关于ListView中getView被重复调用的问题

我用ListView显示数据时,自定义了一个适配器(extends ArrayAdapter),然后重写了getView方法,现在出现一个问题,就是这个getView()方法被重复调用了,比如我的_data中有两条数据,但是log.i("show",house.toString());这句却被执行了4次甚至更多,请问各位这是神马情况?
方法代码如下:
这是自定义的适配器:

package com.hb.puppet.utils;
import java.util.List;

import com.hb.puppet.activity.MetaData;
import com.hb.puppet.activity.R;
import com.hb.puppet.entity.House;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

public class CustomCollectAdapter extends ArrayAdapter<House> {
    private static final String CLASSTAG = CustomCollectAdapter.class
            .getSimpleName();
    private ListView _listView;
    private int _resource;
    private List<House> _data;
    private LayoutInflater _inflater;
    private AsyncLoadImageTask _asyncloader;

    public CustomCollectAdapter(Context context, ListView listView,
            List<House> data) {
        
        super(context, 0, data);
        
        _resource = R.layout.list_item_collect;
        _data = data;
        _inflater = (LayoutInflater) context
                .getSystemService(context.LAYOUT_INFLATER_SERVICE);
        _asyncloader = new AsyncLoadImageTask();
        _listView = listView;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View view = convertView;
        CollectListItemViewCache viewCache = null;
        //
        final int index = position;
        //
        final ViewGroup p = parent;

        if (view != null) {
            viewCache = (CollectListItemViewCache) view.getTag();
        } else {
            view = _inflater.inflate(_resource,null);
            viewCache = new CollectListItemViewCache(view);
            view.setTag(viewCache);
        }
        // 房源数据
        House house = _data.get(position);
        System.out.println(house.toString());
        
        if (house != null) {
            //http://www.xxx.com/xxx.jpg
            String imageUrl = MetaData.HOST + house.getTitlePic();
            ImageView imageView = viewCache.getImageView();
            imageView.setTag(imageUrl);
            //异步加载图片
           new AsyncImageLoaderTask().execute(imageUrl,imageView);
            // 房源标题
            TextView houseTitle = viewCache.getHouseTitle();
            houseTitle.setText(house.getTitle());
            // 房源单价
            TextView housePrice = viewCache.getHousePrice();
            housePrice.setText(house.getSinglePrice() + "元/㎡");
            // 房源面积
            TextView houseArea = viewCache.getHouseArea();
            houseArea.setText(house.getArea() + "㎡");
            // 房源户型
            TextView houseUnit = viewCache.getHouseUnit();
            houseUnit.setText(house.getUnits());
            // 单项删除收藏房源
            Button delButton = viewCache.getDelButton();
            delButton.setOnClickListener(new OnClickListener() {
                public void onClick(View v) {
                    System.out.println("clicked");
                }
            });
        }
        return view;
    }
}

异步加载图片:

 

package com.hb.puppet.utils;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.ImageView;

public class AsyncImageLoaderTask extends AsyncTask<Object, Object, Bitmap>{
    private String classTag = AsyncImageLoaderTask.class.getSimpleName();
    private ImageView _view;
    private HashMap<String, SoftReference<Bitmap>> imageCache;
    
    public AsyncImageLoaderTask() {
        imageCache = new HashMap<String, SoftReference<Bitmap>>();
    }
    
    @Override
    protected Bitmap doInBackground(Object... params) {
        Bitmap bitmap = null;
        String url = (String)params[0];
        _view = (ImageView)params[1];
        if(_view == null){
            Log.e(classTag,classTag + " value of _view is not null");
            return null;
        }
        
        if(url != null){
            //if current url is int imageCache,get this drawable by it,then return the drawable
            if(imageCache.containsKey(url)){
                SoftReference<Bitmap> mapSoft = imageCache.get(url);
                bitmap = mapSoft.get();
                if(bitmap != null){
                    return bitmap;
                }
            }
            //
            URL fromUrl = null;
            try {
                fromUrl = new URL(url);
                HttpURLConnection conn = (HttpURLConnection)fromUrl.openConnection();
                conn.setDoInput(true);
                conn.connect();
                InputStream input = conn.getInputStream();
                bitmap = BitmapFactory.decodeStream(input);
                input.close();
            } catch (MalformedURLException e) {
                Log.e(classTag, classTag + " Method doInBackground -- " +e.getMessage());
            } catch (IOException e) {
                Log.e(classTag, classTag + " Method doInBackground -- " +e.getMessage());
            } catch(Exception e){
                Log.e(classTag, classTag + " Method doInBackground -- " +e.getMessage());
            }
            
            imageCache.put(url, new SoftReference<Bitmap>(bitmap));
        }
        
        return bitmap;
    }
    
    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if(bitmap != null){
            System.out.println("onPostExecute");
            this._view.setImageBitmap(bitmap);
            this._view = null;
        }
    }
}

这是什么样的情况了,看了网上的资料以后我知道原来没有设置器listview 的布局方式不是fill-parent,而是wrap-content,会计算父控件的高度所以造成了一种反复调用情况,从而次数不确定。
更深层次的解释为:

View在Draw的时候分成两个阶段:measure和layout,在measure阶段时主要就是为了计算两个参数:height和width。而且要注意的是,这是个递归的过程,从顶向下,DecorView开始依次调用自己子元素的measure。计算完成这两个参数后就开始layout,最后再是draw的调用。

对于ListView,当然每一个Item都会被调用measure方法,而在这个过程中getView和getCount会被调用,而且看用户的需求,可能会有很多次调用。

而为什么会有很多组次调用呢?

问题就在于在layout中的决定ListView或者它的父元素的height和width属性的定义了。fill_parent会好一点,计算方法会比较简单,只要跟父元素的大小相似就行,但是即使是fill_parent,也不能给View当饭吃,还是要计算出来具体的dip,所以measure还是会被调用,只是可能比wrap_content的少一点。至于自适应的它会一直考量它的宽和高,根据内容(也就是它的子Item)计算宽高。可能这个measure过程会反复执行,如果父元素也是wrap_content,这个过程会更加漫长。

所以,解决方法就是尽量避免自适应,除非是万不得已,固定大小或者填充的效果会比较好一些。

posted on 2013-11-16 07:42  laozhu1124  阅读(9865)  评论(0编辑  收藏  举报

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