針對(duì)listview異步加載圖片這個(gè)問(wèn)題，麥子學(xué)院android開(kāi)發(fā)老師講了一種非常實(shí)用的方法，麥子學(xué)院android開(kāi)發(fā)老師說(shuō)凡是是要通過(guò)網(wǎng)絡(luò)獲取圖片資源一般使用這種方法比較好，用戶體驗(yàn)好，下面就說(shuō)實(shí)現(xiàn)方法，先貼上主方法的代碼：

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package cn.wangmeng.test;

import java.io.IOException;

import java.io.InputStream;

import java.lang.ref.SoftReference;

import java.net.MalformedURLException;

import java.net.URL;

import java.util.HashMap;

import android.graphics.drawable.Drawable;

import android.os.Handler;

import android.os.Message;

public class AsyncImageLoader {

private HashMap<String, SoftReference<Drawable>> p_w_picpathCache;

  public AsyncImageLoader() {

   p_w_picpathCache = new HashMap<String, SoftReference<Drawable>>();

  }

  public Drawable loadDrawable(final String p_w_picpathUrl, final ImageCallback p_w_picpathCallback) {

    if (p_w_picpathCache.containsKey(p_w_picpathUrl)) {

      SoftReference<Drawable> softReference = p_w_picpathCache.get(p_w_picpathUrl);

      Drawable drawable = softReference.get();

      if (drawable != null) {

        return drawable;

      }

    }

    final Handler handler = new Handler() {

      public void handleMessage(Message message) {

        p_w_picpathCallback.p_w_picpathLoaded((Drawable) message.obj, p_w_picpathUrl);

      }

    };

    new Thread() {

      @Override

      public void run() {

        Drawable drawable = loadImageFromUrl(p_w_picpathUrl);

        p_w_picpathCache.put(p_w_picpathUrl, new SoftReference<Drawable>(drawable));

        Message message = handler.obtainMessage(0, drawable);

        handler.sendMessage(message);

      }

    }.start();

    return null;

  }

public static Drawable loadImageFromUrl(String url) {

URL m;

InputStream i = null;

try {

m = new URL(url);

i = (InputStream) m.getContent();

} catch (MalformedURLException e1) {

e1.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

Drawable d = Drawable.createFromStream(i, "src");

return d;

}

  public interface ImageCallback {

    public void p_w_picpathLoaded(Drawable p_w_picpathDrawable, String p_w_picpathUrl);

  }

}

以上代碼是實(shí)現(xiàn)異步獲取圖片的主方法，SoftReference是軟引用，是為了更好的為了系統(tǒng)回收變量，重復(fù)的URL直接返回已有的資源，實(shí)現(xiàn)回調(diào)函數(shù)，讓數(shù)據(jù)成功后，更新到UI線程。

幾個(gè)輔助類(lèi)文件：

package cn.wangmeng.test;

public class ImageAndText {

  private String p_w_picpathUrl;

  private String text;

  public ImageAndText(String p_w_picpathUrl, String text) {

    this.p_w_picpathUrl = p_w_picpathUrl;

    this.text = text;

  }

  public String getImageUrl() {

    return p_w_picpathUrl;

  }

  public String getText() {

    return text;

  }

}

package cn.wangmeng.test;

import android.view.View;

import android.widget.ImageView;

import android.widget.TextView;

public class ViewCache {

  private View baseView;

  private TextView textView;

  private ImageView p_w_picpathView;

  public ViewCache(View baseView) {

    this.baseView = baseView;

  }

  public TextView getTextView() {

    if (textView == null) {

      textView = (TextView) baseView.findViewById(R.id.text);

    }

    return textView;

  }

  public ImageView getImageView() {

    if (p_w_picpathView == null) {

      p_w_picpathView = (ImageView) baseView.findViewById(R.id.p_w_picpath);

    }

    return p_w_picpathView;

  }

}

ViewCache是輔助獲取adapter的子元素布局

package cn.wangmeng.test;

import java.util.List;

import cn.wangmeng.test.AsyncImageLoader.ImageCallback;

import android.app.Activity;

import android.graphics.drawable.Drawable;

import android.view.LayoutInflater;

import android.view.View;

import android.view.ViewGroup;

import android.widget.ArrayAdapter;

import android.widget.ImageView;

import android.widget.ListView;

import android.widget.TextView;

public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> {

  private ListView listView;

  private AsyncImageLoader asyncImageLoader;

  public ImageAndTextListAdapter(Activity activity, List<ImageAndText> p_w_picpathAndTexts, ListView listView) {

    super(activity, 0, p_w_picpathAndTexts);

    this.listView = listView;

    asyncImageLoader = new AsyncImageLoader();

  }

  public View getView(int position, View convertView, ViewGroup parent) {

    Activity activity = (Activity) getContext();

    // Inflate the views from XML

    View rowView = convertView;

    ViewCache viewCache;

    if (rowView == null) {

      LayoutInflater inflater = activity.getLayoutInflater();

      rowView = inflater.inflate(R.layout.p_w_picpath_and_text_row, null);

      viewCache = new ViewCache(rowView);

      rowView.setTag(viewCache);

    } else {

      viewCache = (ViewCache) rowView.getTag();

    }

    ImageAndText p_w_picpathAndText = getItem(position);

    // Load the p_w_picpath and set it on the ImageView

    String p_w_picpathUrl = p_w_picpathAndText.getImageUrl();

    ImageView p_w_picpathView = viewCache.getImageView();

    p_w_picpathView.setTag(p_w_picpathUrl);

    Drawable cachedImage = asyncImageLoader.loadDrawable(p_w_picpathUrl, new ImageCallback() {

      public void p_w_picpathLoaded(Drawable p_w_picpathDrawable, String p_w_picpathUrl) {

        ImageView p_w_picpathViewByTag = (ImageView) listView.findViewWithTag(p_w_picpathUrl);

        if (p_w_picpathViewByTag != null) {

          p_w_picpathViewByTag.setImageDrawable(p_w_picpathDrawable);

        }

      }

    });

if (cachedImage == null) {

p_w_picpathView.setImageResource(R.drawable.default_p_w_picpath);

}else{

p_w_picpathView.setImageDrawable(cachedImage);

}

    // Set the text on the TextView

    TextView textView = viewCache.getTextView();

    textView.setText(p_w_picpathAndText.getText());

    return rowView;

  }

}

ImageAndTextListAdapter是實(shí)現(xiàn)ListView的Adapter，里面有個(gè)技巧就是p_w_picpathView.setTag(p_w_picpathUrl)，setTag是存儲(chǔ)數(shù)據(jù)的，這樣是為了保證在回調(diào)函數(shù)時(shí)，listview去更新自己對(duì)應(yīng)item,大家仔細(xì)閱讀就知道了。

最后貼出布局文件：

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

       android:orientation="horizontal"

       android:layout_width="fill_parent"

       android:layout_height="wrap_content">

    <ImageView android:id="@+id/p_w_picpath"

          android:layout_width="wrap_content"

          android:layout_height="wrap_content"

          />

    <TextView android:id="@+id/text"

         android:layout_width="wrap_content"

         android:layout_height="wrap_content"/>

</LinearLayout>

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標(biāo)題名稱：android實(shí)用技巧：android實(shí)現(xiàn)listview異步加載圖片-創(chuàng)新互聯(lián)
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