Android GridView 异步加载图片

网上的资源普遍上是ListView异步加载图片,比较少有GirdView异步加载图片,参考了ListView异步加载图片的做法把GridView的异步加载图片功能做出来,方法和思想大同小异,本文章把GridView异步加载内存卡和网络图片希望对大家有用。效果图如下:

Android GridView 异步加载图片_第1张图片


一、主界面代码:

    import java.util.ArrayList;  
    import java.util.List;  
      
    import android.app.Activity;  
    import android.os.Bundle;  
    import android.widget.GridView;  
      
    public class MainActivity extends Activity {  
        /** Called when the activity is first created. */  
        @Override  
        public void onCreate(Bundle savedInstanceState) {  
            super.onCreate(savedInstanceState);  
            setContentView(R.layout.main);  
            GridView gridView=(GridView)findViewById(R.id.gridview);  
            List<ImageAndText> list = new ArrayList<ImageAndText>();  
            String[] paths=new String[15];  
            for(int i=0;i<15;i++){  
                int index=i;  
                paths[i]="/sdcard/"+String.valueOf(index+1)+".jpg";//自己动手向SD卡添加15张图片,如:1.jpg  
            }  
            for(int i=0;i<15;i++){  
                list.add(new ImageAndText(paths[i], String.valueOf(i)));  
            }  
            gridView.setAdapter(new ImageAndTextListAdapter(this, list, gridView));  
        }  
    }  

二、以下代码是实现异步获取图片的主方法,SoftReference是软引用,是为了更好的为了系统回收变量,重复的URL直接返回已有的资源,实现回调函数,让数据成功后,更新到UI线程。

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.R.drawable;  
import android.graphics.Bitmap;  
import android.graphics.BitmapFactory;  
import android.graphics.BitmapFactory.Options;  
import android.graphics.drawable.BitmapDrawable;  
import android.graphics.drawable.Drawable;  
import android.os.Handler;  
import android.os.Message;  
import android.util.Log;  
import android.widget.ImageView;  
  
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) {  
             if (imageCache.containsKey(imageUrl)) {  
                 SoftReference<Drawable> softReference = imageCache.get(imageUrl);  
                 Drawable drawable = softReference.get();  
                 if (drawable != null) {  
                     return drawable;  
                 }  
             }  
             final Handler handler = new Handler() {  
                 public void handleMessage(Message message) {  
                     imageCallback.imageLoaded((Drawable) message.obj, imageUrl);  
                 }  
             };  
             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) {  
//      /**  
//       * 加载网络图片  
//       */  
//            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");  
          
        /** 
         * 加载内存卡图片 
         */  
            Options options=new Options();  
            options.inSampleSize=2;  
            Bitmap bitmap=BitmapFactory.decodeFile(url, options);  
            Drawable drawable=new BitmapDrawable(bitmap);  
            return drawable;  
        }  
        
    public interface ImageCallback {  
             public void imageLoaded(Drawable imageDrawable, String imageUrl);  
               
         }  
} 

三、ImageAndTextListAdapter是实现ListView的Adapter,里面有个技巧就是 imageView.setTag(imageUrl),setTag是存储数据的,这样是为了保证在回调函数时,listview去更新自己对应 item。

    import java.util.List;  
      
    import cn.wangmeng.test.AsyncImageLoader.ImageCallback;  
      
    import android.app.Activity;  
    import android.graphics.drawable.Drawable;  
    import android.util.Log;  
    import android.view.LayoutInflater;  
    import android.view.View;  
    import android.view.ViewGroup;  
    import android.widget.ArrayAdapter;  
    import android.widget.GridView;  
    import android.widget.ImageView;  
    import android.widget.ListView;  
    import android.widget.TextView;  
      
    public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> {  
      
            private GridView gridView;  
            private AsyncImageLoader asyncImageLoader;  
            public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, GridView gridView1) {  
                super(activity, 0, imageAndTexts);  
                this.gridView = gridView1;  
                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.griditem, null);  
                    viewCache = new ViewCache(rowView);  
                    rowView.setTag(viewCache);  
                } else {  
                    viewCache = (ViewCache) rowView.getTag();  
                }  
                ImageAndText imageAndText = getItem(position);  
      
                // Load the image and set it on the ImageView  
                String imageUrl = imageAndText.getImageUrl();  
                ImageView imageView = viewCache.getImageView();  
                imageView.setTag(imageUrl);  
                Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {  
                    public void imageLoaded(Drawable imageDrawable, String imageUrl) {  
                        ImageView imageViewByTag = (ImageView) gridView.findViewWithTag(imageUrl);  
                        if (imageViewByTag != null) {  
                            imageViewByTag.setImageDrawable(imageDrawable);  
                        }  
                    }  
                });  
                if (cachedImage == null) {  
                    imageView.setImageResource(R.drawable.icon);  
                }else{  
                    imageView.setImageDrawable(cachedImage);  
                }  
                // Set the text on the TextView  
                TextView textView = viewCache.getTextView();  
                textView.setText(imageAndText.getText());  
                return rowView;  
            }  
      
    }  

四、2个辅助类

public class ImageAndText {  
        private String imageUrl;  
        private String text;  
  
        public ImageAndText(String imageUrl, String text) {  
            this.imageUrl = imageUrl;  
            this.text = text;  
        }  
        public String getImageUrl() {  
            return imageUrl;  
        }  
        public String getText() {  
            return text;  
        }  
}

public class ViewCache {  
  
        private View baseView;  
        private TextView textView;  
        private ImageView imageView;  
  
        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 (imageView == null) {  
                imageView = (ImageView) baseView.findViewById(R.id.image);  
            }  
            return imageView;  
        }  
  
} 

五、Xml配置文件,包括griditem和main:

1、griditem:

<?xml version="1.0" encoding="UTF-8"?>      
<RelativeLayout      
         xmlns:android="http://schemas.android.com/apk/res/android"    
         android:layout_height="100dip"      
         android:paddingBottom="4dip" android:layout_width="fill_parent">  
         <ImageView   
               android:id="@+id/image"  
               android:layout_height="80dip"  
               android:layout_width="80dip"  
               android:layout_centerHorizontal="true"  
               android:scaleType="centerCrop">  
         </ImageView>  
         <TextView  
               android:id="@+id/text"     
               android:layout_width="wrap_content"  
               android:layout_height="wrap_content"  
               android:layout_below="@+id/image"  
               android:layout_centerHorizontal="true"  
               >  
         </TextView>  
</RelativeLayout>

2、main

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:orientation="vertical" android:layout_width="fill_parent"  
    android:layout_height="fill_parent">  
      
    <GridView xmlns:android="http://schemas.android.com/apk/res/android"      
    android:id="@+id/gridview"     
    android:layout_width="fill_parent"      
    android:layout_height="fill_parent"     
    android:numColumns="4"     
    android:verticalSpacing="10dp"     
    android:horizontalSpacing="10dp"     
    android:columnWidth="80dp"  
    android:stretchMode="columnWidth"     
    android:gravity="center"   
    android:background="#ffffff"   
/>   
</LinearLayout> 

文件出处: http://blog.csdn.net/lanpy88/article/details/6671915



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