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android 異步加載圖片縮略圖
https://www.cnblogs.com/oldfeel/archive/2012/05/24/2515972.html
建一個AsyncLoadedImage類繼承AsyncTask異步加載類，調用publishProgress方法更新onProgressUpdate貯存縮略圖信息到Adapter。監聽Adapter Change實現異步加載縮略圖。
main.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:andro
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<GridView
android:
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center"
android:horizontalSpacing="10dp"
android:numColumns="auto_fit"
android:stretchMode="columnWidth"
android:verticalSpacing="10dp" />
</FrameLayout>
MFile.java
public class MFile 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();
}
/*
* 釋放Bitmap內存
*/
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);
}
}
/*
* 初始化文件瀏覽View
*/
private void setupViews() {
sdcardImages = (GridView) findViewById(R.id.sdcard);
sdcardImages.setOnItemClickListener(new fileListener());
fileAdapter = new FileAdapter(getApplicationContext());
sdcardImages.setAdapter(fileAdapter);
}
/*
* 刷新Adapter
*/
private void addImage(LoadedImage... value) {
for (LoadedImage image : value) {
fileAdapter.addPhoto(image);
fileAdapter.notifyDataSetChanged();
}
}
/*
* 點擊監聽
*/
class fileListener implements OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> paramAdapterView,
View paramView, int paramInt, long paramLong) {
}
}
/*
* 異步加載縮略圖到LoadedImage然後調用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";
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, 80,
);
bitmap.recycle();
if (newBitmap != null) {
publishProgress(new LoadedImage(newBitmap));
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
return null;
}
@Override
public void onProgressUpdate(LoadedImage... value) {
addImage(value);
}
@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(8, 8, 8, 8);
imageView.setImageBitmap(photos.get(position).getBitmap());
return imageView;
}
}
/*
* 這是個保存bitmap的類，加入Adapter的ArrayList中，隨著addImage更新Adapter
*/
private static class LoadedImage {
Bitmap mBitmap;
LoadedImage(Bitmap bitmap) {
mBitmap = bitmap;
}
public Bitmap getBitmap() {
return mBitmap;
}
}
/*
* 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();
}
}
最後更新：2017-04-02 17:09:25