GridView异步加载本地图片缩略图

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="vertical" >

<GridView
android:id="@+id/sdcard"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center"

android:numColumns="4"
android:stretchMode="columnWidth"
android:verticalSpacing="1dp"
android:horizontalSpacing="1dp" />

</FrameLayout>

package com.pic.demo;

import java.io.File;
import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.media.ThumbnailUtils;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;

public class AsyncLoadedImageActivity extends Activity {
private GridView sdcardImages;
private FileAdapter fileAdapter;

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

setupViews();
setProgressBarIndeterminateVisibility(true);
new AsyncLoadedImage().execute();
}

/*
* 初始化文件浏览View
*/
private void setupViews() {
sdcardImages = (GridView) findViewById(R.id.sdcard);
sdcardImages.setOnItemClickListener(new fileListener());
fileAdapter = new FileAdapter(getApplicationContext());
sdcardImages.setAdapter(fileAdapter);
}

/*
* 释放Bitmap内存
*/
protected void onDestroy() {
super.onDestroy();
final GridView grid = sdcardImages;
final int count = grid.getChildCount();
ImageView v = null;
for (int i = 0; i < count; i++) {
v = (ImageView) grid.getChildAt(i);
((BitmapDrawable) v.getDrawable()).setCallback(null);
}
}

/*
* 刷新Adapter
*/
private void addImage(LoadedImage... value) {
for (LoadedImage image : value) {
fileAdapter.addPhoto(image);
fileAdapter.notifyDataSetChanged();
}
}

/*
* 点击监听
*/
class fileListener implements OnItemClickListener {
public void onItemClick(AdapterView<?> paramAdapterView,
View paramView, int paramInt, long paramLong) {
LoadedImage loadedImage = (LoadedImage) sdcardImages.getItemAtPosition(paramInt);

showMsg(""+loadedImage.getPicPath());

Intent intentPicView = new Intent(getBaseContext(),
PictureView.class);
intentPicView.putExtra("picPath", loadedImage.getPicPath());
startActivity(intentPicView);

}
}

/*
* 异步加载缩略图到LoadedImage然后调用addImage方法更新Adapter
*/
class AsyncLoadedImage extends AsyncTask<Object, LoadedImage, Object> {
@Override
protected Object doInBackground(Object... params) {
String path = Environment.getExternalStorageDirectory()
.getAbsolutePath() + "/hfdatabase/3/img";

path = Environment.getExternalStorageDirectory().getPath() + "/"
+ "picture";
// path=Environment.getExternalStorageDirectory().getPath() +
// "/"+"image" ;
path = Environment.getExternalStorageDirectory().getPath();
File file = new File(path);
if (!file.exists()) {
file.mkdirs();
} else {
File[] files = file.listFiles();
String[] paths = new String[files.length];
Bitmap bitmap;
Bitmap newBitmap;
for (int i = 0; i < files.length; i++) {
paths[i] = files[i].getPath();
try {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inSampleSize = 10;
bitmap = BitmapFactory.decodeFile(paths[i], options);
newBitmap = ThumbnailUtils.extractThumbnail(bitmap,
120, 120);
bitmap.recycle();
if (newBitmap != null) {
publishProgress(new LoadedImage(newBitmap,paths[i] ));
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
return null;
}

//实时更新UI  onProgressUpdate()方法的参数对应于doInBackground中publishProgress方法的参数，同时也对应于
//doInBackground的第二个参数
@Override
public void onProgressUpdate(LoadedImage... value) {
addImage(value);
}

//更新UI结束后的处理
@Override
protected void onPostExecute(Object result) {
setProgressBarIndeterminateVisibility(false);
}
}

/*
* Adapter
*/
class FileAdapter extends BaseAdapter {

private Context mContext;
private ArrayList<LoadedImage> photos = new ArrayList<LoadedImage>();

public FileAdapter(Context context) {
mContext = context;
}

public void addPhoto(LoadedImage photo) {
photos.add(photo);
}

public int getCount() {
return photos.size();
}

public Object getItem(int position) {
return photos.get(position);
}

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

public View getView(int position, View convertView, ViewGroup parent) {
final ImageView imageView;
if (convertView == null) {
imageView = new ImageView(mContext);
} else {
imageView = (ImageView) convertView;
}
imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
imageView.setPadding(0, 1, 1, 1);
imageView.setImageBitmap(photos.get(position).getBitmap());
return imageView;
}
}

/*
* 这是个保存bitmap的类，加入Adapter的ArrayList中，随着addImage更新Adapter
*/
private static class LoadedImage {
String picPath;
Bitmap mBitmap;

LoadedImage(Bitmap bitmap,String picPath ) {
this.mBitmap = bitmap;
this.picPath=picPath;
}

public Bitmap getBitmap() {
return mBitmap;
}

public String getPicPath() {
return picPath;
}

}

/*
* 消息提示
*/
private Toast toast;

public void showMsg(String arg) {
if (toast == null) {
toast = Toast.makeText(this, arg, Toast.LENGTH_SHORT);
} else {
toast.cancel();
toast.setText(arg);
}
toast.show();
}
}