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：



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：/article/2930510.html