Thứ Hai, 30 tháng 7, 2012

Apply LruCache on GridView

0
04:10
The example "Caching Bitmaps with LruCache" provide a example to Apply LruCache on Gallery. This exercise is GridView version using LruCache.

Reference: http://developer.android.com/training/displaying-bitmaps/cache-bitmap.html#memory-cache

GridView with LruCache


To using android.util.LruCache in the code, targetSdkVersion of "13" is needed to be specified in AndroidManifest.xml.

The layout file, refer to the post "GridView loading photos from SD Card".

package com.example.androidgridview;

import java.io.File;
import java.lang.ref.WeakReference;
import java.util.ArrayList;

import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.app.ActivityManager;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.LruCache;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {

public class ImageAdapter extends BaseAdapter {

private Context mContext;
ArrayList<String> itemList = new ArrayList<String>();

public ImageAdapter(Context c) {
mContext = c;
}

void add(String path){
itemList.add(path);
}

@Override
public int getCount() {
return itemList.size();
}

@Override
public Object getItem(int arg0) {
// TODO Auto-generated method stub
return null;
}

@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return 0;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
if (convertView == null) { // if it's not recycled, initialize some attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(220, 220));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
} else {
imageView = (ImageView) convertView;
}

//Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220, 220);

// Use the path as the key to LruCache
final String imageKey = itemList.get(position);
final Bitmap bm = getBitmapFromMemCache(imageKey);

if (bm == null){
BitmapWorkerTask task = new BitmapWorkerTask(imageView);
task.execute(imageKey);
};

imageView.setImageBitmap(bm);
return imageView;
}

public Bitmap decodeSampledBitmapFromUri(String path, int reqWidth, int reqHeight) {

Bitmap bm = null;
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options);

// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
bm = BitmapFactory.decodeFile(path, options);

return bm;
}

public int calculateInSampleSize(

BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;

if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float)height / (float)reqHeight);
} else {
inSampleSize = Math.round((float)width / (float)reqWidth);
}
}

return inSampleSize;
}

class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap>{

private final WeakReference<ImageView> imageViewReference;

public BitmapWorkerTask(ImageView imageView) {
// Use a WeakReference to ensure the ImageView can be garbage collected
imageViewReference = new WeakReference<ImageView>(imageView);
}

@Override
protected Bitmap doInBackground(String... params) {
final Bitmap bitmap = decodeSampledBitmapFromUri(params[0], 200, 200);
addBitmapToMemoryCache(String.valueOf(params[0]), bitmap);
return bitmap;
}

@Override
protected void onPostExecute(Bitmap bitmap) {
if (imageViewReference != null && bitmap != null) {
final ImageView imageView = (ImageView)imageViewReference.get();
if (imageView != null) {
imageView.setImageBitmap(bitmap);
}
}
}
}

}

ImageAdapter myImageAdapter;

private LruCache<String, Bitmap> mMemoryCache;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

GridView gridview = (GridView) findViewById(R.id.gridview);
myImageAdapter = new ImageAdapter(this);
gridview.setAdapter(myImageAdapter);

String ExternalStorageDirectoryPath = Environment
.getExternalStorageDirectory()
.getAbsolutePath();

String targetPath = ExternalStorageDirectoryPath + "/test/";

Toast.makeText(getApplicationContext(), targetPath, Toast.LENGTH_LONG).show();
File targetDirector = new File(targetPath);

File[] files = targetDirector.listFiles();
for (File file : files){
myImageAdapter.add(file.getAbsolutePath());
}

// Get memory class of this device, exceeding this amount will throw an
// OutOfMemory exception.
final int memClass
= ((ActivityManager)getSystemService(Context.ACTIVITY_SERVICE))
.getMemoryClass();

// Use 1/8th of the available memory for this memory cache.
final int cacheSize = 1024 * 1024 * memClass / 8;

mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {

@Override
protected int sizeOf(String key, Bitmap bitmap) {
// The cache size will be measured in bytes rather than number of items.
return bitmap.getByteCount();
}
};
}

public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemCache(key) == null) {
mMemoryCache.put(key, bitmap);
}
}

public Bitmap getBitmapFromMemCache(String key) {
return (Bitmap) mMemoryCache.get(key);
}

}


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