.setTag(viewholder);
        } else {
            viewholder = (ViewHolder) convertView.getTag();
        }
        
        viewholder.text.setText(mArrData[position]);
        // Load the image and set it on the ImageView
        String imageUrl = "";
        viewholder.icon.setTag(imageUrl);
        Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {

            public void imageLoaded(Drawable imageDrawable, String imageUrl) {
                ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl);
                if (imageViewByTag != null) {
                    imageViewByTag.setImageDrawable(imageDrawable);
                }
            }
        });
        if (cachedImage != null)//说明是从缓存池中得到
            viewholder.icon.setImageDrawable(cachedImage);

        return convertView;
    }

    static class ViewHolder {
        ImageView icon;
        TextView text;
    }
}

在listview中的getview方法中也可以这样用这个方法：
public Drawable getDrawable(AsyncImageLoader asyncImageLoader, String imageUrl, final ImageView imageView) {         
　　Drawable drawable = asyncImageLoader.loadDrawable(imageUrl,new ImageCallback() {                     
　　　　@Override public void imageLoaded(Drawable imageDrawable,String imageUrl) {                        
　　　　　　if (imageDrawable != null)                             
　　　　　　　　imageView.setImageDrawable(imageDrawable);                        
　　　　　　else                             
　　　　　　　　imageView.setImageResource(R.drawable.u6_normal);                     
　　　　}                 
　　});         
return drawable;     
} 

 

//方案二---adapter的优化
public class listviewAdapterDemo2 extends BaseAdapter {

    private String[] mArrData;
    private ListView listView;
    private AsyncImageLoader asyncImageLoader;
    private final LayoutInflater inflater;
    private Map<Integer, View> viewMap = new HashMap<Integer, View>();

    public listviewAdapterDemo2(String[] mArrData, Context mContext, ListView listView) {
        this.mArrData = mArrData;
        this.listView = listView;
        asyncImageLoader = new AsyncImageLoader();
        inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public int getCount() {
        return this.mArrData.length;
    }

    @Override
    public Object getItem(int arg0) {
        return mArrData[arg0];
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    /**
     * 1.控件对象内存为一个
     * 2.每一个postion对应一个view，且不管前进后退，每个postion数据只加载一次
　　　* 但是从节省内容的角度出发，方案一更节省内存
     */
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ViewHolder viewholder;
        Log.d("dd", "Position:" + position+"------");
        convertView = this.viewMap.get(position);
        if (convertView == null) {
            Log.d("dd", "Position:" + position);
            convertView = inflater.inflate(R.layout.list_item_icon_text, null);
            viewholder = new ViewHolder();
            viewholder.icon = (ImageView) convertView.findViewById(R.id.icon);
            viewholder.text = (TextView) convertView.findViewById(R.id.text);
    
            viewholder.text.setText(mArrData[position]);
            // Load the image and set it on the ImageView
            String imageUrl = "";
            viewholder.icon.setTag(imageUrl);
            Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {

                public void imageLoaded(Drawable imageDrawable, String imageUrl) {
                    ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl);
                    if (imageViewByTag != null) {
                        imageViewByTag.setImageDrawable(imageDrawable);
                    }
                }
            });
            if (cachedImage != null)//说明是从缓存池中得到
                viewholder.icon.setImageDrawable(cachedImage);

            
            convertView.setTag(viewholder);
            viewMap.put(position, convertView);
        } else {
            viewholder = (ViewHolder) convertView.getTag();
        }
        return convertView;
    }

    static class ViewHolder {
        ImageView icon;
        TextView text;
    }
}

/**图片下载-adpater优化*/
public class AsyncImageLoader {

    private HashMap<String, SoftReference<Drawable>> imageCache;  
       
    public AsyncImageLoader() {  
        imageCache = new HashMap<String, SoftReference<Drawable>>();  
    }  
   
    public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {  
        //从缓存中检测是否存在
        if (imageCache.containsKey(imageUrl)) {  
            SoftReference<Drawable> softReference = imageCache.get(imageUrl);  
            Drawable drawable = softReference.get();  
            if (drawable != null) {  
                return drawable;  
            }  
        }  
        final Handler handler = new Handler() {  
            @Override  
            public void handleMessage(Message message) {  
                imageCallback.imageLoaded((Drawable) message.obj, imageUrl);  
            }  
        };  
        //缓存中没有则从服务器下载
        new Thread() {  
            @Override  
            public void run() {  
                Drawable drawable = loadImageFromUrl(imageUrl);  
                imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));  
                Message message = handler.obtainMessage(0, drawable);  
                handler.sendMessage(message);  
            }  
        }.start();  
        
        return null;  
    }  
   
    public static Drawable loadImageFromUrl(String url) {  
        Drawable drawable = null;
        //根据url从服务器下载图片
        return drawable;
    }  
   
    public interface ImageCallback {  
        public void imageLoaded(Drawable imageDrawable, String imageUrl);  
    }  
}  

 

//activity---adapter
public class ListviewDemoActivity extends Activity {

    private listviewAdapterDemo1 mAdapter;
    private ListView listview;
    private String[] mArrData;

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

        mArrData = new String[1000];
        for (int i = 0; i < 1000; i++) {
            mArrData[i] = "Google IO Adapter" + i;
        }
        
        listview = (ListView)findViewById(R.id.lv);
        mAdapter = new listviewAdapterDemo1(mArrData,this,listview);
        listview.setAdapter(mAdapter);
    }
}

在main.xml中插入

<ListView
        android:id="@+id/lv"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1" />